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Title:
FLOW METER PROVER APPARATUS AND METHOD
Document Type and Number:
WIPO Patent Application WO/1990/004758
Kind Code:
A1
Abstract:
A flow meter prover (10) having a chain drive piston return mechanism (55) is disclosed. The prover has a fluid displacement measuring cylinder (16) connected in series with a flow meter (12) to be tested. A piston (22) is adapted to travel through the cylinder between two sensors (36, 38) in synchronism with the flow of a fluid through the prover and the flow meter. A rod (32) extending axially through the cylinder and piston is used to return the piston to its beginning position after the completion of a test run. The rod is translated by the chain drive mechanism under the control of a PC or other small computer (44). After a series of runs the computer calculates an average K-factor for the flow meter by comparing the fluid flow, as measured by the flow meter, with the known displacement of the measuring cylinder between the two piston movement sensors.

Inventors:
COHRS GARY D (US)
FRANCISCO EDWARD E JR (US)
Application Number:
PCT/US1989/004670
Publication Date:
May 03, 1990
Filing Date:
October 18, 1989
Export Citation:
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Assignee:
CALIBRON SYSTEMS INC (US)
International Classes:
G01F25/00; (IPC1-7): G01F25/00
Foreign References:
USRE31432E1983-11-01
US4481805A1984-11-13
US4537058A1985-08-27
US4674316A1987-06-23
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Claims:
WHAT IS CLAIMED IS:
1. An apparatus for proving a flow eter comprising: a fluid displacement measuring cylinder; a piston movable through the cylinder between an upstream and a downstream position; a movable rod connected to the piston extending axially through the cylinder to the cylinder's exterior; means for engaging the rod outside the cylinder; means for transporting the engaging means in an upstream direction to bring the piston from the downstream position to the upstream position, the engaging means engaging the rod as the piston is brought upstream and releasing the rod to allow the piston to travel downstream.
2. Apparatus of claim 1 wherein the means for transporting comprises switches for sensing the position of the piston, a motor for driving the transporting means and a controller for regulating the motor operation in response to the switches.
3. Apparatus of claim 2 wherein the switches comprise an upstream position sensor and a downstream position sensor and wherein the controller stops the motor when the piston is sensed by the upstream position sensor and starts the motor when the piston is sensed by the downstream position sensor.
4. Apparatus of claim 1, 2 or 3 wherein the transporting means comprises a chain drive mechanism and the engaging means comprises: a guide plate attached to the rod; and a pusher bar attached to the chain drive which releasably engages the guide plate such that when the piston is in the downstream position the pusher bar moves the guide plate, rod and piston until the piston is in the upstream position.
5. Apparatus of claim 1, 2, 3 or 4 wherein the rod has a downstream facing surface, the transporting means is an endless chain means driven by a pair of spaced apart sprockets, and the engaging means is a pusher attached to the chain means, the pusher having an upstream facing surface which abuts the downstream facing surface on the. rod to engage the rod, the upstream facing surface moving laterally out of and into abutment with the downstream facing surface of the rod to disengage and engage the rod.
6. Apparatus of claim 4 or 5 wherein the chain means moves in an endless loop along a first straight upstream moving path segment parallel to and coextensive with the upstream movement of the rod, a second downstream moving path segment, a third curved path segment between the first and second path segments, and a fourth curved path segment between the first and second path segments, such that the rod is repeatedly carried upstream along the first path segment, released at the third path segment tc travel downstream with fluid flow through the prover, and engaged at the fourth path segment.
7. Apparatus of any of claims 1 through 6 comprising a valve means for providing a fluid bypass of the piston.
8. The apparatus of claim 7, wherein the valve means for bypassing the piston comprises a passage through the piston.
9. The apparatus of claim 7 or 8 comprising means for closing the valve means enabling the fluid flow through the cylinder to drive the piston in a test run from the piston's upstream position to the piston's downstream position in synchronism with the fluid flow through the fluid line.
10. The apparatus of claim 8, wherein the means for closing the passage through the piston comprises a poppet valve attached to the rod.
11. The apparatus of any of claims 1 through 10 comprising means for sensing the movement of the piston through the cylinder during the test run.
12. The apparatus of claim 11, wherein the means for sensing the movement of the piston comprises means for sensing the presence of the piston near the piston upstream and downstream positions.
13. The apparatus of any of claims 1 through 12, wherein the cylinder has an inlet and an outlet connected in series with an operating fluid line through which fluid at a given static pressure flows.
14. A method for operating a flow eter prover having a fluid displacement measuring cylinder with an inlet near one end and an outlet near the other, a fluid displacement measuring piston adapted to travel through the cylinder between an upstream and a downstream position, and a valve which allows fluid to bypass the piston, the method comprising the steps of: placing the prover in a fluid line in series with a flowmeter under test; drawing the piston to the upstream position; closing the bypass valve so that fluid flowing through the cylinder drives the piston downstream in synchronism with the fluid flow through the fluid line; sensing the movement of the piston through the cylinder; opening the bypass valve; activating a chain drive mechanism; engaging a pusher bar on the chain drive mechanism with a guide plate connected to the piston; operating the chain drive mechanism to move the piston using the guide plate from its downstream position to its initial position; disengaging the pusher bar from the guide plate; and deactivating the chain drive mechanism.
Description:
FLOW METER PROVER APPARATUS AND METHOD

Field of the Invention

The present invention relates generally to flow meter provers and in particular to a prover of simple construction with a mechanical piston return.

Background of the Invention

In the use of flow meters to measure the quantity of fluid flowing in a fluid line, it is frequently desirable to determine the accuracy of the meter while it is in service, without disrupting the flow of the fluid being measured. A number of devices have been developed and are in use for such purpose, and are known as in-line flow meter provers.

Provers of the class to which this invention relates operate by causing the fluid stream to pass simultaneously through the meter and through a cylinder containing a moveable fluid barrier, typically a piston which fits snugly into the cylinder. The piston is released at an upstream position and travels with the fluid, passing two detection points, and stopping at a downstream position. The cylinder is then returned by

various means to the upstream position, from which it may be released again for another test run. The two detection points are normally electrical switches actuated by the passage of the piston. A comparison is made of the volume of the cylinder in the space between the two detection points, with a measurement signal from the meter through which the same volume of fluid passes. The type of flow meter to which this class of provers is best applied is one designed to produce a series of electrical impulses, each impulse representing a certain volume of fluid. Flow quantity, as measured by the meter, is determined by counting the total number of impulses produced as the fluid passes through the meter. Such counting may be performed by various types of electronic counting circuits.

Following a proving test run, a numerical factor relating the number of meter impulses per unit of fluid volume is determined by dividing the prover volume by the number of impulses produced by the flow meter during the proving test. This factor is known as a calibration factor, or K factor, and is expressed in terms of volume per impulse.

In existing provers the release and return of the piston involves many difficult mechanical problems which have not been readily overcome. Mechanisms tend to be complex and the prover itself bulky and costly to construct. Some provers utilize complex reversing valves to reverse the direction of flow in the cylinder

and thereby return the piston to its original position. Other designs utilize devices to retract the piston and restrain it in the upstream position or bypass the flow of the piston by means of a poppet or bypass valve when the prover is not being used in a proving test. Provers utilizing valves to reverse the direction of flow are known as bidirectional provers because the proving test may be made with the piston traveling in either direction. Provers utilizing devices to retract and restrain the piston are known as unidirectional provers because the fluid and the piston always travel in the same direction in the cylinder during a test.

In U.S. Patent No. 3,492,856 issued on February 3, 1970 to Francisco, a unidirectional flow meter calibrating apparatus -is disclosed employing a piston within a conduit, where the piston is restrained in the upstream position by means of a complex motor, clutch and cable assembly located upstream of the conduit. A poppet valve, held open by the cable, provides a fluid passage through the piston when the apparatus is not being used for flow measurements. Releasing the cable permits fluid pressure to close the poppet valve setting the piston in motion.

U.S. Patent No. 4,152,922, issued May 8, 1979, to Francisco discloses a prover in which a measuring piston is returned and restrained in its upstream position by means of a second, control piston. The control piston travels through a separate control cylinder and is

linked to the measuring piston by a rod. A source of pressurized air is used to move of the control piston.

In U.S. Patent No. 4,794,785, issued on January 3, 1989, to Cohrs et al. , a similar prover is disclosed wherein the control cylinder is moved by pressurized hydraulic fluid.

In summary, the mechanisms used in prior art provers to return the measuring piston to the upstream position have tended to be complex, costly to manufacture and have often required expensive, external hydraulic or pneumatic propelling apparatus.

Summary of the Invention

The present invention provides a prover which is less complex, easier to maintain and less expensive to manufacture than prior art provers and is adapted to be controlled by a computer. Once testing is commenced, no further operator intervention is required. All test results may be stored in the computer for later retrieval.

The prover is preferably placed in* an operating fluid line in series with a flow meter to be tested. The flow meter comprises a fluid displacement measuring cylinder having near its ends, respectively, an inlet and an outlet. A fluid displacement measuring piston is adapted to travel through the cylinder between upstream and downstream positions. Sensors are located on the cylinder for determining the location of the piston as

it moves through the cylinder. The prover contains a bypass valve permitting fluid to flow through or around the cylinder between test runs. Means are provided for closing the valve at the commencement of each test run. Closing the bypass causes the fluid flow through the cylinder to move the piston from the upstream position to the downstream position in synchronization with the fluid flow through the fluid line. A rod extends axially through the cylinder connected to the piston. The rod is used to cause the closing means to close the bypass valve at the beginning of each test run, and to open the valve and return the piston to the upstream position at the completion of the test run. The rod is driven by a mechanical system comprising a chain drive mechanism, a pusher or puller bar attached, to the chain drive, and a guide plate attached to the rod. At the end of the test run the chain drive is actuated. The pusher bar engages the guide plate and moves the rod and piston from the downstream position towards the upstream position. When the piston reaches the upstream position, the pusher bar is released from the guide plate, the chain drive ceases operation and the prover is set to commence its next test run.

These and other features of the prover are more fully set forth in the following description of the presently preferred embodiment of the invention. The description is presented with reference to the accompanying drawings below.

Brief Description of the Drawings

FIG. 1 is a schematic diagram of a prover incorporating principles of the present invention. FIG. 2 is a partial side elevation view showing several elements of a preferred embodiment of the invention.

FIG. 3 is a sectional view taken through line 3—3 of FIG. 2.

Detailed Description

The present invention provides a prover 10 which is connected in series with a flowmeter 12 under test in a fluid line 14. The prover 10 includes a measuring cylinder 16 with an inlet 18 and an outlet 20 connected to the fluid line 14. A measuring piston 22 is adapted to travel through the cylinder 16 as a fluid barrier between an upstream position near the inlet 18 and a downstream position near the outlet 20. A poppet valve 23 and a plurality of openings 24 are formed in the piston 22 to permit flow of fluid from the line 14 through the cylinder 16 when the piston is at rest. A poppet 26 is adapted to move away and toward the poppet valve orifice 25 to open and close the passage through the piston 22. A.piston rod 32 extends axially through the cylinder 16 and the poppet 26. The rod 32 passes through fluid seals at the ends of the cylinder 16 and is rigidly attached to the poppet 26. Reference is made to U.S. Patent Nos. 4,152,922 and 4,794,785, the disclosures of which are incorporated fully herein by reference, for a description of the specific construction of the described elements of the prover 10, including the seals and bushings thereof, as well as the elements described below.

An upstream sensor 36 and a downstream sensor 38 are used sense the movement of the piston 22 through the cylinder 16. The sensors 36 & 38 may be mounted on the cylinder 16, adjacent to the rod 32 outside- the cylinder

or at any location permitting the movement of the piston

22 to be sensed. The sensors may be magnetic or comprise a photocell and a light source. As the piston 22 travels through the cylinder 16, the position of the piston is detected as it or a specified section of the rod 32 travels past each sensor generating two sequential electrical impulse signals. In a preferred embodiment of the invention, the upstream sensor 36 is mounted near the upstream position of the piston at a distance sufficiently far from the upstream position for the piston 22 to be moving in synchronism with the fluid flow through the fluid line 14 when the piston is detected by the sensor. The downstream sensor 38 is located at a sufficient distance upstream of the piston downstream position for the piston to still be moving in synchronism with the fluid flow when it is detected by this sensor.

The sensors 36, 38 are coupled by a cable 42 to a PC or other small computer 44. The output of the flow meter 12, which could be, for example, an electrical impulse signal where each pulse represents a certain volume, is also coupled by a cable 46 to the computer. The computer contains programming for determining the calibration factor (K factor) of the flow meter. The K factor is computed by dividing the volume of the cylinder through which the piston moves between the sensors 36, 38 by the number of impulses produced by the flow meter 12 during the proving test. The K factor is

displayed on the screen 45 of the computer for each test, as well as an average K factor if a series of tests are run. The test results are additionally stored in the computer for later retrieval.

A base plate 48 supports the cylinder 16 and two rectangular end plates 50, 52. The end plates are vertically mounted on the base plate 48 adjacent to the cylinder. The end plate 50 is affixed to the upstream end of the cylinder. The end plate 52 is spaced apart from the end plate 50 and held rigid in relation to it by a horizontally arranged brace 54 mounted near the top of the end plates. Disposed between the end plates 50, 52 is a twin chain drive mechanism 55 which returns the rod and piston from the piston downstream position to the piston upstream .position at the end of each test run. Mounted either between or outside of the end plates is means for driving the chain drive 55. For this purpose an electric motor 56, having an output shaft mounting a drive sprocket 58, is attached to the base plate 48. The motor 56 is controlled by a signal from the computer 44 coupled to a relay 57 by a cable 59. The drive sprocket 58 drives a drive chain 60 which engages and drives a driven sprocket 62. The driven sprocket 62 is rigidly mounted on a first axle 64 which is rotatably mounted to the end plate 52. A pair of secondary sprockets 66 are affixed, one near each end, of the first axle 64.

A second axle 68 is rotatably mounted to the end plate 50. A pair of tertiary sprockets 70 are affixed to the second axle 68, one near each end. A pair of puller chains 72 are mounted between the secondary 68 and tertiary sprockets 70. Accordingly, operation of the motor 56 drives the drive sprocket 58 and the drive chain 60 causing the driven sprocket 62 and the first axle 64 to rotate. Rotation of the first axle 64 rotates the secondary sprockets 66 causing movement of the puller chains 72 and rotation of the tertiary sprockets 70.

The motion of the puller chains 72 is coupled to the piston rod 32 by a guide plate 74, attached to the end of the rod, and a pusher bar 76. The pusher bar is U-shaped and connected at its ends to the puller chains 72 by elongated chain link pins 84. A pair of guide shafts 78 are mounted between the end plates 50, 52, parallel with the axis of the cylinder 16 and the rod 32, one shaft 78 above each puller chain 72. The guide plate 74 and the end of the rod 32 are supported and guided by the guide shafts 78. Disposed on each side of the guide plate 74 are a pair of guide bearings 80. Each pair of guide bearings 80 embraces one of the guide shafts 78, thereby maintaining the rod 32 and piston 22 in alignment with the guide shafts.

The depth of the U-shape of the pusher bar 76 permits the rod 32 to extend therethrough to the guide plate 74, during the first path segment, without

contacting the pusher bar. When the chain drive mechanism 55 is being driven by the motor 56, the pusher bar 76 travels along a first straight upstream moving path segment between the tertiary sprockets 70 and the secondary sprockets 66, a second straight downstream path segment between the secondary sprockets 66 and the tertiary sprockets 70, a third curved path segment between the first and second path segments around the secondary sprockets 66, and a fourth curved path segment between the first and second path segments around the tertiary sprockets 70.

The motor 56 is started by the computer 44 when the piston 16 is detected by sensor 38 as being at its downstream position. The motion of the chain drive 55 causes the pusher bar 76 to er.gage the guide plate 74. The motion of the pusher bar pushes the rod 32 opening the poppet valve 23. The continued motion of the pusher bar 76 causes the piston 22 to move towards the piston upstream position. The pusher bar 76 disengages from the guide plate 74 as it rotates about the secondary sprocket 66, during the third path segment. The rod 32 is sized in length to permit the guide plate 74 to be released simultaneously with the piston 22 reaching the piston upstream position. After release of the guide plate 74 the rod 32 and pistor 22 are free to commence the next test run.

The pusher bar continues to move until contacting the motor stop switch 82 mounted on the base plate 48

near the tertiary sprockets 70. A signal from the switch 82 is coupled to the computer 44 by cable 84 causing the computer to stop the motor 56. In FIG. 1 the puller chain 72, the rod 32 and contact point between the guide plate 74 and pusher bar 76 are shown for clarity as being located at differing heights above the base plate 48. In the preferred embodiment of the invention these elements are aligned in the same plane, as shown in FIG. 2, to avoid adverse torque. In this embodiment the pusher bar 76 has inboard notches 86, against which the lower slide bearings 80 abut to effect engagement with the guide plate 74.

In operation, prior to a test run, the piston is at rest in the downstream position with the poppet valve 23 held in the open position by means described below. The computer program is started by an operator. After having selected the number of tests to be run and the interval between tests, all further operations of the prover are controlled by the computer 44. ,The computer 44 sends a signal to the relay 57 to start the motor 56. The motor 56 drives the chain drive mechanism 55 causing the pusher bar 76 to move the guide plate 74, rod 32 and piston 22 to the piston upstream position, as described above. After the pusher bar 76 releases the guide plate 74 and rod 32, the continuing movement of fluid through the cylinder causes the poppet valve 23 to close, closing the passage through the piston 22. The piston

22 begins to move downstream through the cylinder 16. By the time the piston 22 is detected by the upstream sensor 36, the piston is moving in synchronism with the fluid flow through the line 14. The upstream sensor 36 sends a signal to the computer 44 starting a timing counter in the program. When the piston 22 activates the downstream sensor 38, a second signal is sent to the computer 44 which stops the timing counter. During the time interval between receipt of the upstream and downstream sensor signals, the computer 44 counts the number of pulses sent by the flow meter 12. The computer 44 then calculates, displays and records the K- factor as previously described.

During the test run, the motor 56 stops when the upstream switch has been contacted. When the downstream or end of volume detector has been actuated, the computer immediately initiates another test run by starting the motor 56 at the completion of the previous test run until the selected number of test runs have been performed.

When the piston 22 reaches the downstream end of the cylinder 16, stops, not shown, cushion the impact of the piston and open the poppet valve 23, as described in U.S. Patent No. 4,152,922. This completes one test run. During the test run, the computer 44 temporarily stops the motor 56 if the pusher bar reaches the stop switch 82 before the piston 22 reaches the downstream sensor 38. Otherwise the motor 56 runs continuously and

the computer 44 immediately initiates another test run at the completion of each previous run until the selected number of test runs have been performed. An important feature of the present invention is its simplicity. Unlike prior art provers, the drive rotates only in one direction. No hydraulic or pneumatic drive, control or compensation systems are required. No complicated rod latching mechanism is necessary. If the motor relay fails or if the chain drive mechanism 55 fails to stop at the proper time or place, no damage to the prover will result. If, for some reason, the chain drive 55 is improperly started and catches the piston 22 in the middle of a test run, it will just stop the movement of the piston, open the poppet valve 23 and transport the piston 22 to the piston upstream position. The use of the computer 44 automates the entire operation of the prover permitting the testing to be carried out unattended. The use of a computer 44 additionally permits testing to be initiated by lesser skilled operators than with prior art provers. The above described embodiment of the invention is only considered to be preferred and illustrative of the inventive concept; the scope of the invention is not restricted to this embodiment. Various and numerous other arrangements may be devised by one skilled in the art without departing from the spirit and scope of this invention. For example, proximity switches could be used for sensing the location of the piston. More or

less than two sensors could be used. The sensors could be mounted other than on the cylinder and could sense the movement of the piston rod rather than that of the piston. More or less than two sets of sprockets and chains may be used. The pusher bar may be of other than a U-shaped configuration having extending means to releasably engage the guide plate or the piston rod. The bypass could be an external valve as disclosed in U.S. Patent No. Re. 32,157 to Waugh et al. The computer could be programed for additional processing and evaluation the stored test data or be operated from a remote location.




 
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