GB1322094A - Acoustic wave liquid-level measuring apparatus - Google Patents

Abstract

1322094 Liquid-level sensing L'ELECTRONIQUE APPLIQUEE 25 Out 1971 49514/71 Heading G4H [Also in Division H4] Liquid level in a deep tank is measured by an ultrasonic pulse-echo system which determines the distance of the liquid surface above either a first transducer arrangement in the lower part of the tank or a second transducer arrangement in the upper part of the tank, either distance being selectively displayed on a two-input digital display device. In the Fig. 1 embodiment, transducers 4 and 5 below open-ended waveguide tubes 23, 30 are pulsed synchronously by transmitters 2 and 3 (transmitter 3 providing a higher carrier frequency than 2). Circuit 10 provides a rectangular gating pulse of duration equal to the twoway travel time of the ultrasonic pulse between transducer 4 and the liquid surface. This gating pulse enables passage of clock pulses from a first generator through gate 18 to a counter 19 constituting the display device. When the liquid level is above transducer 5, the gating pulse output from a circuit 11 (operating in the same way as circuit 10) blocks the passage of clock pulses from the first generator through gate 20 to gate 18 and instead enables passage of clock pulses from a second generator through gate 18 to the counter. To allow for temperature variations, or temperature difference between the top and bottom of the tank, the clock pulse frequencies are made dependent on the acoustic velocity in the liquid. For this purpose the first clock pulse generator comprises a transducer 6, a spaced reflector 49 and transmitter and receiver circuits 12, 14 together constituting a relaxation oscillator, the output of which is frequency multiplied at 16. The second clock pulse generator comprises similar units 7, 50, 13, 15, 17.