Measuring and testing – Volume or rate of flow – By measuring vibrations or acoustic energy
Patent
1994-03-15
1996-09-10
Chilcot, Richard
Measuring and testing
Volume or rate of flow
By measuring vibrations or acoustic energy
7386127, G01F 100
Patent
active
055535054
DESCRIPTION:
BRIEF SUMMARY
FIELD OF INVENTION
The present invention relates broadly to an electronic fluid flow meter and, in particular, to a gas meter for domestic and commercial use.
BACKGROUND TO THE INVENTION
Traditional fluid flow meters in domestic and commercial use generally include some mechanical arrangement such as a bellows, or a vane or impeller which actuates a totalising mechanism. Generally, a mechanical dial arrangement indicates the total volume of fluid that has passed through a meter. Such mechanical arrangements are not highly accurate, especially at low flow rates, such as those required to maintain a gas pilot light. Accordingly, inaccuracies in low flow rate measurement can represent a substantial loss of income to the supplier of gas, and water.
Over recent years, there have been a number of proposals that utilise electronics technology so as to provide for substantially higher accuracy of the fluid flow measurement. Such systems generally incorporate ultrasonic transducers that transmit ultrasonic signals both upstream and downstream to measure the times of flight of the signals, from which the relative speed of the fluid can be calculated. Examples of such devices for use in measuring liquid flow rates, are found in U.S. Pat. Nos. 3,898,878 and 3,329,017 which use amplitude based measurement. U.K. Patent Application No. GB 2,222,254 A identifies that amplitude measurement is generally not practical in gas flow measurement due to substantial variations In amplitude between the transducers. This results in it being difficult to detect the moment of time when a signal is received and thereby accurately determine the time of flight. GB 2,222,254 A disclosed a system which used ultrasonic signals transmitted as packets whereby a phase change is inserted into the middle of each packet, and thus represents an identifiable timing marker from which the time of flight can be calculated.
However, problems arise with the detection of a phase change when measuring fluid flow in a small duct or conduit because the ultrasonic signal is reflected by the wall(s) of the duct which causes multipath propagation. The multipath propagation effectively alters the phase relationship of energy reaching the receiving transducer, and hence, the timing of the phase change is not reliably detectable. Also, the transission of high order acoustic modes, which propagate at speeds lower than the primary wave packet, cause interference with succeeding signals. This can lead to further errors.
It is an object of the present invention to substantially overcome or ameliorate, some or all of the problems of the prior art.
DISCLOSURE OF THE INVENTION
In accordance with a first embodiment of the present invention there is disclosed a method of detecting the time of arrival of an acoustic wave packet transmitted at a particular frequency, said method comprising the steps of detecting the wave packet and forming a received signal therefrom, rectifying and filtering the received signal to form an envelope signal, detecting when said envelope signal crosses a detection threshold to thereby enable the detection of a transition across a predetermined level by said received signal, the transition across said predetermined level representing a determinable number of cycles of said received signal at said particular frequency after the arrival of said acoustic wave packet.
In accordance with a second embodiment of the present invention there is disclosed an electronic fluid flow meter comprising first and second transducers locatable within a fluid, transmitter means for energising one of said transducers to cause emission of one or more acoustic wave packets therefrom for reception by the other said transducer, control means connected to said transmitter means for reversing the direction of transmission of said acoustic wave packets, timer means connected for enablement to said control means for measuring a time of flight of each said acoustic wave packet, said timer means being stopped by a trigger signal output from a receiver means connected
REFERENCES:
patent: 3282101 (1966-11-01), Yamamoto
patent: 4022058 (1977-05-01), Brown
patent: 4480485 (1984-11-01), Bradshaw
patent: 4603589 (1986-08-01), Machida
Bignell Noel
Braathen Colin W.
Collings Anthony F.
Hews-Taylor Kenneth J.
Martin Barry J.
Biegel Ronald
Chilcot Richard
Commonwealth Scientific and Industrial Research Organization
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