Measuring and testing – Volume or rate of flow – By measuring transit time of tracer or tag
Patent
1984-01-17
1985-12-03
Goldstein, Herbert
Measuring and testing
Volume or rate of flow
By measuring transit time of tracer or tag
G01F 170
Patent
active
045559473
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a method and an apparatus for the measurement of fluid flow velocities, for instance in a slurry transport (mixture liquid/solid material) or in a pneumatic transport (dry gas/solid material), but also for the measurement of the velocity of a liquid or gas and mixtures thereof.
In a known device, disclosed in the British Patent Specification No. 1,359,151 at least two transmitter transducers, situated at a predetermined mutual distance seen in the flow direction of the fluid, transmit signals through said fluid to at least two receiver transducers, also situated at a predetermined mutual distance seen in the flow direction of the fluid, in which each receiver transducer receives mainly the signal from the associated transmitting transducer and in which the signals supplied by the receiver transducers are correlated, in order to determine the fluid flow velocity.
In a slurry-transport in dredger conduits irregularities occur continuously in the flowing fluid, such as vortexes in the water carrying the sand and sludge or other material. Moreover this carried material will not be divided evenly, but will appear as clouds, which continuously chang in composition and shape.
The signals transmitted by the transmitter transducer through this mixture are modulated continuously by said irregularities between the transmitter transducers and receiver transducers and these irregularities can be used after demodulating the received signal by means of cross correlation methods for the measurement of the travel velocity of the mixture. In case the distance in the flowing direction of the mixture between the transducers is sufficiently small, said irregularities will have changed to a very small extent only, so that by comparing the demodulated signals from the two receiver transducers by the said cross correlation method, it is possible to determine the time which the mixture needs to travel between the pairs of transducers, from which the fluid flow velocity can then be calculated.
In the method known from above said British Patent Specification use is made of a continuous signal transmitted by the transmitter transducer, from which signal is separated the amplitude modulation by detection, which modulation is then used for correlation.
After thorough research it appeared, that such continuous signal often results in an interference pattern of standing waves in the dredger conduits. In particular in the case of small conduit diameters and low specific mass such interference patterns can be very detrimental for the correlation measurement. Because this interference pattern is determined also by the mixture and need not be the same for the pair of transducers (transmitter/receiver) this phenomenon has not been recognized as an unwanted interference.
Therefore one of the main objects of the present invention is to remove the results of the received signals from the interference patterns of standing waves.
According to the present invention the above object is reached by transmitting pulse-shaped signals by the transmitter transducers having such mutual time separation, that within this time separation standing waves caused by reflections will nearly completely fade out.
In order also to exclude from the velocity measurement interference patterns generated by pulse-shaped signals of too long duration, preferably samples are measured only of the signal received by the receiver transducer as soon as possible after reception by the receiver transducer of the front edge of the transmitter signal.
In connection with the desired equivalence of the two signal processing channels, each comprising a transmitter transducer and a receiver transducer, preferably use is made of the same frequency for these two channels. In order to avoid cross talk between the signal processing channels the pulse-shaped signals are transmitted according to the present invention by the one transmitter transducer within a time separation between the pulse-shaped signals of the other transmitter transducer, in which the tim
REFERENCES:
patent: 3762221 (1973-10-01), Coulthard
patent: 4201083 (1980-05-01), Kurita et al.
Robert C. Waag, et al., "Instrumentation for Noninvasive Cardiac Flow Rate Measurement", IEEE, Proceedings of the International Symposium on Sonics and Ultrasonics, Boston, Mass., Oct. 4-7, 1972, pp. 74-77.
F. J. Thomson, "Broadband Pulsed Doppler Ultrasonic System for the Noninvasive Measurement of Blood Velocity in Large Vessels", Medical & Biological Engineering and Computing, vol. 16, No. 2, Mar. 1978, pp. 135-146.
Goldstein Herbert
IHC Holland N.V.
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