Measuring and testing – Volume or rate of flow – By measuring vibrations or acoustic energy
Patent
1980-06-25
1983-01-11
Kreitman, Stephen A.
Measuring and testing
Volume or rate of flow
By measuring vibrations or acoustic energy
G01F 166
Patent
active
043676545
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a device for measuring the flow velocity of fluids including at least one pair of electro-acoustic transducers to be positioned at the ends of a measurement path, each pair of said transducers simultaneously transmitting acoustic pulses and receiving the same at first and second times dependent on the velocity of the fluid, a clock pulse generator, a transmission circuit, a receiving circuit including an amplifier and a detection circuit for each of the transducers separately, an integration circuit including an integration capacitor for use in processing the difference in propagation time of the acoustic pulses, wherein the transmission and reception times for each of the transducers are determined. A device of this type is known from German Pat. No. 2,854,321.
In fluid flow technology several applications of devices for measuring the flow velocity of a liquid or gas in pipes, ducts and the like are generally known, all utilizing the physical property that pressure or sound waves propagate in a fluid at a velocity which applies to said fluid. Hence the effective propagation velocity with respect to a stationary reference position is the resultant of the flow velocity of the fluid with respect to said reference position plus the propagation velocity of the sound in said fluid.
When presuming for instance a measurement path AB within a fluid having a length L the resultant velocity in the direction from A to B is: L/t.sub.AB =C+Vcos.phi.and the resultant velocity in the direction from B to A is: L/t.sub.BA =C-Vcos.phi., in which V is the flow velocity of the fluid and .phi. is the angle between the flow direction of the fluid and the measurement path AB. Where the sound velocity C is not constant, said velocity being dependent on, among other things the temperature and the salt concentration and the value of said velocity is not always known either it is preferred to use the equation ##EQU1##
In accordance with the known technics both electro-acoustic transducers provided at opposite ends of the measurement path simultaneously emit short acoustic pulses. In this way one avoids moreover disturbing effects of interferences through reflections and other paths than the measurement path as occur when using continuous sound tones.
Where both the transducers provided at opposite ends of the measurement path function as a transmitter and also as a receiver the same value of L applies to both sound transmissing directions. This equality is an important advantage when measuring flow velocities V of a small value with respect to the sound velocity C. When very accurately determining the transmission times as well as the reception times the propagation times as well as the difference in propagation time of both transits may be determined wherein the sound velocity C is included in the calculation.
An object of the invention is now to provide a device having a very simple construction for determining the above function and by means of which at low flow velocities of the fluid a high accuracy of the measurement and a very good zero stability are obtained.
In a device of the type mentioned above the object is attained in accordance with the invention in that the integration capacitor is connected to a potential divider connected to a gate circuit and having in each leg thereof a switching means conductive in the rest condition after the transmission time, two different potentials being supplied in the rest condition to the one leg and to the other leg of said divider whereby the capacitor adjusts itself to the middle of the potential difference, while controlled by the gate circuit the switching means associated with the one transducer is blocked after the first reception time and subsequently the switching means associated with the other transducer is blocked after the second reception time.
The invention will now be described on the basis of an embodiment thereof having reference to the drawings in which:
FIG. 1 shows an example of a measurement path provided within a flowing fluid;
FIGS. 2a and
REFERENCES:
patent: 3623363 (1971-11-01), Dory
Hoogendijk Christiaan J.
Ymker Lucas
Altometer, Productiebedrijf Van Rheometron A.G.
Kreitman Stephen A.
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