WO1996003634A1

WO1996003634A1 - Particle counter for contamination analysis of liquids

Info

Publication number: WO1996003634A1
Application number: PCT/US1995/007842
Authority: WO
Inventors: Holger T. Sommer
Original assignee: Met One, Inc.
Priority date: 1994-07-25
Filing date: 1995-06-20
Publication date: 1996-02-08

Abstract

A particle detection system of the type having an optical particle sensor (37) detecting particles in a liquid stream directed between an inlet (19) and an outlet (55) of the sensor (37). The sensor (37) includes a photodetector producing a signal indicative of the presence and size classes of particles in the stream and a counter (39) receiving the signal to produce a particle count for selected size classes of particles in the liquid. The system includes a source of liquid sample, such as a sample bottle (11) or liquid reservoir (81), in fluid communication with the inlet of the sensor, a source of pressure gas, including a cartridge (21) storing the gas, such as CO2, as a vaporizable liquid under pressure, and means (23-27, 29-31, 17) for directing the pressurized gas to the liquid sample source so as to drive the liquid sample under pressure through the inlet (19) of the sensor (37).

Description

Particle Counter for Contamination Analysis of Liquids

Technical Field

The present invention relates to optical meas¬ uring and testing systems for the detection, sizing and counting of solid particles in liquid samples, such as hydraulic and lubricant oils, and in particular relates to liquid handling or transport means within such sys¬ tems, for dispensing a precise volume of sample material through the optical sensor apparatus at a controlled rate of flow.

Background Art

Devices that detect the presence of particles in fluids are well known and widely used in manufacturing industries. Among the fluids which are commonly moni- tored are water, hydraulic oils and lubricants. For example, the detection, sizing and counting of particles is important for the safe operation of hydraulic equip¬ ment, control systems and lubrication systems, which can fail, or cause related machinery to fail, if excessive contamination debris in the form of ingressed or wear particles is present. Even though filters are used in such equipment to continuously remove particles from the hydraulic fluid or lubricant, the filters can become clogged and may rupture due to excessive pressure build-up across the filter membrane, thereby becoming ineffective at removing particles and possible even releasing previously trapped particles back into the working fluid. Particle detectors are thus used in such systems to detect any increase of particles in specified size classes and report the cleanliness level of the fluid according to categories specified by industry standards (e.g., ISO 4406 and NAS 1638). A typical particle detection system for deter¬ mining the cleanliness of fluids delivers a narrow stream of fluid sample past an optical single-particle sensor. As a particle in the sample stream passes through a light beam directed through the stream, a portion of the light energy is scattered and absorbed by that particle. A detector is positioned to receive light which is scat¬ tered by such particles, or alternatively, light which has not been obscured by a particle and thus transmitted through the sample. Systems based on the light obscura¬ tion technique are generally considered to be more suit¬ able for detecting particles in liquids, although it is less sensitive overall than the light scattering tech¬ nique. Both types of detectors are common. The detector registers a change in the amount of light energy reaching the detector, whenever a particle is present in the beam. The amount of the change in the light energy received by the detector is a measure of the size of the particle scattering or obscuring the light. Electronics associated with the detector process the signal to determine the size and number of particles in each size class which are present in the sample.

In order for these particle sensors to provide an accurate measure of a sample's level of cleanliness, their sample delivery systems should deliver a known quantity of sample fluid past the optical detector. Fur¬ ther, the sample delivery system should ensure that the fluid is not contaminated with particles generated by the sampling device itself or from any remains of a previous sample, and that gas bubbles, which appear as particles, are not produced in the fluid stream. A common method of transferring liquid into the sensor and through the opti¬ cal measurement volume is by supplying filtered com¬ pressed air from a small air compressor or from a house supply line with a remote compressor to drive the liquid by means of gas pressure through the sensor device. In U.S. Patent No. 3,669,542, Capellaro describes an optical particle sensor for counting the number of particles suspended in a liquid sample by measuring the scattering of a focussed light beam pro- jected through a flow stream of the liquid sample. The sample fluid is contained in a bottled or sample contain¬ er, which is initially attached to the sensor in an upright position and then inverted. Sample in the con¬ tainer will flow downwards through an outlet tube and into a flow cell, where particles in the sample are observed through windows in the flow cell and counted. Air is conducted by an air line to the space in the inverted bottle above the liquid sample. Thus, sample is introduced into the flow cell by both gravity and air pressure feed. The entire contents of the sample bottle are run through the flow cell. When the sample fluid has been discharged, the compressed air in the sample container causes air bubbles to appear in the instrument. The scattering of light by the bubbles is sufficiently greater than the scattering by particles in the sample fluid to be discriminated and causes automatic cut-off of the counting operation. A back flush of fluid into the sample container may be provided to ensure a complete count of particles and also to clean the sensor. In U.S. Patent No. 4,181,009, Williamson describes an apparatus for counting particle contamina¬ tion in a liquid, such as hydraulic oil, in which part of the oil traveling from a source to a destination by way of a conduit is forced, by back pressure provided by a check valve, to pass through an on-line by-pass sampling circuit in a continuous flow of oil. This alternate flow path includes a cylinder with a motor-driven piston that moves linearly in the cylinder. The initial portion of the piston's forward movement seals the input conduit opening into the cylinder so that no additional oil can enter the sampling circuit, at which time there is a fixed volume of oil trapped within the sampling circuit. Continued movement of the piston (1) trips a switch that starts operation of a particle counter, (2) ejects the measured volume of sample liquid from the cylinder through the particle counter and (3) trips another switch to stop operation of the counter. The rate of flow through the counter can be precisely controlled, irrespective of oil viscosity, by a selected combination of motor speed and piston size. After inspection, the sampled liquid is returned to the main flow path or collected in a sample bottle for further off-line tests. The volume of liquid which is sampled by a particle detection system is determined in Williamson's case by the known volume of liquid within the cylinder when the piston first seals the conduit supplying the sample. In Capellaro's system, the volume in the sample bottle may be known. Alternatively, a graduated cylinder collecting the fluid after testing can be used to measure the volume. However, all of these techniques are only of marginal accuracy. Another technique is to maintain a constant flow rate through the detector, which, if known, can be integrated over the detection time to provide a more accurate measure of volume inspected than the gradu¬ ated cylinder and related techniques. This can be done in Williamson's case, since the piston drives the liquid sample out of the cylinder past the detector at a rate which is both known and constant. However, in the case of a gas pressure based sample feed, as in Capellaro's system, the flow rate is not known precisely and varies with fluid viscosity. The flow rate establishes itself as a balance between the pressure differential between sample container and drain and the friction due to the sample fluid's viscosity. Thus, the flow rate is very sensitive to changes in fluid viscosity. Whenever a fluid for a different viscosity is to be inspected, the air pressure has to be readjusted in order to transfer the liquid at the same flow rate. A regulator valve may be used to adjust the air supply pressure. However, the viscosity is not always known with accuracy, and in the case of a working system using oils whose viscosities vary with temperature, the viscosity may not even be constant during the testing cycle. One objective of the present invention is to provide a sampler which can deliver fluids of varying viscosity to an optical particle sensor at a known and constant flow rate.

Another objective of the present invention is to provide a device which is sufficiently lightweight and independent of external power sources to be portable for use in the field. However, the requirements of low weight and portability conflict with the high power requirements needed to transfer highly viscous oils through the sensor. For sampling viscous fluids, large, heavy batteries are needed to store the high levels of electrical power needed to run a piston, as in William- son's device, for an acceptable number of fluid sample cycles. In-house devices, in contrast, can use an exter¬ nal electrical source. Likewise, systems which use compressed air, as Cappelaro's, require a large, heavy tank to supply the pressure to drive a sufficient number of fluid samples for field use. Such compressed air tanks or a compressor pump may be used in-house, but are impractical for field use, since they are not portable. Thus, providing a portable field device is a desired objective of the present invention.

Disclosure of the Invention

The above objectives are met with a particle detection system for liquids which separate the electri¬ cal power requirements of the system's electronics from the mechanical requirements of moving a viscous sample liquid through the sensor, by providing energy in the form of C0₂ gas pressure stored as a liquid in a small lightweight cartridge, and which uses a sample collection cylinder at an output end of the sensor unit with a pis- ton that is pulled back at a controlled rate to maintain a constant flow rate for the pressure-driven sample, regardless of the sample's viscosity. The C0₂ cartridge replaces the motor for a piston drive or compressor pump. either of which requires a large, heavy battery, so that a smaller and lighter battery pack can be used solely for the system electronics. Because the C0₂ cartridge stores the C0₂ as a liquid, it is also small, lightweight, and safe and easy to handle compared to the large, heavy can¬ isters that store compressed gas. The CO- provides the force for moving the sample liquid, sufficient to drive even viscous liquids through the sensor unit at a flow rate that, in the absence of a collection cylinder with pistons, would at least equal or exceed the desired con¬ stant flow rate for the sample. The piston, therefore, does not require a powerful motor with the large electri¬ cal power requirements that would be needed if it were to provide the force moving the sample. Rather, it merely backs off at a controlled rate corresponding to the desired constant flow rate of the sample liquid to allow the sample to pass through the sensor unit at that flow rate. No special adjustments in gas pressure, based on an estimate of fluid viscosity, are needed to achieve the desired flow rate. An accurate portable unit is there¬ fore obtained.

More generally, the invention is a diagnostic instrument for analyzing fluid material, such as by counting particles in a fluid sample, which uses a liquid CO. cartridge as a source of pressure to move the fluid through the instrument. The C0₂ from the cartridge is capable of moving fluids of high viscosity through small flow passages, and is ideal for field applications where the instrument is required to be battery operated and stand alone. For example, an instrument that uses the pressure drop across a calibrated sieve as a measure of contamination level of a liquid sample may employ the C0₂ in cartridges to move a predetermined amount of oil through the sieve. Use of the C0₂ cartridge also permits accurate control of the pressure, improving the repeat¬ ability of the measurement. Brief Description of the Drawings

Fig. 1 is a schematic side view of a particle detection system of the present invention.

Figs. 2A and 2B are side elevational views of sample probes in two stages of operation for use in an alternate reservoir sampling mode by the system of Fig. 1.

Best Mode of Carrying Out the Invention With reference to Fig. 1, a particle detection system of the present invention includes a sample bottle 11, typically with a 50 to 150 ml capacity, enclosed within a pressure vessel 13. The pressure vessel 13 may be made of stainless steel. The pressure vessel 13 includes a cap 15, typically attached to the vessel 13 by means of a 15° turn bayonet coupling with an o-ring seal between the vessel 13 and cap 15 to prevent leakage of pressurized gas. The cap 15 has a pair of tubes 17 and

18 penetrating therethrough which convey pressurized gas into the pressure vessel 13 and sample liquid out of the sample bottle 11. Preferably, the bottle 11, pressure vessel 13 and cap 15 with the tubes 17 and 18 are designed to be inverted as a unit, as shown. Accord¬ ingly, the tube 17 for the pressurized gas is long enough to extend nearly to the bottom of the upright bottle 11 so that when bottle 11 is inverted, the pressurized gas enters the bottle 11 above the liquid sample, for little or no bubbling. Likewise, the tube 18 for the sample liquid is short enough so that when the bottle 11 is inverted, all of the sample liquid can be removed through the tube 18. The bottle, pressure vessel and cap are mounted to the rest of the detection system at a coupling

19 in fluid communication with the tube 18 where it exits the cap 15. The coupling 19 is rotatable so that the pressure container unit is mounted first in an upright position and then rotated upside-down to the position shown. This inversion allows any particles in the sample fluid which have settled to the bottom of the sample bottle 11 to be re-suspended in the liquid sample. An optoelectric sensor 20 may be used to verify the position of the bottle 11 and relay this information to a control processor 35. The detection system also includes a C0₂ pres¬ sure cartridge 21 which stores C0₂ at room temperature at about 800-850 psi (5.5 to 6.0 MPa). C0₂ is liquid under such conditions. Thus, a typical cartridge 21 of about 1-1/2 inches (4 cm) diameter and 4 to 5 inches (10 to 12 cm) in length has a capacity of about 8 in³ (130 cm³) and can contain about 64 grams of CO. in liquid form. This far exceeds the amount of material it could contain in gaseous form, even when such a gas is highly compressed. Other gases that undergo a gas-to-liquid phase change at comparable pressures at or near room temperature could also be used, provided they are inert to the sample material and do not corrode any components in the fluid path. However, C0₂ is preferred.

A regulator 23 attached to an output of the C0₂ cartridge 21 reduces the pressure of C0₂ exiting the cartridge 21. The pressure reduction causes the C0₂ to convert from a liquid to a gas. The pressure reduction is chosen, as by turning a knob 24 on the regulator unit 23, so that resulting gas pressure is enough to transfer the most viscous oil expected for the particular applica¬ tion of the system at the desired flow rate through the restrictions in the liquid flow path. Since the pressure reduction chosen is directly related to the consumption of CO., this pressure should also be chosen to be the minimum needed for the particular application. A typical output pressure from the regulator 23 ranges from 60 to 120 psi (0.4 to 0.8 MPa).

Clean, dried, regulated shop air, of up to 120 psi (0.8 MPa) pressure, can be connected to the system through a coupling 25 in order to conserve C0₂, whenever the system is being used in a stationary setting rather than in the field. In either mode, i.e., portable field use or stationary in-house use, the gas passes along -9-

conduits 26 through a filter 27 and a solenoid valve 29 to a fitting 30 for flexible tubing 31 leading to cap 15 on the pressure vessel 13 and through tube 17 extending into the sample bottle 11. The gas flow path 26 and 31 typically has about a 1/8 inch (3 mm) inside diameter.

The filter 27 is preferably capable of removing any 1 μm size particles and larger in the gas, so as to avoid con¬ taminating the sample liquid with any additional parti¬ cles. Solenoid valve 29 receives electrical control signals via signal line 33 from a system processor 35 with user interface. Pressing a start button of the control electronics 35 causes the solenoid valve 29 to open, releasing pressurized gas into the pressure vessel 13 to start the process. The gas pressure provides the motive force for the sample liquid, pushing the liquid through the tube 18 and coupling 19 and through the sensor unit 37.

The sensor unit 37 is an optical particle detector having a laser directing a beam through the liquid sample stream and a photodetector positioned in the beam path to receive laser light which has not been obscured by a particle passing through the beam. Alter¬ natively, the photodetector may be positioned to receive light scattered by the particle. In either case, a change in the light received by the photodetector pro¬ duces a change in the electrical signal output by the photodetector, which is then directed along an electrical signal line 38 leading from the sensor unit 37 to an electronic counter 39. The counter 39 interprets a change in the signal provided by the sensor unit 37 as a particle present in the sample stream. The counter 39 may also interpret the amount of signal change as indica¬ tive of the size of the particle and may keep a separate count of different size classes of particles. Control signals received in signal lines 41 from the system processor 35 may direct the counter 39 to output the particle count through a serial data port 43, write the particle data on a printer 45, or reset the count to zero after each sample cycle. Additional data presentation options are also possible, such as displaying the parti¬ cle data on a video display screen, or sounding an alarm when the sample is determined to fail a particular clean- liness standard. The processor 35 may receive the coun¬ ter data over signal lines 41 and present the data to the system user via the processor's user interface.

A small, lightweight battery pack 47 powers the system electronics, including the counter 39 and processor 35. Because electric power is not needed to drive the sample liquid through the system, ordinary C-size Ni-Cd rechargeable batteries can be used. The battery pack 47 may be recharged, when needed, through a recharging jack 49 that can be connected to an external electric supply. Preferably, the C0₂ cartridge 21 has a capacity that matches that of the battery pack 47, so that both recharging and cartridge replacement are always carried out at the same time. The battery pack 47 also powers the drive controller 51 and stepper motor 52 for the flow control piston 53, but this is also a low power operation since the stepper motor 52 and piston 53 are not used to provide motive force to the sample liquid, as explained below. Rather, all motive power for the sample comes from the pressurized gas from liquid CO- cartridge 21 or through shop air inlet 25.

After passing though the sensor circuit 37, the sample liquid passes through a filter screen 55 and a hydraulic pressure reducing regulator 57 to be directed by a valve 59 into a flow control actuator 61. The filter screen 55 removes only large particles, of 20 μm size or larger, in order to avoid clogging the pressure reducing regulator 57. A screen which has smaller holes, blocking smaller particles, may be used as a particle sensor. The differential pressure of the particle- bearing fluid measured on opposite sides of the screen may be calibrated to indicate particle count.

The regulator 57 is important when the system is used in an on-line supplying mode. In such a mode. -li¬

the sample bottle 11 in its pressure vessel 13 is not used, and the coupling 19 is connected directly to a pressurized fluid conduit directing a sample through the sensor unit 37 at a high line pressure of up to 3000 psi (20 MPa). The regulator 57 is hydraulically actuated and reduces the pressure to about 15 psi (0.1 MPa) prior to the fluid entering the flow control actuator 61. Accord¬ ingly, the actuator 61 need not be designed for high pressures, saving additional weight. The flow control actuator 61 includes a cylinder 63 defining a sample chamber 64 for receiving sample fluid, a piston 53 movable within the cylinder 63 and mounted on the end of a screw 65, and a stepper motor 52, operatively connected to the screw 65 for causing retraction of the piston 53 within the cylinder 63. A stepper motor driver controller 51, responsive to control signals from processor 35, actuates the revolution of the motor 52 with control pulses sent at the desired step rate. Provided the gas pressure applied by C0₂ cartridge 21 to the sample fluid is sufficient to drive even the most viscous liquid sample at the desired flow rate or greater, the speed at which the piston 53 is withdrawn by the stepper motor determines the rate of increase of available volume 64 for the sample in the cylinder 63, and thus the flow rate of fluid into the actuator 61. The speed of the piston 53 is directly linked to the number of revolutions per unit time of the stepper motor 52, so that counting the motor's angular steps, using a sensor 67 associated with the stepper motor 52, provides a very accurate measure of piston speed and, consequent¬ ly, a very accurate measure of sample volume in cylinder 63 and fluid flow rates.

A valve 59 directs the sample flow between the main flow conduits 71 and 72 and the actuator cylinder volume 64. In one valve position, sample liquid flows from the conduit 71 leading from the sensor unit 37 into the cylinder volume 64. In another valve position, forward movement of the piston 53, produced by reversing the stepper motor's direction, expels sample liquid from the cylinder volume 64 into conduit 72, through a check valve 73 and out of the conduit 72 into a drain or sample collector 75. A third valve position may be provided to prevent any fluid flow. The valve may be actuated by processor 35 or may be a hand valve actuated by turning a knob 77. Sensors 79 verify valve position and communi¬ cate that information to the processor 35.

In the on-line sampling mode, use of the pres- surized C0₂ source is not needed, since the fluid pres¬ sure in the conduit attached to coupling 19 provides the energy needed to overcome all flow restrictions in the hydraulic path of the sample.

The particle detection system may be adapted to sample liquid from a reservoir by means of a gas actuated probe connected to coupling 19 and gas tubing 31. As seen in Figs. 2A and 2B, the sample probe has an outer cylindrical wall 81 with fluid inlet apertures 83 at the top. The probe also has an inner opening 85, for con- ducting pressurized gas from the C0₂ cartridge or in-house air line into the probe. A valve ball 87 is large enough to close the top opening 89 and is located inside the probe wall 81. A tubing 86 reaches to the bottom of the probe to convey the liquid out when pressurized.

In the first operating position shown in Fig. 2A, the gas pressure source is off or significantly re¬ duced and the probe is inserted into the liquid reser¬ voir. Liquid flows into the probe through the openings 83 and 89, forcing the valve ball 87 up against the open¬ ing 89, closing the opening 89 when the liquid reaches the top inside of the probe. The liquid fills the probe completely when the probe is submerged below its top. The fluid volume collected by the probes is fixed by the probe inner dimensions. However, use of the flow control actuator 61 in Fig. 1 is necessary to control the tested sample volume and flow rate accurately. In the second operating position shown in Fig. 2B, the probe is still in the reservoir but the gas pres¬ sure source is activated. Pressurized C0₂, from the car¬ tridge 21 in Fig. 1 or an external pressurized air sup- ply, enters the probe through tubing 85, forcing the valve ball 87 against the aperture 89 and forcing the collected sample liquid up through the tubing 86 to the coupling 19 in Fig. 1 and through the sensor unit 37. Pressure should be sufficient to drive viscous liquids at the required flow rate through the sensor unit 37. The probe cycle alternates between the two operating posi¬ tions shown in Figs. 2A and 2B.

Claims

1. A diagnostic instrument for analyzing liquid samples, comprising a sensor unit having a liquid flow passage with an inlet and an outlet and having means for analyzing liquid directed through said flow passage between said inlet and said outlet, a source of liquid sample in fluid communica- tion with said inlet of said sensor unit, and a cartridge storing a source of vaporizable liquid C0₂ under pressure, said cartridge in fluid commu¬ nication with said source of liquid sample so as to drive said liquid sample under gas pressure through said flow passage of said sensor unit.

2. A particle detection system comprising a particle sensor, having an inlet and an outlet, for detecting particles in a liquid directed as a stream between said inlet and outlet, a source of liquid sample in fluid communication with said inlet of said particle sensor, a source of pressurized gas, said source of pressurized gas being a cartridge storing said gas as a vaporizable liquid under pressure, means for directing pressurized gas from said source to said source of liquid sample so as to drive said liquid sample in a flow path under gas pressure through said inlet of said particle sensor.

3. The system of claim 2 wherein said source of liquid sample is a sample container with first conduit means for directing said liquid sample from said sample container to said inlet of said particle sensor, and wherein said means for directing pressurized gas is second conduit means connecting said source of pressurized gas to said sample container. 4. The system of claim 2 wherein said source of liquid sample is a liquid reservoir and said means for directing pressurized gas is a probe having a probe inlet in fluid communication with said liquid reservoir and a probe out- let connected to said inlet of said particle sensor, said probe having an inner conduit communicating with said source of pressurized gas and valve means for controlling collection of said liquid sample from said reservoir.

5. The system of claim 4 wherein said valve means is a ball valve sealing said probe inlet.

6. The system of claim 2 wherein said vaporizable liquid stored by said source of pressurized gas is liquid C0₂.

7. The system of claim 2 further comprising flow control means connected to said outlet of said particle sensor for receiving liquid sample therefrom at a desired flow rate, said flow control means including means for providing a space for collecting said liquid sample and means for increasing volume of said space at a rate equal to said desired flow rate.

8. The system of claim 2 wherein said particle sensor comprises a screen disposed across the liquid flow path, capable of being loaded with particles and means for de¬ tecting the differential pressure on opposite sides of the screen.

9. A particle detection system comprising a particle sensor having an inlet and an outlet for detecting particles in a liquid directed as a stream between said inlet and outlet, means for providing a liquid sample under pressure to said inlet of said particle sensor, said pressure sufficient to direct said stream of liquid through said particle sensor at a volume flow rate of at least a desired flow rate, and flow control means connected to said outlet of said particle sensor for receiving said liquid sample therefrom at said desired flow rate, said flow control means including means for providing a space for collecting said liquid sample and means for increasing a volume of said space at a rate equal to said desired flow rate.

10. The system of claim 9 wherein said particle sensor comprises an optical particle detector receiving said stream of liquid, with a photodetector producing a signal indicative of the presence of a particle in said stream, and means receiving said signal for counting said particles.

11. The system of claim 10 wherein said signal from said photodetector is also indicative of the size of a particle in said stream and said counting means produces a separate count for each of a plurality of size classes of said particles.

12. The system of claim 9 wherein said flow control means comprises a chamber providing said space with a piston reciprocable within said chamber for altering the volume of said space, said piston being actuated by a motor in mechanical communication with said piston to withdraw within said chamber at a speed to create a volume increase of said space corresponding to said desired flow rate.

13. The system of claim 12 wherein said flow control means includes means for measuring said piston speed to obtain an accurate measure of said volume flow rate and sampled volume.

14. The system of claim 13 wherein said measuring means comprises means for counting fractions of revolutions of said motor. 15. The system of claim 9 wherein said means for providing liquid sample under pressure comprises a sample container containing said liquid sample, first conduit means for directing said liquid sample from said sample container to said inlet of said particle sensor, a source of pressurized gas, and second conduit means for directing said pressurized gas into said sample container.

16. The system of claim 15 wherein said source of pressurized gas is a cartridge storing vaporizable liquid under pressure, and connected to said second conduit means.

17. The system of claim 16 wherein said vaporizable liquid is liquid C0₂.

18. The system of claim 15 wherein said source of pressurized gas is an in-house compressed air shop line connected to said second conduit means.

19. The system of claim 9 wherein said means for providing liquid sample under pressure comprises a probe having a probe inlet in fluid communication with a liquid sample reservoir and a probe outlet connected to said inlet of said particle sensor, said probe having an inner conduit communicating with a source of pressurized gas, and valve means for controlling collection of said liquid sample from said reservoir.

20. The system of claim 19 wherein said valve means is a ball valve sealing said probe inlet.

21. The system of claim 19 wherein said source of pressurized gas is a cartridge storing vaporizable liquid under pressure, and connected to said second conduit means. 22. The system of claim 19 wherein said vaporizable liquid is liquid C0₂.

23. The system of claim 19 wherein said source of pressurized gas is an in-house compressed air shop line connected to said second conduit means.

AMENDED CLAIMS

[received by the International Bureau on 4 October 1995 (04.10.95); original claims 4, 19, 22 amended; Remaining claims unchanged (4 pages)]

4. The system of claim 2 wherein said source of liquid sample is a liquid reservoir and said means for directing pressurized gas is a gas actuated probe having a probe inlet in fluid communication with said liquid reservoir and a probe outlet connected to said inlet of said particle sensor, said probe having an inner conduit communicating with said source of pressurized gas, said source being alternately active and inactive valve means responsive both to a liquid sample level in said probe and to alternately high and low gas pressure in said probe for controlling collection and dispensing of fixed amounts of said liquid sample from said reservoir, and means responsive to system control signals for alter¬ nately activating and deactivating said pressurized gas source.

19

14. The system of claim 13 wherein said measuring means comprises means for counting fractions of revolutions of said motor.

15. The system of claim 9 wherein said means for providing liquid sample under pressure comprises a sample container containing said liquid sample, first conduit means for directing said liquid sample from said sample container to said inlet of said particle sensor, a source of pressurized gas, and second conduit means for direct¬ ing said pressurized gas into said sample container.

17. The system of claim 16 wherein said vaporizable liquid is liquid C0₂.

-22-

19. The system of claim 9 wherein said means for providing liquid sample under pressure comprises a gas actuated probe having a probe inlet in fluid communica¬ tion with a liquid sample reservoir and a probe outlet connected to said inlet of said particle sensor, said probe having an inner conduit communicating with an alternately active and inactive source of pressurized gas, valve means responsive both to a liquid sample level in said probe and to alternately high and low gas pressure in said probe for controlling collection and dispensing of fixed amounts of said liquid sample from said reservoir, and means responsive to system control signals for alternately activating and deactivating said pressurized gas source.

21. The system of claim 19 wherein said source of pressurized gas is a cartridge storing vaporizable liquid under pressure, and connected to said second conduit means.

22. The system of claim 21 wherein said vaporizable liquid is liquid C0₂.

23. The system of claim 19 wherein said source of pressurized gas is an in-house compressed air shop line connected to said second conduit means. STATEMENT UNDER ARTICLE 19

Claims 4 and 19 are amended to better define applicant's sample probe (shown in Figs. 2A and 2B of the drawings and described from page 12, line 14 to page 13, line 12 of the specif¬ ication) so as to distinguish it from the fluid flow system taught by Haynes (US-A-4503385) . In particular, the amended claims recite a gas actuated probe with an inner conduit (85) communicating with a source of pressurized gas that has means (e.g., a solenoid valve 29) responsive to system control signals (33, 35) for alternately activating and deactivating the gas pressure source. The probe also includes valve means (e.g., a floating valve ball 87) responsive both to a liquid sample level in the probe (during a full cycle) and to alternately high and low gas pressure in the probe (during and at the end of an emptying cycle) for controlling the collection and dispensing of fixed amounts of liquid sample from a reservoir into which the probe can be inserted.

Accordingly, as defined by the amended claims, the probe employs a sample collection and dispensing cycle that alternates between two operating positions. In a first position, the gas pressure source is off (or significantly reduced) and sample liquid flows into the probe through its inlet (83, 89) when the probe is inserted into and submerged within a liquid reservoir. The valve means closes the inlet opening (89) when the probe is completely filled. The collected fluid volume is fixed by the probe's inner dimensions. During this fill cycle, the collected liquid is not driven through the probe outlet (86) but remains within the probe. In a second operating position, the gas pressure source is activated. Pressurized gas entering the probe through the inner conduit (85) forces sample liquid through the probe outlet (tubing 86). During this emptying cycle, the valve means (87) responsive to the gas pressure maintains the closure of the probe inlet (83, 89) to prevent additional liquid from flowing into the probe. This structure permits measured quantities of liquid sample to be dispensed to the particle sensor.

The probe structure set forth in the amended claims differs from the antechamber structure (52) described in the Haynes document in which sheath liquid flows continuously into and out of the antechamber at a constant flow rate. The sheath flow rate is determined by whether or not a container (28) of sample liquid is in position for dispensing the sample through an aperture (16) for analysis in the chamber (12). When the sample liquid is in position, the sheath liquid flows at a higher constant flow rate than when the sample liquid is not in position. The Haynes struc¬ ture does not use the alternating fill and empty probe cycle that is characteristic of the probe set forth in the amended claims.

Claim 22 is amended to be dependent upon claim 21.

The other claims are unchanged.