CA1174072A

CA1174072A - Apparatus for calibrating fluid flow meters utilizing digital techniques

Info

Publication number: CA1174072A
Application number: CA000433943A
Authority: CA
Inventors: Peter J. Hanowich
Original assignee: Rockwell International Corp
Current assignee: Boeing North American Inc
Priority date: 1980-03-28
Filing date: 1983-08-04
Publication date: 1984-09-11

Abstract

Abstract of the Disclosure Apparatus for calibrating a fluid flow meter under test is disclosed as including a meter prover for directing a known volume of fluid through the meter including a chamber of known volume, a piston to be moved rectilinearly within the chamber and a motor for driving the piston, the chamber being coupled to the fluid flow meter under test to permit the flow of fluid between the fluid flow meter and the chamber.
There is included a measuring device in the illustrative form of a rotary encoder coupled to the fluid flow meter to provide a first indication in the form of a first series of pulses indicative of the fluid flow as measured by the meter, and a second measuring device in the illustrative form of a high precision linear encoder coupled to the meter prover. The linear encoder is responsive to the movement of the piston for providing a second indication in the form of a second series of pulses indicative of the fluid drawn by the meter prover through the fluid flow meter. A control circuit in the form of a microprocessor is responsive to the movement of the piston to enable the accumulation of the outputs of the first and second measuring devices, e.g., counting the first and second series of pulses, and for terminating the accumula-tion, e.g., counting the first and second series of pulses, upon the accumulation of a given quantity or number of the first series of pulses, whereby the accumulated value or number of the second series of pulses provides a calibrated, precise manifestation of the fluid flow through the fluid flow meter as measured by the meter prover.

Description

~74072 /`- `

Ihis is a divisional application of patent appli~ation Serial No. 373,351 filed`~rch 5th, la~l, and is related to r~t~t application Serial No. 373,40S filed March 5th, 1981.
I. DrSCRIP~ION
Backaround of Prior Art This invention, in its preferred form, reiates to meter provers for testins the accuracy of flu.d and in parti-cular gas meters.
In the prior a , U. S. Patent 185,319 of Harris is an early example of the use of a bell-tv?e meter prcver com-prisina a bell-sha~ed container or ~ell that is rectilinea~ly : moved lnto and from a container or kettle filled witn a l_~ui such as oil. Typically, a pulley arrangement is used where~
a pulley is located aDove the bell, with a cord suspended about the pulley having one end attached to the '~ell and ths other end to a set or weights. A conduit is provided from - the bell to the meter tc be tested, whereby as the bell ls drawn upward, a ~luid, e.g., gas, is drawn throuch the meter and into the bell. ~. valve is placed within the conduit and when disposed to its closed position, prevents the flow of the fluid from the meter i!~to the spase defined by the bell and its kettle, thus innibiting the motlon of the bell and the weisht suspended therefrom by the pulley. U~n opening of the ~alve, the fluid -lo~s i~to the bell permitting the weishts to e~ert its force upon the bell, thereby lifting the bell. t;hen t~.e weights are releaaed, the cord and thUC
: the bell are pulled upward, thus creating a vacuum within thc bell, the oil providing a seal to preven. leakage of air otherwise into the be11.
P~

~174072 In order to determine the amount of fluid that is drawn through the meter, the early practice sought to con-trol the extent of movement of the bell, correlating this movement to a givsn quantity of fluid th~t would be drawn through the meter and comparing the known quantity of fluid drawn through the meter and into the meter prover, to the fluid as measured by the meter, typically indicated by the meter's dial positions. Current methods require physical measurements of the dimensions of the bell (bell s'~rapping) which are inconvenient and are subject to a number of possi-ble errors incurred by averaging the non-uniform geometri-cal diameters and the wall thicknesses of the bell and by interpolating the scale markings by eye. The quoted accu-racy of such current methods is about 0.3~ at best. Thus, it can be seen that such a bell-type meter prover, which was the calibrating standard for fluid meters, lacked inherently a high degree of accuracy due to the errors introduced by (1) the visual sightings of the beginning and final points of the bell movement, (2) the visual sightlnss of the initial and ter-minating volume indications by the meter dial, and (3) theinherent inaccuracy of determining the volume of the bell.
The most significant cause of error in this technique was due to the difficulty of accurately measuring and determining the volume of the bell. The bell, i'self, was formed with as great an accuracy as possible, but variations in its diam-eter, and therefore circumference, inherently occurred. ~he taking of many measurements of the circumîerence by bell strap-ping was the best method then devised to obtain the bell's average circumference and therefrom the volume of the cylindri-cal portion of the bell.
The use of the bell-type p-over has persisted for many years with improvemen-s being made thereto primarily in the nature of determining the movement of the bell and in determining thc volume of fluid passed through the meter.
One of the earliest exa-ples of an automated prover system ~ 17~072 01 ~ 3 -02 is found in u.s. Patent 3,050,980 of Dufour et al., which 03 discloses a bell having optical pick offs to sense the movement 04 of its bell, as it is directed upwardly. A conduit is directed 05 from the bell to the meter having a first solenoid actuated 06 valve for controlling the flow of fluid from the meter to the 07 bell, as well as a second solenoid actuated valve coupled to the 08 conduit for permitting discharge of the fluid from the bell as 09 it returns to its downmost position. In operation, the bell, initially filled with air, is lowered into its tank tending to 11 drive air through the meter. A dial hand on the meter register, 12 known as the "prover hand" is detected by means of an optical 13 pick-up to initiate the test, whereby the first valve is opened, 14 while maintaining the second valve closed, to permit a flow of the fluid from the bell through the meter. An automatic 16 airtight test is described wherein both the first inlet and 17 second discharge valves are closed, and as pressure is built up, 18 tests are made for leaks in the system and its valves by 19 measuring the pressure established within the bell.
Further, U.S. Patent 2,987,911 of McDonell suggests a 21 prover system in which first and second temperature sensors are 22 disposed to the outlets of the meter and of the prover, 23 respectively, whereby the temperature differences is calculated 24 to develop a temperature compensation factor Tc, which is used to make a correction in the calculated volume.
26 As suggested by U.S. Patent 3,933,027 of Mehall, 27 efforts were made to improve the bell-type prover system by 28 automating its operation. The Mehall patent '027 suggests the 29 placement of a series of sensing flags with respect to its bell, whereby an optical encoder senses the movement of these flags 31 to provide indications of corresponding volumes of air as 32 drawn by the bell's prover through the coupled meter. Further, 33 a second optical encoder is coupled to the dial of ~ ~740~2 the meter to provide an output as a train of pulses indica-tive of the volume flowing through the meter. At initiation of the meter test, a gate is activated by the first optical encoder to initiate a count ng or timing procedure whereby a S clock signal is applied to each of a bell clock counter and a meter clock counter. The gate passing the clock signals to the bell counter is disabled upon reaching a given count corresponding to a known quantity of fluid as drawn through the meter. When a similar quantity of fluid has been meas-ured ~y tne meter, as indicated by the second optical encoder,a signal therefrom is applied to a gate to terminate the appli-cation o' clock signals to the meter clock counter. At ter-~ination, first and second counts have been accumulate~ within the bell clock and meter clock counters, whereby the ratio thereor may be readily calculated and displayed u~on a suit-able digital display. This ratio is understood to be the meter registration, i.e., the ratio of the actual or calibrated volume of fluid passed throush the meter to that measured by the meter.
U. S. Patent 3,937,Q48 of St. Clair et al provides similar teachings to the Mehall patent '027 disclosing a bell-type automatic meter prover wherein there is further included a device for sensing the series of pulses produced by the meter during a cycle Oc its operation. The volume actually passed through the meter is measured by an encoder which produces a train of pulses indicative of the linear move-ment of the bell and therefore the volume displaced into or out of the bell durins a test. The encoder provides a train of pulses indicative of the volume displaced by the bell; the encoder pulses are accumulated for a given nurllber of meter operation cycles, to calibrate the meter indication of volume with a kno-~n volume of fluid displaced by the bell.
U. S. Patent 3,877,287 of Duntz, Jr. suggests a sub stantially different structure, wherein in place of the bell-type container, a cylinder is used to recci~e a piston driventhrough the cylinder at a controlled rate by a motor rotatively coupled by a lead screw to the piston for driving it through ~ 17~072 01 ~ 5 ~
02 the cylinder as the motor rotates. As a result, the piston is 03 driven at a constant velocity through the precision bore tube or 04 cylinder to drive fluid from the cylinder and through the meter 05 to be tested. The Duntz, Jr. patent '2~7 suggests two ways of 06 measuring the fluid flow rate, the first involving placing a 07 series of holes in a piston rod interconnecting the piston and 08 the ]ead screw, and sensing the movement of the holes past a 09 photodetector. A second method uses an optical encoder coupled to the drive motor to provide an output train of pulses 11 indicative of piston displacement and therefore the actual fluid 12 volume displaced from the cylinder.
13 U.S. Patent 3,631,709 of Smith also discloses a meter 14 prover comprising a piston and cylinder arrangement, wherein the piston is driven via a lead screw by a program controlled 16 motor. Upon actuation, the motor drives via the lead screw the 17 piston through the cylinder, whereby a known volume of fluid 18 (water) is drawn through a series of meters disposed in series.
19 The control program of the motor causes the piston to move at different rates of speed, whereby corresponding fluid flow rates 21 are established through the meters for a single stroke of the 22 piston through the cylinder. A magnet is coupled to a shaft 23 inter-connecting the lead screw and the piston to actuate a reed 24 switch as the piston is drawn through the cylinder, to initiate the counting of pulses derived from a first or master pulser 26 coupled to the motor. The output of the master pulser is a train 27 of pulses and is applied to a register to provide an indication 28 of the actual flow through the meters. Optical encoders are 29 also coupled to each of the meters to provide pulse signals to a second set of registers whereby the measured values of fluid 31 flow measured by the meters may be accumulated and displayed.
32 The standard or actual volume of flow is defined as a specific 33 number of counts from the first or master pulses against which 34 the output from the individual meters is compared. The program control of the motor permits the acceleration of the motor and 36 its piston to a steady state condition before beginninq 37 measurement of the fluid flow through the meter in order to 38 permit any transients in the fluid to settle.

l~ 174~72 As indicatefl abovc, the prior art has dealt with providing automation to the process of testing meters by automatically initiating and terminating the counting of pulses from a first encoder indicative of the standard S volume of fluid drawn thrcugh the meter, as well as the counting of pulses from a second encoder indicative of the volume of fluid measured by the meter under test.
However, the prior art has not dealt with the problem of improving the basic accuracy of the meter prover, i.e., the basic meter calibrating device. At this point in the development of the art, meter provers, particularly those of the bell-type, are only able to achieve an accuracy of I .2~ under optimum conditions. It is thus obvious that the fluid meters calibrated or tested with such provers may lS achieve no greater accuracy themselves. One of the primary reasons for the lac~ of ultimate precision in exist ng meter provers, is the lack of precise methods of and apparatus for measuring withhigh precision the volume displaced within either the bell or the cylinder as disclosed by the above-~0 discussed patents.
It is contemplated by this invention to provide amethod and apparatus for measuring the volume of the test cha~ber of the meter prover with an`accuracy to one part an 106. Once the volume can be obtained with such accuracy, then it is necessary to insure, as taught by this invention, that the structure containins t~e cham~er is rigid and nondeformable.
In the past, thé bell-type enclosures have not provided such a rigid structure so that if they were accidentally jarred, the interior volume may be ch~nged to a degree to affect the accuracy of the bell-t~pe meter prover's readings. As will be disciosed, this invention adopts a tec~mique for measurlng the displacement volume within the meter prover's chamber by senerating electromagnet~c waves and determining the frequency at which resonance is established at first and second positions of a piston to be driven through the housing.
~dopting such a mcthod of mcasuring the container's volur,le requires, as taught by this invention, the use of a housing ~ 17~072 ha~inq a sub~tantiall~ perfect righ~ circular cyiin~er con-figuration so that the frequencies at which resonance i5 established, may be determined sharply to thereby determine the displa~ement volume within the rigia cylinder. Further, in the development of the inventiorl to be described, it became evident that once the volume of the prover had been determined with great accuracy, then it was necessary to determine other parameters as would affect the indication of meter registration or of the volume of fluid as drawn through the meter under test, with similar acc-racy. In this regard, the inv2ntion contemplates methods and apparatus for measur-ing with a high degree of accuracy the temperature ar.d ~res-sure of the fluid within the meter and within the meter prover such that a correction factor may be determined with a similar deyree of accuracy to thereby correct for varia-tions in these parameters that exist in the meter under test and the meter prover of this invention. Such a technique contrasts to the prior art, wherein a meter prover was put into an en~ironmentally conditioned room with limited vari-ations in the temperature and pressure of that room. However,when the precision ~ith which the variables are to be meas-ured approaches 106 as has been achieved by this invention ~or the measurementof the dis~la~em~nt volume Oc the met2r prover, then it becomes necessary to note that these parameters of pres-sure and temperature do vary within the meter prover andwi~hin the fluid flow meter during the course of its test such that to insure desired precisior.,that new methods and apparatus for measuring pressure and temperature must be prov.ded. For example, if there is an error of 1F in the measurement of fluid temperature, there may result an error of .2% in the displac~nt volume Lndicated by the prover. It is contemplated that the meter prover system of this invention is capa~le of achieving an indication of the volume as drawn through the meter under test to a precision of .004%.
With such accuracy, then investigations may be conducted to determine the effects of other factors upon the measure- ¦
ment of fluid flow. ~or example, ehe number of times !

~ ~74072 -Gb-that tcsts are performcd upon a given meter will affect the mcasurcd metcr registration. Furthcr, it is contemplated that the variation in the rate of fluid flow as well as the volume of fluid flow through the meter will affect the indicated measured volume by the meter as well as its meter registration with respect to its standard volume as measured by a meter prover.

(Next pa~e 7) ~ 174072 Brief Summary of the Invention In accordance with this invention, there is dis-closed apparatus for calibrating a fluid flow meter under test, including a meter prover for directing a known volume of fluid through the meter including a housing of known volume, a piston to be moved rectilinearly within the housing and a motor for driving the piston, the housing being coupled to the fluid flow meter under test to permit the flow of fluid between the fluid flow meter and the housing. There is included a measuring device in the illustrative form of a rotary encoder coupled to the fluid flow meter to provide a first indication in the form of a first series of pulses indicative of the fluid flow as measured by the meter, and a second measuring device in the illustrative form of a high precision linear encoder coupled to the meter prover and in particular responsive to the movement of its piston for providing a second indication in the form of a second series of pulses indicative of the fluid drawn by the meter prover through the fluid flow meter. A control circuit in the form of a microprocessor is responsive to the movement of the piston to enable the accumulation of the outputs of the first and second measuring devices, e.g., counting the first and second series of pulses, and for terminating the accumu-lation, e.g., counting the first and second series of pulses, upon the accumulation of a given quantity or number of the first series of pulses, whereby the accumulated value or number of the second series of pulses provides a calibrated, precise manifestation of the fluid flow through the fluid flow meter as measured by the meter prover.
In a further aspect of this invention, the control device responds to a proximity detector for sensing the movement of the piston to be enabled to sense thereafter the next pulse of the first series of pulses, to provide an initiate count signal to start the counting of the first and second series of pulses by corresponding first and second counters within the control circuit.

~ 1~4072 The counts of the first and second series of pulses as counted by their respective counters are compared with each other to provide an indication of meter registration or to provide an indication of error of the reading provided by the fluid flow meter with respect to the fluid as pre-cisely measured by the meter prover.
In a further aspect of this invention, the counter for counting the first series of pulses receives one of a plurality of factors, representing a selected volume to be measured by the meter prover of this invention. The first counter counts down the entered factor and upon reaching a predetermined count, e.g., 0, generates a terminate output signal to terminate the counting by the first and second counters.
In a still further aspect of this invention, there are provided devices for measuring the temperature and the pressure of the fluid during the course of the test of a fluid flow meter. In one illustrative embodiment of this invention, the control circuit operates to sample upon generation of the initiate count signal, values of tempera-ture and pressure. Further, the valu~s of temperature and pressure are summed over the course of the test to provide the averaged values of the temperature and pressure of the fluid.
In a further aspect of this invention, the values of temperature and pressure are derived to provide averaged values of the temperature and pressure within each of the fluid flow meter and the meter prover. To this end, tem-perature transducers are disposed at the inlet and out of the fluid 10w meter under test and at the inlet extremity and upon the piston of the meter prover, whereby outputs may be obtained from each set of the temperature transducers to obtain an averaged-value thereof.
In similar fashion, differential pressure trans-ducers are disposed at the outlet of the fluid flow meterand upon the piston of the meter prover and their outputs are each combined with a reading of absolute ambient 4~7~
01 -8a -03 pressure to obtain averaged values oE the absolute pressure 04 within the fluid flow meter and within the meter prover. The 05 time and space averaged values of temperature and pressure are 06 used to calculate pressure and temperature correction factors to 07 be applied to the volume indications from the first and second 08 measuring devices to provide a corrected indication of fluid as 09 drawn through the meter by the meter prover.
In a preferred embodiment of the invention, apparatus 11 is provided for calibrating a fluid flow meter under test 12 comprising apparatus for directing a known volume of fluid 13 through the meter under test, the directing apparatus comprising 14 a housing of known volume, the housing being coupled to the fluid flow meter under test to permit the fluid to be directed through 16 the flow meter by the directing apparatus. Measuring apparatus 17 is coupled to the directing means for providing a calibrating 18 indication of the fluid drawn by the directing apparatus through 19 the meter. First monitoring apparatus continuously monitors the temperature during the course of a test of a meter, to provide a 21 temperature indication of the fluid, and monitoring apparatus 22 continuously monitors the pressure during the course of a test of 23 a meter, to provide a pressure indication of the fluid. Control 24 apparatus responsive to the initiation and temination of the meter test initiates and terminates respectively the continuous 26 monitoring of the indications of temperature and pressure from 27 the temperature and pressure measuring apparatus.

~174072 01 - 9 ~
02 Brief Description of the Drawings 03 A detailed description of one preferred embodiment of 04 this invention is hereafter described with specific reference 05 being made to the drawings in which:
06 Figure 1 is an elevational view of a meter prover 07 system in accordance with the teachinqs of this invention;
08 Figures 2A and B are detailed, partially sectioned 09 views of the meter prover of this invention as more generally shown in Figure 1, Figure 2C shows the structure for housing the 11 meter prover as shown in Figures 1 and 2A and a control console 12 whereby the operator may control and observe the data output 13 from the meter prover, and Figure 2D shows the display panel of 14 the system control and status module as shown in Figure 2C;
Figure 3 is a functional block diagram of the 16 architecture of the computer system used to sense the several 17 variables of the meter prover system and to control the movement 1~ of the piston through the cylinder of the prover as shown in 19 Figures 1 and 2A, as well as to provide an accurate indication of the meter registration of the tested meter.
21 Figures 4A and 4E show the various signal conditioning 22 and interface circuits as are needed to provide signals into and 23 from the computer system as shown in Figure 3, Figure 4F shows a 24 perspective view of the meter and the manner in which a proximity detector is disposed with regard to its encoder 26 mechanism, and Figures 4G through M show detailed schematic 27 diagrams of the signal conditioning and interface circuits 28 generally shown in Figures 4A and E;
29 Figure 5 shows a high level diagram of the program as executed by the computer system of Figure 3 and apears on the 31 same sheet as Figure 4B;
32 Figures 6A and 6B show in a more detailed diagram, 33 the initialization process effected by the computer system of 34 Figure 3;
Figure 7 shows in a more detailed fashion the steps 36 necessary to calibrate the inputs as applied to the signal 37 conditioning and interface circuits for applying the measure-~ ~74072 02 ments of temperature and pressure of the computer system as 03 shown in Figure 3.
04 Figures 8A to 8H, 8J to 8N and 8P disclose in detail 05 the flow diagram for reading out data stored within the computer 06 system and to enter the conditions under which the meter prover 07 system will test a given meter (the letters I and O are not used 08 for clarity sake), Figure 8A appearing on the same sheet as 09 Figure 6A, and Figures 8K, 8P and 8N appearing together on a sheet following Figure 8L;
11 Figures 9A to 9E~, 9J to 9N, 9P and 9Q show the steps 12 effected by the computer system of Figure 3 to carry out the 13 various tasks and to provide manifestations thereof (the letters 14 I and O are not used for clarity sake);
Figure 10 is a schematic diagram of a circuit for 16 applying a high frequency signal to the microwave antenna within 17 the cylinder of the meter prover as shown in Figures 1 and 2A, 18 for varying the signal's frequency as applied to the antenna 19 whereby the volume of the cylinder may be determined with great accuracy to thereby accurately encode the output of the meter 21 prover's linear encoder;
22 Figure llA through E show variously the input signals 23 applied to and the output signal as developed by the signal 24 conditioner and logic circuits 170a and 170b as shown generally in Figure 4C and more specifically in Figure 4R;
26 Figures 12A and B show respectively a perspective view 27 of a cover to be placed over the piston as shown in Figures 1 28 and 2A, and a cross-sectional view of the spring-like seal 29 disposed about the periphery of the piston cover;
Figure 13 is a graph illustrating the response of a 31 chamber of a right circular cylinder configuration to being 32 excited with high frequency electromagnetic fields in terms of 33 the varying dimensions of the cavity and frequencies of 34 excitation; and Figure 14 is a cavity response curve showing reflected 36 power Pr as a function of the excitation frequency.

~ ~74072 03 Detailed Description of Invention 04 Referring now to the drawings, and in particular to 05 Figures 1 and 2A, there is shown the meter prover system 10 of 06 this invention as coupled to a meter 38 to be tested. The meter 07 prover system lQ includes a cylinder 12 through which a piston 08 14 is driven in rectilinear fashion, by a programmable, variable 09 speed motor 20 such as a servomotor.
The cylinder 12 is supported in upright position by a 11 series of struts 76 (only one of which is shown) secured to a 12 collar 77 which in turn is secured around the exterior of 13 cylinder 12. The upper end of cylinder 12 is closed by a head 14 86 from which a series of struts 88 (only one of which is shown~
extend upwardly. A support pla~e 94 is fixed to the upper end 16 of struts 88 and servomotor 20 is mounted on the top of plate 17 94. The upper end of a lead screw 18 is journalled for rotation 18 in plate 94 by means of bearing 98 and is drive connected to the 19 drive shaft of the servomotor 20 by means of a coupling 100. A
lead nut 22 fixed within a housing 23 is threadedly received on 21 lead screw 18. The lead screw 18 is telescoped within sleeve 22 17, the upper end of which is secured to the housing 23. The 23 lower end of sleeve 17 projects through and is slidingly 24 received in bushing 96 in head 86. The upper end of piston shaft 16 is secured to the lower end of sleeve 17.
26 An intermediate cylinder head 91 separates the upper 27 portion of the interior of cylinder 12 from the lower portion in 28 which the piston 14 is contained. Piston shaft 16 projects 29 through and is slidably received in bushing 93 in head 91, the lower end of shaft 16 being connected to the piston 14.
31 Thus, as the servomotor 20 rotates, the lead screw 18 32 rotates in nut 22 causing the housing 23, sleeve 17, and shaft 33 16 to move vertically in either direction depending on the 34 direction of servomotor rotation.
The bottom of cylinder 12 is closed by a head 60 and 36 the cylinder 12 therefore encloses and defines between 01 - lla -02 the piston 14 and head 60 a variable volume chamber 28. An 03 opening 62 in head 60 places chamber 28 in communication with 04 conduit 30, conduit 32, and meter 38. A first inlet valve 34 is 05 disposed between the cylinder 12 and the meter 3~ to control the 06 flow of fluid, e.g., a gas, therebetween. A second, exit valve 07 36 is connected to the conduit 30 in order to permit the exit of 08 fluid from the cylinder 12 when the valve 36 has been opened.
09 The precise position of the piston drive shaft 16 and therefore the piston 14 is provided by a high precision, linear 11 optical encoder 26 that is coupled to the drive shaft 16 to move 12 therewith. More specifically, the encoder 26 illustratively 13 includes first and second sets of light sources and photo-14 detectors disposed on either side of a linear scale 35 having a high number of scale marks 102. In one illustrative embodiment 16 of this invention, the linear scale 2~ is disposed in a fixed 17 position with respect to movable encoder 26 and includes 40,000 18 scale marks 102 (2500 marks per inch); of course, only a limited 19 number of such a high number of scale marks could be illustrated in the drawings. Thus, as the encoder 26 is moved rectilinearly ~ along the length of the linear scale 24, first and second sets 23 of pulse trains A and A are developed, 90 out of phase with 24 respect to each other, as the light beams generated by the first ~ and second light sources are intercepted by the scale marks 102.
27 The outputs A and A from the optical encoder 26 indicate pre-28 cisely the position of the pistion 14 and likewise the volume of 29 fluid has been drawn through the meter 38. As will be explained, the volume of the chamber 28 within the cylinder 12 is precisely 31 measured, and each output pulse derived from the encoder 26 32 provides a precise indication of an incremental volume as drawn 33 into the chamber 28 within the cylinder 12 as the piston 14 is 34 withdrawn, i.e., is directed upwardly by the servomotor 20.

~ 174072 01 ~ 12 -02 Before the piston 14 is begun to be raised, thus creating a 03 vacuum within the chamber 28, the exit valve 36 is closed and 04 the meter valve 34 is opened to permit a flow of fluid through 05 the meter 38 via the conduit 32, the open valve 34 and a pair of 06 conduits 30 and 32 into the housing 28. During a meter test, 07 the meter 3~ provides via its encoder 40 an output train of 08 pulses indicative of the flow of fluid therethrough. The train 09 of pulses as derived from the meter encoder 40, is compared to the train of pulses derived from the linear encoder 26 to provide 11 an indication of the meter accuracy in terms of the meter 12 registration, a ratio corresponding to the volume measured by the 13 meter encoder 40 to the volume measured by the linear encoder 26.
14 Further, the programmed movement of the piston 14 uses a plurality of proximity sensors 50, 52, and 54, as well as a 16 pair of limit switches 49 and 53. As will be explained, the 17 servomotor 20 drives the piston 14 rectilinearly within the 18 housing 28. As shown in Figures 1 and 2A, the piston 14 is in 19 its uppermost position wherein an abutment 92 on housing 23, 26 contacts and closes the upper limit switch 53 thereby deactuating 21 the servomotor 20 when the piston 14 is driven upward and thereby 22 halting the movement of the piston 14. When the servomotor 20 23 drives the piston in a downward direction as shown in Figure 1, 24 the abutment 92 may then engage the lower limit switch 49 again bringing the piston 14 to a halt. The upper failsafe switch 53 26 and the lower failsafe switch 49 are used to prevent physical 27 damage to the meter prover 10 if for reason of failure, the 28 servomotor 20 should continue to drive the piston 14 to either 29 extremity. If the abutment 92 should engage either of the fail-safe switches 49 or 53, the servomotor 20 will be deenergized and 31 the piston 14 brought to an abrupt halt. Also in a volume self-32 test mode of operation, as will be explained, the proximity 33 detectors 52 and 54 are used to detect the movement of the piston 34 14 between designated locations. In general, the servomotor 20 accelerates the piston 14 to a given speed and the output of the 36 linear encoder 26 is gated by the output of the proximately 37 detector 52 to permit its pulses to be accumulated and counted.

02 The counting of the pulses derived from the linear encoder 26 is 03 gated off, in the volume self-test mode, by the occurrence of an 04 output from the proximity detector 54 indicating the passage of the05 abutment 92 there past. Thereafter, the servomotor 20 is 06 decelerated to a stop. By contrast, in the meter test mode, the 07 piston 14 is driven upward by the servomotor 20 and when the 0~ abutment 92 passes the proximately detector 52, an enable signal is09 generated thereby whereby on the occurrence of the next or leading edge of the next output pulse from the meter encoder 40, the 11 counting of the output pulses of the linear encoder may then 12 begin. In the meter test mode, the counting of the linear encoder 13 pulses is terminated when the counting of the meter encoder pulses 14 has reached a predetermined count corresponding to a volume of fluid drawn through the meter.
16 In order to facilitate an understanding of this inven-17 tion, a brief summary of its operation will now be given, while 18 a more detailed discussion of the operation of the meter prover 19 10 will be provided below. A first or initialization mode deter-mines whether the piston 14 is in its park position as by deter-21 mining whether the proximity detector 50 detects the presence of 22 the abutment 92 as explained above; if not, the servomotor 20 is 23 energized to drive the piston 14 to its park position. If the 24 abutment 92 is in a position to be detected or before the piston 14 is returned to its park position, the second or exit valve 36 26 is opened to permit the exit of fluid driven from the chamber 28 27 through the conduit 30, and then the inlet meter valve 34 is 28 closed to prevent the fluid from being driven therethrough and 29 possibly injuring the meter 38. Upon command of the operator that a meter 38 is to be tested, first meter valve 34 is opened 31 and then the second valve 36 is closed to permit the flow of fluid 32 through the meter 38, the conduit 32, the open valve 34 and the 33 conduit 30 into the chamber 28, as the piston 14 is being driven 34 in an upward direction by the servomotor 20. The piston 14 is gradually accelerated to a given steady state velocity and is 36 maintained at that selected velocity during the course of the fluid37 volume test measurement, while the output pulses of the encoders 26 ~174072 and 40 are accumulated by an ari~hme~ic unit including rcgis-ters to acc~late c~lts indicative of a precisc vo]umc as measured by the linear.encodeL 26 and of the volume as meas-ured by the meter 38, respectively. The meter test is ini-tiated by the passage of the piston 14 past the start-test proximity detector 52 that enables upon the occurrence of the next output pulse or more precisely its leading edge from the meter encoder 40, the counting or accumulation of the meter encoder pulses as well as the linear encoder pulses. Depend-ent upon the desired volume to be drawn through the meter 38under test, the meter test will terminate upon the counting of a number of meter encoder pulses. In particular, the register for accumulating the meter encoder pulses 38 upon counting the predetermined number dependent upon the fluid volume, provides an output applied to the linear encoder sys-tem terminating its counting o~ the input pulses derived from the meter encoder 40. The stored counts indicative of the fluid volume as measured by the meter encoder 40 and ~e linear encoder 26 ~e co~xd,i.e., -~ ratio therebetween is obtained to provide an indication of the meter registration.
In addition, measurements of temperature and pressure are taken in order that the measured volumes may be adjusted for these conditions. In particular a pair of temperature measuring devices 42 and 44 are respectively disposed at the entrance and exit ports of the meter 38. A differential pres-sure transducer 46 is disposed to measure the difference between the pressure established by the fluid in the conduit 32 and ambieht pressure. In addition, temperature measuring devices 48 and 57 are disposed respectively at tne conduit 30 coupled to the chamber 28 and upon the piston 14 to provide indications of the temperature of the fluid within the chamber 28. In addition, a second differential pressure transducer 51 is dis-posed within the piston 14 to provide an indication of the differential pressure between the ambient pressure and that established within the chamber 28. The temperature outputs TM3 and TM4 derived from the temperature measurlng devices 42 and 44, respcctively, are averaged to provide an average meter temperature ~IT, whcreas the outputs TPl and TP2 of the tempcr-ature me~suring devices 57 and 48, respectively, are avera~cd ~ 174072 to provide an indication of the average prover temperature APT. As will be explained in greater detail later, these in-put parameters are used to provide an adjustment of the meas-ured volumes as derived from encodérs 26 and 40 dependent upon S the measured conditions of pressure and temperature.
As shown in Figure 2A, a microwave antenna 70 is disposed in the head 60 to generate microwaves within the cham~er28, whereby lts volume may be accurately determined. It is contemplated that this measurement may be made pexiodically to detect even the minutest changes in the volume of the cham-ber 28. As will be explained, the techniques of establishing electromagnetic waves in the microwa~e range permits an accu-racy to at least one part in 106 of the volume of the chamber 28. In addition, in order to test the accuracy of the tempera-ture sensors 4& and 57, a high precision temperature measuringdevice 68 is also inserted within the condui~ 30. The tempera-ture transducers 48 and 57 may illustratively take the form of a RTD Model No. 601222 temperature transducer as manufactured by Senso-Metrics, Incorporated, whereas the high precision temperature transducer 68 ma~be ofthe type as manufactured by Hewlett Packard under their ~odel No. 1~115A; this transducer 68 must be used with a Hewlett Packard 2804A quartz thermometer.
The p-oximity switches 50, 52, and 54 may illustratively take the form of a proximity switch as manufactured by Microswitch under their designation FMSAS, whereas the limit switches 49 and 53 may be of a type as manufactured by Microswitch under their designations BA-2R-A2 and ADA3721R. The servomotor 20 may illustratively t2ke the form of that manufactured by Control Systems Research, Inc. under their designation NC100 ~C Servo Moto,r/Tachometer. Thè optical encoder 26 and scale 24 may take the form of a Pos-Econ-5 linear encoder as manu-factured by Heindenhain Corporation. As will be explained later in detail, the measurements of pressure and temperature within the meter 38 and within the prover 10 are used to cal-culate a factor ùy which the volume as arawn into the prover 10 ~ 174072 is adjuste~ for ~ese variab].es. In particular, the tem-perature transducers 48 and 57 measurc the temperature at the bottom and tepmost portions of the chamber 28 to obtain a spatial.ly averaged measurement of the temperature across 5 the entire volume within the chamber 28 of the prover 10.
In similar fashion, the temperature transducers 42 and 44 provide indications of the temperatures of the gas at the inlet and eutlet of tne meter 38 whereby a spatial averag-ing of the temperature of the gas flowing through the meter 38 may be obtaine~. The temperature transducers as selectively incorporated into the meter prover 10 are highly stable, low-thermal-mass platinum resistance thermometers and pro-vide accurate readings of these variables whereby the volume as drawn into the meter prover 10 may be accurately dete~-mined.
As shown ir. Figures 2A and B, the proximity devices 50, 52, and 54, as well as the limit switches 49 and 53 are supported upon the upright member 90, which is in turn suppor~ed from one of the upstanding struts 88. One end of the li.near scale 24 is supported from the member 3~
and extends downward substantially parallel to the direction of the motement of the piston 14, having its lower end sup-ported upon an upper portion of the interior of the cylinder 12. Only a limiteZ number of the some 40,000 markings 102 are shown in Figure 2A. In the lowermost portion of Figure 2A, the inlet valve 34 and the exit valve 36 are actuated, res?ectively, from open to closed positions ~y pneumatic actuators 66 and 64, respectively.
In Figure 2A, there is shown a cealing means indi-cated generally at 78 for the piston 14 to prevent the fluidas drawn through the meter 38 and into chamber 28 from leak-ing about the edges of the piston 14 as it i5 moved recti-linearly within the cylinder 12. The detai.ls of this piston seal 78 are disclosed in th.e patent application entitled "Piston Seal", 35 Serial 372,420, filed ~arch 5, 1981 and assigned to t~.R assignee hereof.

~174072 Rcferring now to Figurc 2C, the meter provcr 1~ is shown as being disposed within a ~ontrolled environment formed ~y an enclosurelO4 comprising a prover room 106 for receiving the meter prover 10 and a control room 105, wherein the con-S trol's console is disposedand includes a display unit 111 con-taining a printer and a series of lights for indicating the various states of the meter prover, a CRT terminal 112 includ-ing a keyboard whereby various commands may be input by the operator, and a variety of heat generating equipment including power supplies, motor control, amplifiers, etc. The control of the ambient conditions about the meter prover 10 is insured by disposing the meter prover 10 within the prover room 106 remote from the heat generating display unit 111 and terminal 112. As shown in Figure 2C, the meter 38 to be tested is also disposed within the prover room 106 and is coupled to the meter proverlO bytheconduit 32. The temperature in the prover room 106 is measured by the four temperature sensitive devices RO, Rl, R2, and R3 disposed about the prover room 106 and upon a strut 76 of the prover 10. A barometric pressure transducer 109 and a barometer are also disposed within the prover room 106 to measure the ambient pressure. Electrical connections are made to the various temperature measuring devices as shown in Fig-ure 2C, as well as those temperature and pressure measuring devices as shown in Figures l and 2.~ and are directed through a pair of troughs 110 to the control console disposed within the control room 105. In this manner, the ambient con- ¦
ditions under which the meter 38 to be tested and the meter prover 10 operate can ~e accurately controlled to insure the integrity of the measurements being made upon the meter 38 and the meter prover 10.
Referring now to Figure 3, there is shown a functional bloc~ diagram of the computer architecture of the computer sys-tem implementing the various functions including processing of the temperature and pressure measurements, of the linear encoder t and meter encoder output signals, ana to appropriately close the valvcs 34 and 36. In addition, outpu~s are provided to the C~T
tcrminal 112 to indicate the measured parameters as well as to the system control and the display unit 111 to display the various states of operation of the meter prover system 10, while :

~ 174072 permitting op~rator input through the keyboard of the CRT ter minal 112, of selected meter test functions. The computer sys- , tem includes a central processing Ullit (CPU) 120 of the type ~anuf.actured by `, the assisne~ of this invention under their designation PPS-8 5 Microcomputer, from t~hich address signals are applied from CPU 120 via an address bus 128 to a programmable read only memory (PROM) 124 and to a random access memory (RP~S) 126.
The R~ 126 may take the form of the 256 x 8 RAM as manufac-tured by the assignee of this invention, whereas the PROM 124 10 may take the form of that PROM manufactured by Intel Corpora-tion under their designation 2708. A system clock 122 provides system clock signals (e.g., 200 KHz) to the CPU 120 and may illustratively ta~e the form of the clock generator circuit P,~N 10706 as manufactured by the assignee of this in~ention.
As shown i.n Figure 3, each of the clock 122, the CPU 120, the PROM 124, and ~he RAM 126 are interconnected by an instruction- ~!
dat.a (I/D) bus 140, which may illustratively take the form of a 14-line bus r.ot only i.r.terconnecting the forementioned ele-~ents but also connected to each of the signal conditioning and interface circu ts 130, 132, i34, 136, and 138.
. The circuit 130 conditions and interface the signals indicative of the prover temperature signals TPl and TP2 as E
derived respectively from the temperature measuring devices 57 and 48~ Further, the meter temperature signals T~S3 and TM4 25 as derived from the device~ 42 and 44 are also applied to the circuit 130. As shown in Figure 2C, four addition~l rocm tem- ¦
perature measuring devices R0, Rl, R2, and R3 are provided about the prover room 106 in which the meter prover system 10 as sho~n in Figures 1 and 2A i~ disposed; in this regard it 30 is understood that the ambient conditions about the meter prover system 10 are well regulated in order to maintain stable as possible the ambient temperatureof the meter prover system 10. It is normal practice to sto-e the meters 38 to be tested in this environmcnt for a time to permit them to reach the same 35 ambient conditions at t~hich the meter provcr system 10 is dis-posed. As shown in Fi~urc 3, the temperature sigrals are applied to a si~nal cor.ditioncr and logic circuit 150 and from there vi~ an interfacc circuit 151 to the I/D b~s 140.

~ ~7407~

In similar fashion, the pressure signals are applicd to tll~ conditioning and i.nter~ace ci.rcuit 132, which compriso a signal conditioner and logic circuit 162 and an interface circuit 164. In particular the outputs of the differential 5 pressure measuring device 51 indicating the differential pressure PPl of the prover 10 and of the differential pressure measùring device 46 indicating the meter pressure MP2, and the barometric pressure measuring device 109 indicatins the ambient or atmospheric pressure PB of the prover room 1~6 are 10 applied to the circuit 132. ¦
The output of the meter.encoder 40 and the linear optical encoder 26 are applied to the signal conditioning and interface circuit 134. In particular, the output of the meter encoder 40 is applied to a signal conditioning and logic 15 circuit 170a, whose outputs are applied in turn to interface circuits 171 and 173. A clock circuit 175 applies a signal .
tc the interface circuit 173. In an alternative embodiment of this invention, a proximity detector 27 is used for detect-ing the rotation of the meter encoder 40 and the output of the 20 proximity detector 27 is applied to the signal conditioner and logic circuit 170a. This is illustrated in Figure 3 by 'he .
nput signals designated as rotary encoder pulses and meter test proximity detector; it is understood that only one of these inputs is made at a time to the circuit 170a. The out- ~
25 put of the linear optical encoder 26 is applied via the signal f conditioning and logic circuit 170b and interface 179 to the g I/D bus 140.
In order to provide an indication of the measured parameters, such as temperature, pressure, as we!l as the fluid 30 volumes drawn by the prover 10 and as measured by the meter 38, outputs are applied from the I/D bus 140 via the circuit 136 to the display unitlll whichincludes a hard copy data printer as manufactured by Practical Automation, Inc. under their desig-nation No. DMTP--3. In particular, the circuit 136 includes 35 an int~rface circuit 192a for applying parameter output signals via a signal conditioner and logic circuit l90a to the hard copy printer. Further, the circuit 136 includes an inter- ¦
face circuit 192~ providing the parameter output signals via a cignal conditioner and logic cir~uit l90b to the CRT data terminal 11~. In addition, operator input command signals as input on the terminal's ~;eybo~rd aie transfcrred via logic circuit l90b and the interface circuit 192b to the I/D bus 140. A clock circuit 193 controls the baud rate at which sig-nals may be transferred between the CRT data terminal 112 and thecomputer sys~em. The CRT data terminal 11~ may illustratively take the form of a CRT display as manufactured by Hazeltine Corporation under their designation 1500. Such a terminal permits input commands via the alphanumeric keys upon its key-lC board, as well as to display the commands being entered, andthe operator accessed parametric data.
Finally, there is shown a signal conditioning and interface circuit 138 for interconnecting the I/D bus 140 and the inlet valve 34 and thc exhaust valve 36, as well as to apply the control signals to the servomotor 20.
In addition, the servomotor 20 is associated with a motor control such as the DC Servocontroller as m~nufactured by Control Systems P~esearch, Inc. under their designation NC101 whereby feedback signals indicative of the speed of the ser-vomotor 20 are applied via the iosic circuit 194 to in turneffect the servomotor 20 control. In addition, signals indi-cating the status of the servomotor 20 as well as an input signal from a test mode switch to indica_e whether the rotary encoder ~0 or proximity detector 27 are to be used to measure ~eter flow, is entered via the logic circuit 198 and the interface circuit 200 to the I/D bus 140.
The signal conditioning and in.erface circuit 130 is shown in more detail in Figure 4A, as including two line inputs derived from each of the temperature transducers 57, 48, 42, and 44 indicative respectively of the prover tempera-tures TPl and TP2, and the meter temperatures TM3 and T~S4, and is connected to a multiplexer 149. ~n addition, the four temperature transducers R0, Rl, R2, and R3 disposed about the prover room 106 in which the meter prover system 10 is housed, are applied through the next four inputs to the multiplexer 149. The aforementioned temperature transducers are connectcd into amplifier modules that serve ta develop ~174~72 ~oltage outputs pro?ortional to the temperature sensed andto apply these outputs to the corresponding inputs of the multiplexer 149. In ~his manner, each temperature trans-ducer is associated with its own amplifier modul~ so that its output to the multiplexer 149 may be adjusted to insure a substantially uniform output in terms of voltage amplitude and off-set for each of the temperature transducers connected to the multiplexer 149. The details of the amplifier moduies for each of the transducers shown in Figure 4A will be ex-plained below with respect to Figure 4I along with a detaileddescription of the signal conditionins and l^s_c circuit 130 as c3enerally shown in Figure 4A. The multiplexer 149 serves to time multiplex the inputs at each of. its eight inputs and to scale the temperature signal outputs to be applied one at a time via a multiplexer 15a to an amplifier 152 taking the illustrative form of that amplifier as manu-factured by Analoa Devices under their designation AD522.
The second multiplexer 154 is nor~ally set to apply one of the eight temperature input signals via the operational am-p.ifier 152 to the analog digital (A/D) converter circuit158, which may illustratively take the form of the A/D con-verter as manufactured by Burr Brown under their designa-tion ADC 80. In a calibrate mGde, the multiplexer 154 is actuated to apply a precision, calibrating voltage to the A/D converter 158. As is well known in the art, the DC volt-age of the analog signals is adjusted to a level which may be readily accepted by the A/D converter 158, which in turn converts these analog signals to digital outputs which are applied via its 12 output lines to a parallel input-output (Pl/O) device 160 which may illustratively take the form of that det~ice manufactured by the assignee of this invention under their designation P/N 11696. The PI/O circuit 160 per-mits input commands to be transferred via the I/D bus 140 to the multiplexer 149 to control which,of the inputs is to be sampled at a particular time, as well as to the logic circuit 156 to enable the muitiplexer 154 to apply one of the outputs of thc multiplexer 1~9 or the volta~3e calibration input signal ~174072 to the ~/D converter circuit 158. In operatlon, the CPU 120 placcs a call signal via the I/D bus 140 to the PI/O circuit 160 which responds thereto by enabling a call for information to be read out and converted to digital data to be applied to S ~he I/D bus 140. In addition, a command is derived from the PI/O circuit 160 to time the conversion of the analog signals to digital signals by the A/D converter circuit 158, and a signal indicative of the status of the A/D converter circuit is applied via the PI/O circuit 160 to the I/D bus 140. The voltage calibration signal permits the zero and span of the operational amplifier 152 to be adjusted so that the full amplitude of each input signal may appear at the A/D converter circuit 158.
The conditioning and interface circuit 132 is more lS fully shown with respect to Figure 4B wherein there is shown that the outputs of the transducer 51 and 46 indica ing respectively the prover or piston pressure PPl and the meter pressure MP2 are applied via operational amplifiers 161a and 161b to a multiple.~er 163. In adrlition, the output frcm the pressure trans-ducer 109 for measuring the barometric or ambient pressureof the prover room 106 is applied via operational amplifier 161c to the multiplexer 163. Initially, the CPU 120 trans-mits a command to the multiplexer 163 to select which of the outputs of the pressure transducers 51, 46 or 109 is to be read out via the I/D bus 140 and the parallel input-output (PI/O) circuit 168. In response thereto, the PI/O circuit 168 applies control signals via the four-line bus 169 to the multiplexer 163, to select one of the three pressure indicat-ing signals or a signal indicative of the voltage calibration input signal to be applied to an A/D converter 166, which converts the input analog signal to a corresponding digital signal to be applied to the PI/0 circuit 168 to be in turn transmitted ~ia the I/D bus 140. Next, upon command of the .
CPU 120, the PI/O circuit 168 commands via line 159 the A/D .
circuit 166 to convert the selected analog pressure output signal to a corresponding digital signal to be transmitted .
via the I~D bus 140. The conversion of the input analog data .

~74072 -23- i to digital data rc~uires a discrete time period for the A to D conversion to take place and in addition, for the digital t data appearing upon the 12 output data lir.es of the A/D cir-cuit 166 to stabilize before they are read by the PI/O cir-S cuit 168. ~'hen signal stabilization has occurred on the 12 data lines output from the A/D circuit 166, a status signa]
is generated by the A/D circuit 166. In response to the status signal, the PI~'O circuit 168 reads the data appearing on the output lines of the A~D circuit 166 and applies these signals 10 via the I/D bus 140 to the R~ 126 as shown in Figure 3. After thic pro~ess is completed, the system is able to select another pressure output as derived from another transducer, conve-ting same t~ a digital signal to be transmitted to the P~ 126 as sxplained above.
The interface and conditioning circuit 134 is more fully explained with respect to Figure 4C. The rotary meter encoder 40 is coupled to the meter 38 to provide first and second signals A and A, 90 out of phase with each other, to `~
the signal conditioning and loyic circuit 170a. In par~icular, t ~0 the circuit 170a processes the input signals A to A to elimi-nate poss-ble problems due to jitter of the sisnals as may be imposed by mechanical vibration upon the rotary meter encoder 40. The signal conditioner and logic circuit 170a generates a composite pulse signal corresponding to each set of input pulses of the signals A and A, and applies same to an interval timer 174 including a programmable counter 174a into which is loaded a factor dependent upon the selected volume of fluid to be drawn through the meter 38, in a mann~r that will ~e explained. In particular that factor is placed in the program-mable counter 174a and upon counting down to zero from that fac-tor, a pulse is generated by the interval timer 174 and applied to a logic circuit 177 whose output is applied to in-tiate a CPU
Interrl~t 2 subroutine, whereby t~e testing o~ tne ~eter 38 is terminated, as ~174072 will be explained later in detail with respect to Figure 9J.
The logic circuit 170a is responsive to the input signal A
from the rotary meter encoder 40 to apply a corresponding, conditioned pulse to an interval timer 176, which performs S the operation of recognizing the leading edge of the signal A
to initiate timing or counting of the programmable counter 174a as well as of the counter 176a and of the linear encoder counter 182. More specifically, the CPU 120 controls the meter prover 10 and senses that the piston 14 has been accel-erated from its park position to its start-test position, as indicated by the presence of an ou'put signal from the proximity detector 52. Upon the sensing of the ou.put of proximity detector 52, the program as executed by the CPU 120 periodi-cally, e.g., approximatelv every 40 microseconds, accesses the interval timer 176 to see whether it has received an input signal from the signal conditioner and logic circuit 170a indicative of the leading edge of the input signal A
of the rotary encoder transducer 40. Upon the detectio~ o, the first leading edge cf the output o, the loqic circuit 170a, after the piston 14 has passed the proximity detector 52, an initiate signal is applied to the PI/O circuit 184, which applies an initiate count signal to the counter 182 and also an initiate signal via the I/D bus 140 to the program-mable counter 174a. In this manner, each of the counters 174a, 176a, and 182 are activated to start counting at the same time. In this illustrative example, the pro~rammable counter 174a counts down in response to output signals of the rotary encoder transducer 40.
In a significant aspect of this invention, the ini-tiating and terminating of the meter test, i.e., the counting by the programmable counter 174a and the counter 182, are made responsive to the output of the rotary encoder 40 in that the accuracy of the meter 38 is to be measured. More specifically, the rotary encoder 40 is coupled tothefluid or gas meter 38 as will be more fully described with respect to Figure 4F and upon rotation of its rotatively mounted rod, the rotary meter encoder 40 as coupled thereto will produce a tra;n of pulses 1.

, -25-corresponding to the rotatio~ this tan~ent arm and ~le cyclilg o~
thc met~r's diaphragm. As shown in Figure 4F, the rotary member is connected by coupling arms to the meter diaphragm and its rotation is not linear so that the output of the encoder 40 is in a sense freque,ncy modulated. Therefore, in order to obtain an accurate measurement of the rotary metcr encoder 40, it is desired to count the pulses as derived from the encoder 40 so that the counting begins and terminates at approximately t,he same point in the rotation of the meter's ro-tary member. This is accomplished by initiating the countinin response to the rotary meter encoder 40. In particular, a meter test is conducted by accelerating the piston 14 from its park position to a steady state velocity so that upon its passing the proximity detector 52, disposed at the start-test position, an output is provided therefrom to enable, as will be explained later, the detection of the leading edge of the next output signal from the logic circuit 170a corresponding to the leading edge of the next output signal A of the rotary meter encoder 40. The interval timer 176 responds to the leading edge to effect the simultaneous initiation of the count-ing of the programmable coun.er 174a and the counter 182. Upon the occurrence of the programmable counter 174a being counted down from its selected factor dependent upon the desired vol-ume to be drawn through the meter 38, the interval timer 174 pro-~ides its output to the logic circuit 177 to enable Inter-rupt 2 of the CPU 120, which in turn terminates the counting of the counters 174a and 182 and transfers the respective ; counts to corresponding lccations within the RAM 126. It is -noted that the termination of counting could be implemented . 30 by software, but would involve an additional number of steps thus unduly complicating the programming of this system as well as adding to the time required to carry out the timing ¦ operation as described above. In addition, the effecting of ! the initiating of counting in response to the output of the rotary meter encoder 40 insures a more accuLate test and cali-bration O r the meter 38 under test.

~ 174072 As explained above, tne output: ~rain of pulses as derived from the ro~ary encoder 40 is applied to count down the count initially placcd in the programmable counter 174a. Significantly, the count as placed in the program-mable counter 174a is variable dependent upon the volumedesired to be drawn through the meter 38 and into the chamber 28. The count is based upon the structural dimen-sions of and characteristics of the meter 33, as well as the characteristics of the rotary meter encoder 40 in terms of the number of pulses it generates per revolutiGn. In an illustrati~-e embodiment of this inven.ion, a count of 40,000 is placed in the programmable counter 174a corresponding to a volume of cne cubic foot to be drawn through the meter 40.
~ssuming that the characteristics of the meter 38 and the encoder 40 remain the same for varying volumes, illustrative counts of 20,000 and 10,000 may be stored in the programma-ble counter 174a if it is desired, respectively, to draw one-half and one-fourth cubic foot of fluid through the meter 38. ~y entering a count based upon the characteris-tics of the meter 38 into the the programmable counter 174a which is counted down by pulses derived from the rotary meter encoder 40, a more accurate test of the meter is assured in that the beginning and ending of meter test wi l be effected at the same point in the cycle of the rotation of the meter and 25 its rotary encoder 40, as explained above.
As indicated in Figure 4C, a cloc~ A is derived from the system clock 122 via the CPU 120 and the I/D bus 140 is applied to the interval timer 176. A selected factor is placed into down counter 176a to provide an output from 30 thé interval timer 176 corresponding to a sampling pulse of one pulse per second. In an illustrative embodiment of this invention, the system clock as derived from the clock p 122 is in the order of 200 ~Hz, and the factor placed in the counter 176a is such to provide the desired one pulse per 35 sccond to the logic circuit 178 and therefrom to the motor control board. As will be explained later, this sampling pulse is used to time thc samplin~ of the measurements of pressure and temperature.

~ 174072 8~ Further, the output of the linear encoder 26 is a pair 04 of signals A and A, 90 out of phase with each other, which are 05 applied to a signal and conditioner circuit 170b. The circuit 8~ 170b is similar to circuit 170a in that it processes the 08 inputted signal A and A to shape and condition these input 09 signals eliminating jitter that might otherwise indicate a false output from the linear encoder 26. In addition, the circuit 170b is able to detect the direction in which the piston 14 is moving from the inputted signals A and A and if the outputted signals A and A do not indicate that the piston 14 is moving in 16 the desired direction, no signals are outputted from the signal 17 and conditioner circuit 170b. The circuit 170b provides a train 18 of conditioned pulses corresponding to the linear encoder output 19 to the counter 182, which after initiation counts and accumulates the output of linear encoder 26. The accumulated 21 output of the counter 182 is applied to PI/O circuit 184 and 22 upon command is transferred via the I/D bus 140 to the remaining 23 portions of the computer system.
24 In one embodiment of this invention, a rotary encoder transducer 40 is coupled to the meter 38 and in particular 26 includes an optical encoder rotatively coupled to the domestic 27 meter tangent arm of the meter 38 to detect the rotation of the ~ tangent arm as gas flows therethrough to provide a plurality of output signals A and A as explained above. In an alternative 31 embodiment of this invention, the proximity detector 27 may be 32 used to detect the mechanical rotation of the domestic meter 33 tangent arm of the meter 38 by a mechanism that will be explained 34 later to provide an output signal to a signal conditioner and logic circuit 170c, which is in turn connected to the interval 36 timer 176 and to the interval timer 174. Due to the arrangement of 37 the mechanical mechanism coupled to the tangent arm of the meter 38 38, the proximity detector 27 produces a signal of lesser resol-39 ution than that produced by the optical encoder 26, as it detects the rotation of the meter tangent arm; the particular advantage of 41 the proximity detector arrangement is that of the relative sim-42 plicity of its mechanical and electrical structure. The choice - ~ 174072

-2~-of whet.lcr to usc the pro~imity d~ector 27 or thc rotary encoder transducer 40 is ;na~c by the opcrator hy throwlng a switch 191, as shown in Figure 4K, When the operator deter-mines to use the pro~imity detector 27, the programmable co~nter 174a is encoded with numbers of 8, 4, and 2 corre-sponding to measured volume flows of one cubic foot, one-half cubic foot, and one-fourth cubic foot. The operator initiates the entering of the appropriate factors ~lhether for the proximity detector 27 or for the rotary encoder 40, by first ~hrowing the switch 191 to the appropriate position and entering the test volume via tne keyboard of the CRT
terminal 112.
In Figure 4F, there is shown a perspective view of a typical meter 38, which measures the fluid flow ~y the use of two diaphragms, only one of which is shown as 1202; the flow meter as shown in Figure 4F is more fully eY.plained in U. S. Patent 2,544,665 dated March 31, l9Sl. ~s shown, a flag rod 1203 senses the flcxing of tne diaphragm 1202 to cause the arm 1204 to oscillate. A second diaphrasm (not shown) and an assoclated flag rod (not shown) cause arm 12C6 to oscillate in an alternate cycle. As explained in the noted patent, the combination of the arms 1206 and 1204, and the arms 1208 and 1210 cause the tansent ar~ 1214 to rotate as described in said patent. ~ metallic target 1212 at the point of intersection of the arms 1208 and 1210, is rotated past the proximity detector 27, whereby an output is provided to the logic circuit 170c to be processed as explained above.
The conditioning and interface circuit 136 is more fully shown with respect to 4D, wherein communication is made between the printer llla~ the display unit 111 for printiny out desired ?arametera as measured by the meter prover s~stem 10 including the measured flow rate(s) and the percentage(s) of error for the tests performed. ln particular, the printer llla is coupled to the I/D bus 140 via a first logic circuit 130b, and a ~arallel data controll~r (PDC) 192b, which may illustratively take the form of the PDC as manufactured by the assignee of this invention uoder thei~ dcsignation number 10453 and provides a two-way controlled access betw~en the I/D bus ~ 174072 140 and the printer 111~. Thus, on con~and through thc PDC
192b, a signal is deve'o~ed by the logic circuit l90b whereby the printer llla is strobed and an appropria~e acknowledging signal (AC~O) is transferred via the logic circuit l90b and the PDC 192b to indica~e that the printer llla is available for printing. If the printer l]la is busy, an appropriate busy signal will be transmitted back to the I/D bus 140. If a command has been issued to print data, the control portion of the signal is transmitted via the PDC 192b and the logic circuit l90b to control the printer llia to print that data which appears upon the data channel derived from the logic circuit l90b.
Further, the operator may ent~r appropriate com-mands upon the keyboard of the CRT terminal 112 that is inter-connected via the logic circuit l90a and a serial data con-troller (SDC) 192a to the computer system via the IJD bus 140.
The SDC l9~a may illustratively take the form Oc that SDC as manufactured by the assignee of this invention under their model No. 1093Q. The SDC 192a is capable of receiving the ssrially oriented data as derived from the CRT terminal 112 including instructions entered by the operator upon the terminal's keyboard. The SDC 192a converts these serial sig-nals inputted from the logic circuit l90a at an appropriate baud rate set by the clock 193, and transmits a set of digi-tal signals via the I/D bus 140 to the CPU 120. In turn,data to be displayed upon the CRT terminal 112 is transmitted by the I/D bus 140 via the SDC 192a and by the logic circuit l90a to be displayed upon the terminal's CRT.
The signal conditioning and interface circuit 138, as shown in Figure 4E, interfaces between the I/D bus 140 and the first or inlet valve 34 and the second or exhaust valve 36, as well as to provide signals to and from the motor control. ~Sotor control signals in terms of speed and direction are applied via the I/D bus 140 to be receivcd and transmitted 35 via the PI/O circuit 196 to a lo~ic circuit 194a whereby these r digital signals are applied to the motor control to effect a g corrcsponding action of the servomotor 20. Simi~arly, at the t ~ppropriate ti~c un~er the control o the exccuted program, signals are developed to close or to open the valves 34 and 36 ~ 174072 !
by actuDting their corresponding solenoids 66 and 64, respec-tively; these valve control signals are applied via the PI/G
circuit 196 and the logic circuit 194b to a pair of pneumatic valves disposed wi~hin the control room 105 as seen in Figure ~t 2C, whereby a 50 psi supply of air is selectively applied to each of the ~alve solenoids 66 and 64, respectively, to open and close these valves upon command. In this manner, the l heat generated by the valve solenoids is removed from the temperature controlled prover room 106. In addition, each of thesolenoids66 and 64 includes a proximity detector to determine whether the valve is open or closed. The output signals developed by the proximi-y detectors 50, 52, and 54 to determine the approximate position of the piston 14 are applied via a logic circuit 194c and .he PI/O 196 to the I/D bus 140.
A one second sa~pling clock ia developed from the encoder board (as explained above) and is applied via the losic cir-cuit 194d to the PI/O circuit 196. Similarly, the operator may actuate a switch to determine whether the meter fluid flow is to be o~tained from the proximity detector 27 or from the encoder 26, as shown in Figure 4C; this command signal is applied via the PI/O circuit 196 to the I/D bus 140. In order to achieve proper control over the servomotor 20, the motor status in terms of its speed, direction, and measured torque is applied via the logic circuit 198b and the PI/0 circuit 200 to the I/D bus 140.
The display unit 111 includes a front panel as shown in Figure 2D and is provided to display a series of lishts and backlighted pushbuttons variously indicating .~he condition of the system. As shown in ~igure 2D, the display panel includes the pxinter llla for providing printouts of the flow rate and the percentage of the fluid through the meter 38. In addition, there is included a plurality of lights lllb to llle. The light lllb is energized to indicate that a self-test of the meter prover 10 is being run, as will be explained. The standby li~ht llle indicates that power has becn applied to the meter prover 10 and that an initialization process ha~ been started to place the prover 10 in its standby mcde. h~ile in this stan~y node, a series of ~ 174072 key~oArd responses are required of the operator and upon completion of cntry of thc data via the ~eyboard of the C~T
terminal 112, the meter prover 10 will automatically go into the test in progress mode as indicated by the energization of the test in progress liaht lllc; in this mode, the meter 38 is actualli being tested. Upon completion of a meter test, the test completed indicator light llld is energized.
~t this time, the final percent accuracy is calculated and is printed out on the hard copy printer llla. In addition, there is included a backlit stop pushbutton lllg and a bac~-lit reset pushbutton lllf. If du^ing any phase of the opera-tion, the restart pushbutton lllf is depressed, the meter prover 1~ will respond as if pGwer is initially applied, as ~ill he more fully explained with respect to Figure 9H. The 15 stop pushbutton lllg is depressed only when an emergency situ-ation occurs that may cause damage to tne prover 10. Upon depressing the stop pushbutton lllg, the servomotor 20 is quickly decelerated to a halt and the prover 10 is locked up in its stop mode until primars- power is removed and reapplied.
Upon reapplication of power, the meter prover 10 will return to the standby mode. During the course of the executicn of the program, appropriate signals are generated and applied via the I/D bus 140, the PI/O circuit 200, and the logic and driver circuit 198a to energize the appropriate indicator lights lllb to llle.
The signal conditioning circuits as shown in the functional bloc~ diagrams of Figures 4~ to 4E are shown in more detail in the schematic diagrams of Figures 4G to M.
The signal conditionirg circuit 130 as generally shown in Pigure 4A is more specifically shown in the schematic dia-grams of Figures 4G, 4H, and 4I.
In Figure 4G, there is shown the multiplexer 149 as comprising a plurality of relays having mercury wetted relay contacts, which reduce resistance presented thereby and are coupled to the channels connected to the amplifier modules for providing to its relay of the multiplexer 149, a vol~age corresponding to the temperature as measured by one of the prover tcmp~rature transduocrs 57 or 48, the meter temperature ~32-transducers 44 or 42, or one of thc roo~ temperature trans-ducers R0 to R3. A selected channel is applied by the ener-gized relay of the multiplexer 149 via the second multiplexer 154, as shown in Figure 4G, and the amplifier 152 to the A/D
con~erter 15~, as shown in Figure 4H. In Figure 4H, there i5 shown the PI/0 circuit 160 as being coupled by the I/D bus 140 to the CPU 120. In addition, an output is derived from the PI/0 circuit 160 to be applied to a HEX to one decoder 153, as shown in Figure 4G, which in turn enerqizes one of a plurality of drivers 155 to close the corresponding relay of the multi-plexer 149; the PI/0 circuit output is also applied via the logic circuit 156 ~s comprised of an AND gate 156a, an inver-ter 156b, and a logic translator 156c to the multiplexer 154.
Further, with respect to Figure 4H, when the output of a selected one of the temperature measuring modules is applied to the A/D con~erter 158, a convert signal is applied to the A/D
converter 158 from the PI/0 circuit 160 via the expander cir-cuit 153. In response to this convert signal, the A/D con-verter 158 converts the inputted analog temperature signa' to a correspondin~ digital signal to be transmitted via the PI/0 circuit 160 to the I/D bus 140, and transmits an end of conversion status signal via the conductor 147 to the PI/0 160.
Referring now to Fisure 4I, there is shown a schema-tic diagram of an amplifier module to which each of the tem-perature measuring devices may be applied and amplified toprovide a voltage output signal to be applied via a corre-sponding channel to the multiplexer 149. Illustratively, the temperature measuring devices may comprise a resistance tem- -perature device as manufactured by Senso-Metrics under their designation No. 601222. The resistance temperature device (RTD) is coupled as one arm of a resistance bridge 201 com-prised of the RTD, and resistors Rl, R2, and R3. The excita-tion voltage, as applied to the a and b terminals of the bridge 201, as well as the output voltage as derived from the tcrminals c and d thereof are coupled to a conditioning cir-cuit 203 as illustratively mad~ by Analog Devices under their dcsignation Modcl 2~31. Basically, the conditioning circuit 203 incluùcs ~n operational amplii~er 205 to which is applied ~ 174072 the output of the bridye 201 to be amplified before being applied to a Bessel filter 207 whereby selected frequencies may be removed before being f~lrther amplified by an ope-a-tional amplifier 209 to be applied to a corresponding channel of the multiplexer 149. An extremely stable voltage sup~
ply serves to energize the circuit 203 and may illustratively comprise a voltage supplv as manufactured by Analog Devices under their designation AD584. As indicated in Figure 4I, the gain of the ôperational amplifier 205 is controlled by the resi.stance R4 plaoed between terminals 10 and 11 of the circuit 203, while the output offset is adjucted by setting the potentiometer R5 ccupJed to--the terminal-29 of-the circuit-- -203. In addition, the voltage and current as applied to ener-gize the bridge 201 are respectively controlled by adjusting the potentiometers R7 and RG.
The signal conditioning circuit 164 as generally shown in ~igure 4B is shown in more detail by the schematic diagram of Figure 4J. The PI/O circuit 168 is shown as being coupled to the I/D bus 140 and to the CPU 120 to provide trans-m.ission of data therebetween. A further input is made fromthe A/D converter 16~ via corresponding set of inverters 167 to the PI/O circuit 168. The pressure transducers 51, 46, and PB are connected respectively via the amplifiers 161a, b, and c to the multiplexer 163. As indicated in Fisure 4J, the multiplexer 163 i- made up of a corresponding plurality of relays which are energized to apply a selected output as derived from one of the pressure transducers to the A/D con~ t v~rter 166. The PI/O circui~ 168 determines which of the relays of the multiplexer 163 is to be energized by applying 30 control ~ignals via the bus 169 to the logic circuit 165 com- .
prised of a binary coded decimal to decimal converter and decoder 165a, which in effect selects which of the relays of the multiple~er 163 to be energized and applies a high going signal via a corresponding output via a set 165b of logic translators to a corresponding set 165c of power drivers, whereby ~ corresponding relay of the multiplexer 163 is energized to apply the corresponding tcmperature output to ~ ~4072 the A/D converter 166. Next, the PI/O 168 applies a convert signal via conductor 159 to the A/D converter 166, which con-verts the inputted analog signal to a corresponding digital signal, and transmits a status signal to the PI/O circuit 168.
In Figure 4K, there is shown a schematic diagram of the conditioning circuit 134 as generally shown in the func-tional block diagram of Figure 4C. The PI/O circuit 184 is shown as being coupled by the I/~ bus 140 to the CPU 120 and being coupled to the counter 182 comprised of a pair of coun-ters 182a, 182b. In turn, the signal conditioner and logic circuit 170b is shown as com~rised of a series of NOR gates 169 and a flip flcp 169e whose o~tput is appli~d via a NAND ~ate 180 and an inverter to an input of the counter 182a. The output of the linear encoder 26 is applied via corresponding logic translators and inverters to the aforementioned NOR gatesl~9 of thesignal conditioner and logic circuit 170b. The rotary meter encoder 40 is applied to the sign21 conditioner and logic circuit 170a that is similar to the signal conditioner and lo~ic circuit 17Ob to provide a composite signal to the interval timer 174 and a conditioned signal corresponding to the A signal to the interval timer 176.
It is unde~stood that the I/C circuits designated 174 and 176 of Figure 4X, also include the programmable counters 174a and 176a, respectively. The output of the interval timer 174 is applied via the lo~ic circuit 177 comprised of a ~AND gate and a pair of NOR gates as show,. in Figure 4~, to the Interrupt 2 input of CPU 120. The output of ~nterval timer 176 is applied to the control board of the servomotor 20.
As shown n Figure 4~, the signal conditioner and logic circuit 170a is comprised of first and second inputs receiving respectively the output signals A and A as developed by the rotary meter encoder 40. As shown respectively in Figures llA and llB, the A signal lags the A signal to provide, as will be explaine~ an indication of the direction of rotation in which ~le meter encoder 40 is m~vins. It is understood that the meter encodcr 40 is designed for this particula- system to rotate in a clockwise direction, and if jitter or mechanical vibration is imposed upon the meter encoder 40, at least ~ 174072

-3~-momentaril5~, the A sign~l ma~ appear to be leadirlg the A sig-nal; Fiyure llC shows the outpu' signal A as it would appear as if it leads the A signal by 90, this condition being un-d~sired, indicating an erroneous signal condition. The signal S conditioner and loqic circuit 170a is designed to eliminate such conditions as will now be explained. The A and A signal are each applied through a level shifter and inverter circuits to NOR gates 181a and 181b, respectively. ~he output of the NOR gate 181a is coupled to an input of the NOR gate 181b and theoutput of the NOR gate 181b is coupled via an inverter to an input of a NOR gate 181c. As shown in Figure 4K, an inverted signal, i.e., 180 out of phase with an input to the NOR gate lgla, is supplied to a NOR aate l~ld, whose output is applied to the other input of the NOR gate 181c. The ef-fective output of the signal conditioner and logic circuit170a is der ved from the output of the NOR gate 181c as shown in Figure llD, assuming that the meter encoder 40 is rotated in a clockwise or desired direction, and is applied to the interval timer 174 to be counted as explair.ed above. However, if even on a relatively short time basis, the A signal appears to be leading the A signal, a DC (or logic zero signal) output signal will be derived from the NOR gate 181c indicatins the presence of jitter or some other erroneous signal. In simi-lar fashicn, the signal conditioner and logic circuit 170b receives the A and A signal as derived from the linear encoder 26, these signals being also illustrated by Figur~s llA and llB respectively. In similar fashion, the A and A signals are applied to a similar set of NOR gates 169a, b, c, and d. The output of NGR gate 169c is applied to a latch as comprised of a pair of NOR gates interconnected as shown in Figure 4X. In similar fashion, if the A si~ as derived from the linear encoder 26 is lagging its A signal, theoutput as shown in ~igure llC
will be applied via the latch 169e to the interval timer 176 to be counted by its counter ~76a. A further set of NOX gates is also included in the signal conditioner and logic circuit 170b to provide an output signal as applied to the input 22 of the interval timer ~76 to indicate t-e occurrence of ehr A -nl74072 --3~--signal leading the ~ signal as derivcd from thc linear encoder 2G, indicating that thc piston 14 i~ b2ing driven in a reverse condition, i.e., is being driven by the servomotor 20 in a downward dir~ction toward its park position.
In Fisure 4L, there is shown a schematic diagram of the signal conditioner and logic circuit 136 as generally shown in Figure 4D. Data is tranferred between the parallel data controller (PDC) 192b and the C~U 120 via ~e I/D bus 140 and direct connections to the CPt~ 120. The output of the PiC circuit 192b is coupled to a logic c_rcuit l90b and by a plurality of lines as shown on the right hand side of the PDC 192b. The logic circuit l90b is primarily comprised o~ a logic trans-lator connected to each of its outputs. A NAND gate is incor-POrated into the logic cixcuit l90b to provide a reset signal to the printer llla. As shown in Eigure 4L, a strobe signal is applied to th~e printer lllawhi^h in turn applies an acknowledge signal tPCKO) t~ the PDC circuit 192b, whereby data may be trans-mitted to be printed by the printer llla under the control of a set of s-gnals so marked. In addition, a busy signal may be developed by the printer lllat~inhibit the transmission of data from the PDC circuit 192b to the printer llla. Further, the SDC circuit l9~a is coupled viathel/D bus 140 and direct connec-tions to the CPU 120; its output as taken from the right-hand side of the SDC circuit 192a is applied via the locic circuit l9~)a to provide data into and from the CRT terminal 112 under the control of preselected signals a s provid~d by the circuitry as shown on the left-h~nd side and desiqnated control; briefly, the control signals provide fixed sigilals to determine the mode of operation of the CRT terminal 112. The logic circuit l90a coupled to the data out signal comprises a logic trans-lator and an inverter circuit in the form of a line driver while tlie data input line is processed to invert the si~nal before application to the SDC circuit l9~a. The cloc~; cir-cuit 193 applies a signal via a logic circuit l9S comprised of logic translators to the cloc~; inputs of t~e SDC circuit 192a.
The signal co;-ditioning circuit 138 as generally shown in Figure 4E is more completely shown in the schematic ~ 174072 drawing of Figure 4.~. ~he PI/O circuit 200 is coupled to the CPU 120 ~y the I/D d~ta ~us 190 and those direct co~lection. ~t Ihe top and bottom so indicated. The outputs as v~riously taken from the PI/O circuit 200 are coupled by thelogic circuit 198a to variously e~ergize the lights as shown on the system contxol and display unit 111. The logic circui~ 198a is comprised of a logic translator ,or each output of the PI/O circuit 200 ana a p]urality o' drivers to energize the corresponding lights.
In addition, signals from the switch mechanisms of reset and stop pushlites lllf an~ lllg are applied via the logic circuit 198a and in particular to a set of NAND gates as shown in Figure 4M whose outputs are applied via inverters to the PI/O circuit 200. A
second PI/O circuit 195 is coupled by the I/D data bus 140 and direct connections to the CPU 120. A set of its outputs are applied via a logic circuit 194a to control various functions including direction and velocity of the servomotor 20; the logic circuit 194a receives seven inputs that are coupled via a set of NOR gates and series connected inverters and logic translators to a corresponding plurality of drivers, whose outputs serve to control the direction and velocity of the servomotor 20. Further, two outputs of the PI/O circuit 196 are applied via a logic circuit 194b comprised of a series connected inverter and a logic translator to a driver before being applied to control the pneumatic s~lenmas 66 and 64 associated with the valves 34 and 36. A set of five inputs are derived from the logic circuit 194c which processes inputs from the proximity detectors 50, 52, and 54; the logic circuit 194c comprises a circuit of resistors and diodes as coupled via inverters to corresponding inputs of the PI/O circuit 196.
The logic circuit 194d is coupled to the logic circuit 170a shown in Figure 4C and comprises a series of NO~ gates, the input signal comprising a one-second clock signal to control the sampling of the various pressure and temperature signals.

~174072 -3~-R~crring now to Figurc 5, there is shown a high levcl flow diagram of the various steps of the program as storcd within the PROM 124 and ex2cuted ur.der the control of the CPU 120 using data as er,tered into the RAM 126. Initially, the yower is applied to the computer svstem in step 210.
Typicaliy, t~e power supply for _he computer system as shown in Fisure 3 can take the form of that supp]y as manufactured by Power Mate under their designations Power Mate EMA 18/24B
and EMA 12/SD; Analog Devices-925; Datel-MPS 5/12, MPS 5/3, and MPD 12~3; and Practical Automation-PS6-28. Thereafter, step 214 zeroes or erases the storage locations ~ithin RAM
126, be,ore entering an initiaiizing su~rout~ne 300, whereby the various portions of the computer system are initialized as will be e~plained later in detail with respect to Figures 6A and 6B. It is noted that at various points during the course of the program, a return is made via ent-ance point 212 to step 214 to restart the operation of the program. As shown in Figure 4B, there is a switch 139 to be set to indi-cate whether it is desired to calibrate parts of the prover system 10 or to run a meter test. If the switch l3a is dis-posed to its calibrate mode, the decision step 216 moves to step 400 wherein a subroutine is exec~ted to calibrate the various analog inputs such as derived from the temperature and pressure measuring devices as shown in Figures 1 and 2A, and the corre~ponding A/D converters to which these signals are applied, as will be explained in more detail with respect ir to Figure 7. As the 5v51em moves to step 500, the operator can recall data from the various input measuring devices such ~-as temperature measuring devices 42, 44, 48, and 57; the pres-sure measuring devices 51 and 46; and the output of the linear encoder 20. In addition, the operator may also initiate vari-ous of the meter self-tests. This subroutine will be described in more detail with respect to Figures 8A to P. After gather- ¦
ing the apprGpriate data, the p-ogram moves to step or routine 35 900 wnerein a test or a series of tests of a meter 38 is carried t out by the meter prover system iO and the results thereof ~ 174072 ~39-dlsplayed or recorded upon the CP~T or print~r. The routine 900 will be explained in more detail with recpect to Figures 9A to Q.
Referring now to Figures 6A and 6B, there is shown theinitializing routine 300 wherein in step 302, a command is sent via the I/D bus 140 to cause the logic circuit 198a, as shown in Fisure 9E, to energize the standby lite llle.
In step 304, a scaling factor corresponding to a one cubic foot test is transferred from the RUI 126 to the programmable coun-ter 174a within the interval timer 174 as shown in 4C, to appro-priate.y scale the output of the meter encoder counter 179a whereby upon counting an appropriate number of pulses, e.g., 40,000, the logic circuit 177 outputs a pulse indicative that one cubic foot o~ fluid has been drawn through the meter 38.
Next, in step 3G5, the interru?ts associated with th~ CPU 120 are enabled to permit at any time later in the program the interrupts to be executed if t~e operator, for example, de-presses the reset ?ushbutton lllf or the stop pushbutton lllg.
Up to this point in the initialization subroutine 300, the in.errupts associated with the push~uttor.s lllf and lllg could not be enabled, but after execution of step 306, these lnter-rupts are available to be serviced. Next in step 308, the cir-cuitry shown in Figure 4C as associated with the rotary meter encoder 40 is initialized. In particular, the loyic circuit 170a is initialized, the interval timers 174 and 176 are cleared, the ~I~O circuit 184 is disposed to a selected mode, the logic circuits 177 and 178 are reset and the progra~mable counters 174a and 176a are programmed with the factors to be e~tered therein to be counted down. In step 310, a command is sent via the PI/O circuit 196 to the logic circuit 194b to effect opening of the second exhaust valve 36. In particular, the proximity detector associated with the valve 36 is accessed and if the valve 36 is not open, the proqram will wait until the valve 36 is open. Further in step 310, the control circuitry associated with the servomo~or 2a is initialized in that .he s ~ d of the servomotor 20 is setto zero,and a signal is applied to thc servomotor 20 to maintain it in a stationary condition, ~ 174072 while a logic circuit for sensing the torque of the servo-~tor 20 is rcset; the noted logic circuit is coupled to sense the control current f lowing to the servomotor 20. In step 312, the logic circuit 192b is initialized to its static I/O
mode with "hand-shaking" output capabilities, and the logic circuit l90b clears and prepares the ascociated printer llla to begin printing. In step 314, the SDC 192a is programmed to insure that the data may be transmitted between the CRT ter-minal 112 and the CPU 120, and the logic circuit l90a of Figure 4D similarly instructs CRT terminal 112 to clear and prepare itself for operation to receive data as well as to clear the CRT display. Next in step 316, any data s~ored in the A/D converter 166, as shown in Figure 4B, is cleared and the multiplexer 163 is set to its first channel whereby the output of the transducer 51 is applied by the multiplexer 163 to theA/D converter 166. Step 318 clears the conditioning and interface circuit130, and in particular clears any data stored in the A/D circuit 158, as shown in Figure 4A, as well as to set the multiplexers 149 and 154.to their first channels whereby tle output volta~e of the pro~er temperature transducer ~odule is applied via the multiplexers 149 and 154, and the operational amplifier 152 to the A/D circuit 158. In step 320, co~mand signals are sent via the l/D bus 140, and the PI/O
circuit 196, as seen in Figure 4E, to cause the logic circuit 194b to actuate the solenoid 66 to open and then close the first or meter valve 34 and to actuate the solenoid 64 to close the second or exhaust valve 36. When it is desired to open or close one of the valves 34 or 36, the proximity detector associated therewith is interrogated and i~ it is determined to be in the desired position, no further action is taken; if, however, the valve is not in the desired position, the logic circuit 194b provides an output to actuate the associated pneumatic sole-noid to ca~se the valve to open or close, as desired. In step 322, the program continues to a subroutine as will be explained with respect to Figure 6B whereby the piston 14 is returned to its park position, i.e., the lowermost position corresponding to the position of the proximity detector 50 as seen in Figures 1, 2A and 2~.
In Figure 6B, the subroutine 322 for returning the piston 14 to its lowermost position is shown. ln ste~ 324, a con-trol signal i5 sent via the I/~ bus 140, the ~I/0 circuit196 to cause the logic circuit 194b to clo~e the first or meter valve 32. Next, step 32~ determines the position of the piston 14 which may be anywhere from its lowermost to its topmost position as seen in Figure 1; in particular, step 326 causes the PI/O circuit 195 tv interrogate the logic circuit 194c to determine ~f the output of t~.e proximity detector 50 as seen in Figures 1 and 2 is high or one, and if so, the subroutine mc~-es to the final step 346 wherein a command is sent to the PI/O circuit 196 of Fiyure 4E to con-lS dition the lo~ic circuits194a and 198b so that the motorcontrol for ~he servomotor 20 is set for zero speed and further to set the interval timer 176 as seen in Fiqure 4C to indicate that the output of the encoder is in i~s starting position, i.e., to set the counter 176a to zero preparing t to start generating one second sampling puises. If the piston 14 is not at its park position, the cubroutine proceeds to step 328, wherein a determination is made as to whether the piston 14 is disposed in ~n intermediate position, i.e., theabutmer.t 92 is disposed between the proximity detectors SQ and 52 as shown in Figures 1 and 2A and B; if piston 14 is so disposed, the sub-routine moves to step 330, whereby control signals are sent via the PI/O ci-cuit 196 to set the logic circuit 194a to drive the servomotor 20 in a countercloc~wise direction, and furthe~
i~ step 332, the speed is controlled to accelerate to a selected speed, i.e., the ninth of sixteen speeds. However, if step 326 determines that the piston 14 is in its uppermost position, i.e., its abutment92 is above the proximity detector 52, step 334 sets the logic circuit 194a of Figure 4E to set the lowest specd, i.e., speed 1 of 16 and to rotate the servomotor 20 in a countercloc~wise direction, before procceding to s~ep 336 wherein the logic circuit 194a effects acccleration of the servomotor 20 to its ncxt highest speed up to a maximum of its ~ 174072 twe~fth speed. At that point in step 338, the logic circuit 194c is accessed to determine whether the piston 14 is dis-posed at the proximity detector 52 and i~ not, step 336 accel-erates the piston to its ne~t higher sp~ed until step 338 determines that the piston 14 is at the proximity detector 52. At that point, the logic circuit 194a maintains the cur-rent speed of servomotor 20, until in step 342, the park proximity detector 50 detects the presence of the piston 14 at which time, step 344 controls the logic circuit 194a to decelerate the piston 1~ to a stop position before entering the step 346 wherein the motor control is set for zero speed.
If the operator has set the calibrate/run switch to its calibrate position, the program moves to the subroutine 400 as more fully shown in Figure 7. Initially in step 402, a command is sent to the logic circuit l90a of Figure 4D to clear the CR~ terminal 112. Step 404 displays a suitable - message upon the CRT screen indicating the meter prover sys-tem 10 has entered into a calibrate mode indicating, as sho~n in Figure 7, the various parameters that may be so calibrated.
Next, step ~06 returns the cursor as displayed upon the CRT
to its left-hand margin waiting for the operator to make a suitable entry. Next after operator entry via the keyboard of the CRT terminal 112, step 408 interrogates the key~oard to determine which of the possible ~eys has been depressed.
For example, if it is determined that one of the sets of keys T and O, T and 1, T and 2, T and 3, T and 4, T and 5, T and 6, or T and 7 has ~een depressed, the subroutine moves to step 410, wherein a corresponding channel is selected by the multiplexer 149. Next in step 412, a select co~mand signal is transmitted via the PI/O circuit 160 to the multiplexer 149, whereby the selected channel is connected via the multi-plexers 149 and 154, the amplifier 152, to the A/D converter 158. Next, step 414 applies a convert signal to the A/D cir-CUit 158 whereby in step 41G the temperature as measured is displayed. At this point, the operator can calibrate the se-lected temperature transducer module to provide a correct read-ing by adjustin-7 the zero and span of the operational amplifier of the module, this procedure being repeated until an accurate ~ 174072 reading is displaved upon the CRT. Thou~h detailed explana-tion will not be given, it is realized that the similar keys P ar.d 1, P and 2, and P and B may be also operator activated, wher~by the gains of the operational amplifiers 161a, 161b, 161c of Figure 4B may be similarly adjusted in order to give accurate readinqs. In similar fashion, the keys T and O, T
and 1, T and 2, T and 3, T and 4, T and 5, T and 6, and T ana 7 may be depressedand their respective amplifiers and circuits may be adjusted to provide accurate readin~s. Upon pressi~g of the keys V and P, as determined by step 408, the routine moves via step 450 to step 452, whereby a command signal is sent v_a the PI/O circuit 168 of Figure 4~ to cause the mul-tiple~er 163 to apply the voltage calibrate input sisnal V to the A4D con-verter circuit 166, which converts these inputs in step 4~4 to digital values.
,5 The voltage calibra~e input signal is adjusted to set the zero and full scale values of the A~D converter 16~, ~ese v~lues being appropriately dis-played in step 456 upon the CRT terminal 112. In similar fashion if the V and T keys of the keyboard is depressed, the routine proceeds via s ep 4~2 to step 444, wherein the vol tage calibrate input signal VT is applied to the A/D converter circuit 158 of Figure 4A and its zero and full scale values may be similarly adjusted. If any other key is depressed upon the keyboard, step 408 branches via step 456 to step 45%, wherein that character is rejec~ed to return to the starting point of step 408 again.
The data input and retrieval subroutine as broadly shown in Figure S as step or routine 500, is more fully ex-plained with res~ect to Pigures 8A to 8P, an overview of the routine 500 being shown ir Figure 8A. Initially, a co~mand is given via the I/D bus 140 to the lo~ic and driver circuit 198a of Figure 4E to energize the standby light llle. Next in step 504, which is more fully shown in Figure 8C, a deter-mination is made if a self-test is desired, and if so, that subroutine is executed. Ncxt in step 506, it is determined whether it is desired to display the room temperatures, and if so, a display upon the CRT of the termin 1 112 is made, as will be more fully explained with res3-d to Figure 8H. In

4 0 7 ?.
01 ~ 4~ ~
02 step 508, an examination of the keyboard is made to see if the 03 operator wishes to recall data pertaining to previous meter 04 accuracy tests and if any data is required, that data is displayed 05 upon the CRT display; the subroutine 508 will be more fully 06 explained with regard to Figure 8J. In step 510, appropriate 07 flags are set automatically to permit, at a later time during the 08 meter test, the pressure and temperature parameters to be monitored 09 and displayed; the subroutine for executing such display is more fully explained with respect to Figure 8K. In step 512, the sub-11 routine for setting the test volume desired and the manner in which 12 it is entered into the programmable counter 174a of the interval 13 timer 174 is set out in more detail with the subroutine as shown in 14 Figure 8L. Next in step 514, it is necessary for the operator to enter via the CRT terminal keyboard a select test flow rate or 16 rates, as will be more fully explained with regard to the subroutine 17 of Figure 8M. In step 516, the operator sets the number of times to 18 repeat a certain test; for example, the meter may bç tested three 19 times for a flow rate or for a selected volume and flow rate. The entry of the repeat commands is explained with respect to the 21 subroutine of Figure 8N. Thereafter, step 518 sends clear commands 22 via the logic circuit 190a whereby any data stored in the buffers 23 associated with the CRT terminal 112 are cleared. At this point, 24 step 520 makes a decision as to whether the volume of the meter 38 is to be determined with the output of the proximity detector 27 or 26 with the output of the rotary encoder 40. If the switch is set to a 27 logic "zero", a flag is set in step 522 to conduct an encoder type 28 test, whereby if the switch is set to a logic "one" position, a flag 29 is set in step 524 to conduct the proximity detector type test.
Continuing the routine 500 as shown in Figure 8B, the system 31 obtains and displays upon the CRT the meter temperature and pressure, 32 and the prover temperature and pressure as measured during the meter 33 test, as follows. Next, step 528 displays, if instructed, upon the 34 CRT data indicative of the pressure and temperature within the meter 38 and the prover 10. Once the test volume, either one cubic foot, 36 one-half cubic foot, or one-fourth cubic foot, has been set by entry 37 of the operator upon the CRT terminal 112, the entered value is ~ 174072 decoded in step 530, and the chosen value ~ displayed m step 532 ~y t~e C~T as TEST VOL. = x CU. FT. Thereafter, the desired flow rate or rates that are entered upon the keyboard are decoded in step 534 and the chosen rates are displayed upon the CRT in-

5 step 536 as: FLOW RATES are QX,QX--QX. In similar fashion in step 538, the number of repeats for any particular test(s) with respect to flow rates or volumes are decoded and in step 539, the selected number of repeats per flow rate or volume is displayed upon the CRT as: NO. OF TESTS PER
FLOW RATE = X. At this point, a carriage return line feed instruction is carried out in step 540 whereby a cursor as placed by the CRT terminal upon the CRT is removed.
The subroutir.e 504 is more fully shown in Figure 8C, wherein a desired self-test(s) is selected. Initially in step 542, the data storage buffers associated with the CRT
of the CRT terminal 112 are cleared by commands generated by the logic circuit 190a. In step 544, the CRT displays,as shown in Figure 8C, an indication of the various self-tests that may be conducted, e.g., volume ~', leakage L, or NO;
the operator selects one of these self-tests by depressing the appropriate key of the keyboard. In step 546, the cur-sors, as shown in Figure 8C, are flashed to prompt the opera-tor to respond to select the self-tests, whether volume V, leak L or NO. In step 548, the sub,outine moves to the desired self-test dependent upon which key has been selected in step 544. If for example, the volume self-test V has been selected, a volume self-test sequence is output to the CRT
in step 552 and the volume self-test i5 executed in step 554 as will be more fully explained with respect to Figure 8E.
If a leak test has been chosen, the subroutine moves through step 558 to provide a display upon the CRT indicating the selected test and to initiate the leak self~test, which is executed in step 560 as will more fully be described with respect to the subroutine of Figure 8D. Next the subroutine determines in step ~56 whether there is another input to be dealt with and the subroutine returns to step 546. If the operator pressed t~e escape key as detcrmined by step 548, ~ 174072 the subroutine exits via step 562 to the entry point 212 of the main diagram as shown in Figure 5 whereat the program begins. If the operator strikes the N and O keys, as detected by the step 548, the subroutine exits via step 566 and returns 5 to the routine as shown in Figure 8A to continue with the next step 506. If any other key is struck, the subroutine exits via step 558 to- reject that character in step 570 and to return to step 548 to recognize another key.
The leak self-testing subroutine 560 is more com-10 pletely shown with respect to Figure 8D. The leak self-test is a test to provide an indication of the integrity of the prover system's seal. Initially in step 572, the logic cir-cuit 198a in Figure 4E energizes the self-test and test in pr~gre~ss lights lllb and lllc. Next in step 574j the--subroutine 322 for lS returning the piston to its park position as explained above with respect to Figure 6B, is executed. Next, a command sig-nal is issued in step 574 via the PI/O circuit 168 to set the multiplexer 163 to receive the signal via the second channel from the pressure transducer 51 (pressure PPl~. Next in step 576, the 20 logic circuit 194b is commanded to apply actuating signals to the solenoids for effecting the closing of the first inlet and second exhaust valves 34 and 36. In step 578, a command is issued via the PI/O circuit 196 to actuate the logic cir-cuit 194a of Figure 4E to direct the servomotor 20 to drive 25 the lead screw 18 in a clockwise direction at a relatively slo~ speed corresponding to "1". The servomotor 20 cannot be energized as directed by step 578, until the prohibition built into the program is defeated as by depressing a momentary switch ~not shown) coupled to the logic circuit 194c, there-30 by permittirlg the operation of the servomotor 20with both valves 34 and 3Ç closed. Normally, the servomotor 20 may not be operated if the valves 34 and 36 are closed, thus preventing possible damage to the piston seal. Ne~t in step 580, an indication of pressure is input into the A/D converter 166 35 in step 580 and a check is made in step 582 to determine whether the pressure has increased by a certain amount as indicated by the data stored in the A/D circuit 166, i.e., ~ 174072 has the vacuum increase exceeded 1.38 inches of water? If the vacuum has not increased to beyond 1.38 inches of water, the subroutine cycles back and repeats step 580. If the vacuu~ inside the chamber 28 has increased to beyond 1.38 inches of water, the subroutine moves to step 584 whereby a command is given through the PI/O circuit 196 to cause the servomotor 20 to stop. In step 586, a 20-second wait is loaded into a register within the RAM 126 and counted down to provide a time for leakage to occur in the chamber 2~.
Next, in step 588, a convert signal is applied to the A/D
converter 166 of Figure 4B, to determine the pressure now being sensed by the pressure transducer 51. In step 590, the subroutine waits for the one-second clock signal which is developed from the logic circuit 178 of Figure 4C and is applied via the logic circuit 194d of Figure 4E to decre-ment in step 592 the 20-second count placed in the register within the ~1 126. Step 592 determines whether this regis-ter in the RAM 126 has been decremented to zero, and if not, the subroutine returns to step 588, whereby for each second of a 20-second interval, the piston pressure as derived from ~the transducer 51 is obtained and is displayed upon the CRT
thus providing a continuous monitor of the prover pressure so that the operator may determine whether there are any leaks within the chamber 28 during the 20-second test. The count decrementing continues until the register is zero as deter-mined by step 592, at which time a command is issued in step 594 to cause the logic circuit 194b to actuate the solenoid to open the second exhaust valve 36. At this point, the posi-tion of the piston 14 is determined in step 596 by checking the status of the pro~imity detectors 50 and 52 by accessing the logic circuit 194c. At this time the test is complete and a command is issued to the logic circuit l90a to energize the test complete and self-test indicators. Finally, in step 322, the piston 14 is returned to its park position by the sub-routine as shown in Figure 6B, before returning to step 556as shown in Figure 8C.

1 ~74~072 In Figure 8E, the volume self-test subroutine 554 is shown in more detail. First, step 600 commands the logic circuit 198ato energize the self-test and test in progress indicators lllb and lllc. The volume self-test is entered to obtain an indication of the accuracy of the linear encoder 40. Step 332, as shown in Figure 6B,returns the piston 14 to its park position before command signals are issued in step 602 via the logic circuit 194b to actuate the solenoids to open the first, inlet valve 34 and to actuate the solenoid to close the second exhaust valve 36. Next, a command is made in step 604 to load the speed buffer, i.e., an addressed portion within the R~M 126, with its maximum speed of 16.
Next in step 606, the servomotor 20 is accelerated to the speed as stored in this buffer in accordance with the subroutine as will be discussed with respect to Figure 8F. Next in step 608, the counter 182 and the prosrammable counter 174a as shown in Figure 4C are inhibited a~d are reset to zero. Step 610 checks the status of the proximity detector 52 to deter-mine whether the piston 14 has been drawn to its start-test 2~ position, and if not, the check is repeated until the piston 14 reaches this position. When the piston 14 has reached its start-test position, the program moves to step 612 wherein the programmable counter 174a is disabled and the linear counter 182 is enabled to count the linear encoder pulses as the piston 14 is drawn from the proximity detector 52 to ~roximity detector 54. In step 614, the status of the dis-abled proximity detector 54 is checked periodically until the piston 14 is disposed thereat, at which time the sub-routine moves to step 616 to disable the linear counter 182.
In step 618, the cumulative n~mber or count from linear encoder counter 182 is transmitted via the PI/O circuit 184 to a designated location within the ~1 126. In step 620, a suitable series of command signals are transmitted to the losic circuit 194a whereby the servomotor 20 is decelerated to a stop condition as ~-ill be described with resp~ct to the subroutine shown in Figure 8G. ~ext in ste? 622, flags are set indica~ hat the piston 14 is not between the proximity ~ 174072 02 detectors 50 and 52. In ste~ 624, the logic and driver circuit 03 198a energizes the self-test and test complete lights lllb and 04 llld. At this point in step 626, the count of the counter 182 05 indicative of the travel of the piston 14 between the proximity 06 detectors 52 and 54 is transferred from its location within RAM
07 126 to be displayed by the CRT of the terminal 112 and a~ the 08 same time clears counter 182. Next, the piston 14 is returned to 09 its park position by step 332 as shown in Figure 6B, and step 628 causes the logic and driver circuit 198a to energize the standby 11 light llle, before returning to step 556 as shown in Figure 8C.
12 The accelerating motor subroutine generally indicated 13 in Figure 8E by the numeral 606 is shown in more detail in Figure 14 8F, wherein in step 630 a command is sent via the I/D bus 140 to disable the counters 182 and 174a of Figure 4C. Next, an enable 16 command is sent to the logic circuit 194a by step 632 to command 17 the servomotor 20 to rotate in a clockwise direction, thus 18 raising the piston 14. At this point, speed 1, i.e., the lowest 19 speed, is loaded into a speed compare buffer within the RAM 126 by step 634. In step 636, a command is given to the logic 21 circuit 194a to increase incrementally the speed of the 22 servomotor 20 and the actual speed as stored in the speed compare 23 buffer of the RAM 126 is compared with the final designated speed 24 stored in the speed buffer and if they are equal, i.e., the servomotor 20 has been accelerated to the desired speed, the 26 subroutine moves to step 646. If not, step 640 implements a wait 27 period of approximately 0.25 seconds before sampling via the 28 logic circuit 194c the status of the proximity detector 52 and if 29 not at this position, step 644 increments the desired speed by 1 before returning to step 636 in which the new speed is disposed 31 in the speed compare buffer of the RAM 126. If the piston 14 has 32 been driven into its intermediate position as detected by step 33 640, the subroutine moves to step 642, to set a flag indicating 34 that the piston 14 has been prematurely brought to its inter-mediate position and the subroutine is returned to step 604, as 36 shown in Figure 8E. As seen in Figure 8F, the normal operation is 37 for the piston 14 to be accelerated to the desired speed and then 38 to periodically test the output of the proximity detector 52.

~ 174072 Upon deten~ning m step 646 that the piston 14 has reached the start-test position as indicated by the output of the proximity detector 52, the subroutine branches to step 970 as wili be explained with respect to Figure 9E to assess and determine the occur-rence of the rising edge of the next pulse A from the rotarymeter encoder 40, wherebv as will be explained further the meter test is begun by applying the pulse outputs derived from the rotary meter encoder ~O and the linear encoder 26 into their respective counters 174a and 182.
The subroutine to decelerate the servomotor 20 as indicated in step 620 of Figure 8E is more fully explained with respect to the subroutine shown in Figure 8G. Initially in step 648, the counter 174a and the counter 182 as seen in ~igure 4C fDr respectively receiving the rotary and linear encoder outputs are first disabled and then reset. In step 650, the load speed compare buffer within the RAM 126 is loaded with the speed 16, i.e., the highest speed available.
Next, in step 652, the actual speed as stored in the speed buffer of R~S 126, is compared with the high speed 16 as 2C loaded into the speed compare buffer and if not equal, the speed as loaded into the speed com?are buffer is decremented until the actual speed equals the speed loaded into the speed compare buffer, at which time the subroutine moves to step 656 and the speed as stored in the speed compare buffer is decremented. In step 658, a command is issued to the logic circuit 194a to deceleratethe servomotor 20 to that new speed as disposed within the speed buffer of the R~ 126. In step 660, the actual speed is compared with zero, i.e., the servo-motor 20 is stopped, and if not stopped, a 0.2 second wait or delay is implemented in step 662, before again decrement-ing the motor speed by steps 656 and 658. This process con-tinues until the servomotor ~0 has been brought to a stop, i.e., the speed equals zero at which time step 660 returns the subroutine to step 622 of Fisure 8E.
In Pigure 8H, there is shown the subroutine 506 for operator entry via the kevboard O r the CRT te~inal 112 of the selected tem?c atures within the prover room 106 to be ~ 174072 displayed and the steps for so displaying them upon the terminal'~ CRT. It has been shown that knowledge of the temperature ~7ithin the prover room 106 is helpful to investi-gate the level of control that may be exercised upon the meter prover 10 within the room 106. The subroutine as shown in Figure 8H permits the operator to display any of the four room temperature outputsR0, Rl, R2, and R3, from the tem-perature measuring devices shot~ within Pigure 2C as being disposed about the prover room 106. These temperatures can continue to be accessed and displayed upon the CRT of the terminal 112 until the operator terminates this action by pressing the N and O keys of the terminal's keyboard. Ini-tially in step 664, a command is sent to the logic circuit l9~a, wh~re~y vi2 the control input, the buffers associated with the CRT ter~inal 112 are cleared. Thereafter, step 666 causes the logic circuit 190a to display an indication, as shown in Figure 8H, of the possible room temperature devices that may be accessed, i.e., the room temperature devices R0, Rl, R2, or R3. If the operator does not desire to access and display any of these temperatures, the 1~ and O ~eys are struck. In step 668, a carriage return line feed is output so that the cursor is flashed, indicating that an operator response is required. In step 670, an interroga-tion is made of which key is actuated via the logic circuit 190a and if the keys R and 0 corresponding to the room tem-perature device R0, are actuated, the subroutine moves via step 672a to step 674a whereby a control signal is issued vià the l/D bus 140, PI/O circuit 160 to cause the multi-plexer 149 to select its fifth input whereby a voltage repre-sentative of the room temperature transducer R0 is appliedvia the multiplexers i49 and 154 to the A/D converter 158.
In step 676a, a convert signal is applied via the PIjO cir-cuit 160 to the A/~ converter circuit 158 to c~nvert the analog input signal to binary digital data. Next, step 678a converts the binary digital data to decimal data and, step 680a converts that data to a floating point decimal for-mat by processes ~ell known in the art. In step 682a, the ~ 174072 02 digital floating point decimal data is converted to digital F in 03 accordance with the formula:
04 [ (RAW DIGITAL NUMBER) (7.326007326 x 10-3~(9)] ~ 32 = F

06 In step 6~4a, suitable data is generated out from the logic 07 circuit 190a to display the room temperature in degrees 08 Fahrenheit upon the CRT display. In similar fashion, step 670 is 09 able to detect the operator actuation of each of the pairs of keys corresponding to R0, Rl, R2, and R3 room detectors to access 11 these detectors as connected to the multiplexer 149 of Figure 4A
12 and to process and display the selected data upon the CRT
13 display. In step 69~, a determination is made as to whether 14 another input is desired, and the process returns to the lS beginning of step 670. If the operator presses the escape key, 16 the routine moves through step 6~6 to return via entry point 212 17 to the beginning of the program as seen in Figure 5. If the N
1~ and O keys are depressed, the program proceeds to step 6~8 and 19 return~ to the next subroutine or step 508 as seen in Figure 8A.
If an extraneous key is depressed, the subroutine exits throu~h 21 step G90 and rejects the character in step 692 before returning 22 to the beginning of step 670.
23 The subroutine 508 as generally indicated in Figure 8A
24 for sampling data from previously conducted tests is carried out by the subroutine 508 which is more clearly shown in Figure 8J.
26 The subroutine may be entered after a meter test has been executed.
27 First, in step 696, the CRT, in particular its buffers and display, 28 are cleared of previously stored data. ~ext, step 69~ displays by 29 actuating the logic circuit l90a to have the CRT display the possible test parameters that may be accessed and displayed, namely 31 K, the number of counts from the linear encoder 26; TP, the 32 temperature of the prover; TM, the temperature of the meter; PM, 33 the pressure of the meter; PP, the pressure of the prover; and the 34 percentage of error from the previous test. If none of these values are desired to be displayed, the operator may depress keys N
36 and O corresponding to NO at which time the program advances to the 37 next step. In step 700, the cursor is flashed indicating ~ 1~4072 ~ -53-to the operator to select one of these parameters or NO by pressing the corresponding keys In step 702, if the linear encoder counts are selected by depressing the key K, the subroutine branches through step 704a to step 706a, whereby the count of the linear encoder register within the R~ 126 is accessed and read out and applied via the logic circuit l90a to be dis-played upon the CRT. In similar fashion, if the keys corre-sponding to the temperature of the meter prover are actuated upon the keyboard by the operator, the process proceeds from step 702 via step 704b to step 706b wherein the contents of the prover temperature buffer, a designated location within the RA~1 126, is transferred from the RAM 126 to be displayed upon the CRT. In similar fashion, each of the meter tempera-ture TM, the prover temperature TP, t~e prover pressure PP, or the meter pressure PM may be similarly accessed from a corre-spondins location within the RAM 126 and displayed upon the CRT. Also the percentage of error of the difference between the standard volume as drawn by the prover system 10 and that actually measured by the meter 38 is calculated with respect to the standard volume and may be likewise displayed upon the CRT. If a second or further key has been pressed, step 716 returns the subroutine to the beginning of step 700.
If the escape key has been depressed, the subroutine moves through step ?08 to exit via entry point 212 to the beginning of the program as shown in Figure S. If any extraneous key is depressed, the routine proceeds through step 712 to reject the mista~en character in step 714 before returning to the beginning of step 702. After the operator has observed any and all parameters that he desires to observe upon the CRT, he presses the N and Q keys whereby the prosram returns to the next step or subroutine.
Routine 510 as generally shown in Figure 8A is eapa-ble of accessing and displaying the parameters as are automat-ically ~easured and monitored du_ing the course of a tes$, and is shown in greater detail in Fisure &~. First in step 718, the buffers associated with the CRT are cleared, before ~ 174072 steps 720, 722, 724, and 726 set flags in appropriate loca-tions within the RAM 126 to access the prover and meter tem-peratures and the meter and prover pressures. Thus, the flags are set to permit display upon the CRm of these parameters automatically,and thereafter the routine 510 returns to step 512 as shown in Figure 8A.
Step 512, as generally shown in Figure 8A, for setting the desired volume to be drawn through the meter 38 is more - fully ex~lained with respect to the subroutine shown in Figure 8L. Initially, the CRT terminal 112 is cleared in step 742, before in step 746 displaying upon the CRT the pos~ible volumes, e.g., one cubic foot, .5 and .25 cubic feet, that may be selected by the operator to be drawn through the meter 38 to be tes~ed. In step 748, the cursor is flashed to prompt the operator to make his volume selection. Upon actuation by the operator of the key corresponding to each of the selectable volumes as sensed in step 750, the s~brcutine 512 mcves to enter the correspcnding volume. For example, if the appropriate key is depressed indicating a desire to enter a value corresponding to one cubic foot, the subroutine moves via step 752a to step 754a wherein the scaling factor corresponding to one cubic foot is set in a known position in the RAM 126. The scaling factor will be subsequently transferred from this RAM location to the rotary encoder counter 174a. After selection of any of the desired test volumes, the subroutine returns to the next step 514 as shown in Figure 8A. If the escape key is selected, the subroutine moves through step 756 to retur~ to the main program via entry point 212. If a wrong key is accidentally depressed, the subroutine moves through step 758 to reject that entered character in step 760 before returning to the begin-ning of step 150.
Next in the prosram is step or subroutine 514 wherein the desired flow rate at which the fluid is to be drawn through the meter 38 s set; zs e~plained above, the selected flow rate in turn determines the speed a~ which the servomotor 20 is controlled to rotate ~ raise the piston 14 as shown in Fi ~e 1.
~eferrin~ now to Fisure 8!~, step 762 initially clears the ~ 174072 buffers associated with the CRT terminal 112 and in step 764, the possible flow rates from Q0 to QF are displayed upon the CRT, it being understood that Q0 corresponds to a minimum flow rate, e.g., 20 cubic feet per minute, and QF corresponds to a maximum flow rate, e.g., 400 cubic feet per minute. Step 766 causes the cursor to flash on and off to prompt the opera-tor to make his selection of flow rate. In step 768, an interrogation is madè of the keyboard to determine which key the operator has depressed and if for example, the flow rate Q0 is depressed, the subroutine exits via step 770a to step 772a wherein the flag for the particular rate Q0 is set in a designated location within the RAM 126. Next, step 774a causes the selected flow rate Q0 to be displayed upon the CRT;
then, the system returns with the response of "ANOTHER?" and 'lashes the cursor to indicate that a user response is required.
If a further rate is to be also tested, step 784 returns the routine to the beginning of step 766 whereby a second and per-haps further flow rates may be tested within a single set of tests. If the operator depresses the escape key, the routine moves through step 776 and entry point 212 to the main program as shown in Figure 5. If a wrong key of the keyboard of the CRT terminal 112 is depressed, the routine moves through step 780 to reject the incorrect character in step 782 before returning to the beginning of step 768. If no further flow rates are to be selected to test the meter 38, the operator presses the N and O keys, whereby the routine returns via step 778 to the next step 516 as shown in Figure 8A.
Step or routine 516 for setting the number of repeat tests that is to be set for each of the selected flow rates may be entered via the operator keyboard in a manner more specifically shown in Figure 8N. Initially, the buffers asso-ciated with the CRT terminal 112 and the display screen of the CRT are cleared in step 786, before the possible number of tests or retests for flow rate, i.e., 1, 2, or 3, is displayed upon the CRT. Step 790 flashes the cursor on the CRT to prompt the operator to make his selection of the flow rate. Step 792 detects which of the terminal keys is depressed and if for examplc, a Xc, is dcpressed indicating only one test per flow rate is to bc conducted, the subroutine proceeds through step ~ 174072 794a to step 793a, wherein the output "1" is displayed upon the CRT before returning to the next step 518 of the main pro-gram as seen in Figure 8~. If two tests are to be made, the subroutine exits via step 794b to step 793b wherein a command is made to copy the flow rate flags for one repeat and in step 796b to set a flag for a second repeat in a designated area of the RAM 126. In step 796b, an indication of 2 is displayed upon the CRT. If a selected test is to be repeated three tLmes, the subroutine carries out a similar series of steps 794c, 793c, and 796c. If an incorrect character is depressed upon the keyboard, the routine moves through step 795 to reject the incorrect character in step 797 before returning to the begir.ning of step 792. If the operator presses the escape key, the routine exits via step 198 to entry point 212 whereby a 1~ return is made to the main program as shown in Figure 5.
Subroutine 528, as generally shown in Figure 8A, dis- -plays temperature and pressure data as the meter test is being conducted, as more fully shown by the subroutine illustrated in Pigure 8P. Initially, the CRT cursor is moved to a ho~e position and the CPU 120 addresses that location within the RAM 126 where the TM flag has been set automatically during the previous subroutine 510. Since the TM flag has been set, the content of the meter temperature buffer, i.e., an address-able location within the RAM 126, is transferred via the logic circuit l90a tQ be displayed upon the CRT as indicated in step 802. After the display, the subroutine moves to step 806 which examines that location of the R~M 126 where the TP
out flag indicating that there was an indication to ~onitor during a test the prover temperatu-e TP has been set, and the output of the prover temperature buffer is transferred to be displayed upon the CRT. Aftex such display, the subroutine moves to step 810, which accesses the previously set meter pressure PM flag and outputs the content of the pressure buf-fer, i.e., a known location in the R~bl 126 to be displayed upon the CRT. After display, step 814 accesses the previously set PP out buffer flag, and the contents of the prover pressure buffer is transferredto be displayed upon the C~T. After the display of such information, the subroutine returns to the next step 530 as indicated in Figure 3B. The values output at this ~174072 time correspond to the values currently stored in the RAM
buffers. If a test has not yet been run, zeroes are initi-ally stored in the RAM 126 and will be output and displayed as TM - 0.0 Deg. F. This step formats the display so that when a test begins, the system will replace the zeroes with appropriate numbers.
The execution of the tests of the meter 38 by the meter prover system 10 as well as the output of the results to the printer and CRT is performed by the routine generally identified In Figure 5 by thenumeral 900, as will now be explained in greater detail with respect to Figures 9A to 9P Tn Figure 9A, there is shown a high level diagram of the various steps or subroutines that are necessary to effect the test of the meter 38 starting with step 322 as shown above with respect to Figure 6B to return the piston 14 to its park position, i.e., its bottom-most normal position with respect to the cylinder 12 as shown in Figures 1 and 2A. Next, routine 902, as will be more fully explained with respect to Figure 9B, determines the type of test, i.e., will the volume measured by the meter 38 be determined by theproximity detector 27, or by the rotary optical encoder 40 as shown in Figure ~C, and the particular volume that is to be drawn through the meter 38;in particular step 902 loads the appropriate volume factor into the p~ogrammable counter 174a as well as to store the appropriate divisorin the buffer EORP of the R~ 126. Nextj step 904 determines for the condition that one test per flow rate is to be made, the flow rate to be executed for that test; in particular the system addresses that location where the flow rate flags are stored wit~n the R~1126 to determine the appropriate flcw rate to ~e used in the particular test. If the flow rate is so located, the routine moves to step or routine 906a to dete-rmine which flow rate is to be executed and to obtain that flow rate and execute that subroutine as more specif~cally shown in Figures 9C and D.
If it is decided in step 908 that two tests for each flow rate are to be conducted, the routine addresses those areas in the ~ 126 for the corresponding flow rate flags and executes 117~0~2 the tests at the programmed flow rate in step 906b. If three tests per flow rate are called for, it is first determined in step 912 whether the flow rate for the three corresponding rates have been entered, and if yes, step 906c calls the flow S rate flags from the designated locations within the RAM 126 and executes the tests of the meter 38 at these flow rate(s).
Thereafter, the command is sent to the logic and driver cir-cuit 198a to energize the standby indicator before returning to step 216 as shown in Figure 5.
Determining of the test type and volume to be meas-ured is generally shown as subroutine 902 in Figure 9A, and will be more fully explained with respect to Figure 9B wherein initially the prosr2~mable counter 174a and the counter 182, as shown in Figure 4C, are disabled and reset in step 918. At this point, in ~tep 919, the status of the encoder/proximity detector switch is determined to decide whether the fluid vol-ume passing tnroughthe meter 38 is to be determined by the output of the proximity detector 27 or by the output of the rotary encoder 40. If the output of the rotary encoder is chosen, the subroutine moves to step 920 to test for the presence or status of the one cubic foo. flag within the desig-- nated location of the P~M 126, and if present, that factor~
which is equivalent to one cubic foot of output pulses from the output of the optical rotary encoder 40, is stored by step 922 in tne RAM EORP, i.e., a designated location of the RAM 126, and the factor number is loaded ir.to the programmable counter 174a.
At this point, the subroutine moves to return to the next step 904 of the program shown in Figure 9A. If the one cubic foot flag is not present, step 924 checks the status of the one-half cubic bit or flas and if present as determined by step924, the programmable counter 174a as shown in Figure 4C is loaded by step 926 ~ith an equivalent count and a corresponding factor is stored in the EORP buffer location of the RAM 126, before returning to step 904 of Figure 9A. If the one or one-half cubic foot flags are not present, step 928 looks for the presence of the one-fourth cubic foot flag as previously entered by the operator into its system RAM 126, and step 930 loads the progr~m~le counter 17~a ~ith a count corres~onding to one-fourth cubic foot, and a corres?ondin~ factor is stored in the EORP buffer location of the RA~1 126.

h 174~72 If no flag is present corresponding to one cubic foot, one-half cubic foot, or one-fourth cubic foot, step 932 automatically deter~Lines that a one cubic foot test should be rur~ to test the meter 38.
If on the other hand, step 919 determines that the 5 output of proximity detector 27 is to be used to me2sure the fluid flow through the meter 38, the subroutine moves to step 934 wherein the status of the one cubic foot flag within the RAM 126 is checked and if set, the programmable counter 174a of Figure 4C is set by step 936 with a binar~ number equivalent to 10 one cubic foot of volume and a factor, normally to 8, is set in the EORP buffer location of RAM 126 before returning to the main program. If the one cubic foot flag has not been set, the subroutine moves to step 938 wherein a check of the status o the one-half c-lbic foot flag is made and if present, a rac-15 tor corresponding to one-half of one cubic foot, normally 4, is stored in step 940 in the prograrnnable counter 174a and also within the EORP buffer location of the RAM 126, before returning to the main program. If the one-half cubic foot flag has not been set, the subroutine moves to step 942, wherein the status 20 of the one-fourth cubic foot flag is chec~ced and if present, a factor equivalent to one-fourth of a cubic foot, normally 2, is entered by step 944 into the programnable counter 174a and in the EOFP
buffer location of RAM 126 before returning to the main pro-gram. If none of the one, one-half, or one-fourth cubic foot 25 flags have been set, the subroutine automatically in step 946 sets the meter prover system 10 to conduct a test drawing one cubic foot of fluid through the meter 38.
me next routine 904 and the foll~wing routines, as shown in Figure 9A are a series of steps to deterlTine which of the flow rates are to 30 be conducted and how many times each flow rate is to be tested.
Referring now to Figure 9C, step 948 actuates the logic and driver circuit 198a to energize its test in progress light lllc before moving to step 950 to determine whether the flow rate(s) as stored in the RA.~. 126 to be conducted i5 one of Q0 to Q7 35 and if so, the routine moves to step 952a wherein it is deter-mined whe-her the test is to be conducted at the Q0 flow rate and if yes, a speed 0 is loaded in step 954a into the speed ~ 17407~

02 buffer location of RAM 126 and thereafter in step 956a, the meter 03 prover system 10 executes the test of the meter 38 at that 04 selected flow rate and outputs the results to the printer, as 05 will be more fully explaine~ with respect to Figures 9E and F.
06 ~owever, if the test is to be conducted at the Ql rate, a similar 07 set of steps 954b and 956b are conducted whereby the speed 1 is 08 loaded and is executed in these respective steps. Similar sets 09 of steps 952c to 952h, 954c to 954h, and 956c to 956h are conducted whereby corresponding flow rates are entered into the 11 speed buffer and are executed. If the decision in step 950 was 12 no, the routine proceeds immediately to step 958 as shown in 13 Figure 9D, wherein a decision is made by examining the flags 14 disposed in the designated areas of the RAM 126 to determine whether a flow rate of Q8 to QF has been selected and if yes, the 16 subroutine continues to step 960a; if not, the subroutine returns 17 to the next step 908 as seen in Figure 9A. Step 960a determines 18 whether a meter is to be tested at the flow rate corresponding to 19 the flow rate Q8 and if yes, step 962a loads a speed 8 into the speed buffer of the RAM 126 and at that point executes by step 21 964a the testing of the meter 38 by the meter prover system 10 at 22 that specific servomotor speed and flow rate. In similar 23 fashion, steps 960b to 960h, 962b to 962h, and 964b to 964h are 24 conducted whereby tests at the various flow rates and corresponding motor speeds are conducted before returning to the 26 next step which may be step 908 or 912 to determine the number of 27 tests per flow rate that are to be conducted.
28 In Figures 9C and D after the flow rate at which a 29 particular meter is to be tested was chosen, the actual test was conducted by steps 956 and 964. The actual meter test 31 conducted by the meter prover system 10 is carried out in the 32 subroutine shown in Figures 9E and F. First, step 966 commands 33 the logic and driver circuit 198a of Figure 4E to energize the 34 test in progress light lllc. Next, step 332, as shown in Figure 6B, returns the piston 1~ to its park or lowermost position, as 36 shown in Figures 1 and 2A. Step 968 commands the logic circuit 37 194b to effect the opening of the inlet valve 34 and closure of 38 the exhaust valve 36. As indicated above, a particular speed ~ 174~072 has been stored ~ the speed bufferofthe RAM 126 and the servomotor 20 is driven under the control of the logic circuit lg4a to that speed in accordance with the subroutine 606 as shown in Figures 8F. Of significance, routine 606 senses that the piston 14 has been accelerated from its park position to the start-test position as indicated by the output of the proximity detector 52, and that the piston velocity has sta-bilized. Next in step 970, the outputs as derived from the rotary encoder 40 and the linear optical encoder 26, are inhibited by the signal and logic conditioning circuits 170a and 170b, respectively, from beins entered into their respec-tive counters 174a and 182, and the time divisors or factors as originally selected based on the test volume are entered into the programmable counte~ 174a. In step 972, after the piston has reached ~he start-test position as deter-mined by step 600, the output of the rotary encoder 40 is accessed periodically, e.g., every 40 microseconds, to detect the occurrence of the rising edge of the next pulse ~herefrom as provided at the input to the interval timer 176. If this has not occurred, the subroutine checks in step 974 t~e status of the proximity switch 54 and if the piston 14 is at that posi-tion, i.e., towards its uppermost position within the cylinder 12, there is an ndication of a failure and the subroutine exits via exit point 975 into an interrupt subroutine as will be explained with respect to Figure 9G. Otherwise, upon oc-c~rrence of the leading edge of the output of the rotary en-coder transducer 40, the routine moves to step 976, wherein the A output of the rotary transducer 40 is applied by the signal conditioner and logic circuit 17Oa to the interval timer 174 and in particular to its programmable counter 174a. Fur-ther, step 976 enables the counter 182 to start counting the pulses derived from the linear encoder 26, and the programmable counter 174a to count the pulses from the rotary encoder 40.
In addition, step 976 enables at this point in time the counter 176a to count the system clock indicated in Figure 4C as clock A (e.g., 200 ~Hz) by dividing the system clock by an appropriate factor to output via the logic circuit 178 a ~ 174072 one-second sampling signal, whereby the various values of temperature and pressure are sampled. In addition, an output is derived via the interval timer 174 to enable the logic cir-cuit 177, which is otherwise disabled, thus permitting an end S of test interrupt to be developed and in particular to apply a one logic or high signal upon the counting down of the inputted count by the programmable counter 174a to apply a signal to the Interrupt 2 input of the CPU 120 to initiate an inter-rupt subroutine which will be explained in detail later with respect to Figure 9J, Next in step 528, the data in terms of the pressures and temperatures currently being measured in the meter 38 and in the chamber 2~ are outputted as discussed above with respect to Figure 8P. Next, in step 980, the status of the counter 176a within the interval timer 176 is tested, and 1~ if no pulses have been accumulated, the subroutine returns to the beginning of step 980 to wait for the occurrence of the first pulse output from the counter 176a. If a pulse or pulses have been detected at the output of the counter 176a, the sub-routine moves to step 982 wherein the counter 176a is reset to zero. Thus, the counter 176a will be reset to zero upon the occurrence of the one per second pulse output from the logic circuit 178. Next in step 984, the meter pressure L~2 as derived from the outputs of the pressure transducer 46, the prover room pressure derived from the pressure transducer PB, the ~5 prover pressure PPl as derived from pressure transducer 51, the neter temperatures ~ and ~ 4 as derived from tne t~ature trans-ducers 42 and 44, resFectively, and the prover temperatures TPl and TP2 as derived from the temperature transducers 57 and 48,are placed within designated locations within the RAM 126 to be available for the calculations to be performed upon them, as will be explained. Next in step 986, which will be more fully ex-plained with respect to Figure 9L, the pressure and tempera-ture data is converted to a floating point decimal form and in step 988, as more fully explained with respect to Figure 9M, the data is accumulated and averaged. ~s will be explained in detail later, the ~alues of pressure and temperature within ~ 174072 62a-the meter 40 and within the chamber 28 are accumulated periodically, e.g., every second, from a point in time when the volume meter test is begun until it is terminated, whereby each or the samples so taken may be summed and S divided by the number of samples to time average the tem-perature and pressure parameters. Thus, the temperature and pressure parameters are cgnsidered to be taken or monitored continuously durins the test of a fluid flow meter. A final sample of these parameters is taken even after the programmable counter 174a has counted down.
Next in step 990, a determination is made of whether the test is over by ~Next page 63) ~ ~74072 interrogating the INT2 register and if the test is over, the routine moves on to the further steps as shown in Pigure 9F;
if not, the subroutine returns to the beginning of step 528 to output the current values in the pressure and temperature buffers of the R~ 126 and to continue the meter test. The generation and storing of an end of test flag permits the meter test to end anywhere in the interval between the sam-pling pulses for taking the measurements of pressure and tem-perature. Thus, as will be explained with respect to ~igure 9J, the end of test flag is set upon the occurrence counting down the meter encoder register 174a within a designated~ por-tion of the R~M 126 indicating that the test has ended. How-ever, the one-second sampling pulses deri~ed from the logic circuit 178 o~ ~is~re 4C is still to occur in order to obtain the last pieces of temperatulre and pressure data. Thus, the subroutine as seen in Figure 9E and in particular step 990 permits the test to end and the final items of pressure and temperature data to be gathered before the meter prover sys-tem 10 is shut down. The use of the logic circuit 177 to sense the timing out of themeter encoder counter 174a permits a rapid and efficient end of test signal or flag to be generated.
If software were employed, it would be necessary to repeatedly access the status of tne programmable counter 174a to deter-mine whether it has counted down, thus ~onsideraly complicating the program to be stored within the PROM 124 and reducing the accuracy of the timing of test termination.
From the above, it is seen that a meter test is initiated and terminated in response to the output of the meter rotary encoder 40. As explained above, the mechanism coupling the encoder 40 to the diaphragm of the meter 38 generates, in a sensé, a frequency modulated signal thus making it desirable to initiate and to terminate the counting of its output at appro~imately the same point i~ the cycle of rotation of the rotar~ encoder 40. To this end, the pis.on 14 is accelerated from its park position to a substantially constant velocity before passing the start-test position as determined in step ~6, at which point the test assesses periodically, e.s., e~er~ ~0 microseconds, the occurrence of ~ 174072 the rising edge of the next A pulse from the rotary meter encoder 40. That next pulse A from the rotary meter encoder 40 initiates the counting down of the programmable counter 174a into which has been loaded a count indicative of the test volume to be drawn through the meter 38 under test and at the same time to initiate the countin~ ofthe counter 182, which counts the output of the linear encoder 26 to provide an accurate indication of the te-t volume drawn into the prover 10. Upon the countinc down of the counter 174a, a signal is applied to the logic circuit 177 to effect a CPU
Interrupt 2 which as shown in F gure 9J disables the counters 174a and 182, thus terminating the counting of each. Thus, the count as stored within the counter 182 indicative of the pulses derived from the linear encoder 26, is actuated to initiate and to terminate its counting in response to the out-put of the rotary meter encoder 40, thereby insuring that the count stored in the counter 182 accurately corresponds to a count as stored within the programmable counter 174a, which is indicative of the fluid measurement made by the test meter 38.
Referring now to Figure 9F, in step 992 the final values of the aforementioned pressures are obtained after the end of test flag has been set and are converted to a floating point decimal before being accumulated and averaged.
The final values of pressure and temperature are outputted via 25 the logic circuit l90a of Figure 4D to be displayed upon the CRT termQnal112 in a manner in accordance with the subroutine as described above with regard to Figure 8P. Next in step 994, the count accumulated in the counter 182 is converted to a floating point decimal form and in step 620, the servomotor 20 is decelerated to a stop in accordance with the sub ~utire620 discussed above with respect to Figure 8G. ~hereafter, step 996 provides command - signals via the PI/O circuit 196 and logic circuit 194b to actuate the solenoid associated with the second exhaust valve 36 to open same and to actuate the solenold associated with the first, inlet valve34 to close ~he inlet valve. Wext in ~ 174072 step 998, the various parameters as have now been finally collected are used to calculate the volumes as indicated by the output of the linear optical encoder 26 and the meter rotary optical encoder 40 in a manner that will be explain~d in greater detail with respect to Figure 9N. In step 1000, a command is sent to the logic and driver circuit 198a to energize the test complete indicator llld and thereafter, in step 1002, the output results as calculated in step 998 are transferred to the hard copy printer as will be more fully explained with respect to Figure 9P, and the piston 14 is returned to its lowermost normal, or park position ~y step 322, as more fully shown in Figure 6B. At this point the program returns to the beginning of step 952a of Figure 9C
to determine whether repeated or different flow rate tests lS are to be made.
In Figure 9G,the interrupt subroutine 975 is shown and is entered primarily when the stop pushbutton lllg is depressed by the operator, or when in step 974 of Figure 9E there has been a determination of failure due to the combination of an absence of ro'ary encodex countS, and the presence of the piston ~_ at its upper position corresponding to the placement of the proximity switch 54. Upon pressing the stop button lllg, the ser~omotor 20 is quickly decelerated to a halt and the system is "locked up" in its stop mode until the primary power is removed and then reapplied. Upon reapplication of power, the meter prover system 10 will return to its standby mode. Under either condition, the program enters via point 975 as shown in ~igure 9G and in step 1004, causes the logic and driver circuit 198a to actuate a light behind the stop pushbutton lllg. In step 1006, the current motor speed as derived from the logic circuit 198b is stored in the speed compare buffer of the RP~I 126. Next, the servomotor 20 is decelerated in accordance with the deceleration subroutine 620 as shown in Fi~ure 8G. Thereafter, step 1008 sends com-mands to the logic circuit 194b to cause the associated sole-noid to open the second exhaust valve 36 and to actuate the associated solenoid to close the first, inlet valve 34. At this point the subroutinc soes into a wait step 1010 until ~ow~r is rcmo~e~ and then reapplied.

~ 174072 As shown in Figure 9H, an Interrupt 1 routine is entered when the operator presses the reset button lllg of the system control and status module 111 whereby the program being conducted is interrupted and exits to step 1012, where-in the logic and driver circuit 198a is controlled to energizethe light behind the reset button lllg. Next in step 1014, the current speed of the servomotor 20 is read via the logic circuit 198b and is stored in the speed compare buffer, i.e., an addressable location of the RAM 126. At that point, the servomotor 20 under the control of the logic circuit 194a is decelerated to a stop condition by the subroutine 620 as shown in Figure 8G, and the return is made to the program via point 212 and in particular to the step 214 as shown in Figure 5.
lS ~ third interrupt subroutine, as referred to above with respect to steps 976 and 990 of Figure 9E, is shown in Figure 9J as automatically implemented at the end of the meter test when the interval timer 174 outputs a pulse via its logic circuit 177 to the Interrupt 2 input of the CPU 120, this pulse occurring after the down counting of the input of one of the factors corresponding to one, one-half, or one-fourth cubic foot of the test volume to be drawn by the meter prover system 10 through the meter 38. Initially, the status of the system is storad in step 1018 in appropriate locations within the R~l 126 and in step 1020, the counters 174a and lB2 of Figure 4C
are disabled and the stored count of the linear counter 182 is stored in appropriate locations within the RAM 126, before each of the counters 174a and 182 is reset. In step 1024, a one or flag is disposed within the test over register of RA~I
126, upon the occurrence of the counting down of one of the aforementioned factors or parameters by the counter 1~4a.
Thus, the end of a test may occur midway between the one-second sampling pulses that are used to obtain measurements of pressure and temperature. Thus, it is necessary to wait to obtain that final set of measurements of pressure and temperature and this is done by setting the end of test flag immediately upon the occurrence of the down counting of the ~ 1740~2 aforementioned factors. The meter prover system 10 will con-~inue to operate to accumulate data as indicated in Figure ~E
until step 990 occurs, at which time the test over register o the RAM 126 is accessed to see whether a test over flag has been 5 set and if so, then the test is brought to a halt. If still running, in step 1028, the status of the system is recalled and the meter prover system operation continues at the point of interruption within the meter test routine as shown in Figure 9E.
The routine 984 generally indicated in Figure 9E
for inputting the values of pressure and temperature is more fully shown in the subroutine shown in Figure 9K, wherein the initial step 1032, an indication of the differential pressure as obtained from the differer~tial pressure measurins device 46 15 is converted into binary data by the A/D converter 166 and is stored in a designated location within the RAM 126. Similarly, a differential pressure as measured by the piston pressure transducer 51 is converted by the A/D converter 166 into binary data and is stored by step 1034 in a desisnated location of the R~l 126.
20 Similarly, the barometric pressure as measured by the transducer 10~ disposed in the prover room 106 in which the meter prover system 10 is housed, is converted by the A/D converter 166 into binary data and is stored b~ step 1036 in a designated lccation in ~;~e RAN 126. Similarly in steps 1038, 1040, 1042, the temperature 25 inputs TPl, TP2, T~13, and IM4 from the temperature measuring devices 57, 48, 42, and 44, are converted to binary data by the A/D converter 158 and are stored within designated locations at the R~M 126, before returning to step 986 of Figure 9E.
Step 986 as generally shown in Figure 9E is more 30 fully shown in the subroutine of Figure gL where in step 1046, each of the temperatures corresponding to the prover tempera-tures TPl and TP2, and the meter temperatures TM3 and TM4 is converted from a binary voltage to degrees Fahrenheit in a floating decim~l format and then is stored in a designated 35 location within the R~S 126. Next in step 1048, in similar fashion, the binary voltages indicative of the precsures P2, and the barometric pressure PB are taken from their designated locations within the RAM 126 and are converted ~ 174072 to pounds per square inch (psi) in a floating point decimal format and are restored in designated locations in the R~
126, before returning to step 988 as shown in Figure 9~.
The subroutine or step 988 as shown in ~igure 3E
for accumulating and averaging the test data is more fully shown with respect to the subroutine shown in Figure 9M. In step 1050, the digital values of the first and second prover temperatures TPl and ~P2 are added together to provide an Average Prover Temperature (ATP). This value is in turn added to the accumulated previous values of ATP, thus accu-mulatin~ a series of N samples of the ,~ver~ge Prover ~empera-ture du ing the conducting of a meter test. In step 1052, the meter temperatures T~3 and TI14 are added together to obtain an Average Meter Temperature (~M) and this new value is added to the previously accumulated values of the Average Meter Temperature AT~ to obtain a quantity indica-tive o N consecutive samples of the ATl1 taken during the course of a meter test. In step ~054, a value of the ambi-ent or barometric pressure FB is added to the sum of the barometric pressure PB plus the differential ?ressure MP2 taken between the ambient pressure and the pressure established within the meter 38 to obtain an Average ~eter Pressure (APM). The Average ~eter Pressure is added to the previouslv accumulated values of the Average ~eter Pressure to obtain a quantity indicative of N consecutive samples of the APM
taken during the meter test. In step 1056, a value Or the ambient or barometric ?ressure P~ is added to that differen-tial pressure as obtained from the differential pressure PPl transducer 51 to obtain an Average Prover Pressure ~APP).
The Average Prover Pressure (APP) is added to the previously accumulated values of the Average Prover Pressure to obtain a quantity indicative of ~I consecutive samplings of the APP
taken during the meter test. In step 1058, the number of samples N of each of the values taken above in steps 1050, 1052, 1054, and 1056 is determined, whereby in succeeding steps an average value of each of these parameters may be obtained by dividing the accumulated ouantity ky the factor N.

~ 1~4072 Step 99~, as sh~Jn in Figure 9F, will now be explained in more detail with respect to Figure 9N. As indi-cated above, the accumulated values of average pressure tem-perature (ATP), average meter temperature (ATM), average meterpressure (P~sP), and average prover pressure (APP) are indica-tive of N samples taken during the course of the meter test and in step 1060 these average values are obtained for each of the temperatures and pressures. Next, in step 1062, the percent error of the output of the meter encoder 40 of the fluid passing through the meter 38 with respect to the stan-dard volume passed therethrough as drawn by the meter prover system 10 is caluclated in accordance with the indicated ~quation. ~he values of meter pressure PM, prover pressure PP, prover temperature TP, and meter temperature TM are those averaged values as determined from step 1060, whereas the prover volume count K was obtained as an indication of the accumulated counts that was produced by the linear encoder 26 and accumulated within the counter 182, these counts be-ng indicative of a selected standard volume, e.g., one cubic foot, one-half cubic foot, or one-fourth cubic foot. As shown in Figure 9N, the ratios of PM to PP, and TP to TM
provide, respectively, pressure and temperature correction factors. As explained above, there exist differences of fluid temperature and fluid pressure between the fluid within the meter prover 10 and the fluid meter 38 under test. The noted ratios as determined by step 1062 provide appropriate correction factors whereby the differences in temperature are compensated for to give an accurate indication of percent error of the meter reading of fluid volume with respect to that calibrated indication or reading provided by the meter prover 10. The factor K* is represe~tative of those counts as stored in the programmable counter 174a indicati~e of the fluid flow as measured by the meter 38. As shown in step 1062, the factor X~ is multiplied by a constant C to convert the count, e.g., 40,000 for one cubic foot, to a value of the volu~e to ~e dr~wn through the meter 40. In the illustrative 17~072 -69a-example, where the factor K* as entered into the programma-ble counter 174a is 40,000, the constant C is chOsenas ~0lOOO .
Further, the number of counts as derived from the linear encoder 26 and counted by the counter 182 is multiplied by a calibration factor which, as will be explained later in detail, is derived by accurately measuring the volume of the chamber 28 of the meter prover 12 and correlating the pre~
cisely measured volume to the series of pulses outputted by the linear encoder 26. In an illustrative example of this invention, for a selected volume of one cubic foot of the chamber 28, it was de.ermined that 38,790 output pulses were derived from the linear encoder 26. Thus, the calibra-tion factor would be selected as i~ers~ of ~his count or 38--79-0 In similar fashion, if a different volume was to be drawn through the meter 38 and the programmable counter 174a was to be programmed with a count corresponding to a different flow, it would be necessary to determine a differ-ent calibration factor corresponding to that volume as defined within a selected region of the chamber 28. In practice, the count of 38,790 is obtained empirically by moving the piston 14 along a length of the chamber 28 corresponding to precisely one cubic foot and calculating or otherwise determining the number of pulses as outputted by the linear encoder 26. Similar measurements and encoding will be taken empirically to determine the counts for one-half and one-fourth cubic feet flow corresponding to the output of the linear encoder 26 as the piston 14 is moved distances from the start-test position along the cylinder 12 corresponding illustratively to one-half cubic foot and to one-fourth cubic foot volumes within the cylinder. Thus, the actual counts and therefore the corresponding calibration factors for one-half and one~fourth cubic feet will correspond precisely to these vol~mes as defined by thecyl~rical wall of chamber 28. In this manher, a calcula~ion of the percent error between the reading of the meter 38 and the actual volume as drawn into the c~amber 28 can be made with great accuracy, by the use of calibration factors that have been determined ~Next page 70) ~ 1740 ~2 in accordance with the precise volume of the corresponding regions of the cylindrical wall of tlle chamber 28.
After the step 1062 has been executed, the program returns to the next step 1000 as shown in Figure 9F.
S The calculation of the average temperatures and pressures as generally disclosed in step or subroutine 1060 of Figure 9N is more completely shown by the subroutine as set out in Figure 9Q, as previously indicated in step 1050, each measurement of temperature is added to the previous measurement to obtain a total indicative of accumulated dis-crete measurements of prover temperature ATP during the course of a single test.As indicated in step 1064 as shown in Figure 9Q, this accumulated value of A~P is divided by the number of samples AVCTR = N + 2 and added to 459.67 to provide the final averaged temperature FTP of the prover in degrees Kelvin. In similar fashion in step 1066, the value of the temperatures TM3 and TM4 are added successively to each other during the course of the meter test to provide an accumulated value of the avera~e temperature ATM of the meter during the course of the test, and the ATM is divided by the number of samples or counts of the one-second sampling clock which is in turn added to 459.67 to give a final averase temperature FTM in terms of degrees Kelvin. In similar fashion, in step 1068, the accumulated values of the average pressure APM of the meter as accumulated during the test is divided by the number AVCTR of samples taken during the test to provide a final FPM of the meter in terms of pounds per s~uare inch absolute. In step 1070, the accumulated values of the average prover pressure APP as accumulated during the course of a meter test are divided by the number AVCTR of samples to provide an indication of the final pres-sure of the prover FPP in terms of pounds per square inch absolute, before returning to the next step 1062 as shown in Figure 9~.
The accuracy of the meter prover 10 to measure the volume drawn through the meter 38 is dependent and is limited by the variations in the measurements of fluid pressure and temperature during a meter volume test. The variations in fluid pressure and temperature as occur during a meter volume test run are greater than those variations that may occur in the measurement and calibration of the volume of the meter prover. Thus in general, the actual volume of fluid delivered through the meter 38 as the piston 14 is moved from a first to second position may be approximated by the following expression:

V~(Vl-V2)[1+( /Tl)-l /Pl)] + V2[( /Tl)-( /Pl)]
where Vl, Pl, and Tlare respectively the initial volume, fluid pressure and temperature existing within the chamber 28 of the prover 10 at the beginnlng of a meter volume test run, ~P and ~ are the corresponding changes in pressure and temperature that occur durins the test, and oT and GP are the mean deviations from Tl and Pl at the fluid meter 38.
As explained above, the logic circuit 178 as shown in Figure 4C provides a one-second clock signal that samples the output of the temperature transducers 42, 44, 48, and 57, as well as the pressure transducers 46 and 51 to provide sam-ples of these variables throughout the volume meter test run.
As discussed above, the periodic samples of the meter tem-perature TM3 and TM4, and the prover temperature TP1 and TP2 as obtained in step 984 of Figure 9E are summed`in steps lOS0, 1052, 1054, and 1056 of Figure 9M to~ether to obtain a spatially averaged meter temperature and prover temperature, which are time averaged by being sampled and summed over the test run as explained with respect to steps 1064, 1066, 1068, and 1070 of Figure 9Q. In this manner, the continuous changes in both pressure and temperature are measured at the fluid meter and the prover 10. By so averaging in a spatial and time sense, the variations in temperature and pressure that would otherwise cause an error in the calculation of the change of volume may be avoided. Temperature changes in the fluid as dra~ into the meter prover as caused by adi batic expansion across a pressure drop of 1.5"H2O can be as large as 0.5~F, c3using an error in the calculation by as much ~s ~ 1~4072 0.1~. Thus, it is necessary to monitor accurately the fluid pressurP and temperature throughout the system and apply the necessary corrections in order to obtain the "true" volume drawn into the meter prover 10. For an accuracy of 0.05% in volume, the parameters~Tand oP between the chamber 28and ~he meter inlet need to ~e monitored to an accuracy of better than + 0.1F and + 0.05"H20),respectively. The temperature transducers and pressure transducers described above with respect to Figure 1 have such a capability to achieve the desired accuracy for temperature and pressure measurement and provide the desired accuracy in the measurement of the volume.
Step 1002, as shown in Figure 9F as outputting the results of the conducted tests upon the meter 38 to the hard copy printer, is more fully shown in Figure 9P. In the first step 1072, the printer is strobed by the logic l90b to initializeits operation and thereafter the percent error as calculated previously in step 1062 is printed out upon the . printer. Next, in step 1074, a line feed command is applied for the printer to advance its paper by one line, before in step 1076, the flow rate at which the test was conducted is displayed in step 1076. In step 1078, ten line feed command signals are applied to the printer to feed the paper ten lines before returning to step 322 in Figure 9F.
A significant aspect of this invention resides in the method of accurately measuring the volume of the chamber 28 of the cylinder 12 and to use that measurement to.accurately cali~rate the output of the linear encoder 26 to provide a manifestation of volume per pulse output of the linear enco-30 der 26. As indicated in Figure 2A, the linear encoder 26 includes a scale 24 with a high number of accurately, closely spaced markings 102, whereby the optical encoder 26 provides a train of output pulses corresponding to the passage of each such ~arking past the optical encoder. By accurately correlating the number of such output signals to the pre-cisely determined volume of the chamber 28, the linear ~ ~74072 01 _ 73 _ 02 encoder 26 may be encoded with a corresponding high degree of 03 accuracy to thereby improve the calibrated indication of meter 04 registration or error of the meter 38 under test.
05 In such a calibration procedure, it is first necessary 06 to measure the volume of the chamber 28 with great accuracy. A
07 method of volume measurement is employed including the 08 establishing of a high frequency, electromagnetic field within 09 the cavity; the principles of such measurement method will now be explained. The inside dimensions of the regularly shaped 11 chamber 28 completely surrounded by conducting walls can be 12 accurately determined by measuring the frequencies at which 13 resonant conditions occur for the electromagnetic field 14 established within the chamber 28. For a given geometry, the electromagnetic fields within the chamber 28 can assume a 16 variety of spatial configurations. At discrete frequencies, the 17 electromagnetic energy confined within the chamber 28 is stored 18 (resonates) over time intervals long compared with its wave 19 period and these resonant solutions are designated as the normal modes of the chamber 28. The ratio of the energy stored to that 21 dissipated per cycle of the resonant frequency is defined as the 22 quality factor or "Q" of the resonance. The quality factor Q is 23 a measure of the dissipative losses due to the ohmic resistance 24 of the walls to the electrical currents induced by the electromagnetic fields. For a given normal mode, the resonant 26 frequency is uniquely determined by the dimensions of the 27 chamber 28 and the propagation velocity of light in the medium 28 filling the volume. Consequently, by simultaneously measuring 29 the resonant frequencies of a number of normal modes equalling the linear dimensions specifying the volume (one for a sphere, 31 two for a right circular cylinder, and so forth), the volume of 32 the chamber 28 can be determined to an accuracy comparable to 33 the precision of the frequency measurements.
34 For a given chamber geometry, there is an infinite set of normal modes whose resonant frequencies will have a ~ 174~72 lower bound value corresponding to a free-space wavelength of the order of the linear dimensions of the chamber 28, but no upper bound. A volume change caused by a mechanical displacement of one of its linear dimensions will, in turn, S change the resonant frequency of the low ordered modes by approximately the same fraction.
Briefly, as shown in Figure lO, means in the form of the antenna 70 is provided to establish or generate an electromagnetic field within the chamber 28 and to extract therefrom a relatively small portion of the stored electro-magnetic energy to be measured by the circuit of Figure lO.
As will be explained in detail later, measurements are made to determine the frequencies f at which resonance occurs within chamber 28. The selection of the configuration of the chamber 28 is significant for if an arbitrarily shaped chamber is used, the mathematical relationship between the resonant frequencies f and the dimensions of such a chamber may have no closed or analytical solution. Thus, the cham-ber 28 is selected to be of a regular geometry to assure that the dissipated losses and the effects of coupling are negligible and to provide known Maxwell equations defin-ing the relationship between the chamber dimensions and the resonant frequencies subject to the boundary conditions that the electrical field E be radial and the magnetic field H be tangential to the totally enclosed surfaces of the regularly shaped chamber 28. Under these conditions, the field solutions for the chamber 28 will takeona relatively simple form and recognizable perturbations can be predicted.
Thus, in a preferred embodiment of this invention, the chamber 28 is selected to be a right circular cylinder as is formed by the inner surface of the cylinder 12, the head ~0, and the exposed surface of the piston 14. It is recognized that a chamber 28 of such a configuration permits the piston to be driven therethrough to displace a known fluid volume, as explained above. The normal modes of the electromasnetic field established in the chamber 28 being ~ 174072 configured as a right circular cylinder are divided into two general classes: the transverse electric modes (TE) for which the electric field is zero along the cylindrical ~z) axis of the chamber 28, and the transverse magnetic modes (TM) for which the magnetic field is zero along its cylindrical axis. They are further specified by three integers Q, m, and n, which are defined for the TE modes in terms of the cylindrical coordinates, r, 9, and z by:
.

Q = number of full-period variation of Er with respect to ~;
m = number o~ half-period variation of E3 with respect to r;
n = number of half-period variation of Er with respect to z.

A similar set of indices exist for the TM modes for which the integers Q, m, n are correspondingly defined in terms of the components of the magnetic field; Hr and Ha.
The solutions for the resonant frequencies of the normal modes are expressed in terms of the geometrical dimen-sions and roots of Bessel functions by the general expression:

f = (c/D)~( Qm)2 + (~)2(D-)2ll/2 (1) where D is the diameter, L is the length, c is the speed of light in the meaium filling the cavity volume and xQm are given respectively by:
XQm = mt root of JJQ~x) = O for the TE-modes, XQm = mth root of JQ(x) = O for the TM-modes.
Numerical values for these Bessel roots correspond-ing to the various lower ordered TE and TM modes are taken from the following table:

~17~7~
-7~-Transverse Electric Modes Transverse Magnetic Modes ~TE) ~TM) TE XQm TM ~m 11 1.84118 01 2.40483 21 3.05424 11 3.83171 01 3O83171 21 5.13562 31 4.21009 02 5.5~008 41 5.31755 31 6.38016 12 5.33144 12 7.01559 A plot of the ~uantity ~fD)2 vs ~D/L) of equation 1 is a strai~ht line with intercept ~cXQm/~) and slope (cn/2) . Such a mode chart is shown in Figure 13 for the lower modes of the right cylindrical chamber 28 for values of n up to 2. Figure 13 shows graphically the relative resonant frequency values as a function of the geometric parameter ~D/L)2 and the variation in resonant frequencies as the linear dimension L is changed. It is also useful in predicting the number of resonances expected to be encoun-tered in a given.frequency range for any fixed D/L ratio as well as the values of L at which two different modes are degenerate in frequency, and hence would interfere with each other.
The mode chart of Figure 13 is used to determine the modes of electromagnetic field excitation, the expected resonant frequencies of the selected modes, and the dimen-sion in terms of the diameter D and length L of the chamber 28. In an illustrative embodiment of the chamber as shown in Figure 10, the diameter D is set equal to 12" and the variation in the length L is from 10" to 30". Consequently, the corresponding values of (D/L) have the range of values from 1.44 to 0.16. If the frequency range of observation is between 500 MHz to 1000 MHz, then ~fD) will vaxy between 2.32 x 10 and 9.29 x 102 (cycles/sec)2cm2. The number of resonant modes e~pected to be encountered over the variation in length L for this configuration between the range of 500 to 1000 MHz is then just given by the number of lines included ~ 17A072 in the rectangle shown on the mode chart of Figure 13. As can be seen, at L = 10", there are only three modes which occur between 500 to 1000 MHz. These are, namely, the TMolo mode occurring at approximately 755 MHz, the TE
mode occurring at 830 MHz and the TMoll mode occurring at 960 MHz. On the other hand, for L = 30", there are eight modes, namely TElll, TE112, TMolo, TMoll~ TM012' T 211' TE~12, and TE113 which for purposes of clarity, are not shown in Figure 13. At any intermediate position, the num-ber of modes and their resonant frequencies f can be obtainedfrom the intersection of ~he vertical line corresponding to the desired (D/L)2 value with the lines designating the various modes. Since the measurements of the resonant fre-quency of any two disti~ct mL~es uniquely specify both D
and L, the other modes may be used either as a redundancy check on the measurements or as a meansfor evalua.ing the effects of perturbation caused by deviation of the geometry from the idealized case as well as any higher ordered cor-rection terms which may be present.
In a qualitati~e sense, it is understood that the electric and magnetic field components of the electromag-netic field are perpendicular to each other and have a defined relation at a resonant frequency to the dimensions D and L of the chamber 28 of a regular geometry and in ~5 particular the diameter and length of the chamber 28, as shown in Figure 10. As will be explained, the relationship between the resonant frequency and the dimensions D and L
for a particular mode can be related by a mathematical expression. The chamber 28 having a right circular cylinder configuration has two unknown dimensions that define its volume, i.e., its diameter D and its length L. Thus, it is necessary to provide two mathematical expressions that may be solved simultaneously for the unknown values D and L, and therefore it is necessary, as indicated above, to establish electromagnetic fields within the chamber ~8 of two distinct modes and obtain the resonant frequencies of 1 1~4072 these two modes whereby the values of D and L and thus the volume of the chamber 28 may be calculated. As will be explained, the modes of excitation are selected to deter-mine resonant frequencies with correspondingly high quality factors whereby the effects of perturbations to introduce errors into the measurement of D and L may be minimized.
The TMolo mode line has zero slope, as shown in Figure 13, and is therefore independent of the dimension L
of the ch~r and is only a function of the diameter.
This unique property can therefore be used to identify this mode in experimental measurements. The TMolo mode of exci-tation can be used to obtain an independent measurement of the dimension D. Furthermore, it can be seen that the rate of change of the resonant frequency for any given mode as a function of the dimension L is solely determined by the last index n. Consequently, the frequencies of the modes lll 011' and TE2ll will shift by the same amount as L is varied whereas the TEll2, TMol2, 212 will all shift together at twice the rate. Consequently, the tuning properties of these modes can be used to determine the relative change in the length L to very high accuracy once the absolute diameter of the cavity has been determined.
The quality factor or Q of the cham~er 28 at resonance as excited in a given normal mode is important in two respects. First, it determines the sharpness of the resonant freguency response and therefore limits the ulti-mate accuracy with which the resonant frequency can be measured experimentally. More important, the quality factor Q is a measure of the order of magnitude of the expected deviation of the resonant frequency from the idealized results as given by equation l. In general, the higher the Q for a given mode, the more accurate the theoretical expres-sions are in terms of determining the geometrical dimensions of the cavity. Thus, the modes for exciting the chamber 28 are selected to provide the highest quality factors Q, and thus provide the more accurate determination of the dimension and thus the volume of chamber 28.

~ 17~072 For a volume comprised of perfectly conducting walls, the unloaded or intrinsic QO of the chamber is infinite and the frequency solutions to the resonant normal modes are exact. For walls of finite resistivity, the electric and magnetic fields within the chamber 28 penetrate into the walls to a distance defined as the skin depth ~, which is given by the expression ~ z [~p/l2o~2~]l/2cm ~ (2) where ~ is the permeability of the wall material, ~ is the free-space wavelength in cm, and P is the resistivity (d.c.) of the walls in ohm-cm. Since a finite skin depth makes the apparent dimensions of the ch~ as seen by the electro-magnetic fields somewhat large~ tha~ the actual geometrical dimensions, the dissipative effect caused by the ohmic losses on the walls perturbs the resonant frequency of the normal modes and shifts them to a lower value. A measure of this perturbation is the value of the ratio of the skin depth to the free-space wavelength or ~ ), which can be calculated via equation 2 by using known values of the d.c.
resistivity and permeability of the wall material-. For a cavity made of copper (~ = 1, p = 1.72 x 10 6 ohm-cm~, the skin depth is equal to 3.8 x 10 5~1/2cm. At 1000 MHz (~ = 30 cm), the ratio (~/~) is approximately equal to 7 x 10 6. This correction to the resonant frequency caused by the finite conductivity is clearly negligible for the present application. For series 300 stainless steel, (~ =
1, p = 72 x 10 6 ohm-cm), the raio of (~ ) at 1000 MHz is 4.5 x 10 5 which is becoming non-negligiblP compared to to the desired overall accuracy of 0.01~ in absolute volume accuracy. In a preferred embodiment, the walls of the cham-ber 28 are chrome-plated, (~ = 1, P = 13 x 10 6 ohm-cm), tha corresponding value of~(ô/~) is equal to 2 x 10 5 at 1000 MHz. Consequently, on the base of theoretical calcu-lations, the correction to the resonant frequency of the normal modes in the cha~ber 28 of a right circular cylindex configuration should be negligible and the expression given by equation 1 should be adequate in giving an overall volume determination to an accuracy better than 0.01~.
In practice, however, the theoretical skin depth value for a given material is never achieved due to a variety of reasons, including wall imperfections, material impurities, and residual surface contaminations. Conse-quently, it i5 necessary to experimentally determine the effective skin depth by measuring the Q of the chamber 28 for selected of the preferred modes of excitation, and if necessary, apply the appropriate correction to the volume determination due to this effect.
The expression QO Qf the chamber 28 is obtained by evaluating the ratio of the energy stored to the dissi-pative losses occurring on the walls per cycle of the lS electromagnetic oscillation, which can be written as, Qo ~ ~ (3) where H is the normal mode magnetic field vector and ~ is the skin depth. The Q factors in terms of the normal modes and geometrical shape for the chamber 28 of a right cylin-drical cavity are given by the following expressions:For TE modes:

Q ~ /X~m~2~cx2 ~ p2R2]3/2 ~x21m + p2R3~ (l~)(p~ )~~ ' (4) 'm For TM modes:

Q ~ m P~ ] for ~0 (5 X~m for n - o where R = ~D/L), P = n~/2 and all other symbols are as previousl~ defined.

~ 174072 2y evaluating the right hand sides of the above expressions for a given mode and cavity geometry and divid-ing it by the experimentally determined Q, an effective ~/A can be obtained. A direct comparison of the result 5 obtained with the calculated via equation 2 then gives a quantitative evaluation of the magnitude of the perturba-tion expected in the volume determination of the chamber 28.
The chamber 28 is coupled to an external measure-o ment circuit as shown in Figure 10 whereby microwave power 10 is introduced into the chamber 28 to establish an electro-magnetic field therein and to extract reflected power therefrom. The chamber 28 is a reflection type cavity requiring only one coupling device in the form of the anten-~a 70. As will be explained in detail later, the resonant 15 characteristic, and in particular the resonant frequency of a given normal mode, is determined by measuring the power reflected from the antenna 70 as a function of the incident microwave frequency. The use of a reflected type chamber 28 permits minimal perturbation from an idealized cavity 20 response and permits an implementation by the use of a directional coupler 1106 which allow sampling of the reflected power without interference from the incident power.
As shown in Figure 10, the power output of a sweep genera-tor 1100 is applied to excite the antenna 70 while the 25 reflected power may be transferred by the coupler 1106 to a crystal detector 1110.
The presence of the coupling device in the form of the antenna 70 introduces an additional loss term in the dissipation of the resonant electromagnetic energy 30 stored within the chamber 28, namely, the amount of power extracted for measurement. This is usually defined as an equivalent coupling Q or Qc as distinguished from the "unloaded" Q of the cavity or QO. In addition, the inter-action of the cavity with the rest of the circuits of 35 Figure 10 via the antenna 70 need to be taken into account in order to derive an accurate description of the "cavity-coupling" syste~ for evalu~ting the appropriate expressions in the present invention.

~ ~74072 Itcan be shown that for a reflection-type chamber 28, i.e., a chamber for which po-~er is introduced and extracted by a single antenna 70, the ratio of the reflec-ted power to the incident power near a resonance is given by the expression, 1/4(q Q )2 + (~0 ^ ~)2~vO2 (6) (Pr/Po) 1/4(~ + ~ )2 ~ (vO ~ 0 where v is the frequency, vO is the resonant frequency, QO is the unloaded Q of the cavity resonance, and Qc is the coupling Q which is proportion,al to the power loss through the coupling device.
At the resonant frequency vO, the ratio of the re~lected power to the incident power is de~ined as the reflection coefficient for the given normal mode, i.e.
(pr/po)~ , ~ s ~ ~ (Qc ~ Qo) /(Qc + Q0) ( ) For ~ = 0, the cavity is considered to be 100% coupled and Qo = Qc This condition corresponds to the low-frequency equivalent circuit case where the load impedance is matched to the generator impedance.
Combining equations 6 and 7, and eliminating Qc' the unloaded QO of the normal mode is given in terms of the measurable parameters by, r 0 ~Pr/Po)] /(~ ~ ~o)(l + ~1/2) (8) Therefore, by measuring ~ and the frequency width at some arbitrary power level (Pr~Po) on the cavity resonant response curve, the quantity QO can be determined. If a "half-power" point is defined such that Pl/2 ~ )/2 , ~. 174072 01 ~ ~3 ~
02 then the frequency difference corresponding to the two 03 half-power points is known as the "half-width" of the resonant 04 response and is given by 05 ~= 2(~1/2- ~ O) 06 where 1/2 is the frequency corresponding to the half-power 07 points. For this case, equation 8 further reduces to, 08 QO = 2~o/~ ~ )/(1+~1/2) . (10) 09 The value of QO' therefore, varies between (~O/~) and (2~o/~)r depending on the degree of coupling.
11 A pictorial representation of the chamber reponse 12 curve, together with the defined parameters, is shown in Figure 13 14. The center frequency of the response, ~ O~ corresponding to 14 a minimum of the reflected power, is the resonant frequency of the normal mode.
16 It is understood that the frequency measurin~ circuit 17 as shown in Figure 10 effects a change of the resonant 18 frequency, i.e., frequency pulling, caused by the interaction 19 between the chamber 28 with the elements of the circuit of Figure 10. In the circuit as shown in Figure 10, wherein the 21 frequency of the sweep generator 1100 is varied by a factor of 22 approximately 2, the directional coupler 1106 receives the 23 output power of the sweep generator 1100 and applies a relatively 24 small portion thereof to the antenna 70. In particular, the power applied to the auxiliary or output port of the directional 26 coupler 1106 is approximately 80% of the output of the sweep 27 generator 1100. The chamber 28 is connected to the main input 28 port, and the crystal detection 1110 is connected to the third 29 port of the directional coupler 1106 to measure the microwave power reflected from the chamber 28. The use of the directional 31 coupler 1106 results in a factor of 100 attentuation or "padding"
32 between the sweep generator 1100 and the load as imposed by the 33 antenna 70. As a result, the sweep generator 1100 is respect-34 ively isolated from the antenna 70,~i.e., the coupling system, to insure that no interaction occurs to perturb the chamber ~ ~407~

response. As a result of the isolation imposed by the coupler 1106 between the antenna 70 and the generator 1100, the amount of frequency pulling is determmed by the quality factor Q
of the chamber 28, the coupling coefficient ~, and the VSWR between the crystal detector 1110 and the cavity coupling system. Assuming that the sweep generator 1100 is totally decoupled from the cavity 28, a cavity 28 ha~ing a quality factor Q of 5,000, a coupling coeffi-cient ~ of .S and a residual VSWR of 2, will provide a fre-quency pulling in the order of 1.3 x 10 5 or .0013~. Thisdeviation is an order of magnitude better than required to achieve desired overall measurement of the chamber volume to an accuracy of better than .01%.
Further, an analysis of the ca~ity 28 and its associated resonant frequency measuring system, as shown in Figure 10, have shown that perturbations due to distor-tions in the geometry of the chamber 28 whether due to the out of roundness of the cylindrical shape of the cavity 28 or to small localized surface irregularities and deforma-tions, indicates that such perturbations can be compensatedfor by ta~ing the following precautions. First, if the machine tolerance of the chamber 28 is such that the diameter D of its cylindrical configuration is m~intained to within the limits of 12 mills out of roundness, then the dlameter D and thus the volume of the chamber 28 can be determined with an accuracy in the order of 10 5 or less and, thus such deformation may be neglected for the present method of measuring volume. Similarly, the shift in the chamber reso-nant frequencies for any normal mode caused by a small inward or outward dent on the interior wall of the chamber 28 is deemed negligible if the hole dimension is well below the cut-off wavelensth of the electromagnetic field estab-lished within the chamber 28 and the hole does not couple electromagnetic field to another structure; under these conditions, the frequency pulling will be approximately ~ 174072 proportional to the ratio of the cube of the hole diameter to the volume of the chamber 28. Thus, as a practical matter, the frequency pulling for inward or outward dents in the walls of the chamber 28 is negligible; for example, a 1 inch diameter hole as placed within a chamber 28 having a diameter of approximately 12 inches and length of 20 inches will provide a change of the resonant frequency by only 7 parts in 10 .
Considering the effect of the inlet 62 as well as the openings to receive the transducers 51 and 57 within the piston 14, these openings or holes may be filled with metallic plugs during the volume measurement and calibration to virtually eliminate these sources of error from effect-ing the determination of the resonant frequency.
15In order to satisfy the accuracy requirement of .01% in the measurement of the displacement volume of the chamber 28, the resonant ~requency measuring circuit as shown in Figure 10 should be capable of measuring the reso-nant frequencies of the normal modes as established within the chamber 28 to 1 part in 105. The circuit, as shown in Figure 10, is designed to reduce systematic error which can effect the measurement of the resonant frequencies f, such distortions due to impedance mismatch between the sweep generator 1100 and the antenna 70, variations and fluctu-ations of the microwave power, extraneous noise, and sensi-tivity to component drifts. As shown in Fisure 10, the microwave power source takes the form of the sweep genera-tor 1100 which may illustratively take the form of that generator manufactured by Texscan under their model desig-nation VS80A. The sweep generator 1100 may be operatedillustratively at a fixed frequency (CW) or automatically to sweep through a range between 50 K~z and 300 .~Hz at a rate set between .05 Hz and 30 KHz. In addition, the out-put of the sweeD cenerator 1100 may be controlled by its vernier ~nob llOOa to sweep at an operator control change of frequency throush the noted range. Tne output of the ~ 174072 sweep generator 1100 is applied by a coaxial cable to a directional coupler 1102 which acts as a transformer whereby a portion of the energy applied across the coupler 1102 i5 trans~erred to a frequency counter 1108, which in an illustra-tive embodiment of this invention may take the form of thatcounter manufactured by Fluke Corporation under their model designation No. i920A. As will be explained later, the counter 1108 displays the frequency at which a standing wave is established within the chamber 28. In turn, the output of the coupler 1102 is applied by a similar coaxial cable to a second coupler 1104 and in turn via the direc-tional coupler 1106 to be applied to the microwave antenna 70. As shown in Figure 10 and in more detail in Figure 2A, the microwave antenna 70 is a simple metallic loop 70a and is insulated by an insulator 7~b from the head 60 of the chamber 28.
As is well known in the art, the energy reflected through the antenna 70 from the chamber 28 upon occurrence of a standing wave decreases significantly in comparison to that enery reflected at other frequencies. This is known as the resonance condition, and the associated frequency as the resonant frequency. Thus, as the frequency of the out-put of the sweep generator 1100 is varied, a resonant fre-quency is selected at which a standing wave occurs within the chamber 28 dependent upon the configuration and dimensions of the chamber 28. The frequency at which the standing wave is established determines, as will be explained, the chamber dimensions in terms of the diameter D and the length L, and therefore the volume of the chamber 28. To detect the power drop at the resonant frequency, the coupler 1106 is connected to the crystal detector 1110, which converts the microwave power reflected through the antenna 70 to a d.c. signal. In turn, the crystal detector 1110, which may illustratively take the form of a Hewlett Packard crystal detector Model 3; No. 423A ~NEG), a?plies its d.c. output to the Y input of an oscilloscope 1112. The oscilloscope 1112 may illustratively ~ 17A072 ~ -87-take the form of a ~extronix oscilloscope manufactured under their Model No. T922R. The X input to the oscilloscope 1112 is provided by the sweep generator 1100, so that when the generator 1100 is set in the sweep mode, the reflected power response of the chamber 28 is a function of the input signal frequency and is displayed upon the oscilloscope 1112. As seen in the expanded display 1112a, the power reflected through the antenna 70 dips to a minimum 1113, at the reso-nance frequency in a manner shown in Figure 14. The fre-quency at which the minimum 1113 occurs is displayed uponthe counter 1108. The second coupler 1104 applies micro-wave power to a crystal detector 1114 which provides a corresponding d.c. signal to be amplified by an operational amplifier 1115 ~nd applied to the sweep generator 1100 to provide a level control upon the output of the sweep genera-tor 1100, whereby substantially an even power drain is placed upon the sweep generator 1100 as it sweeps through that frequency at which a standing wave occurs.
The circuit of Figure 10 is operated in the fol-lowing fashion to obtain a measurement of the resonant fre-quency. First, the sweep generator llOQ`~ is set for wide sweep to permit essentially all of the normal mode reso-nances to be displayed simultaneously on the screen O r the oscilloscope 1112 whereas the resonant response for any particular mode can be displayed individually by an appro-priate choice of sweep width and sweep center frequency.
Unambiguous identification of the modes can be made by measuring their resonant frequencies for a particular set-ting of the piston position within thecha~ber 28, and using equation 1, or alternatively, by moving the piston position and comparing the rate of change of their resonant frequen-cies as a function of piston position with those shown in Figure 13.
, The resonant frequency f of any given mode is measured by first displaying the response curve on the oscilloscope screen and then switching the sweep generator 1100 to its C~ mode and manually tuning the fine frequency ~ ~7407~

knob llOOa until the voltage displayed on the oscilloscope 1112 is a minimum. The display on the frequency counter 1108 when this minimum is reached is then the resonant frequency of the cavity normal mode. As a convenience, S the second beam of the oscilloscope 1112 can be used to better define the position of this minimum by setting the system in the sweep mode and manually changing the verti-cal position of the second beam so that it just touches the bottom of the resonant response curve. When the genera-tor 1100 is switched to operate in its CW mode, the reso-nant frequency f of the chamber 28 is then the frequency setting of the generator 1100 corresponding to condition when the two beams coincide. In a preferred embodiment, by simultaneously reading the frequency counter output l; while the two beams are exactly coinciden., the effect due to frequency drifts of the generator 1100 is eliminated so that the measurement can be made to a much higher degree of accuracy than the inherent stability of the sweep genera-tor 1100. In addition, since the measurement depends only on establishing the minimum in the chamber response curve, it is independent of non-linearity in the response of the detector 1100 as well as fluctuations in the incident microwave power with time. Repeated measurements on a given mode indicate that resonant frequency of the chamber 28 can be determined to an accuracy better than + 3 KH7 or approximately 5 parts in 106.
Now, a first embodiment of the method for pre-cisely measuring the volume of a section of the chamber 28 will be explained in greater detail. Generally, the method of this invention involves measuring the resonant frequen-cies of the chamber 28 for two different modes of excita-tion. As an example, consider the right cylindrical cham-ber 28, and measure the resonant frequencies in the TMolo and TEl11 modes. Both modes are non-degenerate and their resonant frequencies can be determined to an accuracy of ~ 1740~2 1 part in 107 or better with standard techniques. The TMolo mode (parallel plate mode) is dependent only on the average diameter (D) of the chamber 28 and is independent of the cavity height (L), whereas the TElll mode is depen-dent on both (D) and (L). Therefore, from the measurementof the two frequencies, the volume of the cham~er 28 can be determined. For the case of TMolo mode:
~D 1 01 ~1 = resonant wavelength _ X0l or D = ~ (11) where D = diameter, X0l = 1st Bessel root or Jo(X) = 0 ~or the case of TElll mode:

~2 = resonant wavelength = ~2X11~2 + -1 2 (12) ~ ~D J L
- where D = diameter, L _ length or height of cavity, Xll =
1st root of Jl(x) = 0.
Combining the 2 results give ~ = 01 ~1~ L = 1/2~ 2 ~Xll~ ] (13) In terms of the resonant frequencies, the results can be expressed as:

~ 2 L ~f2 XCl¦ ] (14) where Xll = 1.8412, X0l ~ 2.4048i and c = speed of light in the medium filling the cavity, (air for the present applica-tion) ~

~ 174072 --so--In terms of the total volume of the chamber, 4- L = ~1 ~2X012 ~1 ~22 ~Xllll2]

~fl~ ~X~ -1/2 ~15) As can be seen, the volume is, to first order, proportional to ~3 or l/f . Therefore dv ~ 3 [d~ or 3ldf) (16) Hence, the freq~encies can be measured accurately to 1 part in 107 as by the counter 1108, and thus the theoretical accuracy for v is of the order of 3 parts i~ 107.
The method can be used to continuously measure the change in volume of a right circular cy~inder 12 caused by a positive displacement of its piston 14. Both the volume of the chamber 28 before and after the piston motion, as well as the rate of change of volume can be measured in a simple manner. For the arrangement shown in Figure 10, as the piston 14 moves from position X to position Y, the TMolo mode resonant frequency will remain constant (or chanse slightly due to non-uniformity in the diameter of the cylin-der) and the TElll mode resonant frequency will shift by an amount proportional to the displacement ~L. At position X, the resonant frequencies fl and f2 are measured and are inserted within equation 2 to provide an indication of a first volume Vl. Thereafter, the piston 14 is moved to a second position Y and a second set of resonant frequencies fl~ f2' for the modes TMolo and TElll, respectively, are taken and a second volume V2 is calculated in accordance with equation 15. Finally, a displacement volume ~V is calculated b~ subtracting the first determined volume ~ 174~72 Vl as determined at position X from the value V2 of the second volume as determined at position Y. In addition, by continuously monitoring the T~olo resonant frequency, the variation of the diameter of the chamber 28 (due to machining imperfections) between Ll and L2 can be measured as a function of L. In a similar manner, the rate of change of volume can be measured by continuously monitoring the resonant frequency of the TElll mode.
Perturbations to the above relationships includé
dielectric properties of air, the presence of coupling con-duits 30 and 32, and the other gas inlet 62, surface irregu-larities, finite electrical conductivity of the wall matexial of the chamber 28 and degeneracy due to mode crossing. To 1st order, so long as the isre~larities are small compared to ~ (which will be on the order of 30 cm or larger), the perturbations will be proportional to the volume change.
Hence, the method will average over deformities and give a measurement which will be proportional to the true volume of the chamber 28.
The coupling conduits 30 and 32 and gas inlet 62 are made with sizes well below the cut off wavelength or the microwaves and should perturb the resonant frequency at most by 1 part in 105 and can be corrected for in the 1st order.
Similarly, the perturbation due to the finite electrical conductivity of the wall material of the chamber 28 should be of this same order of magnitude if the walls are fabricated or plated with a high-conducting metal such as copper, silver, gold, or aluminum, and reasonable care is taken in polishing. As an example, the theoretical skin-depth for co?per at 300 Mc/s is 3.8 x 10 4 cm. The perturbation on the volume is of the order of the ratio of the skin-depth to the linear dimension of the resonant cavity which, for a right circular cylinder with a radius of 50 cm, is approximately 7.6 x 10 6. The actual skin depth can be estimated from the dissipative losses in the ~ 174072 cavity which are directly related to the quality factor or Q of the cnamber,which can generally be experimentally measured to about 1~ accuracy. Consequently, a f.irst order correction can be applied which will reduce the uncer-tainty to better than a few parts in 107.
The resonant frequency change between vacuum and air in the cavity is given by, vacuum/f air) = (~)1/2 (17) where E i5 the dielectric constant for air at microwave frequencies, which for dry air at STP, has the value ~S ~ = 536.5 x 10 6. Hence the frequency change from vacuum to air is of the order oE 2.7 x 10 4. Since ~ for dry air is accurately known at microwave frequencies as a function of pressure and temperature, this shift can be corrected for to an accuracy of at least 1 part in 106.
The expression ~ t,p / ( lj20c, latm] = (P/760)/ [ 1 + 0.00341 (t-20)]
can be used to correct for the pressure and temperature depend-ence of ~ to better than 0.1% accuracy. Since the perturba-tion in frequency is only 2.7 x 10 4 initially, we canexpect an overall accuracy in the resonant frequency deter-mination of the order of 10 7 if the barometric pressure is monitored to better than 0.1~ (or about 1 mm of mercury).
The water vapor (relative humidity) contribution to the dielectric constant of air can be expressed as:

( l)water vapor x 10 = 5.00 (273 16~ p ~18) where T is the temperature as measured by a precision tem-perature device in ~egrees Kelvin and P is the partial pres-sure of water va?or in millibars. For ~ = 20C (293K), the saturation vapor pressure (100% relative humidity) is 23 millibars. Hence, for this extreme case, ~ )water vapor x 10 - 100 which is approximately ~ 174072 1/3-as that for dry air. Again, this effect can be corrected to the 1st order by measuring the relative humidity, and an accuracy of the order of 10 7 can be achieved in determin-ing the vacuum resonant frequency of the cavity.
Both the TElll and the TM010 are not degenerate in frequency with any other resonant TEM modes. Accidental degeneracy due to spurious mode-crossing can be avoided by choosing the dimensions of the volume properly. The condi-tions for mode-crossing, between D~L>O to D/L = 3 are:
D/L = 0.45; D/L = l; and D/L = 2.14 (at D/L=0.45, the TMo1o mode is degenerate with the TE112 mode; at D/L = 1, the TMolo mode is degenerate with the TE
mode; at D/L = 2.14, the TElll mode is degenerate with the ~Mllo mode). Therefore, ~y choosing D/L ratios other than those values, interactions with spurious modes are avoided and the resonant behavior of the cavity will be well-defined and the formulas for calculating the resonant frequencies from the dimensions of the chamber 28 are rigorously valid.
As an illustrative example, suppose we choose to work in the region of l<D/L'2.14 and require that the net traverse of the piston 14 displace a volume equal to 8 cu. ft.
(2.2652 x 105 cc). Then the following configuration can be used:
D = 104.88 cm Ll = 52.44 cm = final piston position Y
L2 = 7~.66 cm = initial piston position X.
Hence, the net displaced volume is, ~(104.88) (26.22) = 2.26;2 x 105 cc.
Also, as can be seen, the D/L ratio varies from 1.33 for the initial position to 2 for the final position, which are well 3~ within the desirable operating range. For this case then:
fl = resonant frequency of T~olo mode = 219.0 Mc/s f2(i) = initial value of TElll mode = 253.9 Mc/s (D/L =1.33) f2(f) =final value of TElll mode = 331.5 ~Ic/s (D/L = 2) ~ 174072 Similarly, for the case of 2 cubic feet total volume, the frequencies are:
fl = 347.6 ~c/s f2(i) = 403.0 Mc/s f2(f) = 526.2 l~c/s The dependence of frequency for an incremental chane in L can be expressed as f ~1-3739)(L2/D2) + l~ L (l9) which for D/L = l.33 gives, (~f/f) = l.l ~'L/L) ~20) and for D/L = 2 gives, (~f/f) = l.5 (~L/L).
As can be seen, the uncertainty in measuring L is nearly equal tD that ~or ~he f2equency measurement. Consequ~ntly, very high precision can be obtained for determining the volume displaced in this dimension configuration.
It is also informative to estimate the quality factor Q of the resonant modes, since the precision in measuring the resonant frequencies will depend, ~o a great extent, on the sharpness of the resonances. For the Tr~olo mode:
Q- = 0.22 for D/L = 1.33, Q~ = O.l9 for D/L = 2.
Where ~ is the skin depth given by ~ = [(~p)/l20~2~]l/2, P is the resistivity of the wall material of the chamber 28, ~ is the wavelength, and ~ is the permeability of the wall material.
If the chamber 28 is made of copper, P = 1.7 x lO 6, = l and ~ = 4.43 x lO 4cm at 219 Mc/s. Therefore Q = 6.8 x lO4 for D/L = l.33 and Q = 5.9 x 109 for D/L = 2.
Depending on the coupling coefficient, the width of the resonance curve at the half power points varies between ~2fo/Q) and (fO/Q) where fO is the resonant frequency. Conse-quently, the width of the resonance curve for the values of Q
computed are:
at fO = 219 Mc/S: 3.2 ~ ~f ~ 6.4 Xc/s for Q = 6.8 x 104 and 3.7 ~f ~ 7.4 kc/s for Q = 5.9 x 104 Since fO can be us~ally determined to an accuracy of 10 of f or better, we can ex?ect an accuracy of the order of 10 7 in determining fO. This in turn implies accu-racy of this order in the measurement of the diameter D of the chamber 28.
Similarly, for the TElll mode:
Q~ = 0.28 for D/L = 1.33, ~ = 0.27 for D~L - 2, which gives, Q = 7.5 x 10 at 253.9 Mc/s and Q = 5.5 x 10 at 331.5 Mc/s.
As before, the widths of the resonance curves are, 3.4- f - 6.8 kc/s at 253.9 ~c/s and

6.0- f - 12.0 kc/s at 331.5 Mc/s.
Again adapting the criteria that fO can be deter-mined accurate to 10 of ~f, then for the worst case of (12.0 kc/s) ~fO/fO~4 x 10 7. From the expression previously derived for D/L - 2, Qf Therefore, ~L/L) can be determined to (4 x 10 7)/1.5- 2.7 x 10 7.
It is also possible to calculate the,perturbation on the resonant f-equency of a cavity mode due to the presence of a gas-inlet and outlet opening 62 on ~hR head 60 of the cylinder 12. From the Adiabatic Invariance theorem and a knowledge of the field configuration inside the cavity, the frequency pulling caused by the hole can be estimated in a straightforward manner. If the hole dimension is well below the cut-off wavelength (which will be rigorously true for the case under consideration), then the frequency pull-ing will be proportional to the ratio of the cube of the hole diameter to the volume of the chamber 28.
Illustratively, the expression for the change in the resonant frequency of the TMolo mode caused by the opening 62 l~c3ted at the center of the plate 60 is given by, ~ :~74072 ~af/fO) = (d )/8D L(Xol)Jl (X0l) (21) where d is the diameter of the hole Jl(Xol) is the value of the Bessel function Jl at X0l, and ~f is the frequency shift.
Upon numerical evaluation using D = 104.88 cm L - 52.44 cm, X0l = 2.40483 and Jl (X0l) = 0.2695l then (Qf/fO) = 3.35 x 10 ?d3 As can be seenl for d of the order of 2 cm or less the frequency shift is only of the order of 2 x 10 6, Con-sequentlyl the shift is very small and with an appropriate initial calibration procedure, such as covering the opening 62 with a matching metallic plugl this effect can be vir-tually eliminated as a systematic error in the precision of the method.
Coupling of the microwave energy to the chamber 28 lS for the two modes T~olo and TElll can best be accomplished by placing a coaxial feed line terminated in the antenna 70 at a position approximately 1/2 way out from the center of the end plate 60 of the cylinder 12 with the loop oriented along a radius. The magnetic field at this location is about 90% of the maximum field intensity inside the cavity for both modes. Consequentlyl both modes are energized to the same degree of coupling with high efficiency. In addi-tion, by placing the coupling on the head 60l the coupling wlll r.ot be affected by the movement of the dis~
placement piston 14.
In the followingl a description will be given of a second preferred method of measuring a displacement volume within the chamber 28 and using this accurately determined volume to calibrate the train of pulses as provided by the opticall linear encoder 26. In a similar manner to that described abovel the piston 14 is moved from a first posi-tion as indicated in Figure lO by the designation Lll to a second position indicated by the designation L2 having moved through a displacement of ~L. The cylinder 12 is inherently rigid whereby the calibra~ion processl as will be describedl ~ 1~4072 may be only carried out occasionally to insure that no long term systematic changes, such as dimensional deformation of the cylinder 12, misalignment and malfunction of the opti-cal linear encoder 26, or distortion of the piston 14 has occurred. In order to maximize the absolute measurement accuracy of the microwave volume calibration, it is neces-sary that the mechanical configuration of the cylinder 12 be as close as possible to that of a perfect, totally enclosed right circular cylinder and thereby eliminate or reduce all possible sources of systematic perturbations which could potentially affect the microwave measurements.
Referring now to Figure 12A, certain mechanical modifications are made. First, the physical gap that exists between the piston 14 and the walls of the chamber 28 must be effectively blocked to prevent the escape of microwave energy through that gap. ~s explained in the above-identified application, ;-nr entitled "Piston Seal", because of the nature of the seal between the piston 14 and the wall of the chamber 28, the gap is considerable. A cover 11 is made of a suitable metallic material, such as stainless steel, and further, has a series of springlike fingers 15, as shown in detail in Figure 12B, disposed between the piston 14 and the inner periphery of the chamber 28, which, when the cover 11 is in place over the piston 14, project into the gap between the piston 14 and the wall of the chamber 28, the fingers being in close contact with the piston 14 and the wall.
The fingers 15 act as a short circuit reflectlng the elec-tromagnetic field that would otherwise be directed through the noted gap. In an illustrative embodiment, the spring-like fingers 15 are made of a beryllium copper. Further, the pressure and temperature sensors 51, 57, 48, and 68 are removed and are repl~ced by appropriate blank metallic plugs, confisured to provide a substantially flush surface with the inside walls of the chamber 28. Further, the fluid ~74072 ~.

inlet opening 62 in the head 60 is covered by a metallic plate to provide a substantially flush surface across the the top of the head 60. In addition, the inside peripheral walls of the chamber 28 are cleaned with a suitable solvent to remove any residual traces of the oil as may have seeped from the piston seal. Noting that the required calibration is determined by a displacement volume ~V and not by the absolute volume of the chamber 28, the above-described mechanical modifications do not affect the accuracy of the calibration process. Once the measurements, as will be described, are made for the modified chamber 28, the same set of measurements may be carried out immediately after-w~s with the chamber 28 restored to its normal operating configuration and a set of appropriate calibration factors can be generated to relate the two sets of measurements.
The results of the second measurements can then be used as a data base from which subsequent checks of the absolute calibration can be compared without going through the full procedure of modification and reassembly of the chamber 28.
8riefly, the volume measuring and calibration process includes the step of moving the piston 14 to a first position indicated by the designation Ll in Figure 10, by manually rotating the rotary member 19 of the servomotor 20.
At the first position, the antenna 70 is energized with electromagnetic energy of a first mode TElll and a second mode TE112, selected to minimize the above-discussed per-turbations. The frequencies fl and f2 at which resonance is established for each modeare detected by observing the counter 1108. Then, the piston 14 is moved through a dis-tant dL to a second position as indicated by the designationL2, whereat the antenna 7~ is energized again with electro-magnetic energy of the first and second modes and correspond-ing frequencies at which resonance is established for each of the modes are noted. The output of the optical, linear encoder 26 is 2p~1' ed to a counter, which counts the linear ~ 1740~2 encoder pulses as the piston 14 is moved through the dis-tanoe ~L. The diameters Dl and D2 of the chamber 28 at each of the first and second p~sitions corresponding to the desig-nations Ll and L2 are calculated. At this point, a calcu-lation of the aL is made using the previously calculatedvalues of Dl and D2. The calculated value of ~L is divided by the number of pulses derived from the linear encoder 26 as counted during the movement of the piston 14 through the dist~e ~L to provide a length calibration factor using the measurements of Dl and D2. The volume ~V corresponding to that volume as defined by planes passing through the points Ll and L2 and the inner periphery of the chamber 2~ is expressed by a mathematical expression in terms of the di-ameters Dl and D2 and ~L. If the output of the optical, lS linear encoder 26 is to be calibrated for a given volume, e.g., one cubic foot, that value is disposed in this equation and it is solved for the calculated values Dl and D2 to provi~e _hat value of ~L corresponding to the movement of the piston 14 to draw one cubic foot of fluid through the meter 38. The calculated value of ~L is multiplied by the previously calculated length calibration factor to provide that number of pulses that will be output by the optical, linear encoder 26 as the piston 14 is moved a length ~L
to draw the one cubic foot into the chamber 28. As explained above, the count as derived from the linear encoder 26 is used to calculate the calibration factor as incorporated within the calculation carried out in step 1062, as shown in Fig~re 9N. In particular, the calibration factor is the reciprocal of tne counts so derived for one cubic foot of fluid drawn into the chamber 28 and provides a correction to the calculation of percent error in the reading o the meter based upon a precise measurement of the volume of the chaF~er 28, as e~plained above.
First, it is necessar~ to measure the frequencies at w~ich the standing wave conditions are established at ~ 17~0~2 the positions Ll and L2. The calculation of diameters Dl and D2, as will be explained, requires a value of the speed of light, which changes for varying ambient conditions of temperature, pressure, and relative humidity. Corrections for changes in the speed of light are expected to be small, and the calculation of the speed of light is made typically once or twice during the course of a calibration process of the optical, linear encoder 26.
The speed of light in vacuum, Co, is 2.997925 x lOlO cm/sec. The corresponding value c for air is obtained by dividing Co by the refractive index of air at the wave-length of observation. For the microwave region (f<30GHz), the refractive index, n, is related to the atmospheric parameters by the equation:
(n-l) x 1o6 = 77-6 (p + 4810e ) (22) where P is the total pressures in millibars (1 bar = 106 dynes/cm2 = 0.986923 standard atmosphere - 75.0062 cm Hg at OC), T is the temperature in degrees Kelvin, and e is the partial vapor pressure of water in millibars. The speed of light is then given by c Co/n Co / ll ~ T (P + ~ ) x lO ~ (23) The temperature and barometric pressure can be directly obtained from the readings of a thermometer and a barometer placed near the meter prover lO.The partial vapor pressure of water can be deduced from the relative humidity data obtained with a sling psychrometer through the use of the psychrometer formula, or more conveniently, via the use of a standard table such as the Smithsonian Physical Table #640.
In order to calculate a value Of A L, there is needed to determine the average value of the diameter of the chamber 28 and more specifically, to determine the values of the diameters Dl and D2 at the locations Ll and L2, respectively. The calculation Dl and D2 is carried out with great care since the resulting uncertainty in the volume is ~ 1740~2 approximately twice the uncertainty of this measurement.
As explained above, the piston 14 is moved to the first position corresponding to the designation Ll at which the frequencies fl and f2 for which the resonant standing wave S condition is established for the two different modes.
The preferred method is to measure simultaneously the reso-nant frequencies fl and f2 of two different modes of the same electrical characteristics as a function of the piston position L and solve for the average diameter D by using the appropriate theoretical expression.
~n a prefe.red embodiment wherein the chamber 28 has the configuration of a right circular cylinder, the pair of modes preferred for this purpose are the TElll and TE112 modes. As will be discussed, it has been demonstrated ~hat the quality factor Q obtained by excitation in these modes is high thereby reducing the effects of perturbations upon the measurements of resonant frequency. The average diameter of the cylinder at any fixed position of L is given by the expression:
[4f2 (L)-fl (L)] / (24) where f2 is the resonant frequency of the TElll mode and f is the resonant frequency of the TE112 mode, and c is the speed of light in air as calculated by equation 23. By using two different modes of electromagnetic wave energy excitation, the various perturbations such as skin-depth variation, reac-tive frequency pulling caused by the antenna 70, the degree of divergency of the inner periphery of the chamber 28 from being a perfect riSht circular cylinder are compensated for and the absolute value of D is obtained with great accuracy.
By exercising care in the taking of measurements of the fre-quencies upon the counter 1108, as shown in Figure 10, abso-lute accuracies of the values D as a function of L may be obtained in the order of one part in 10 or 0.1 mill out of a 12 inch diameter. This degree of accuracy is of the same order of the changes in the volume of the chamber 28 - ~3L740~2 due to thermal expansion and contraction as disposed in a temperature stabilized environment where the temperature is maintained within range of + 1P.
In order to confirm these measurements as well as to provide a quantitative means for evaluation of the order of magnitude of the expected perturbations in the system of measurement, the diameter may be independently determined by measuring the resonant wave frequencies by generating electromagnetic waves of the TMolo mode within the chamber 28. With such a mode of excitation, the resonant frequency is independent of the length L and there~ore for a perfectly uniform cy~inder, should not change as the position of piston 14 is varied. Howev~r, excitation in the TMolo mode is sub-ject to other various perturbations which need be considered to achieve the same degre~ of accuracy as for the two modes discussed above. For the TMolo mode, the average diameter is given by the expression:
D(L) = 0.7654799c/f (25) where f is a resonant frequency of the TMolo mode.
Once the average diameter D of the chamber 28 as-a function of L has been determined to the desired degree of accuracy, the value of ~L is obtained and related to the observed number of pulses from the optical, linear encoder 26 in order to obtain the length calibr2tion factor in terms of length per pulse interval or number of pulses per inch.
The piston position is set at Ll, and the resonant frequen-cies at fl and f2 for the selected modes TElll and TE112 are measured. The piston 14 is then moved by cranking the rotary member 19 to a new position L2 and the resonant frequencies of the same modes are remeasured, while counting the number of optical encoder pulses during the movement of the piston 14 from its first to its second position. The number of pulses is divided by ~L = Ll-L2 to provide the desired length calibration factor. The distance aL = (Ll-L2) should be large enouch such that the calibration accuracy is not limited by the accuracy in the pulse count (+ 1 in this case) ~ 1 7~072 and the calibration should be performed over a number of OL
intervals to insure that no non-linearity effects exist in these measurements.
For the TElll mode, the change in distance GL is given by the expression:

oL = (L -L ) = C2~ ~22_~ 5860)671C3~ _ [fl2_(0-58(L6)lc~i ] (26) where f2 and D~L2) are the TElll mode resonant frequency and the previously determined average diameter at piston position L2,and fl and D(Ll) are the respective values at position Ll.
For the TE112 mode, the change in distance oL is given by the expression:

~L = ~L2-~) = C ~ 22- ~0 D8(LO~71c~ ] _ ~f 2_~0.5860671CJl ~ (27) where the various quantities are defined in a similar manner as above.
Similar expressions can be written for any mode of excitation, and more than one mode can be used to check the internal consistency and absolute accuracy of these measure-ments.
The absolute calibration of the displacement volume ~V between the piston positions Ll and L2 is provided by the following expression:
2 1 (~/4)~D2 (~L) + (D22-D 2)L~ (28) where D2 and Dl are the averaged diameters of the cylindrical cross-sections as taken at piston positionsLl and L2 and ~L = (L ~1) It is evident from an observation of the equation 28 that knowing values of D2 and Dl, if we assume for calibration purposes a given value of the absolute displacement volume ~V, e.g., one cubic foot, that the corre-sponding value of ~L, i.e., that distance through which the piston 14 must be moved in order to draw one cubic foot of fluid into the chamber 28 of the meter prover 12, may be ~ 174072 calculated. The o~ject of the calibration is to obtain the number of pulses as derived from the optical linear encoder 26 that are output for any desired displacement volume ~V
and is obtained by multiplying the obtained value of ~L for 5 a given volume by the length calibration factor to provide the equivalent number of pulses that are output by the optical linear encoder 26.
The selection of the TElll and TE112 modes to excite the cavity 28 was based upon repeated determinations 10 using a number of normal mode resonances to determine the quality factor Q for each of the modes. These determina-tions of the Q of a normal mode require the measurements of the ratio of the reflected power (Pr) to the incidentpo~
(Po) at the resonant frequency, and the frequency width of 15 the response curve corresponding to the half-power level defined by Pl/2 = ~Po + Pr)/2. It is desired that the d.c.
voltage response of the crystal detector 1110 be linear with input microwave power. This condition can be satis-fied by operating the crystal detector 1110 in the so-called 20 "square law detection" region corresponding to a d.c. level typically less than 20 millivolt. If necessary, the line-arity of the response can be verified by the use of the step attenuator located on the sweep generator 1100. Once established, the coupling coefficient (Pr/Po) can be 25 measured directly on the screen of the oscilloscope 1112 in terms of the corresponding voltage ratio. The half-power level then can be calculated as an equivalent voltage.
The half width of the response curve, as shown in Figure 14, is just the difference between the two frequency settings 30 as set on the sweep generator 1100 corresponding to the half-power levels on ither side of the resonant frequency as observed on the oscilloscope 1112. The Q of the resonance is calculated by using the expression given by equation 10.
35 From these determinations of Q, it was demonstrated that ~ ~4072 --1 o s -TElll mode has a quality factor Q of approximately 6,000 to

7,000 over the runningrange of the piston 14, while the TE112 mode has a quality factor Q of 8,000 to 10,000. As indicated above, the quality factor is a measure or the S order of magnitude of the expected devia~ion of the reso-nant frequency from the idealized results as provided by equation 1. Thus by using these modes, the resonant fre-quency may be measured with a greater accuracy and those perturbations as would arise due to in sur-face imperfections as well as for the effects of skin depth andfrequency pulling may be minimized. Thus, the use of the modes TEl11 and 'rE112 are believed to provide determinations of gre~ter accuracy of the rescnant frequency, and thus of the average diameter D and of the volume displacement between the two piston positions.
Thus, there has been described a meter prover ~hat is capable of measuring fluid and in particular, gas flow through a meter with a high degree of precision. In one aspect of this invention, the volume of the cylinder in.o which the fluid is d_awn is measured with extreme accuracy and is compared to the output of the encoder which detects movement of the cylinder's piston, whereby indication cf the volume drawn into the cylinder is provided with -ing high degree of accuracy. This standard or calibrated volume is compared with the output of the meter under test to provide an indication of meter registration, as well as the percentage of error of the meter fluid reading from the actual or calibrated volume indicated by the optical encoder of the meter prover system. Further, the meter prover sys-tem is controlled by a computer system whereby a number oftests are made in which parameters of meter and prover tem-perature and pressure are taken lnto consideration to adjust the indication of the measured volume of fluid flow, as well as to take repeated tests under varying conditions. In particular, var~ing volumes of fluid may be drawn by the meter prover throuqh the meter by entering corresponding r count factors lnto a counter of the computer and counting the selected count to zero, to terminate the meter test. In a further aspect of this invention, a new and novel method is S employed for determining with high precision the volume of ~he cylinder into which the fluid is drawn for a given dis- j placement of the piston. This accurate measurement is determined by the frequencies at which standing waves are .
established for first and second piston positions to provide 10 a precise indication of the fluid volume and the output of the optical encoder coupled to detect the movement of the piston.
Numerous changes may be made in the above-described apparatus and method, and different emSodiments of the inven-15 tion may be rr.~.ade without departing from the spirit thereof;
therefore, it is intended that all matter contained in the foregoing description and the accompanying drawings shall be interpreted as illustrative and not in a lir.liting sense.

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. Apparatus for calibrating a fluid flow meter under test, said apparatus comprising:
(a) means for directing a known volume of fluid through the meter under test, said directing means comprising a housing of known volume, said housing being coupled to the fluid flow meter under test to permit the fluid to be directed through the flow meter by said directing means;
(b) measuring means coupled to said directing means for providing a calibrated indication of the fluid drawn by directing means through said meter;
(c) first means for continuously monitoring during the course of a test of a meter the temperature to provide a temperature indication of the fluid;
(d) second means for continuously monitoring during the course of a test of a meter the pressure to provide a pressure indication of the fluid; and (e) control means responsive to the initiation and termination of the meter test for initiating and terminating respectively the continuous monitoring of the indications of temperature and pressure from said temperature and pressure measuring means.

2. Apparatus for calibrating as claimed in claim 1, wherein said initiating and terminating means samples the temperature indication and pressure indication during the course of the meter test, sums each of the temperature and pressure indications sampled during the course of the meter test and divides each sum by the number of samples taken during the course of the meter test to provide respectively the continuous indications of fluid temperature and pressure.

3. Apparatus for calibrating as claimed in claim 1, wherein said temperature measuring means comprises a first temperature transducer disposed at a first end of said housing and a second temperature transducer disposed upon said piston remote from said first transducer.

4. Apparatus for calibrating as claimed in claim 3, wherein said control means comprises means for summing the outputs of the first and second temperature transducers to provide an averaged signal indicative of the temperature of the fluid within said housing.

5. Apparatus for calibrating as claimed in claim 4, wherein there is further included second means for measuring the temperature of the fluid within the fluid flow meter.

6. Apparatus for calibrating as claimed in claim 5, wherein said second temperature measuring means comprises third and fourth temperature transducers disposed respectively at the inlet and outlets of the fluid flow meter.

7. Apparatus for calibrating as claimed in claim 6, wherein there is included means for summing the outputs of said third and fourth temperature transducers to provide a second averaged indication of the fluid temperature within the fluid flow meter.

8. Apparatus for calibrating as claimed in claim 7, wherein there is further included correlating means comprising means responsive to the first-mentioned and second averaged indications of the fluid temperature to provide a temperature correction factor for processing the indication of the volume of fluid measured by the fluid flow meter to compensate for the difference in fluid temperature within the fluid flow meter and within said housing.

9. Apparatus for calibrating as claimed in claim 6, wherein there is included first means for measuring the pressure of the fluid within said housing and second means for measuring the pressure of the fluid within the flow meter under test.

10. Apparatus for calibrating as claimed in claim 9, wherein said first pressure measuring means comprises a first differential pressure transducer disposed upon the piston for measuring the difference in pressure between that of the fluid within said housing and the ambient pressure about said housing, said second pressure means comprising a second differential pressure transducer disposed at the outlet of the fluid flow meter of the flow meter under test for measuring the difference between the pressure of the fluid passing from the fluid flow meter and the ambient pressure about the fluid flow meter, and there is further included a third pressure transducer for measuring the absolute ambient pressure about the fluid flow meter under test and said housing.

11. Apparatus for calibrating as claimed in claim 10, wherein there is included means for summing the output of said third transducer to the sum of the output of said third transducer and the output of said second transducer to provide a first average absolute pressure of the fluid within said housing, and second means for summing the output of said third transducer and the output of said first transducer to provide an indication of a second average absolute pressure of the fluid within the fluid flow meter.

12. Apparatus for calibrating as claimed in claim 11, wherein there is included correlating means comprising means responsive to the first and second average absolute pressures to provide a pressure correction factor for processing the indication of the fluid volume measured by the fluid flow meter to compensate for the differences in the fluid pressure within the fluid flow meter and within said housing.

13. Apparatus for calibrating as claimed in claim 11, where there is included a second measuring means coupled to the fluid flow meter under test to provide a second indication of fluid flow as measured by the fluid flow meter.

14. Apparatus for calibrating as claimed in claim 13, wherein said control means comprises means for providing a precise indication of the volume of fluid passing through the flow meter under test as a function of the first and second indications of fluid flow, and the average absolute pressures of the fluid within said housing and the flow meter and the average absolute temperatures of the fluid within the flow meter and said housing.

15. Apparatus for calibrating as claimed in claim 14, wherein said volume indicating means is further responsive to a calibration factor indicative of that precise output by said first measuring means for a given volume of fluid as drawn by said directing means.

16. Apparatus for calibrating as claimed in claim 15, wherein said measuring means comprises a first transducer disposed at a first extremity of said housing and second temperature transducer disposed at said piston to respectively provide first and second indications of fluid temperature.

17. Apparatus for calibrating as claimed in claim 16, wherein there is included means for summing the first and second indications of said first and second temperature transducers to provide an averaged indication of the housing fluid temperature.

18. Apparatus for calibrating as claimed in claim 17, wherein there is included second temperature measuring means disposed at the inlet and outlet of the fluid flow meter for measuring the temperature of the fluid within the fluid flow meter.

19. Apparatus for calibrating as claimed in claim 18, wherein said second temperature measuring means for providing third and fourth temperature transducer means for providing third and fourth temperature indications of the fluid temperature at the inlet and outlet of the fluid meter, and there is further included means responsive to the third and fourth temperature indications for summing and providing a second average indication of the temperature of fluid within said fluid flow meter.

20. Apparatus for calibrating as claimed in claim 19, wherein there is included correlating means comprising means responsive to the first-mentioned and second average indications of temperature to provide a temperature correction factor for processing the indication of the volume of fluid measured by the fluid flow meter to compensate for the difference in fluid temperature within the fluid flow meter and within said housing.

21. Apparatus for calibrating as claimed in claim 19, wherein there is included first means for measuring the pressure of the fluid within said housing and second means for measuring the pressure of the fluid within the fluid flow meter.

22. Apparatus for calibrating as claimed in claim 21, wherein said first pressure measuring means comprises a first differential pressure transducer disposed upon said piston for measuring the difference in pressure between that of the fluid within said housing and the ambient pressure about said housing, said second pressure means comprising a second differential pressure transducer disposed at the outlet of the fluid flow meter under test for measuring the difference between the pressure of the fluid passing from the fluid flow meter and the ambient pressure about the fluid flow meter, and there is further included a third pressure transducer for measuring the absolute ambient pressure about the fluid flow meter under test and said housing.

23. Apparatus for calibrating as claimed in claim 2, wherein there is further included second means for summing the output of said third pressure transducer to the sum of the output of said third transducer and the output of said second pressure transducer to provide an average absolute pressure of the fluid within said housing, and third means for summing the output of said third pressure transducer and the output of said first pressure transducer to provide an indication of the average absolute pressure of the fluid within the fluid flow meter.

24. Apparatus for calibrating as claimed in claim 23, wherein there is included second measuring means coupled to the fluid flow meter under test to provide a second indication of fluid flow as measured by the fluid meter.

25. Apparatus for calibrating as claimed in claim 24, wherein there is included control means including means responsive to the movement of said piston for enabling the accumulation of the first and second indications of the fluid flow to provide an indication of the relative accuracy of the meter under test.

26. Apparatus for calibrating as claimed in claim 24, wherein there is included means for providing a precise indication of the volume of fluid passing through the flow meter under test as a function of the first and second indications of fluid flow, and the average absolute pressure of the fluid within said housing and the fluid flow meter, and the average absolute temperatures of the fluid within the flow meter and said housing.

27. Apparatus for calibrating as claimed in claim 26, wherein said volume indicating means is further responsive to a calibration factor indicative of that precise output by said first mentioned measuring means for a given volume of fluid as drawn by said directing means.