GB2388193A

GB2388193A - Flowmeter and method of use

Info

Publication number: GB2388193A
Application number: GB0208377A
Authority: GB
Inventors: David Clarke; Ray Keech
Original assignee: ABB Metering Ltd; Elster Metering Ltd
Current assignee: Elster Metering Ltd
Priority date: 2002-04-11
Filing date: 2002-04-11
Publication date: 2003-11-05
Anticipated expiration: 2022-04-11
Also published as: GB0208377D0; GB2388193B

Abstract

A flow meter has a movable rotor (120) comprising central bush (122) and vanes (124), mounted in a flow path through the apparatus. Fluid flows in through inlet (106) and out through outlet (108) causing the rotor to rotate. Impedance measuring electrodes (130) are mounted in the inlet and outlet to obtain a measure of impedance of the fluid path through the meter to determine flow rate, fluid composition or to indicate the physical condition of the meter such as fouling, or damage due to wear. The impedance measured is typically electrical but may also be optical or acoustic impedance. A time varying component of the measured impedance may be used and frequency or shape of such a component may be processed to give the desired flow or meter parameter.

Description

(' 1 2388 1 93

Plow Apparatus The present invention relates to flow apparatus, and particularly but not exclusively to a flow meter for measurement of flow of liquids. In a preferred embodiment, the S present invention relates to a flow meter having a moving element such as a rotor or vane. Mechanical flow meters are in widespread use in many industries including oil and gas, chemical processing and medical. A common construction is the rotor type flow 10 meter, where flow is directed through a chamber and causes a helical or vatted rotor to revolve. The rotor can be linked to a counter either directly via a sealed bearing arrangement, or more preferably using a magnet to drive a rotor on the exterior of a sealed housing. In some cases an inductive sensor may be used to detect motion of the magnet. By monitoring the number of revolutions or rate of revolution of the rotor, a 15 value for the flow rate can be derived.

There is advantage in coupling the rotor or vane to the detector magnetically, since this avoids the need for a sealed bearing. A potential disadvantage is that inductive coupling may suffer from slip, where the detector 'misses' a cycle or part of a cycle 20 of the rotor or vane. Also, having a permanent magnet on the rotor may contribute unwanted moving magnetic fields.

Moving part flow meters frequently suffer from contamination, fouling or even breakage in service. These factors often cause loss of accuracy and may result in the 25 need for regular maintenance, recalibration and replacement of flow meters. As well as the associated maintenance cost, there may also be significant down time costs for the period when the flow meter and any associated process is out of service.

Meters without moving parts are known, such as electromagnetic or coriolis type flow 30 meters, however in certain applications moving part flow meters are still preferred as they may tolerate a wider range of fluids.

( 2 It is an object of the present invention to provide equipment to overcome or ameliorate deficiencies in prior art flow apparatus, particularly flow meters.

In a first aspect the invention provides a flow meter comprising means defining a 5 fluid flow path with a moveable element arranged to move in response to fluid flow therein, and means for obtaining a measure of impedance of a flow path through the meter to determine at least one characteristic of said flow meter.

This novel apparatus, in which a moveable element responds to flow (as in a 10 conventional mechanical meter) but in which at least one characteristic is determined based on impedance measurement, may prove an advantageous alternative in certain applications. The flow meter will Mically comprise a housing defining an internal chamber with 15 an inlet and an outlet. Typically the moveable element is arranged in the housing so as to cause periodic variations of impedance of a flow path through the meter as the element moves in response to fluid flow.

The housing is preferably made of an electrically insulating material, such as a 20 plastics material resin or ceramic, to reduce conductance (reciprocal impedance) substantially through the housing. This characteristic might also be achieved by a housing having an electrically insulating fluid contact surface. The moveable element preferably has a fluid contact surface of a material having substantially different conductivity to that of the fluid being measured in order that variations of impedance 25 can be observed more easily. The moveable element (or at least the surface thereof) may be made of a good electrical conductor e.g. a metal but more preferably comprises an electrical insulator such as plastics material.

The moveable element is typically a rotor having a plurality of blades, but may 30 instead comprise an oscillating vane or a piston, typically reciprocating and/or rotating. The moveable element may be designed to create a varying impedance, or even a particular impedance waveform when in use.

In a preferred embodiment there is provided a first electrode on one side of the moveable element and a second electrode on the other, preferably opposite side of the moveable element to facilitate impedance measurement. The electrodes may comprise ring or point electrodes, and are preferably connected to signal processing apparatus.

5 The electrodes are most preferably located in the inlet and outlet manifolds, in contact with the fluid passing through the meter.

In this way a fluctuating impedance signal can be extracted, and the rate of fluctuation can be used to determine the rate of movement of the moveable element. In one 10 application of the invention the characteristic of the flow meter which is determined is the rate of fluid flow thaethrough. Both the mass flow rate and volumetric flow rate may be determined. This may be achieved by using the measured impedance of the fluid flow path to determine the rate of movement of the moveable element e.g. the rate of revolution of a rotor, or equally the frequency of oscillation of a vane and 15 hence to determine the flow rate through the flow meter.

There may further be provided one or more additional electrodes disposed to sense the impedance through a fluid path in the region of the moveable element. This may, for example, facilitate detection of the direction of flow. In a preferred arrangement, 20 three electrodes may be positioned to determine both flow rate and direction. This may be advantageously achieved so that at least two time-varying impedance waveforms can be extracted and wherein the relationship between the waveforms varies with direction of flow. For example impedance between first and second electrodes may have a waveform which leads that of impedance between first and 25 third (or second and third or third and fourth) electrodes for flow in one direction, for example corresponding to clockwise rotation of a rotor and which lags for flow in the other direction.

Another characteristic which may be determined from the measured impedance signal 30 is Me physical condition of the flow measuring apparatus. This may be used in checking for fouling, contamination or damage e.g. due to wear. This may also be used to monitor for cavitation.

( 4 Preferably a measure of the "shape" of the impedance waveform is obtained. This may be obtained by digitizing the signal. The shape may be measured directly or indirectly, for example by measunug properties such as peak ratios and/or by performing Fourier or other component analysis on the waveform.

A further characteristic which may be determined is a calibration factor or a measure of calibration accuracy or reliability for the flow meter. This may be used in conjunction with a separate counter to calculate flow rate, or as a stand alone, self calibrating flow meter. In particular, if the movement of the moveable element is 10 monitored by other means, for example by means of a conventional counter or a magnetically or inductively coupled sensor, the measures obtained based on the impedance measurement and from the other means may be compared. This may be used, for example to detect slip in any mechanical or magnetic linkage. Alternatively, this may be used to compare movement of the unloaded element to the element when 15 coupled to a mechanical counter (preferably under the same or known flow conditions) to determine a measure of calibration accuracy based on the effect of mechanical loading of the moveable element. For example, it may be found that the rate of rotation is a relatively linear function of flow rate up to a point at which mechanical loads inhibit movement of the movable element. Operating conditions 20 may be determined based on information obtained using the impedance measurements. Although the invention is particularly applicable to flow meters, the inventive technique can be extended to other flow components having movable elements.

In a second aspect the invention provides apparatus for determining a characteristic of a fluid flow component composing means for obtaining a measure of impedance of a fluid path through a fluid flow component having a moveable element in the flow path. As noted, typically the fluid flow component will be a flow meter and the moveable element will move in response to fluid flow. However other fluid flow components such as a pump with an externally driven moveable element are possible using the same inventive principle. In such a case, a measure of pump perfonnance and/or

pump physical condition may be obtained, and contamination or cavitation may be detected. Again the apparatus will preferably comprise a plurality of electrodes disposed to 5 sense the impedance through a fluid path in the region of the moveable element. This will typically comprise a first electrode on one side of the moveable element and a second electrode on another, preferably opposite, side of the moveable element for the purpose of obtaining a fluctuating impedance signal, said electrodes typically being connected to signal processing equipment, substantially as described above.

Embodiments may be used to monitor a flow process having multiple inlets and outlets, and multiple flow measurlag apparatus.

Although the invention is primarily intended to operate measuring electrical IS impedance, this may be extended to use optical "impedance" (e.g. light transmission properties) and/or acoustic impedance, as either or both of these may similarly be affected periodically by movement of the movable element. In such a case an optical and/or acoustic transducer may be positioned in place of (or in addition to) the electrodes used to measure electrical impedance.

In a further aspect, the invention provides a method of determirung a characteristic of a flow apparatus comprising measuring impedance of a fluid path through the flow apparatus having a moveable element therein which element moves with fluid flow, the method comprising obtaining a measure of impedance of the fluid flow path; and 25 determining at least one characteristic of said flow apparatus based on the measured impedance. The or each characteristic may include flow rate through the flow apparatus and/or an indication of the physical condition of the flow apparatus.

The method may include extracting a time-varying component of the measured impedance and may further comprise obtaining a measure of frequency of variation of

the time varying component and/or obtaining a measure of shape of the waveform of the time-varying component.

Preferred features of the apparatus aspects may be applied to the method aspects and 5 vice versa. The method or portions thereof may be implemented in software, preferably on a digital signal processor arranged to receive impedance measures and the invention extends to a computer program or computer program product.

Further preferred embodiments of the invention may include a combination of some 10 or all or the features described in the aforementioned aspects.

In a preferred embodiment of the method aspect, the invention provides a method for determining a characteristic of a flow meter comprising: measuring a time-varying electrical impedance of a fluid path through the meter 15 which impedance varies as a moveable component of the meter moves with fluid flow and determining a characteristic of the flow meter based on the time varying impedance. In a preferred embodiment of the apparatus aspects, the inventdon provides a flow 20 meter comprising: a housing defining a fluid flow path defying an inlet portion and an outlet portion; a moveable element in the fluid flow path which movable element is mounted in the housing to move in response to fluid flow; 25 a first electrode positioned in the housing on one side of the moveable element; a second electrode positioned in the housing on another, preferably opposite, side of the moveable element; impedance measuring apparatus connected to the first and second electrodes for measuring electrical impedance between the first and second electrodes; 30 a processor coupled to the impedance measuring apparatus for processing the measured electrical impedance to deternune at least one characteristic of said flow meter.

( 7 An embodiment of the invention will now be described by way of example with reference to the accompanying drawings in which: Figure 1 is an exploded view of a flow meter according to a preferred s embodiment. Figures 2 and 3 are schematic illustrations of different configurations of the flow meter.

Figure 4 shows illustrations of possible waveforms produced from impedance measurements. 10 Figure 5 shows a block diagram of an embodiment of a controller which contains signal processing apparatus A flow meter, generally indicated by numeral 100 consists of a moulded plastics material housing 102,103 defining a generally cylindrical internal chamber 104, a 15 fluid inlet 106 and a fluid outlet 108. There is a mounting peg 110 which extends axially into the chamber 104. A (preferably insulating, in this case plastics material) rotor 120 has a central bush 122 which is rotatably mounted concentric with the chamber 104 on the mounting peg 110. The mounting peg 110 and fixing 122 form a bearing arrangement to allow the rotor to rotate about its axis within the chamber 104.

20 The rotor has four vanes 124 which extend generally radially towards the periphery of the chamber. The inlet and outlet are aligned offset from and orthogonal to the axis of the rotor, such that a passage of fluid through the chamber 104, from inlet 106 to outlet 108, will impose a force on the vanes 124, and cause the rotor 120 to rotate.

25 Mounted inside the inlet 106 and outlet 108 are ring electrodes 130 132. These are located so as to be in electrical contact with a fluid passing through the flow meter 100, but so as not to interfere with the rotor 120. The electrodes are connected to a controller (shown schematically in Figure 6) located on the exterior of the housing 102, 103 via trailing leads 136. The controller contains signal processing apparatus 30 and preferably includes an interface with a display.

The signal processing apparatus will typically comprise an input stage for buffering and signal amplification, a processing stage including filters, peak detectors and

( 8 frequency detectors, an output stage, and a memory such as a RAM module but the various functions may be integrated as required. The signal processing may be achieved by analogue techniques but more preferably uses a Digital Signal Processor.

Thus the processing electronics are preferably able to extract an oscillating signal 5 from the electrodes and select required frequency components, and may also determine average peak amplitudes and differences in successive peak amplitudes or perform other desired processing to extract a measure of the waveform shape from the signal. The signal processing apparatus preferably uses AC measurement of impedance to reduce electrolytic effects in the flow meter. Electrical impedance 10 measurement has the significant benefit that it is generally tolerant of variation of position of electrodes and does not require special transducers other than simple electrodes, which may be made substantially flush with the housing walls.

Figures 2 3 show the rotor in two different configurations. In Figure 2, the vane 15 202 lies substantially perpendicular to and blocks what would otherwise be a direct conducting path between electrodes 210 and 212. The vane, which is made of an electrically insulating material forms a barrier to charge flow, and a high impedance is detected between the electrodes 210, 212. If the rotor forms a near seal with the housing, a very high impedance peak will be detected and small deviations in the seal 20 will substantially affect the peak impedance value. In Figure 3 the rotor is advanced (by the action of a fluid flow for example) and now the direct conducting path between the electrodes 210, 212 is only partially obstructed by insulating vanes 202 and 204, and a lower impedance is detected.

25 As the rotor turns through a cycle there will be fluctuations in the impedance across the flow meter as measured between the electrodes. This is due to the varying position of the vanes or blades relative to the housing. There will tend to be a maximum and a minimum value and, since the vanes of the rotor are spaced regularly, there will be a periodic rise and fall in measured impedance as the rotor turns. Thus the continuous 30 rotation of the rotor gives rise to an oscillating waveform.

Figure 4a shows a typical oscillating output. The peaks 400, 402, 404 indicate a high impedance configuration of the vanes, and the troughs 401, 403, 405, indicate a lower impedance configuration of the vanes. In a configuration with four vanes, the period

( 9 of time 410 between four complete cycles is the time taken for one complete revolution of the rotor. A frequency detection circuit within the controller can therefore process the varying impedance waveform to determine the rate of revolution of the rotor. By using a calibration factor' this rate can be used to determine the flow S rate through the flow meter 100.

This general relationship between the movement and geometry of a rotor and the output signal is not limited to electrical measurements, and indeed an analogous relationship could be observed in the case of acoustic or optical measurements, 10 although this requires additional transducers. Furthermore the same principle could be applied to a flow meter which uses a piston or an oscillating vane to monitor fluid flow, the output being correlated to the position of the piston or vane.

In this embodiment the apparatus can be used as a complete replacement for 15 mechanical or inductive coupling of the rotor to a counter on the exterior of the housing. There is advantage in this since frictional resistance and mechanical complexity is reduced compared to mechanical coupling, and the magnetic field

associated with an inductive coupling is avoided. Manufacture of the rotor can also be simplified since no fixed magnet is required. Alternatively, the apparatus may 20 complement a mechanical or conventional measuring apparatus, for example to provide a consistency check.

Figure 4b represents an oscillating output for the case shown in Figure 4a, when one of the vanes has been damaged. Peaks 430, 432 & 434 indicate a high impedance 25 configuration of the vanes. The regions of the signal 436 438 are representative of a vane which, due to some form of damage (e. g. being partially or completely broken or missing or perforated), no longer presents a high impedance path to the electrodes.

Figure 4c again shows an oscillating output for the case illustrated in Figure 4a, but 30 where the flow meter has accumulated debris or contamination, deposited on the rotor or housing, or simply trapped in the cavity. This fouling may cause the peak to peak amplitude to be altered from the normal running condition shown in Figure 4a. In Figure 4c the peak to peak amplitude 462 is shown to be increased.

By monitoring for varying frequency components, or measuring amplitude differences, either averaged or between successive peaks, or by performing other processing to determine waveform shape characteristics the controller can monitor the S physical condition of the flow measuring apparatus for fault conditions such as damage or breakage of vanes, or contamination or fouling in the flow chamber. This may be achieved for example by comparison with a reference value or signal for normal operation. The waveform or portions thereof may be displayed or stored for visual inspection. Pattern recognition algorithms may be employed.

There is advantage in this since cleaning of the flow meter or replacement of parts can be performed as and when necessary and the monitoring apparatus may signal a fault or maintenance condition. Inspection intervals can be more accurately determined and down time can be reduced.

Figure 5 shows a block diagram of an embodiment of a controller which contains signal processing apparatus. The control input in Figure 5 is optional, and could be omitted in which case the embodiment may function as a simple electronic register.

20 Although the invention has been described here by way of an example the invention is not limited to this example, and may include modifications of detail or alternative combinations of features. For example, although a rotor with four vanes has been described here, a rotor with a different number of vanes may be chosen. Likewise, although a planar rotor has been described, a helical rotor is possible. Output 25 waveforms described are purely illustrative; other varying waveforms may be processed to determine at least one characteristic of the flow meter.

Each feature disclosed herein may be provided independently or in combination with other features unless otherwise stated.

Claims

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Claims

1. A flow meter comprising means defining a fluid flow path with a moveable element therein which element is arranged to move in 5 response to fluid flow, and means for obtaining a measure of impedance of a fluid path through the flow meter to determine at least one characteristic of said flow meter.

2. A flow meter according to Claim 1 wherein means for defining a fluid I O flow comprises a housing defining an internal chamber an inlet and an outlet. 3. A flow meter according to Claims 1 or 2 wherein the means defining a fluid flow path has an electrically insulating fluid contact surface.

4. A flow meter according to any preceding claim wherein said moveable element has an electrically insulating fluid contact surface.

S. A flow meter according to any preceding claim wherein the moveable 20 element is a rotor having a plurality of vanes or blades.

6. A flowmeter according to any preceding claim wherein the moveable element is a piston.

25 7. A flow meter according to any preceding claim wherein the moveable element is positioned so that passage of fluid causes periodic variations of impedance across said fluid flow path.

8. A flow meter according to any preceding claim wherein the moveable 30 element is designed to create a varying impedance between a plurality of electrical contacts, said contacts being disposed so as to sense the electrical impedance through the fluid in the region of the moving element.

9. A flow meter according to any preceding claim furler comprising means for extracting a time varying component of said measured impedance. s 10. A flow meter according to any preceding claim wherein the mews for obtaining a measure of impedance comprises a plurality of electrodes disposed to sense the impedance through a fluid path in the region of the moveable element.

11. A flow meter according to any preceding claim wherein said at least one characteristic of said flow meter includes a parameter of the fluid flow therethrough.

15 12. A flowmeter according to Claim I 1, wherein said fluid flow parameter includes at least one of the following: volumetric flow rate; mass flow rate; presence of particulate material in the flow; 20 presence of air in the flow; an empty pipe condition.

13. A flow meter according to any preceding claim wherein said at least one characteristic of said flow meter includes an indication of the 25 physical condition of the flow meter.

14. A flow meter according to Claim 13 wherein said physical condition includes at least one of the following: fouling of the flow meter; 30 solid deposition; damage to the moveable element; damage to the housing; presence of entrapped air; an empty pipe condition;

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cavitation. 15. A flow meter according to any preceding claim wherein a measure of the shape of the impedance waveform is obtained.

16. A flow meter according to Claim 15 further comprising storing or displaying at least a portion of the impedance waveform.

17. A flow meter according to Claim 13 and IS wherein the indication of 10 physical condition is based on the measure of shape of the impedance waveform. 18. A flow meter according to any preceding claim wherein said at least one characteristic of said flow meter includes a calibration factor.

19. A flow meter comprising means defining a fluid flow path with a moveable element therein which element is arranged to move in response to fluid flow, means for obtaining a measure of impedance of a fluid path through the flow meter and means arranged to determine 20 the fluid flow rate through the meter based on the measure of impedance. 20. Apparatus for determining a characteristic of a flow component comprising means for obtaining a measure of impedance of a fluid 25 path through a fluid flow component having a moveable element in the flow path.

21. Apparatus according to Clann 20 wherein the moveable element is positioned so that passage of fluid causes periodic variations of 30 impedance through said fluid flow path.

22. Apparatus according to Claim 20 or 21 wherein the means for measuring impedance comprises a plurality of electrodes disposed to

sense the impedance through a fluid Pam in the region of the moveable element. 23. Apparatus according to any of Claims 20 to 22 further comprising 5 means for extracting a fluctuating component of said measured impedance. 24. Apparatus according to any preceding clann further comprising means for dennining average peak amplitudes and differences in successive 10 peak amplitudes for the fluctuating component of the measured impedance. 25. Apparatus according to any preceding claim further comprising means for filtering and detecting selected frequency components of the 1 S fluctuating component of the measured impedance.

26. Apparatus according to any preceding claim wherein electrical impedance is measured.

20 27. A method of determining a characteristic of a flow apparatus comprising measuring impedarwe of a fluid path through the flow apparatus having a moveable element herein which element moves with fluid flow; the method comprising obtaining a measure of impedance of the fluid flow path, and detennining at least one 25 characteristic of said flow apparatus based on the measured impedance. 28. A method according to Claim 27 wherein said at least one characteristic includes flow rate through the flow apparatus.

29. A method according to Claim 27 or 28 wherein said at least one characteristic includes an indication of Me physical condition of the flow apparatus.

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30. A method according to any of Claims 27 to 29 including extracting a time-vaying component of the measured impedance.

31 A method according to Claim 30 further comprising obtaining a 5 measure of frequency of variation of the time varying component.

32. A method according to Claim 30 or 31 further comprising obtaining a measure of shape of the waveform of the time-varying component.

10 33. A method for determining a characteristic of a flow meter comprising: measuring a time-varying electrical impedance of a flow path through the meter which impedance varies as a moveable component of the meter moves with fluid flow and determining a 15 characteristic of the flow meter based on the time varying unpedance. 34. A flow meter composing: 20 a housing defining a fluid flow path defining an inlet portion and an outlet portion; a moveable element in the fluid flow path which movable element is mounted in the housing to move in response to fluid flow; a first electrode positioned in the housing on one side of the moveable element; a second electrode positioned in the housing on another, preferably 30 opposite, side of the moveable element;

impedance measuring apparatus connected to the first and second electrodes for measuring electrical unpedance between the first and second electrodes; 5 a processor coupled to the unpedance measuring apparatus for processing the measured electrical unpedance to determine at least one characteristic of said flow meter.

35. A flow meter according to Claim 34 further comprising a third 10 electrode, wherein the impedance measuring apparatus is connected to the Bird electrode for measuring electrical impedance between the Bird electrode and at least one of the first and second electrodes and wherein the processor is arranged to detennine a flow direction based on at least two impedance measurements.

36. A flow meter substantially as herein described or as illustrated in Me accompanying drawings.

37. A flow component substantially as herein described or as illustrated in 20 the accompanying drawings.

38. A method of operating a flow meter substantially as herein described or as illustrated in the accompanying drawings.

25 39. A computer program or computer program product containing instructions for performing a method according to any of Claims 23 to 300r35.