GB2083612A

GB2083612A - Bubble flow meter

Info

Publication number: GB2083612A
Application number: GB8029007A
Authority: GB
Original assignee: Individual
Current assignee: Individual
Priority date: 1980-09-09
Filing date: 1980-09-09
Publication date: 1982-03-24
Also published as: GB2083612B

Abstract

A liquid flow meter consists of a section of pipe 3 of known volume through which the liquid flows, injection means 6 operable to pump a bubble of air 5 into the liquid at the upstream end of the section so as to fill the cross sectional area of the section and be carried by the flow, and an LED light source 17 and photodiode detector 18 located at the downstream end of the section to detect the passage of the bubble which detection initiates injection of another bubble and represents the flow of a section volume of fluid since detection of the preceding bubble. Detections may be summated to give total flow or measured with respect to time or some other variable to determine flow rate. A setting reservoir 20 and a fine by-pass duct 24 prevent extraneous bubbles reaching the detector 18. <IMAGE>

Description

SPECIFICATION Liquid flow metering This invention relates to the metering of liquid flowing in a pipe.

It is known to measure the flow rate of a liquid in a pipe by the positioning of an impeller in the pipe to be rotated by the passage of liquid, the rotational speed of the impeller being measured and related to the velocity of the liquid flowing over it and a signal therefrom being integrated or otherwise operated on to determine the volume of liquid flowing for a given time or other unit. Such schemes are difficult to implement in terms of mounting the impeller satisfactorily and in getting a required and consistent relatiqnship between impeller rotation and liquid velocity, particularly at low flow rates. Furthermore a compromise must be made between accurate measurement produced by filling the pipe with the impeller and the disruption of flow rate caused by the obstruction ofthe impeller.

Other schemes have been employed based upon cooling of spaced electrical conductors, the production of vorteces by bluff bodies, or the pressure exerted on a solid body in the pipe by the flow of liquid but such arrangements tend to be expensive or inaccurate.

It is an object of the present invention to provide a method of, and apparatus for, measuring the flow rate of a liquid in a pipe.

According to one aspect of the present invention a method of metering the flow of liquid through a pipe comprises passing the liquid, or a known proportion of the liquid, through a section of known volume, regeneratively injecting a bubble of gas into the pipe at the upstream end of the section so as to fill the cross-sectional area of the pipe and be carried along by the flow, in response to the detection of a preceding bubble at the downstream end of the section, each detection representing the passage of the volume of liquid held by the section.

The method may further include counting the detections to totalise the quantity of liquid flowing, for example, in order to indicate when a preset quantity has passed, or may involve timing the interval between pulses in orderto determine the flow rate with respect to time, or may involve measuring some other parameterforthe interval between successive bubbles in order to relate the flow to that parameter.

According to another aspect of the present invention a liquid flow meter comprises a section of pipe of predetermined volume;through which all, or a known proportion of the liquid is caused to flow injection means operable to inject into the liquid in the pipe at the upstream end of the section a bubble of gas of sufficient volume to fill the cross-sectional area of the pipe, detection means mounted at the downstream end of the section responsive to the passage of a bubble in the liquid to cause injection of a further bubble by the injection means and produce a detection signal indicative of the flow through the pipe of a volume of liquid corresponding to the volume of the pipe section.

Embodiments of the present invention suitable for direct flow metering and in measuring the flow rate of petrol to a carburettor of an internal combustion engine, will now be described by way of example with reference to the accompanying drawings, in which Figure 1 is a sectional elevation through a simplified flow meter, Figure 2 is a block circuit diagram of a circuit for controlling metering up to a preset volume of liquid, and Figure 3 is a block circuit diagram of a circuit for measuring the fuel consumption rate of a vehicle.

Referring to Figure 1 the flow meter is mounted in a liquid pipeline 1 through which liquid is caused to flow by some external means. The flow meter comprises a pipe 2 having a section 3 of known volume extending from an upstream end 4to a downstream end 5. At the upstream end is injection means 6 comprising a solenoid operated pump having a chamber 7 formed by a body 8 and a piston 9 slidable in the body on an injection stroke by a solenoid 10 and on a return stroke by spring 11. The piston 9 has a plurality of thorough apertures 12 and a flexible diaphragm 13 adjacent the face so that on the return stroke air is drawn through the apertures and lifts the diaphragm whereas on the driven stroke the diaphragm closes the apertures as the air in the chamber is compressed.The chamber has a fine outlet tube 14 which extends through the wall of the pipe 2 and ends in one more orifice 15 at the longitudinal axis ofthe pipe, defining the upstream end of the section. The, or one of the orifices 15 is coaxial with the pipe and faces into the flow of liquid. The chamber7 and solenoid 10 are dimensioned and rated so that the air forming the bubble is injected quickly to prevent the air being carried away by the liquid in a series of small bubbles and of sufficient quantity to form a bubble completely filling the cross-sectional area of the pipe. The cross-sectional area of the tube 14 is considerably smaller than the pipe 2 so as not to impede the flow of liquid.

The downstream end is defined by detection means 16 comprising a source of optical radiation, an infra-red LED 17 and a photodiode detection means 18 located on the same side of the pipe as each other and a reflector 19 located on the opposite side of the pipe. The pipe at this point, at least, is transparent and the remainder of the pipe may be transparent if desired. The LED 17, photodetection means 18 and reflector 19 are juxtaposed so that when a bubble is in the transparent portion the beam is passed through the pipe to the reflector and back through the pipe to the detection means. At other times, when the liquid fills the transparent portion, the beam is either blocked or refracted on its two journeys through the liquid and misses the photodetection means.

The beam is conveniently in the infra-red portion of the spectrum although radiation of other frequen cies may be used and the detection means may include (not shown) a modulatorofthe source and discrimination means for the received radiation to eliminate any effects of ambient light. The flow meter further comprises a settling reservoir 20 in the pipe 2 upstream of the sections 3 and through which liquid flows to reach the pipe section.

The settling reservoir 20 consists of a closed container having inlet and outlet ports 21 and 22. The reservoir is arranged to be operatively mounted with the outlet port 22 at the bottom of the reservoir and the inlet port 21 near the top so that any air or other gas dissolved in the liquid tend to separate in the reservoir and form an "atmosphere" 23 at the top of the reservoir. A by-pass duct 24 extends from the upper part of the settling reservoir to join the pipe 2 at 25, beyond the section in which measurements are made. The by-pass duct bleeds gas, or liquid if the reservoir contains no gas, from the reservoir and the passage of liquid in the pipe 2 at the junction with the duct entrains gas or liquid into the liquid of pipe 1.The by-pass duct 24 ensures that any extraneous bubbles of gas are not passed along the pipe section 3 to the detection means while avoiding the problem of venting gas or vapour from the reservoir 20. If desired provision may be made for venting the gas or vapour matter. As stated, in the absence of any gas the duct 24 will bleed liquid from the reservoir which will by-pass the measuring arrangement and introduce inaccuracy into the flow rate measurement. However as the flow rate is proportional to the fourth power ofthe pipe or duct diameter if the duct diameter is much smaller, say less than 25% of the pipe section 3 diameterthe measurement inaccuracy will be less than 1%.

The relationship between the injection means and detection means is shown by the circuit arrangement 30. A power supply 31 causes LED 17 to be illuminated. Photodetector 18 feeds signals in response to the detection of radiation to threshold means 32 which has a threshold set to respond only to signals over a predetermined magnitude as representing detection of a bubble in the pipe section 3.

The threshold detector is connected to an output terminal 33 and to the trigger of a bistable with a delay circuit 34. The bistable when triggered by detection of a bubble provides a pulseto a driver amplifier 35 to energise solenoid 10 of the injection means and the delay circuit 34 resets it a shorttime later.

The circuit thus regeneratively causes a bubble to be injected into upstream end of the section 3 in response to the detection of a previously injected bubble being detected at the downstream end of the section. Clearly the regenerative nature of the apparatus requires some initiating action to cause the cycle to begin. This may be achieved mechanically by arranging for the downstream end of the section to be at a high-point in the pipe such that a bubble in the section at the end of a preceding measurement operation will move no further than the detection means before commencement of the next measurement operation and its detection will start the injection cycle. This is suitable only when the liquid remains in the section.Where the apparatus is newly installed in a pipe or the pipe empties, the cycle may be initiated electrically, for instance, by a trigger input 36 to the bistable. Alternatively, or in addition, a timing circuit 37 may be connected to the input of the bistable 34 to trigger it after a predetermined time interval. The output of the bistable may be taken to a reset terminal 37' of the timing circuit to reset it each time a detected bubble triggers the bistable so that bubbles are injected on a time basis only either at the commencement of operation when no bubble has been detected by the end of the timer interval, or where a bubble is lost (for example by fragmenting) or is otherwise not detected.The time interval chosen is a compromise between recommencing injection as soon as possible after a bubble should have been detected and the extraneous injection of bubbles at very low flow rates.

Several modifications may be made to the apparatus described above.

The purpose of the settling reservoir 20 is solely to provide a means of preventing gas, such as air, trapped in the liquid from forming bubbles in the pipe section and it will be appreciated that if the liquid is known to be free of such dissolved gas or other removal means exists prior to the section the reservoir 20 and by-pass duct 24 may be omitted.

The pipe 2 may also be provided with a restriction and orifice shown ghosted at 39, immediately upstream of the section 3. This provides a pressure drop to liquid flowing therethrough which encourages formation of a bubble in the liquid and the ability of a forming bubble to temporarily block the flow through the orifice during its formation enables it to grow quickly to fill the cross sectional area of the pipe.

Alternatively the pipe may be reduced in crosssectional area of the start of the section at both sides of the point at which the bubble is injected so as the bubble is injected into a smaller pipe to encourage it to fill the pipe.

Clearly the gas injected into the liquid may be other than air and the injection means may take other pump form.

The pipe section 3 which requires a transparent portion at the detection region may, as mentioned above, the transparent throughout and formed of a plastics material.

The optical detection is achieved by a combination of refraction through the liquid (or lack of it) and reflection from 19. It will be appreciated that the reflector 19 could be omitted and the LED 17 and photodetector 19 be located at opposite sides of the pipe.

The detection means 16 may be made more immune to the reception of ambient radiation by replacing the LED source 31 with a modulator circuit and threshold detector 32 with a demodulator or phase sensitive detector.

The pipe 2 and its section 3 is arranged also to take all, or substantially all, of the liquid. In situations where liquid flow requires a larger diameter pipe than that in which a pipe-filling bubble can conveniently be formed one or more further parallel pipes may be used, the pipe 2 passing a known proportion of the liquid and the measuring circuit being scaled accordingly to indicate the overall flow rate.

The output signal appearing at output terminal 33 comprises a series of pulses, each representing the detection of a bubble and of the passage through the section 3 of a volume of fluid equal to the volume of the section. There will be inaccuracies due to the volume occupied by the bubble and the delay between detection of one bubble and the formation of the next. The length of the section may be chosen to maximise the volume of fluid therein in relation to the bubble volume and the time of passage along the section in relation to the injection delay to minimise any inaccuracy.

The pulses appearing at terminal 33 may be utilised in different ways related to the fluid flow and examples of circuits which utilise the pulses are shown in Figure 2 and 3.

Referring firstly to Figure 2, a circuit to enable the metering of a predetermined quantity offluid is shown. The length of pipe section 3 is chosen so that the section contains a unit volume of liquid being dispensed. A manually operated switch 40 is connected to bistable 34 (Figure 1) to initiate a bubble and to a setting input of a bistable latch 41 which provides a signal on line 42 to a dispensing pump (not shown) which causes fluid to flow through the section 3. A counter 43 as an input 44 connected to terminal 33 by which to receive and count detector pulses and a reset input 45 connected to reset the counter by the leading edge of the latch output on line 42. The counter has a plurality of parallel outputs 46 each addressable by a switch 47 connected to a reset input of bistable latch 41.

In operation the switch 47 is selected to a count corresponding to a number of unit volumes required to be delivered. Operation is commenced by actuating switch 40 which causes the pump to begin dispensing fluid and the counter to reset. As each unit of liquid is dispensed a pulse is produced from terminal 33 and the counter increments until a total quantity corresponds to the switch position and whereupon the latch 41 is reset and the pump stopped; an integral number of unit volumes having been delivered. Clearly this basic circuit is capable of elaboration in many ways.

A further circuit is shown in Figure 3 and relates to the use of the meter in a miles-per-gallon meter for measuring fuel consumption of a vehicle.

The circuit comprises a bistable latch 50 having a reset input connected to terminal 33. A set input 52 is connected to terminal 33 by way of delay element 53. When set the latch provides an enable signal to a counter 54 and when reset provides an enable signal to a multiplier circuit 55. The counter 54 is connected to receive pulse signals representing distance travelled by the vehicle from an odometer device or other transducer shown at 56 and feeds the increasing total to one set of inputs ofthe multiplier 55. A constant generator 57 feeds a constant signal (representing the relationship between odometer pulses and the distance unit, the mile, and the volume of the pipe section 3 and the volume unit, the gallon,) to a second set of inputs of the multiplier. The Constant Generator thereby provides a ready means of calibrating the device.The multiplier has an output connected to a display 58 and also to a reset terminal of counter 54.

In operation a first pulse received from 33 resets latch 50 and causes multiplier to produce an output to the display (which should be zero) and to reset the counter 54 (which should be empty). After the delay of element 53 the latch 50 is set and counter 54 enabled to count odometer pulses.

When the next pulse is produced at 33, the latch is once more reset the counter is disabled, the counter total then multiplied by the constant, displayed, and finally the counter is reset. After the delay period of 53, the latch is set and counting continues until the next bubble is detected.

Thus the display 58 displays a figure in miles per gallon which is updated with each section volume of fuel used. The delay 53 need only be as long as is necessary to perform the multiplication and counter reset and will be short in comparison to the physical quantities being measured.

As an alternative to the multiplier and constant generator, a store may be employed as a look-up table to which each count is referred to provide the corresponding figure for display.

The circuit shown in Figure 3 may be adapted with simpie modification to display a flow rate with respect to time, for example, gallons per minute. The odometer 56 is replaced by a clock and the multiplier followed by a circuit which gives a reciprocal for display, or a stored look-up table is in reciprocal form.

Claims

1. A method of metering the flow of liquid through a pipe comprising passing the liquid or a known proportion of the liquid through a section of known volume, regeneratively injecting a bubble of gas into the pipe at the upstream end of the section, so as to fill the cross-sectional area of the pipe and be carried along by the flow, in response to detection of a preceding bubble at the downstream end of the section, each detection representing the passage of the volume of liquid in the section.

2. A method as claimed in claim 1 in which the liquid is passed through a closed settling reservoir to enable gas dissolved in the liquid to separate therefrom prior to the liquid entering the section and any gas so separated is entrained by the liquid through a by-pass ofthe section after the liquid has passed through the section.

3. A method as claimed in claim 1 or claim 2 in which the gas of the bubble is air.

4. A method as claimed in any one of claims 1 to 3 in which the gas is injected by a pump through a fine tube extending through the wall of the section.

5. A method as claimed in claim 4 in which the tube discharges through at least one orifice substantially on the longitudinal axis of the pipe section.

6. A method as claimed in any one of claims 1 to 5 in which each bubble is injected after a predetermined time interval if no bubble is detected during the time interval.

7. A method as claimed in any one of claims 1 to 6 in which the bubble is detected by passing it through a substantially transparent portion of the tube section and detecting a change in the optical properties of the contents of the section.

8. A method as claimed in claim 7 in which the bubble is detected by detecting a beam of optical radiation at the substantially transparent portion and locating a detectorto receive radiation only when not refracted away therefrom by liquid in the portion.

9. A method of metering liquid flow through a pipe substantially as herein described with reference to and as shown by the accompariying drawings.

10. A liquid flow meter through a comprising section of pipe of predetermined volume through which all or a known proportion of, the liquid is caused to flow, injection means operable to inject into the liquid in the pipe at the upstream end of the section of bubble of gas of sufficient volume to fill the cross-sectional area of the pipe, detection means mounted at the downstream end of the section, responsive to the passage of a bubble in the liquid to cause the injection of a further bubble by the injection means and produce a detection signal indicative of the flow through the pipe of a volume of liquid corresponding to the volume of the pipe section.

11. Apparatus as claimed in claim 10 in which the injection means comprises a spring-returned solenoid-operated pump having valve means arranged to inject air from a chamber into the pipe when the pump is stroked by the solenoid and arranged to draw atmospheric air into the chamber during the restoring stroke.

12. Apparatus as claimed in claim 11 in which the valve comprises a flexible diaphragm arranged to bear against apertures in a rigid piston contained in a cylinder and forming one wall of the chamber.

13. Apparatus as claimed in any one of claims 10 to 12 in which the injection means comprises a tube considerably smaller cross-sectional area than the pipe extending from the chamber through the wall of the pipe by way of which the gas is introduced into the pipe.

14. Apparatus as claimed in claim 13 in which the tube has at least one aperture therein adjacent the end thereof in the tube.

15. Apparatus as claimed in claim 14 in which the aperture, or one of the apertures, is substantially at the longitudinal axis of the pipe.

16. Apparatus as claimed in claim 15 in which the aperture is coaxial with the pipe and directs the gas forming the bubble in the opposite direction to the flow of liquid through the pipe.

17. Apparatus as claimed in any one of claims 10 to 16 in which the pipe is provided with a flow restr iction and orifice immediately upstream of the injec tion means to reduce the liquid pressure in the pipe section and encourage the formation of the bubble.

18. Apparatus as claimed in any one of claims 10 to 16 in which the pipe is provided with a portion of reduced cross-sectional area into which the injection means injects the bubble.

19. Apparatus as claimed in anyone of claims 10 to 18 including a settling reservoir comprising a closed container having an inlet port and having an outlet port coupled to the pipe section and arranged i to be mounted with the outlet port near the bottom of the container and a by-pass duct having a cross sectional area (much) less than the pipe extending from the other end of the container from the outlet port (near the top of the container) extending to the pipe beyond the section and open through the wall thereof such that the contents ofthe duct are entrained by the flow of liquid along the pipe.

20. Apparatus as claimed in claim 19 in which the pipe of said section is coiled around the container wall of the settling reservoir.

21. Apparatus as claimed in anyone of claims 10 to 20 in which.the pipe section is formed of plastics material.

22. Apparatus as claimed in any one of claims 10 to 21 in which the pipe section has a transparent portion at the location of the detection means.

23. Apparatus as claimed in claim 22 in which the detection means comprises a source of optical radiation located so as to direct a beam of radiation into the transparent portion of the pipe and photodetection means located so as to receive radiation of the beam by way ofthetransparent portion when a bubble is in the portion but to miss the beam refracted by liquid in the portion.

24. Apparatus as claimed in claim 23 in which the source and photodetection means are mounted on the same side of the pipe portion as each other and on the opposite side of the pipe portion to a reflector located so as to reflect radiation of the beam received by way of a bubble to the photodetection means also by way of the bubble but either not to receive radiation refracted by the liquid orto reflect in a direction in which it will not reach the photodetection means.

25. Apparatus as claimed in claim 23 or claim 24 in which the optical radiation is in the infra-red portion ofthe spectrum.

26. Apparatus as claimed in any one of claims 23 to 25 in which the detection means includes means to modulate the beam and discrimination means responsive only to the reception of said modulated beam.

27. Apparatus as claimed in any one of claims 23 to 26 in which the source is a light emitting diode and the photodetection means is a photodiode.

28. Apparatus as claimed in any one of claims 10 to 27 in which the circuit means comprises timing means operable to inject a bubble after a predeter mined interval from injection of a preceding bubble.

29. A flow meter substantially as herein described with reference to, and as shown by the accompanying drawings.