WO2001063221A1

WO2001063221A1 - Bi-directional flow sensor with integral direction indication

Info

Publication number: WO2001063221A1
Application number: PCT/US2001/004438
Authority: WO
Inventors: Harold M. Miller; Charles A. Woringer
Original assignee: Data Industrial Corp
Current assignee: Data Industrial Corp
Priority date: 2000-02-24
Filing date: 2001-02-12
Publication date: 2001-08-30
Anticipated expiration: 2002-08-24
Also published as: AU2001236910A1

Abstract

A flow sensor (20) for measuring the direction and flow rate of a fluid flowing through a pipe (51). The flow sensor includes a rotatable paddle wheel impeller (21) and a sensor arrangement for generating signals as the paddle wheel blades pass the sensors. A micro-circuit interprets the signals and generates an output corresponding to the direction as well as the speed of rotation of the impeller.

Description

BI-DIRECTIONAL FLOW SENSOR WITH INTEGRAL DIRECTION INDICATION

FIELD OF THE INVENTION

The present invention relates to an insertion type flow sensor for determining flow characteristics of a fluid, and more particularly, to a paddle wheel impeller flow sensor including an integral sensor and circuit arrangement for determining the direction and flow rate of a fluid flowing through a pipe.

BACKGROUND OF THE INVENTION

The use of flow sensors for measuring the direction and the velocity of fluid flow in closed conduits is well known. Typical flow sensors include those reported in U.S. Patent No. 3,610,039 issued to Althouse et al.; U.S. Patent No. 4,109,526 issued to Rosso; and U.S. Patent No. 3,299,702 issued to Hulme. Each of these flow meters are characterized by a turbine rotor situated within the flow stream and being rotationally driven by the fluid. Two distinct, independent sensors, e.g. induction pickups, having a relatively large spacial separation are implemented in proximity to the turbine vanes for producing two independent phase-shifted signals corresponding to the approach and retreat of each vane of the turbine impeller relative to the sensors during their rotation thereof. The flow sensors of the prior art are connected to separate structure including circuitry for converting the signals associated with the rotation of the impeller and corresponding to the dynamics of fluid flow, into conveniently measured analogs thereof. These analogs, by calibration, are used to measure the direction and rate of fluid flow through the closed conduit.

The bi-directional flow sensor devices of the prior art, as evidenced by the aforementioned prior art references, utilize rotors of the turbine type. Turbine rotors are characterized by a rotational axis that extends coaxially to the conduit the turbine is situated in and therefore, the rotational axis is parallel to the direction of fluid flow. Accordingly, the sensors used with turbine rotors are generally spacially separated within the plane of rotation of the turbine rotor, or in other words, these sensors are perpendicularly arranged relative to the fluid flow. Furthermore, turbine rotors include a plurality of vanes that are helically arranged. Turbine rotors are designed to be rotated by the flow stream contacting the helical vanes in a tangential direction.

Because of the helical nature of the vanes, a substantial part of the turbine rotor must be exposed to a cross-section of the fluid flow through the conduit in order to rotate the turbine. For example, in each of the prior art references discussed above, the outer diameter of the turbine rotor is approximately equal to the diameter of the conduit. As a result, the turbine rotor flow sensors are relatively large, resulting in relatively high rotary moment of inertia. In addition, turbine rotors are relatively awkward and costly to install within a pipe or conduit.

Paddle wheel impeller flow sensors provide several significant advantages over turbine rotor flow sensors. Paddle wheel impellers are shaped, disposed and rotated in a substantially different manner compared to turbine rotors. Paddle wheel impellers have blades that are arranged perpendicularly relative to a fluid flowing through a pipe or conduit, in contrast to the helically disposed vanes of turbine rotors. Additionally, the rotational axis of paddle wheel impellers is disposed perpendicular to the direction of fluid flow, in contrast to the parallel orientation of turbine rotors. As such, paddle wheel flow sensors are not required to protrude a substantial distance into the flow stream in order to provide accurate flow measurements. As a result, paddle wheel flow sensors are smaller, less intrusive and possess a smaller rotary moment of inertia, relative to turbine rotor flow sensors, thereby minimizing hydrodynamic disturbances in the fluid flow. Paddle wheel flow sensors also provide accurate measurement of the fluid velocity in the area of flow impinging upon the impeller.

The small size and unobtrusive operation of paddle wheel flow sensors allow them to be readily installed into any pipe or conduit, including a pipe which already has a fluid flowing therethrough. A retrofit, called a hot-tap operation allows the paddle wheel flow sensor to be inserted into a pre-existing pipe-line, without interrupting the flow, by putting a fitting on the pipe, then boring the pipe and inserting the sensor. Such a retrofit would not be possible with a full pipe size turbine impeller flow sensor. Furthermore, paddle flow sensors are about 1/5 the cost of turbine flow sensors and installation costs are about 1/10 of turbine flow sensors.

Existing paddle wheel flow sensors do not provide a bi-directional flow measurement capability in a self-contained device. In order to determine the direction of flow through a pipe or conduit, it has been necessary to install two non-bilaterally symmetric sensors or to install one bilaterally symmetric sensor between two pressure sensors. Alternatively, in systems with two pumps, a bi-directional flow measurement has been achieved by reading the velocity from a single bilaterally symmetric sensor and inferring direction from knowledge of which pump is operating.

In the known two non-bilaterally symmetric sensor arrangement, the direction of flow is determined by installing the sensors in a manner such that the upstream side of each of their respective flow directions is arranged facing each other. (The upstream side is usually the sensor side of higher sensitivity.) Thus, for any flow direction, one of the sensors will show a higher flow velocity reading. The direction of flow is then inferred from the sensor with the higher reading.

In the known single bilaterally symmetric sensor arrangement, the direction of flow is determined by installing pressure sensors on each side of the bilaterally symmetric sensor. The direction of flow is then inferred from the pressure sensor reading which is higher or lower.

As a result, a need exists for an integral paddle wheel flow sensor capable of measuring both direction and velocity of fluid flow through a pipe. A need also exists for a flow sensor having the above noted features that is easily installed, relatively cheap to manufacture, and can produce output signals that can be read by existing equipment. SUMMARY OF THE INVENTION

The present invention provides an integral paddle wheel flow sensor capable of accurately measuring both direction and velocity of a fluid flow. More particularly, it provides a bilaterally symmetric paddle wheel flow sensor including a sensor pickup unit and corresponding circuitry located within the flow sensor housing. The flow sensor of a preferred embodiment of the present invention includes a giant-magneto resistive (GMR) sensor arrangement that generates overlapping, out-of-phase signals as the at least partially magnetized paddle wheel blades of the impeller rotationally approach and retreat from close proximity relative to the sensors. A circuit interprets these signals and generates a final output from the flow sensor corresponding to the direction and the flow rate of the fluid flow.

In another preferred embodiment of the present invention, the flow sensor structure, including the impeller and the housing, is geometrically symmetric. Geometric symmetry of the flow sensor allows the sensor to present the same profile to the fluid flowing through the pipe, irrespective of the fluid flow direction. Such structure plays a part in the capability of the flow sensor of the present invention to accurately measure flow in either direction through a pipe or conduit, without re- calibration or the use of additional sensors beyond the housing of the paddle wheel flow sensor.

Still other objects, features, and attendant advantages of the present invention will become apparent to those skilled in the art from a reading of the following detailed description of embodiments, taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described in more detail with reference to preferred embodiments of the apparatus and method, given only by way of example, and with reference to the accompanying drawings, in which:

Fig. 1 shows a preferred embodiment of a paddle wheel flow sensor operably connected to a pipe in accordance with the invention; Fig. 2 shows a longitudinal cross-sectional view of the paddle wheel flow sensor of the present invention;

Figs. 3a-3e show several views of the impeller lower housing of the flow sensor of the present invention; Fig. 4a shows a perspective view of a preferred embodiment of a paddle wheel impeller of the flow sensor of the present invention;

Fig. 4b shows a cross-section of the preferred embodiment of the paddle wheel impeller as illustrated in Fig. 4a;

Fig. 4c shows a cross-section of another preferred embodiment of the paddle wheel impeller of the flow sensor of the present invention;

Figs. 5a-5b illustrate the amplifier/detector signal processing portion of the micro-circuit of the present invention;

Fig. 6 shows a first preferred embodiment of a part of the direction sensing micro-circuit of the present invention; Fig. 7 shows a second preferred embodiment of the direction sensing micro- circuit of the present invention;

Fig. 8 shows the output of the parts of the sensing micro-circuits as shown in Figs. 5a-5b when the rotation of the impeller is in a clockwise direction; and

Fig. 9 shows the output of the parts of the sensing micro-circuits as shown in Figs. 5a-5b when the rotation of the impeller is in a counter-clockwise direction.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Generally speaking, the present invention provides a bi-directional paddle wheel flow sensor including an integral sensor and circuit arrangement for determining the direction and the flow rate of a fluid flowing through a pipe. The flow sensor of the present invention is particularly useful since it is capable of providing accurate bidirectional flow measurements using a paddle wheel impeller housed as an integral unit, without re-calibrating the flow sensor or implementing additional external sensors. In addition, the flow sensor of the present invention conveniently produces output signals which can be read and processed by standard electrical monitoring equipment. Since the bi-directional paddle wheel flow sensor of the present invention is housed in a self- contained integral unit, it can be readily inserted into a pipe or conduit without substantially disrupting the fluid flow therethrough, thereby minimizing hydrodynamic disturbances.

Referring initially to Fig. 1, the flow sensor 20 of the present invention relates to a self-contained device, capable of being inserted into a fluid carrying pipe or conduit 51 containing a stream of fluid flowing in either possible direction. For example, the flow sensor 20 can be inserted into a pipe interconnecting a pump and a reservoir in which a fluid flows from the pump to the reservoir, or from the reservoir to the pump. The flow sensor 20 of the present invention operates to provide a final output signal corresponding to both the direction and the rate of fluid flow as it travels through the pipe or conduit 51. Fig. 1 shows a preferred embodiment of the present invention, in which the flow sensor 20 is inserted via a branch connection of an appropriately sized tee fitting 53 into an operable position within a pipe 51. The longitudinal axis of the flow sensor is arranged substantially perpendicular to the pipe 51 carrying the fluid.

Reference is made to Fig. 2, which shows a more detailed preferred embodiment of the bi-directional flow sensor 20 of the present invention. The flow sensor 20 includes a lower housing 23 with an extending lower skirt portion 24 of the housing forming a concave opening 25 at one end of the lower housing 23. Within the concave opening 25, a magnetic paddle wheel impeller 21 including a plurality of impeller blades 45 is rotatably held via a bearing arrangement 33. The upper portion of the flow path through the impeller cavity is skirted to enable the predominant flow through the cavity to react on the impeller on its lower half. This enhances the flow impinging on that half of the impeller, thus improving the impeller's response to flow. When inserted into the pipe or conduit 51, the fluid flow operates to rotate the impeller 21 at a velocity proportional to the instantaneous average fluid velocity of the fluid. Located directly above the concave opening 25, housing the paddle wheel impeller 21, is a sensor pickup unit 27. Sensor pickup unit 27 is situated in close proximity to the impeller 21 so to be capable of picking up a magnetic flux emitted from the magnetic impeller blades 45 as the blades pass the pickup unit 27. Sensor pickup unit 27 includes a sensor arrangement including at least two sensors 29, 31. The sensors 29, 31 possess a relatively small spacial separation. As shown in Figs. 1 and 2, the sensors are spatially separated within the plane of rotation of the turbine rotor, or parallel to the fluid flow. For the given geometry, the preferred spacing between the sensors is between .050" and .150", and more preferably the spacing is about .0625". This spacial separation provides both sufficient time differentiation between the two channel detector pulses, while also ensuring pulse overlap which is fundamental to the bi-directional sensing scheme of the present invention. Each of the sensors 29, 31 generates a signal whenever an impeller blade 45 approaches and retreats from each of the sensors 29, 31.

A tubing carrier or upper housing 35 is attached to an end of the flow sensor lower housing 23. As shown in Figs. 1 and 2, lower housing 23 may be threaded into the tubing carrier 35, thereby permitting a radial adjustment of the flow sensor 20 with respect to the fluid carrying pipe or conduit 51, so as to locate the impeller at a desired distance within the pipe or conduit 51.

The flow sensor 20 of the present invention is capable of accurately measuring a fluid flow through a pipe in two directions. Accurate bi-directional flow measurements are possible due in part to the geometric symmetry of the paddle wheel impeller 21 and of the lower housing 23. Geometric symmetry allows the flow sensor 20 to present the same profile to the fluid flowing through the pipe whether the flow is coming from right to left, or left to right, in relation to the sensor as shown in Fig. 1. The flow sensor 20 of the present invention also possesses bilateral symmetry. Bilateral symmetry is defined as the geometric identity, except as a mirror image, of all geometric characteristics as arranged around a plane normal to the flow stream and passing through the rotary axis of the impeller. This results in flow streamlines in the flowing fluid being identical whether flow intersects the plane of symmetry from either the right or left sides of that plane. Referring to Figs. 3a-3e, and in particular to Fig. 3b, one embodiment of the flow sensor lower housing 23 is shown and includes a center axis 26 representing the longitudinal axis of the housing. The flow sensor lower housing 23 is bilaterally symmetric about the center axis 26 for facilitating bi-directional flow measurements as discussed above. In addition, lower skirt portion 24 is provided with apertures 28 for rotatably mounting the paddle wheel impeller 21 to the flow sensor lower housing 23 by way of the bearing arrangement 33.

Referring now to Fig. 3e, which illustrates a bottom view of the lower skirt portion 24 of the flow sensor lower housing 23, the varying thicknesses of the walls making up the lower skirt portion 24 and defining the concave opening 25 are shown. Specifically, the walls making up the lower skirt portion 24 include a pair of oppositely arranged sidewall portions 30 each having a substantially constant thickness and each defining a circular inner sidewall having a curvature. The maximum distance between the circular inner sidewalls defines an inner sidewall diameter D. The remaining wall structure making up the lower skirt portion 24 includes additional sidewall portions having widening wall thicknesses which reach a maximum thickness at the apertures 28. The apertures 28 are used to rotatably mount any of the preferred embodiments of the paddle wheel impeller 21 to the flow sensor lower housing 23.

Fig. 4a shows a perspective view of a preferred embodiment of a paddle wheel impeller 21 of the present invention. An axis 47 passes through the rotational center of the paddle wheel impeller 21 and another axis 49 passes through the center body of each of the plurality of blade portions 45. Each of the blade portions 45 have a generally planar first side surface and a generally planar second side surface which is substantially parallel to the first side surface. During operation, the generally planar side surfaces are capable of being disposed substantially perpendicular to a fluid flowing in either direction through a pipe, as shown in Fig. 1. The paddle wheel impeller 21 is radially symmetric about axis 47 and bilaterally symmetric about each axis 49. Other preferred embodiments of the paddle wheel impeller 21 of the present invention also possess geometric symmetry along similar axes. The geometric symmetry of the paddle wheel impeller 21, and of the flow sensor 20 in general, allows a fluid flowing at a particular speed in either direction through a pipe to rotate the paddle wheel impeller 21 at a substantially similar angular velocities. Consequently, a fluid flow rate is capable of being accurately monitored and measured by the integral flow sensor unit 20 as the fluid flows in either direction through a pipe without re- calibrating the sensor structure or electrical monitoring equipment. Accordingly, it is no longer necessary to use a separate flow sensor to measure a flow rate for each flow direction, as has been required in the past. Thus, the flow sensor 20 of the present invention simplifies installation and reduces cost.

Fig. 4b shows a cross-section of a preferred embodiment of the paddle wheel impeller 21 shown in Fig. 4a. The paddle wheel impeller 21 includes a hub portion 41, a plurality of stem portions 43 and a plurality of impeller blades or blade portions 45. Each of the blade portions 45 is attached to the hub portion 41 by way of a single stem portion 43. Additional details of the structure of the preferred embodiment of the paddle wheel impeller 21 shown in Figs. 4a and 4b including the bearing arrangement 33 is described in greater detail in commonly assigned, U.S. Patent Application Serial No. 09/066,954, filed April 28, 1998, the disclosure of which is hereby incorporated by reference. In addition, while the paddle wheel impeller 21 is illustrated as having four impeller blades or blade portions 45 in Fig. 4a, it is contemplated that the preferred embodiments of the paddle wheel impeller could include any number of blade portions 45, as long as the paddle wheel impeller remains geometrically symmetric along axes 47 and 49.

Notwithstanding the number of blade portions 45 included in a particular paddle wheel impeller 21, each blade portion 45 is characterized as having an outer edge in the shape of a circular section having a curvature. The curvature of each of the blade portions 45 is shaped to substantially correspond to the curvature of the circular inner sidewalls of the oppositely arranged sidewall portions 30 of the flow sensor lower housing 23. Furthermore, a paddle wheel diameter d, or swept diameter, is defined as the maximum distance measured from an outer edge of a blade portion 45 to an outer edge of an oppositely arranged blade portion 45, one such paddle wheel diameter d being shown in Fig. 4b. However, when the paddle wheel impeller 21 includes an odd number of blade portions, whereby a particular blade portion does not have a corresponding oppositely arranged blade portion, the paddle wheel diameter d is determined by the swept diameter of the blade portions, as would be appreciated by one of ordinary skill in the art. The paddle wheel diameter d is slightly shorter than the inner sidewall diameter

D, such that the paddle wheel impeller 21 is capable of rotating freely when rotatably mounted to the flow sensor lower housing 23. As a result, when the paddle wheel impeller 21 is in the position shown in Fig. 2, at which point one blade portion 45 is shown rotatively entering into the concave opening 25 and the oppositely arranged blade portion 45 is shown rotatively exiting the concave opening 25, a relatively small clearance is formed between the outer edges of the blade portions 45 and the corresponding circular inner sidewalls of the sidewall portions 30. The optimal dimensions of the flow sensor, including the overall shape of the paddle wheel impeller, the paddle wheel diameter d and the small clearance formed between the outer edges of the blade portions 45 and the corresponding circular inner sidewalls of the sidewall portions 30, are determined by considering various parameters. For example, to increase the amount of torque applied to the paddle wheel impeller by the fluid being measured, it is beneficial to maximize the paddle wheel diameter d while minimizing the rotary moment of inertia of the impeller. To improve hydrodynamic performance, it is beneficial to nnnimize the small clearance formed between the outer edges of the blade portions 45 and the corresponding circular inner sidewalls of the sidewall portions 30. Furthermore, to prevent the paddle wheel impeller from jamming due to any particulates in the measured fluid, a sufficiently sized small clearance is necessary to prevent the particulates from lodging between the blade portions 45 and the circular inner sidewalls of the sidewall portions 30.

Preferred dimensions of the flow sensor can be expressed as a ratio of the inner sidewall diameter D to the paddle wheel diameter d. For example, when the dimension of the inner sidewall diameter D is .870" and the dimension of the paddle wheel diameter d is .800", a ratio of 1.0875 is produced. Accordingly, when the inner sidewall diameter D is 8.7 % larger than the paddle wheel diameter d, it has been found that accurate bi-directional flow measurements can be obtained with the flow sensor of the present invention. Furthermore, it has been found that accurate bidirectional flow measurements can be obtained with a preferred ratio range between 1.4500 and 1.0875, a more preferred ratio range of between 1.2429 and 1.0875 and a still more preferred ratio of about 1.0875. Accordingly, it is preferable to form the inner sidewall diameter D approximately 45% to 8.75% larger than the paddle wheel diameter d to provide accurate bi-directional flow measurements.

Regarding the preferred dimensions of the clearance between the blade portions 45 and the circular inner sidewalls, it has been found that a preferred clearance is between .135" and .035", a more preferred clearance is between .085" and .035" and a still more preferred clearance is about .035". For example, the most preferred clearance of about .035" is formed when the dimension of the paddle wheel diameter d is .800" and the dimension of the inner sidewall diameter D is .870". Furthermore, it has been found that accurate bi-directional flow measurements can be obtained when the dimension of the paddle wheel diameter d is between .600" and .800" and the dimension of the inner sidewall diameter D is between .670" and 1.160", and the clearance between the blade portions 45 and the circular inner sidewalls is within the preferred range of clearances as set forth above.

While the outer edges of the blade portions 45 as shown in Figs. 4a and 4b are illustrated as substantially semi-circular sections, one of ordinary skill in the art would appreciate that the outer edges of the blade portions 45 could be formed with a different arc length while having the shape of a circular section, as for example shown in Fig. 4c and discussed below.

Fig. 4c shows a cross-section of another preferred embodiment of the paddle wheel impeller 21 of the present invention. Similar to the preferred embodiment of the paddle wheel impeller shown in Figs. 4a and 4b, the paddle wheel impeller 21 of Fig. 4c includes a hub portion 41 and a plurality of impeller blades or blade portions 45, each attached to the hub portion 41 by way of a single stem portion 43. Also, each of the blade portions 45 has a generally planar first side surface and a generally planar second side surface which is substantially parallel to the first side surface. The blade portions 45 of the paddle wheel impeller 21 of Fig. 4c are characterized as having outer edges in the shape of circular sections, the circular sections extending between lateral cuts taken from the ends of each of the blade portions 45. The circular sections have curvatures which substantially correspond to the curvatures of the circular inner sidewalls of the oppositely arranged sidewall portions 30 of the flow sensor lower impeller housing 23. As with the preferred embodiment of the paddle wheel impeller as shown in Figs. 4a and 4b, a relatively small clearance is formed between the outer edges of the blade portions 45 and the circular inner sidewalls of the sidewall portions 30 as the blade portions 45 enter and exit the concave opening 25 of the lower impeller housing 23. The preferred dimensions of the paddle wheel diameter d, the inner sidewall diameter D and the clearance between the blade portions 45 and the circular inner sidewalls, as discussed above in relation to the paddle wheel impeller of Figs. 4a and 4b, could also be used with the paddle wheel impeller 21 of Fig. 4c to obtain accurate bi-directional flow measurements. Furthermore, the paddle wheel impeller 21 as shown in Fig. 4c also possesses geometric symmetry along the axis 47 passing through the rotational center of the paddle wheel impeller 21 and the axis 49 passing through the center body of each of a plurality of blades portions 45.

The flow sensor 20 of the present invention is capable of providing accurate bidirectional flow measurements by minimizing hydrodynamic disturbances in the fluid flow during operation. Hydrodynamic disturbances are minimized as a result of the geometric configuration of the flow sensor 20, in particular, the geometric configuration of the paddle wheel impeller 21 and the flow sensor lower housing 23. The formation of small clearances between the outer edges of the blade portions 45 and the circular inner sidewalls of the sidewall portions 30 as the blade portions 45 enter and leave the concave opening 25, minimizes the amount of fluid that can enter into the concave opening during operation of the flow sensor 20, which reduces cavitation and the generation of hydrodynamic disturbances in the fluid flow. In addition, the shape of the outer edges of the blade portions 45 maximizes the surface area exposed to the fluid flow during operation, which results in a more responsive paddle wheel impeller that is capable of providing more accurate fluid flow measurements. To monitor the rotational characteristics of the paddle wheel impeller 21 of the present invention, at least a portion of the impeller is magnetized. The impeller 21 can be magnetized in at least two methods. For example, the entire impeller can be fabricated entirely from a magnetic material or the impeller can be made from a plastic material which has magnetic inserts inserted into the blades 45. In either of these two preferred embodiments, the magnetized paddle wheel blades emit a magnetic field of varying intensity depending on their rotational position relative to the sensors 29, 31.

The structural design of the flow sensor of the present invention results in a flow sensor with a high turndown ratio. Turndown ratio is defined as the maximum usable flow rate the flow sensor can operate at divided by the minimum flow rate the flow sensor can operate at. The flow sensor 20 has a turndown ration of at least 30: 1 and conceivably in excess of 250:1. In comparison, turbine flow meters have turndown ratios of 10:1. As a result, the flow sensor 20 of the present invention can be used in a wider range of flow speeds, as well as with fluids with a wider range of Reynolds numbers.

As discussed above, the flow sensor of the present invention includes an integral sensor pickup unit 27 for sensing the position of blades 45 of the impeller 21, as shown in Fig. 2. In a preferred embodiment of the invention, the sensor pickup unit 27 includes giant-magneto resistive (GMR) devices. GMR devices are commercially available sensors from Nonvolatile Electronics, Eden Prairie, MN, which operate according to a magneto-resistive effect, such that when the devices are put in communication with a magnetic field, their resistive properties are altered. GMR sensors include small magnetic shields that are plated over two of four equal resistors of a Wheatstone bridge, an arrangement of resistors where four resistors are connected in a square pattern with each resistor forming a single side of the square. The small magnetic shields protect the resistors from an applied field and allows them to act as reference resistors. Since the protected resistors are fabricated from the same material as the active resistors, they have the same temperature coefficient as the active resistors. The two non-protected GMR resistors are both exposed to the external field. The bridge output is therefore twice the output as compared to a bridge with only one active resistor.

In the present invention, changes in resistance due to the presence of a magnetic flux from the impeller blades are used to produce a quasi-sinusoidal signal. This signal indicates the position of an impeller blade 45 relative to the GMR sensors 29, 31 as the blade rotationally approaches and retreats from close proximity to each of the GMR sensors. GMR sensors offer stable operation and relatively low power requirements. Additionally, GMR sensors are capable of being used at high temperatures of up to 150°C. While it is preferable to use GMR sensors, it is contemplated that a variety of different known sensors may be implemented, possessing a relatively small spacial separation therebetween, into the flow sensor without deviating from the invention. Other alternative, less desirable, yet functional sensors include fiber optic guides optical pickups, inductive and differential transformer pickups, capacitative pickups, Hall- effect sensors, etc. Each of these alternative sensing arrangements relies on the dual pulse overlap scheme to differentiate the direction of the paddlewheel rotation.

During operation, the paddle wheel impeller 21 of the flow meter 20 is rotated at a velocity that is proportional to the instantaneous average fluid velocity of the fluid flow. The signals produced by the sensor pickup unit are evaluated by micro-circuitry located within the flow sensor housing which produces the final output corresponding to fluid flow rate and direction. The operation of the micro-circuits and the terms used to describe the micro-circuits should be known to anyone familiar with the art.

As shown in Figs. 5a and 5b, the sensor pickup unit 27 including flow sensors 29, 31 of the present invention are each implemented as part of an amplifier/detector signal conditioner circuit. The circuits, each include an operational amplifier (Ul) configured as a 15X AC amplifier, followed by a comparator stage (U2) with positive feedback employed to provide positive switching and hysteresis. These circuits operate to produce a channel A output pulse corresponding to a signal sensed by GMR sensor 31 and a channel B output pulse corresponding to a signal sensed by GMR sensor 29, see the right-hand side of each circuit at CH A and CH B in Figs. 5a and 5b, respectively. These output pulses are produced by the respective circuits shown, as each magnetic blade 45 passes each of the sensors 29, 31 during rotation of the paddle wheel impeller 21. The output of each circuit is shown in Figs. 8 and 9.

The relatively small spacial separation between the GMR sensors 29, 31 is optimized, as previously discussed, such that given any particular direction of rotation of the paddle wheel impeller 21, one sensor is triggered prior to the other sensor so that there is an overlap, or phase-shift between both GMR sensor 'ON' states. From these output pulses, it would be within the skill of one of ordinary skill in the art, or routine to determine the direction and the flow rate of the fluid flowing in the pipe in a further part of the circuit. If the two sensors are separated by too great a distance, the pulsed or 'ON' state of both sensors will not overlap. Conversely, if the sensors are too close together, the sensors may not trigger in the correct sequence due to component tolerance.

The overlapping, phase-shifted channel A and channel B output pulses are further evaluated to ultimately deliver final output signals from the flow sensor 20 corresponding to the direction of fluid flow and the flow rate. The present invention contemplates utilizing either a Pulse/Direction Realization Mode circuit (Fig. 6) or a Dual Output Realization Mode circuit (Fig. 7) to evaluate the phase-shifted output pulses produced by the circuits of Figs. 5a and 5b and deliver the final output signal. A particularly desirable feature of the paddle wheel flow sensor of the present invention is the ability to produce a final output signal which can be read and processed by standard electrical monitoring equipment without modification.

The Pulse/Direction circuit of Fig. 6 will be discussed first, as it forms the basis for a description of the Dual Output Realization circuit of Fig. 7. Assuming the flow in the pipe is in such a direction to cause the impeller to flow in a clockwise direction, as shown graphically in Fig. 8, the first pulse to be produced by the signal conditioning circuitry is from GMR "B" (or CHB in Fig. 6). This pulse is applied to the clock input of the D flip/flop of the Pulse/Direction circuit. As the state of the D input (connected to CHA) is low during the low to high transition of the clock input of the flip/flop, the output of the flip/flop (DIRECTION) is set to a low state indicating one direction of flow. Conversely, when the flow is in the opposite direction, the CHA pulse precedes the CHB pulse and thus when the CHB signal transitions from a low to high state, the output of the flip/flop (DIRECTION) is set to a high state signaling the opposite direction of flow. A pulse indicating the rate of flow is provided by the CHA signal. The description of the Dual Output Realization circuit of Fig. 7 builds on the discussion above. As can be seen in Fig. 7, the D flip/flop associated with the "B" PULSE output has its D and clock inputs wired to the CHA and CHB signals, respectively, in a fashion identical to the PULSE/DIRECTION circuit shown in Fig. 7. The D flip/flop associated with the "A" PULSE output has its D and clock inputs wired in an opposite fashion, i.e., to the CHB and CHA signals, respectively. As per the previous description, the output of the B channel flip/flop is set uniquely high when the flow is in one direction, and the output of the A channel flip/flop is set uniquely high when the flow is in the opposite direction. The AND gates associated with each channel only permit the CHA and CHB pulses to be passed on to the "A" PULSE or "B" PULSE outputs when either the A channel or B channel flip/flops are set high, depending on the direction of impeller rotation.

The design of the micro-circuit is not limited to the discrete logic illustrated in Figs. 5a, 5b, 6 and 7. As is known to one or ordinary skill in the art, the discrete logic could be replaced with a smaller and cheaper microcontroller, such as a single, low cost 8-pin microcontroller, without affecting the utility of the basic design concepts disclosed. In addition, as is clearly evident, the microcontroller is securely fastened within the housing of the flow sensor by any known attachment mechanism. If the microcontroller is implemented into the flow sensor of the present invention, it is contemplated that a switch could be designed into the chip to allow the flow sensor to provide final output signals either as described in the Dual Output Realization Mode or in the Pulse/Direction Realization Mode.

While the invention has been described in detail with reference to preferred embodiments thereof, it will be apparent to one skilled in the art that various changes can be made, and equivalents employed, without departing from the scope of the invention.

Claims

WHAT IS CLAIMED IS:

1. A bi-directional insertion flow sensor for measuring a flow rate and a direction of a fluid flowing through a pipe, comprising: a housing; a paddle wheel impeller including a plurality of blades rotatably held by the housing; a pickup unit located within the housing and including a sensor arrangement located in close proximity to the impeller blades, for generating signals in response to an impeller blade rotatably moving past the pickup unit; and a micro-circuit located within the housing and connected to the pickup unit for receiving the signals generated by the pickup unit and producing an output indicating the flow rate and the direction of the fluid flow.

2. The bi-directional flow sensor of claim 1, wherein the output produced by the micro-circuit includes one of a pulsed signal from a first channel, corresponding to the flow rate and the direction of the fluid flow in a first direction, and a pulsed signal from a second channel, corresponding to the flow rate and the direction of the fluid flow in a second direction.

3. The bi-directional flow sensor of claim 1, wherein the output produced by the micro-circuit includes a pulsed signal from a first channel, corresponding to the flow rate of the fluid flow, and a signal from a second channel, corresponding to the direction of fluid flow.

4. The bi-directional flow sensor of claim 1 , wherein the operation of the micro-circuit is performed by a microcontroller.

5. The bi-directional flow sensor of claim 1, wherein the operation of the micro-circuit is performed by discrete logic.

6. The bi-directional flow sensor of claim 1, wherein the paddle wheel impeller is located at least partially within the housing of the flow sensor.

7. The bi-directional flow sensor of claim 6, wherein the paddle wheel impeller is located in a concave opening of the housing.

8. The bi-directional flow sensor of claim 1, wherein the pickup unit includes giant-magneto resistive devices.

9. The bi-directional flow sensor of claim 1, wherein the pickup unit includes a Hall-effect sensor arrangement.

10. The bi-directional flow sensor of claim 1, wherein the paddle wheel impeller is fabricated from a magnetized material.

11. The bi-directional flow sensor of claim 10, wherein the paddle wheel impeller is made of a plastic material with magnetic inserts inserted into the impeller blades.

12. The bi-directional flow sensor of claim 10, wherein the paddle wheel impeller is fabricated entirely from a magnetic material.

13. The bi-directional flow sensor of claim 1, wherein the housing has a longitudinal axis and the housing is bilaterally symmetric about the longitudinal axis.

14. The bi-directional flow sensor of claim 1 , wherein the paddle wheel impeller has a central axis around which the impeller rotates and through which the impeller is radially symmetric.

15. The bi-directional flow sensor of claim 1, wherein each impeller blade has a central axis and each impeller blade is bilaterally symmetric about the central axis.

16. The bi-directional flow sensor of claim 1, wherein the housing is a lower housing and is releasably connectable to a tubing carrier or upper housing.

17. The bi-directional flow sensor of claim 1, wherein the flow sensor is inserted into the pipe such that the paddle wheel impeller is in contact with a fluid flowing through the pipe and is rotated by the fluid at a velocity proportional to the instantaneous average fluid velocity of the fluid.

18. A bi-directional insertion flow sensor for measuring a flow rate and a direction of a fluid flowing through a pipe, comprising: a housing having a longitudinal axis, the housing being bilaterally symmetric about the longitudinal axis; a paddle wheel impeller including a plurality of magnetic blades rotatably held by the housing of the flow sensor and located partially within a concave opening of the housing, the paddle wheel impeller having a central axis around which the impeller rotates and through which the impeller is radially symmetric, each impeller blade having a central axis and each blade is bilaterally symmetric about its central axis; a pickup unit located within the housing and including at least two giant- magneto resistive devices located in close proximity to the impeller blades, the sensor pickup unit generating signals in response to an impeller blade rotatably moving past the pickup unit; and a micro-circuit located within the housing and connected to the pickup unit for receiving the signals generated by the pickup unit and producing an output indicating the flow rate and the direction of the fluid flow.

19. The bi-directional flow sensor of claim 18, wherein the output produced by the micro-circuit includes one of a pulsed signal from a first channel, corresponding to the flow rate and the direction of the fluid flow in a first direction, and a pulsed signal from a second channel, corresponding to the flow rate and the direction of the fluid flow in a second direction.

20. The bi-directional flow sensor of claim 18, wherein the output produced by the micro-circuit includes a pulsed signal from a first channel, corresponding to the flow rate of the fluid flow, and a signal from a second channel, corresponding to the direction of fluid flow.