GB2083624A - Measuring flow or movement - Google Patents

Abstract

The invention relates to apparatus for measuring flow or movement in which irregularities in temperature and/or density are induced in moving material by an ultrasonic beam generated by a transducer 4. The ultrasonic beam is modulated by a wave form having good correlation properties so that e.g. a portion 5 of material flowing through a pipe 1 is affected to a varying degree as indicated by the density of shading in the drawing. The portion 5 is detected by detectors at 11 and 12 spaced distance d along the pipe 1 and the output of detector 11 is subjected to a delay at 17. The delayed output of 11 is correlated at 18 with the undelayed output of 12 and the delay 17 adjusted by manipulating the control 17A until the correlator output is a maximum. The delay value is then noted, this being a measurement of velocity. <IMAGE>

Description

SPECIFICATION Apparatus for measuring flow This invention relates to apparatus for measuring the flow of material or objects and in particular to that kind of apparatus in which irregularities are deliber ately introduced into the material and in which the measurement is made by observing the movement ofthe irregularities.

Apparatus of the aforesaid kind has been used in the past for measuring the velocity of fluid flowing through a pipe. One such flow meter introduces irregularities in the form of bubbles. This technique has the disadvantages (a) that the bubbles may con stitute an undesirable impurity (b) that the introduc tion of bubbles may significantly affect the flow rate and (c) that the pipe carrying the fluid needs to be modified to allow the bubbles to be introduced.

Another known flow meter introduces irregularities in the form of vortices. This technique however also requires modification of the pipe for the insertion of a suitable vortex inducing body in the flow path. It also obviously affects the flow rate.

This invention provides apparatus for measuring the velocity of a material or object moving along a path comprising identifying meansfortransmitting ultrasonic waves through the material at a particular position along the path thereby identifying a part of the material which is at that position and measuring means for detecting and measuring the velocity of the thus identified part.

In this description the term "measuring the veloc ity" is defined as including processes of detecting whether or not a velocity exceeds a threshold value and producing a control signal which performs a control function without necessarily operating avis- ible, tangible or audible display or alarm device.

Such a control signal could, for example, be used to maintain the flow velocity at a desired value.

The ultrasonic waves affect the density, tempera ture and/or other physical properties ofthe material to an extent which makes the affected part recognis able by the measuring means.

In one embodiment of the invention the measur ing means includes two detectors spaced at different positions downstream of the identifying means, each detector being adapted to respond to move ment of the identified part past it. The velocity ofthe fluid can then be calculated knowing the distance between the detectors and the time interval between -the instants when the detectors respond.

In the aforementioned embodiment of the inven tion, each detector is preferably an ultrasonic detec tor and has associated with it an ultrasonic transmit ter arranged to transmit ultrasonic energy through the fluid to the receiver. In this system the identified part of the fluid affects the ultrasonic energy passing through the material from the transmitter to the detector, e.g. by changing its phase, by producing a Doppler shift or by deflecting the direction of prop agation.In orderthatthe detectors of the aforementioned embodiment should be able to distinguish between the "identified parts" of the material and other chance variations in physical properties it is desirable that the identifying means include a facility for producing an ultrasonic frequency carrier signal modulated by a readily distinguishable waveform, preferably one having good correlation properties such as a Barker Code or a waveform approximating to this. In a system employing this technique the output of the more upstream of the two detectors is passed through a variable delay device and is then correlated with the output of the other detector. If the delay is adjusted so that the correlation coefficient is a maximum the delay value is then equal to the time taken for the identified part of the material to pass between the detectors.From this time value the speed of flow can be determined.

The technique described in the immediately preceding paragraph is applicable to systems in which the identifying means is other than ultrasonic. For example, a suitably modulated microwave beam, laser beam or heater could be used to "mark" the part of the material to be identified. Alternatively a mechanical device could be used. For example, an adjustable bluff body, positioned within a fluid flow path, could be moved in accordance with a signal having the required good correlation properties.

Accordingly, the invention also provides apparatus for measuring the velocity of a material or object comprising means for producing a signal which defines a predetermined waveform, a transducer arranged to receive the said waveform and operative to convert it into variations of a physical property of a part of a material or object flowing past the transducer, and means for measuring the velocity of movement of the said part.

One particular way in which the invention may be performed will now be described by way of example with reference to the accompanying schematic drawing of a fluid flow meter constructed in accordance with the invention.

Referring to the drawing, a pipe 1 conducts a fluid in the direction shown by the arrow. A sine wave generator 2 produces sine waves at an ultrasonic frequency and these are amplitude modulated at 3 to produce pulses each of which varies in amplitude according to a predetermined waveform chosen for its good correlation properties. The pulses are produced at a repetition frequency determined by a timer 3A.

Each modulated pulse is applied to an ultrasonic transducer 4 which, during each pulse, transmits ultrasonic waves into a region of the fluid such as that indicated at 5. The effect of this is to change certain physical characteristics, particularly temperature and density, of the fluid and since the amplitude of the ultrasonic waveform is modulated during each pulse, the said temperature and density of the region 5 of the fluid varies as illustrated very schematically by the changes in the density of shading on the drawing. The region 5 is thus identified or marked by modulations in the temperature, density or other The drawings originally filed were informal and the print here reproduced is taken from a later filed formal copy.

physical property.

Downstream of the transmitter 4 are two further ultrasonic transducers 6 and 7 each of which receives a continuous ultrasonic frequency signal from a sine wave generator 8. The ultrasonic waves from transducer 6 and 7 are transmitted along paths 9 and 10 to respective receivers 11 and 12. The phase of the ultrasonic signal arriving at 11 and 12 depends on the length of the paths 9 and 10 and of course on the speed of propagation of ultrasonic waves through the fluid medium. This speed of propagation depends on the density and so the phase ofthe signal arriving at first 11 and then 12 varies in accordance with the aforementioned waveform when the region 5 of fluid passes across the respective paths 9 and 10.

The outputs from transducers 11 and 12 are processed by automatic level control circuits 13 and 14 to make them of approximately equal strength and the phase information is then extracted by phase sensitive detectors 15 and 16 which receive their reference from the sine wave generator 8. The outputs of detectors 15 and 16 are analogue signals whose amplitudes represent the phase of the waves received at 11 and 12 respectively. The output of detector 15 is fed through a variable delay device 17 to one input of an analogue correlator 18; whilst the output of detector 16 is fed directly to the other cor relator input.

The correlator 18 consists of two delay lines 19 and 20 from which an equal number of taps are taken (onlyfour being illustrated in the drawing).

The outputs appearing at corresponding taps of each delay line are multiplied by circuit components 21 and the results of multiplication are added at 22 to produce a correlation function at the correlator out put23.

A sample and hold circuit 28 retains the highest correlation function produced during a preset time interval after transmission of each pulse from the transducer 4. This time interval is defined by a delay circuit 29 and a monostable 30 and is sufficiently long to allow the region 5 to pass transducers 7 and 12 before the end ofthe time interval, even for very slowly moving fluids. This highest correlation function is displayed on an indicator 31. The sample and hold circuit 28 and the indicator 31 are reset for each transmitted pulse.

In operation a graduated control 17A of the variable delay 17 is manipulated so as to sweep throughout its delay range. When a position is found where the correlation coefficient indicator 31 indicates a maximum correlation coefficient it can be assumed that the signals in the delay lines 19 and 20 of the correlator are the same. This condition will pertain when the contents of lines 19 and 20 are derived from phase modulation caused by passage of the fluid region 5 across paths 9 and 10. Itfollows that the delay value as indicated by the graduated control 1 7A is a measure of the time taken for the region 5 to travel the known distance d between paths 9 and 10 and thus is also a measure ofthe fluid velocity.

The control 17A can be graduated in velocity units but it would alternatively be possible to graduate it in volume units to show the volume of fluid passing through the pipe per unit time. It may be desirable in certain circumstances to provide a facility for auto matically sweeping the variable delay unit 17 through its range of delays and automatically noting or holding the delay value pertaining when the output of circuit 28 is a maximum. This can be done using a delay lock loop system.

Whilst the invention is particularly applicable to systems where two detectors such as shown at 11 and 12 are spaced along the path to measure the time taken for a part ofthe fluid to flow between them, other forms of velocity measurement are possible. For example, a Dopplar system can be used to measure the Doppler shift caused by reflection of ultrasonic waves from the part 5 of the fluid.

The invention was devised specially for measuring the flow rate of fluids in a pipe but it is also applicable to almost any form of flow measurement. For example, it could be used to measure the velocity of marine craft by sensing the flow rate of water relative to the hull. Similarly it could be used to measure the velocity of an aircraft relative to the airthrough which it is moving. The invention is not only applicable to measurement of the velocity of fluids. It could also be used for measuring the velocity of solid matter such as a moving part of a machine, material moving along a conveyor belt, and vehicles moving along a road.

New claims or amendments to claims filed on 18th December 1981 Superseded claims 1 to 10 New or amended claims: New claims 1 to 5 as per attached sheet 1. Apparatus for measuring the velocity of a material or object comprising means for producing a signal which defines a predetermined waveform, a transducer arranged to receive the said waveform and operative to convert it into variations of a physical property of a part of a material or object flowing past the transducer, and means for measuring the velocity of movement ofthe said part.

2. Apparatus according to claim 1 in which the measuring means includes two detectors spaced at different positions downstream of the said transducer, each detector being adapted to respond to movement of the said part ofthe material or object past it, and means for measuring the time taken for the said part to travel between the detectors.

3. Apparatus according to claim 1 or 2 in which the signal is ultrasonicand the transducer is an ultrasonic transducer.

4. Apparatus according to claim 2 in which an output of the more upstream of the two detectors is connected, through a variable delay device, to one input of a correlator and an output of the other, move downstream, of the two detectors is connected to another input of the correlator.

5. A fluid flow meter according to claim 1 and substantially as described with reference to the accompanying drawings.

Claims (10)

1. Apparatus for measuring the velocity of a material or object moving along a path comprising identifying means for transmitting ultrasonic waves through the material or object at a particular position along the path thereby identifying a part of the mat erial or object which is at that position and measur ing means fordetecting and measuring the velocity of the thus identified part.

2. Apparatus according to claim 1 in which the measuring means includes two detectors spaced at different positions downstream of the identifying means, each detector being adapted to respond to movement of the identified part past it.

3. Apparatus according to claim 2 in which each detector is an ultrasonic detector and has associated with it an ultrasonic transducer arranged to transmit energy across the path to the detector.

4. Apparatus according to claim 2 or 3 in which the identifying means includes means for producing an amplitude modulated ultrasonic frequency carrier signal.

5. Apparatus according to claim 4 in which an output of the more upstream of the two detectors is connected, through a variable delay device, to one input of a correlator and an output of the other, more downstream, of the two detectors is connected to another input of the correlator.

6. A fluid flow meter according to claim 1 and substantially as described with reference to the accompanying drawings.

7. Apparatus for measuring the velocity of a material or object comprising means for producing a signal which defines a predetermined waveform, a transducer arranged to receive the said waveform and operative to convert it into variations of a physi cal property of a part of a material or object flowing past the transducer, and means for measuring the velocity of movement of the said part.

8. Apparatus according to claim 7 in which the measuring means includes two detectors spaced at different positions downstream of the said trans ducer, each detector being adapted to respond to movement of the said part of the material or object past it, and means for measuring the time taken for the said part to travel between the detectors.

9. Apparatus according to claim 7 or 8 in which the signal is ultrasonic and the transducer is an ultrasonic transducer.

10. Apparatus according to claim 8 in which an output of the more upstream of the two detectors is connected, through a variable delay device, to one input of a correlator and an output of the other, move downstream, of the two detectors is con nected to another input of the correlator.