GB2572802A - Flowmeter - Google Patents

Abstract

A liquid flowmeter comprises a pair of wedge units having parallel sides, base, top, two ends, one of which is inclined at an acute angle with respect to the base, said inclined end having a piezoelectric transducer mounted thereon, and in which the wedge units are mounted on a pipe, duct or channel so that the piezoelectric transducers are aligned with each other in the direction of liquid flow in the said pipe with the inclined ends of the wedge units mounted facing away from each other so that one inclined end is directed upstream of any flow and the other inclined end is directed downstream of any flow. Each of the pair of wedge units may be mounted in a slot in a printed circuit board mounted on a pipe. The base of each wedge unit may be extended to form lips, at either end, the lips engaging beneath the board. The piezoelectric transducer may be separated from the top of the inclined end by half the wavelength of the piezoelectric transducer. Pressure plates may be mounted atop each transducer. The wedge units may have holes passing from one side to the other to scatter stray acoustic waves. The end of the wedge unit opposite the inclined end may be provided with an acoustic scattering surface.

Description

[0001] This invention relates to flowmeters for sensing and measuring liquid flow in a duct, pipe, channel or the like.

Background Art [0002] Known flowmeters generally comprise a paddle inserted into the pipe, duct or channel concerned. A flow of liquid past the paddle will turn the paddle at an angular velocity related to the speed of the flow past the paddle and the physical properties, such as viscosity of the liquid concerned. The angular velocity of the paddle is then measured mechanically. The measurement is then converted, knowing the physical properties of the fluid and the dimension of the pipe, duct or channel into which the paddle has been inserted into a flow rate. A common use for a meter of this kind is as a water meter for measuring consumption of water on a premises; but in industry similar meters are used in the control of production processes, for example metering flow of liquids. Meters of this kind can also be used to identify leaks in a water supply system or industrial processes by metering flows when none should be occurring.

[0003] Such meters have to be inserted into the pipe, duct or channel concerned, which runs the risk of leakage occurring between the meter and the pipe. There are also mechanical issues resulting in wear of bearings and other components with the associated risk of breakdown or inaccurate readings. When a faulty meter is discovered, it has to be physically replaced, which means stopping the liquid flow through the pipe, duct or channel concerned interrupting supplies of the water or liquid in the pipe.

[0004] In this invention “liquid” can include up to 10% dispersed solids, such as dust or sediment, or gases. The word “meter” includes leakage detection systems, in which leakage is detected by measuring water flow.

Disclosure of Invention [0005] According to the present invention a liquid flowmeter comprises a pair of wedge units having parallel sides, base, top, two ends, one of which is inclined at an acute angle with respect to the base, said inclined end having a piezoelectric transducer mounted thereon, and in which the wedge units are mounted on a pipe duct or channel so that the piezoelectric transducers are aligned with each other in the direction of liquid flow in the said pipe, duct or channel with the inclined ends of the wedge units facing away from each other so that one inclined end is directed upstream of any flow in the pipe, duct or channel and the other inclined end is directed downstream of any flow in the pipe, duct or channel.

[0006] In one arrangement a liquid flowmeter as aforesaid comprises a pair of wedge units mounted on an outside surface of a pipe, duct or channel though with the liquid of interest flows.

[0007] In another arrangement the flowmeter comprises a pair of wedge units mounted in a slot in a board, the board being mounted on a pipe, duct or channel through which liquid flow is to be monitored.

[0008] Ideally in such an arrangement the base of each wedge unit is extended to form lips at either end engaging beneath the board.

[0009] The board of such an arrangement may be a printed circuit board having thereon the circuit for generating and/or analysing the received signals of the piezoelectric transducers.

[0010] As an option the board is shaped to the outside the pipe, duct or channel through which the liquid to be monitored flows.

[0011] Ideally in a flow meter according to the present invention the inclined ends of the wedge units are inclined at an angle of between 39° and 45° to the base of the wedge units.. To maximise the transmission of acoustic waves into the wedge units and thus into any pipe, duct or channel to which they are attached a matching plate is mounted atop each piezoelectric transducer whose thickness is half the wavelength of the piezoelectric transducer.

[0012] To maximise the transmission of acoustic waves into the wedge units and thus into any pipe, duct or channel to which they are attached a pressure plate is mounted atop each piezoelectric transducer and/or half wavelength matching plate.

[0013] To reduce interference with acoustic waves of interest the wedge units may have holes passing from one side to the other to scatter stray acoustic waves. In one arrangement such holes are arranged diagonally from the corner between the bottom of the wedge unit and the non-inclined end wall and the corner between the top and inclined end. For similar reasons, the end of each wedge unit opposite the inclined end may also be inclined or provided with an acoustic scattering surface possibly with the scattering surface comprising vertical V-shaped grooves and/or horizontal V-shaped grooves.

[0014] In one arrangement the edges of each wedge unit inclined to the base has inclined groove with a surface parallel to the inclined edge of the wedge unit and the piezoelectric transducer is mounted on the surface of the inclined groove. The sides of groove may each have an inclined slot, the slots being opposite one another and to receive between them an upper pressure plate, the upper pressure plate having a threaded screw or bolt passing though, with one end of the bolt bearing against a lower pressure plate covering the piezoelectric transducer but electrically insulated from the piezoelectric transducer.

[0015] In one arrangement the wedge units comprise a thermoplastic preferably polyether ether ketone.

[0016] Silicon rubber may also be another possible material.

[0017] As a further development, the invention can form part of a heat flow metering system by providing one or more thermocouples on the pipe, duct of channel to which the flow meter is attached. Provided the pipe, duct or channel has good thermal conducting properties, the thermocouples can be mounted on the outside of the pipe. This can be particularly useful for the metering of neighbourhood heating systems.

[0018] Other features of the invention are described in the examples of the invention described below with reference to the accompanying drawings.

Brief Description of Drawings [0019] Figure 1A shows is a perspective view from above one end of a first wedge unit, without the piezoelectric transducer mounted for use with a flow meter of the current invention;

[0020] Figure 1B shows is a perspective view of the other end of the first wedge unit;

[0021] Figure 2 shows the wedge unit of figures 1A and 1B with a piezoelectric transducer mounted thereupon;

[0022] Figure 3 shows the wedge unit of figures 1 and 2 with the lower pressure plate fitted;

[0023] Figure 4 shows the wedge unit of figures 1 to 3 with the upper pressure plate in place.

[0024] Figure 5A shows side view an alternative wedge unit with a piezoelectric transducer in place;

[0025] Figure 5B shows an end of the wedge unit of figure 5A looking in the direction of the arrow;

[0026] Figure 6 show a further alternative wedge unit with a piezoelectric transducer in place;

[0027] Figure 7 shows the use of a piezoelectric transducer as shown in figures 1 to 4 as a flowmeter;

[0028] Figure 8 shows a flowmeter constructed using a pair of piezoelectric transducers as shown in figure 6, a top view is seem in figure 8A and a side view in figure 8B; figure 8B also shows schematically connections to a control and analysis module and a display and the meter mounted on a pipe; and [0029] Figure 9 shows a similar flowmeter to that of figure 8 but arranged to follow the pipe shape and in addition to provide hear flow measurements.

Description of Examples of the Invention [0030] In figures 1A and 1B, a wedge unit 10 for use in a flowmeter according to the invention comprising a block 12 of PEEK which is a hard, electrically insulating material. The wedge unit 10 has parallel sides 14, base 16 and top 18, with one end 20 inclined at an acute angle to the base 16. The other end 21 is orthogonal to the base.

[0031] The inclined end 20 has a machined out groove 22, whose surface 24 is parallel to the inclined end face 20 of the block. The sides 26 each have a slot 28 which is parallel to the inclined end face 20 and the surface 24 of groove 22. The lower part 30 of the groove 24 is widened out. The top 18 of the block 12 has a partial cut out 32 as shown.

[0032] The wedge angle between the inclined end 20 and the base 16 is cut away to present an upright surface 34 from the base and step 36. This is to provide strength at the end of the device; it will also allow the wedge unit more easily to be fitted into board as in figures 8A and 8B. The base has a flange 38 to enable the wedge unit to be fitted to a pot.

[0033] Detail for end 21 on the block 12 is visible in Figure 1A, vertical and horizontal V-shaped grooves 40 and 42 are cut into the surface of the end 21, forming a plurality of pyramids 44. The edges of each of the grooves are at right angles to one another. The pyramids 44 serve to reflect and scatter incident acoustic waves thus reducing reverberations in the block.

[0034] In figures 2, 3 and 4, a piezoelectric transducer 50 has been placed in the groove 22 with connections 52 to a cable 54. A thin layer of silicon grease is used to bed in the piezoelectric transducer, which is then covered by a thin layer of electrical insulation, such as PTFE tape 56 with a stainless steel lower pressure plate 54 placed over the piezoelectric transducer 50 and insulation as seen in figure 3. An upper stainless steel pressure plate 58 is a sliding fit in slots 26 and overlays the lower pressure plate 54. A threaded bolt 60 engages with internal threads around a hole through the upper pressure plate 58. The bolt 60 has a load spreading end bearing against the lower pressure plate 53, so that tightening the bolt 60 causes the lower pressure plate to bear against the piezoelectric transducer holding it in place against the inclined bottom face 24 of groove 22.

[0035] Once assembled the block 12 with the piezoelectric transducer 50 is placed into a rectangular stainless steel box with an open rectangular bottom so that the rim 38 rests on the edge of the box with the base 16 of the wedge unit exposed. The cable 54 is threaded out through a hole in the box for external connection, and the box filled with potting compound around the block 12. For added security the block 12 has holes 46 passing through from the base 16, through which screws may be inserted to engage in the closed top of the box.

[0036] The cables connect the transducer to control and analyse chips to pulse the piezoelectric transducer 50 and to analyse any sensed acoustic signal.

[0037] In figures 5A and 5B a wedge unit 60 for use in a flow meter comprises what was originally a rectangular a block of PEEK with parallel sides 62, a base 64, a top 66 and ends 68 and 70. One end 68 is perpendicular to the base; the other end 70 is cut or machined to incline at an acute angle 7 to the base 64. The angle 72 between end 70 and base 64 in this example is 45o and would normally be designed to be in the range 39o to 45o.The wedge angle 72 is cut off at 74 to enable the wedge unit to be mounted in a board as described below with reference to figures 8A and 8B.

[0038] The base 64 is extended at either end to form lips 76 to enable the wedge unit to be mounted in a board as described below. A rectangular piezoelectric transducer 80, having connecting leads 82, is glued, using Araldite® or similar proprietary adhesive to the inclined end 70 leaving a space 84 on the inclined end 70 and the top of the wedge unit 66. The space 84 is chosen to be the resonant wavelength of the transducer 80, which for the design used is 2.88mm.

[0039] In figure 5A the dotted lines 88 indicate the main route of an acoustic wave from the transducer 80 through the wedge unit 60. However some scatter occurs which may interfere with the acoustic waves of interest; to reduce this holes 86 pass between the two sides 62 of the wedge unit In this case the holes are arranged in a line between the corner between the base 64 and end 68 to the corner between the inclined end 70 and top 66.

[0040] In the wedge unit in figure 5 the end 68 opposite the inclined end may have cut grooves similar to those shown in figures 1 to 4 to suppress stray acoustic waves.

[0041] To maximise the acoustic signals going in the wedge units and minimise loss from the top of the piezoelectric transducers, a stainless steel pressure plate 90 is mounted over the piezoelectric transducer 80, with a thin insulation layer 92 between the transducer 80 and plate 90 of PTFE or similar. The plate 90 is held in place by screws 94, with springs 96 between the screw head and the pressure plate to apply pressure to the pressure plate and thus the piezoelectric transducer 90. Silicon grease rather than glue is applied between the piezoelectric transducer and the inclined end 70 of the wedge unit.

[0042] In figure 6 a wedge unit similar to that in figure 5 is shown. The difference between the wedge unit of figure 5 and that of figure 6 is that the previously vertical end 68 now has an inclined section 99. The lower part inclined section ends to leave a small vertical section of the end wall 68, as before, to allow easier fitting to a board as in figures 8 and 9. This design may reduce scatter of acoustic waves further. As in figure 5, a stainless steel plate may optionally bear on the transducer 80, instead of it being glued in place.

[0043] In figure 7 a flowmeter for measuring fluid flow in a pipe 100 is constructed using two wedge units and transducers as described in figures 1 to 4. The wedge units and transducers are potted in rectangular boxes 104 and 106 mounted one downstream of the other in the direction of flow of liquid 102 in the pipe. The bases 16 of the wedge units in the boxes contact the outside of the pipe 100. The transducers 50 which are mounded on inclined ends of the wedge units are indicated. The boxes 104 and 106 are clamped to the pipe by metal bands or similar ties 107. The cables 54 from each transducer are connected to a control and analysis module 108 which in turn is connected to a display.

[0044] As liquid 102 passes through the pipe 100, the upstream piezoelectric transducer in box 104 is pulsed. The acoustic wave is refracted on entry into liquid in the pipe and is directed downstream. Depending on the specific configuration and pipe diameter the wave may or may not be reflected from the opposite side of the pipe towards the downstream box 106 or it may pass directly to the downstream box 106. The pulse is detected by the transducer in box 106, and the time between transmission and detection calculated in the control and analysis module 108. The piezoelectric transducer in downstream box 106 is then pulsed, and this travels upstream in a similar way to upstream box 104 where it is detected by the piezoelectric transducer in box 104. The time taken will be based on the acoustic velocity of the liquid less the speed of flow of the liquid; thus by using the two time measurements to eliminate the effect of distance travelled the flow velocity can be determined. Multiplying the flow velocity by the internal cross sectional area of the pipe will give the volumetric flow rate of the liquid, by knowing the density of the liquid the mass flow rate can be calculated. It should be noted that the mounting of boxes 104 and 106 should be such that the piezoelectric transducers in the two boxes are aligned with one another in the direction of flow in the pipe.

[0045] The computations required are carried out in the control and analysis module and displayed on the display. The module can be programmed to calculate flow velocity, volume rates, and mass flow rates and accumulated measures of each of these. As a further option a pair of thermocouples 112 can be attached to the pipe 100, assuming it is made of thermally conducting material and that the temperature on the pipe’s external surface is reflective of the temperature of liquid 102 in the pipe. By combining measures of inlet and outlet temperature with flow, it is possible for the heat flow rate through the pipe to be calculated. This is useful should a system of heat metering be needed for premises.

[0046] The flow meter of figure 7 is rather cumbersome and a neater design is achieved by mounting the wedge units on a board. This is shown in figures 8A and 8B.

[0047] In figures 8A and 8B a glass fibre reinforced resin board (the same material from which printed circuit boards are manufactured) 120, had a pair of longitudinally aligned slots 122 cut into it. Two wedge units 60 of the kind described in figures 5A and 5B are inserted through the slots with their lips 76 engaged beneath the board 120 and their tops 66 and ends 68, 70 projecting above the slots. The wedge units are inserted so that the inclined ends 70 face in opposite directions, outward from the ends of the cards. Piezoelectric transducers are mounted on the inclined ends with connectors 82 to the control an analysis and analyses module 108 with a display as in figure 7. Each of the wedge units 60 has holes 88 as described with reference to figure 5 and the fronts of the wedges formed between the inclined ends 70 and the bases 64 are cut away 74 to allow the wedge units 60 to sit snugly in the slots 122.

[0048] The assembly is mounted in a rectangular pot 123 - shown schematically in figure 8B with potting resin 124 holding the components in place. Screws 125 penetrate the bottom of the board into the ends of the pot to hold the board 120 in place on the bottom on the pot 123 leaving the bases 64 of the two bases 64 of the wedge units 60 exposed. The connections 82 to the transducers are run through holes in the pot to the control and analysis module 108. A metal band 126 passes through the pot 123 above the board 120, then externally around the pipe 100, the band is then tightened around the pipe bringing the bases 64 of the wedge units 60 to bear on the outside of pipe 100.

[0049] As liquid 102 passes through the pipe 100, the upstream piezoelectric transducer 80A is pulsed, with an acoustic wave entering the fluid and passing downstream at the velocity of the liquid plus the acoustic velocity of the liquid 102. The pulse is detected by the downstream transducer 80B, and the time between transmission and detection calculated in the control and analysis module 108. The downstream piezoelectric transducer 80B is then pulsed, and this acoustic wave travels upstream to upstream transducer 80A where is detected. Calculations of the flow velocity, volumetric flow rate, and mass transfer can be made in the control and analysis module 108 in exactly he same way as described with reference to figure 7.

[0050] It is also possible to fit a pair one or more thermocouples 126 to the board 120 so that they contact the pipe when the pot is attached to the pipe. This will enable temperature measurements to be combined in the control and analysis unit with mass flow rates to enable heat transfer rate though the pipe to be measured.

[0051] In a further development, rather than having the control and analysis module 108 as a separate modular item, the board 120 is a printed circuit board and components marking up the analysis part of module 108 are mounted and printed on the board 120 around the wedge units 60. The display unit 110 becomes an external reader but provided with functionality to control operation of the flowmeter. It can also be used as a data input unit to provide the analysis tools with information about the viscosity, and density of the liquid in the pipe and the pipe dimensions. For a fixed use flow meter, say a water meter to measure water flows through fixed dimension pipes, the flowmeter would operate permanently at a fixed pulse rate and the information about the physical properties of water and pipe dimensions would be hard coded into the analysis tools.

[0052] For a fixed use flow meter, say a water meter to measure water flows through fixed dimension pipes, the flowmeter could operate permanently at a variable pulse rate, in order to optimise power use on for example a battery operated device and the information about the physical properties of water and pipe dimensions would be hard coded into the analysis tools.

[0053] Although wedge units as shown in figure 5A and 5B are used to illustrate the embodiment of figure 8, the wedge units of figures 6 can be used aa can those of figures 1 to 4, albeit with bigger slots, [0054] A still further development is show in figure 9. In the arrangement of figure 8 the board 120 is flat so that its edges are away from the pipe. For a long term installation, this could result in some build-up of dirt between the pipe and the underside of board 120. To minimise this risk a contoured arrangement has been developed. A printed circuit board 127 is used instead of the flat board 120 of figure 8 with the wedge units 60 mounted in slots; transducers 80 are mounted on the inclined ends 70 of the wedge units exactly as in figure 8. Components 132 of the analysis tools are mounted on the board 127 with connecting circuits printed on the board as is usual for a printed circuit. The board 127 is fitted to the open base of a rectangular pot 123. A resin potting compound 124 fills the empty space in the rectangular pot. The bottom edges 134 of the rectangular pot 123 are shaped to conform to the curvature of board 127. The base 64 of the wedge units 60 is in contact with the external surface of pipe 100. A silicon rubber fillet fills the space between the external surface of the pipe 100 and the underside of the printed circuit board 127. One or more adjustable metal bands, ties or clamps 138 is fitted to the outside of the pot 123 and passes around the pipe 100. The band or clamp can be tightened so that the bases 64 of wedge units 60 bear hard onto the outside surface of pipe. 100 Operation of this flowmeter is analogous with that shown in figure 8.

[0055] Although all the examples given relate to a flowmeter on a pipe, the flowmeters described can be applied equally easily to a duct or a channel.

[0056] In each of the illustrated examples contact between the wedge unit and the outside of any pipe, duct or channel can be enhanced by applying a thin layer of silicon grease between the base of the wedge and the outside surface of the pipe, duct or channel.

[0057] There are a number of suitable commercial piezoelectric transducers which can be used with this invention. In the illustrated examples, the transducer used was from PI Ceramics GmbH of Lederhose, Thuringia, Germany - model PIC255.

Claims (20)

1. A liquid flowmeter having a pair of wedge units having parallel sides, base, top, two ends, one of which is inclined at an acute angle with respect to the base, said inclined end having a piezoelectric transducer mounted thereon, and in which the wedge units are mounted on a pipe, duct or channel so that the piezoelectric transducers are aligned with each other in the direction of liquid flow in the said pipe, duct or channel with the inclined ends of the wedge units mounted facing away from each other so that one inclined end is directed upstream of any flow in the pipe, duct or channel and the other inclined end is directed downstream of any flow in the pipe, duct or channel.

2. A liquid flowmeter according to claim 1 in which the liquid flowmeter comprises a pair of wedge units mounted on an outside surface of a pipe, duct or channel though which the liquid of interest flows.

3. A liquid flowmeter according to claim 1 in which each of the pair of wedge units is mounted in a slot in a board, the board being mounted on a pipe, duct or channel through which liquid flow is to be monitored.

4. A liquid flowmeter according to claim 3 in which the base of each wedge unit is extended to form lips at either end, said lips engaging beneath the board.

5. A liquid flowmeter according to claim 3 in which the base of each wedge unit is extended to form lips at either end, said lips carrying a deformable gasket such that on mounting the flowmeter to a pipe the gasket compresses and applies a consistent mounting force engaging beneath the board.

6. A liquid flowmeter according to claim 3 or 4 in which the board is a printed circuit board having thereon the circuit for generating and/or analysing the received signals of the piezoelectric transducers.

7. A liquid flowmeter according to claim 3, 4, or 5 in which the board is shaped to the outside the pipe, duct or channel through which the liquid to be monitored flows.

8. A liquid flowmeter according to any preceding claim in which the inclined ends of the wedge units are inclined at an angle of between 39° and 45° to the base of the wedge units.

9. A liquid flowmeter according to any preceding claim in which the piezoelectric transducer is separated from the top of the inclined end by half the wavelength of the piezoelectric transducer.

10. A liquid flowmeter according to any preceding claim in which pressure plates are mounted atop each piezoelectric transducer.

11. A liquid flowmeter according to any preceding claim in which the wedge units have holes passing from one side to the other.

12. A liquid flowmeter according to claim 11 in which the holes are arranged diagonally from the corner between the bottom of the wedge unit and the noninclined end wall and the corner between the top and inclined end.

13. A liquid flowmeter according to any preceding claim in which the end of each wedge unit opposite the inclined end is also inclined.

14. A liquid flowmeter according to any preceding claim in which the end of the wedge unit opposite the inclined end may be provided with an acoustic scattering surface.

15. A liquid flowmeter according to claim 13 in which the scattering surface comprises vertical V-shaped grooves and/or horizontal V-shaped grooves.

16. A liquid flowmeter according to any preceding claim in which the edge of each inclined end has an inclined groove with a surface parallel to the inclined edge of the wedge unit and the piezoelectric transducer is mounted on the inclined groove surface.

17. A liquid flowmeter according to claim 15 in which each side of the groove has an inclined slot, the slots being opposite one another and to receive between them an upper pressure plate, the upper pressure plate having a threaded screw or bolt passing through it, with one end of the bolt bearing against a lower pressure plate covering the piezoelectric transducer but electrically insulated from the piezoelectric transducer.

18. A liquid flowmeter according to any preceding claim in which the wedge units comprise a thermoplastic.

19. A liquid flowmeter according to claim 18 in which the wedge units comprise of polyether ether ketone.

20. A liquid flowmeter according to any preceding claim additionally comprising more or more thermocouples.