GB859915A - Improvements in or relating to measuring systems utilising pressure waves - Google Patents

Abstract

859,915. Ultrasonic measuring apparatus. BAILEY METERS & CONTROLS Ltd. Sept. 12, 1958 [Sept. 13, 1957], No. 28892/57. Class 40(7). Variations in a characteristic of a body of fluid are measured by counting the number of times, or the rate at which an electronic oscillator circuit loaded by an electro-mechanical transducer projecting pressure waves through the fluid towards a reflecting surface goes into oscillation. Relative movement between electro-acoustic transmit/receive transducer 1, Fig. 1 and reflecting surface (or medium discontinuity) 3 causes the transducer to move successively through nodes PNI-Z and anti-nodes PANI-Z of the pressure standing-wave pattern. Electronic oscillator circuit 5 is adjusted such that when the go-and-return path length r = w (1 + 2n)/2, where w is the wavelength in the intervening medium and n an integer, the load imposed by the transducer on the oscillator circuit is sufficiently low for oscillations therein to build up; when r = wn the imposed load inhibits oscillations. In an alternative arrangement separate transmitting and receiving transducers are used, Fig. 2 (not shown). As applied to monitoring of water level in tank 20 ultrasonic piezo-electric transducers 21A, B are connected to equal-frequency oscillators 25A, B the separation between transducers 21B and tank base being increased by metal layer 28. Detector 29A provides an output pulse to a counter such as described in Specification 859,914, when circuit 25A goes into oscillation and similarly for detector 29B and circuit 25B, the indicated counter number being increased by unity when a pulse from detector 29B follows one from detector 29A and decreased by unity on the reverse sequence. Where liquid surface agitation causes incident wave dispersion a float with a submerged horizontal reflecting surface may be used. Liquid flow through a pipe is measured by using plates on the tips of a rotatable vane as reflectors, a single transducer being employed and the oscillator circuit detector feeding (1) a counter to give quantity flow and (2) a pulsefrequency measuring device to give velocity of flow, Figs. 4 and 5 (not shown). To measure furnace gas temperature the reflection path length is fixed but the change of wavelength w with temperature is utilized Fig. 6 (not shown).