GB1073194A - Fluid speed measuring system - Google Patents

Abstract

1,073,194. Ultrasonic fluid-flow meters. COMPAGNIE GENERALE DE TELEGRAPHIE SANS FIL. Sept. 9, 1964 [Sept. 13, 1963], No. 36992/64. Heading H4D. In a system for measuring the flow velocity of a fluid in a pipe, an acoustic signal is propagated diagonally across the pipe in both directions between two transducers both as a continuous wave signal and as a pulse signal. In the embodiment of Figs. 1 and 2, two transducers (1 and 2) are connected through a reversing switch to a transmitting signal generator (5) and a receiving amplifier (7). During a first measurement phase transmitted and received signals from generator (5) and amplified (7) are heterodyned in mixers (11 and 8) respectively with signals from a local oscillator (9), and are then phase-compared on a phase-meter (15). With the reversing switch (30, 40) in its first position (I), acoustic signals travel from transducer (1) to transducer (2) and the phase-meter (15) indicates a propagation time T 1 ; with the switch (30, 40) in its second position (II), the phase-meter (15) indicates the propagation time T 2 from transducer (2) to transducer (1). A computer (16) derives the value T 2 -T 1 . During a second measurement phase, control pulses from a monostable circuit (18) open a gate (17) to feed the transmitting transducer periodically from the signal generator (5). The monostable circuit (18) is triggered by a feed-back signal from the receiving transducer, and hence acoustic pulses are generated at a repetition frequency 1/T 1 or 1/T 2 according to the position of a reversing switch (101, 102) connecting the transducers (1, 2) to the gate (17) and receiving amplifier (7). These repetition frequencies are measured on a meter (19), and the computer (16) derives the value 1/T 1 - 1/T 2 and then computes the product (T 2 - T 1 )(1/T 1 - 1/T 2 ) from which the fluid flow velocity may be calculated without a knowledge of the speed of sound in the fluid.