Patent GB-1344106-A (GB)
Title: Ultrasonic flowmeter systems
IPC: G01F1/66
Filed: 1971-04-19
Abstract: 1344106 Ultrasonic fluid flowmeters WEST-  INGHOUSE ELECTRIC CORP 19 April 1971 [6 March 1970] 23221/71 Heading H4D  A flowmeter includes a pair of transducer means, first and second feedback paths connecting the output of one transducer means to the input of the other and vice versa, means for causing the same number of pulses to be transmitted from each transducer means during a predetermined time and means coupled to both feedback paths for determining the fluid flow rate from the time differences between corresponding received pulses in the respective feedback paths. Timing circuit 9, Fig. 4, enables A- and B-gates 10, 11 which enable astable multivibrators 3, 7 in each loop A, B. These produce pulses which are transmitted through the sing- around loops A, B. The A loop pulses are counted by counter 15 which on reaching a preset number, N, produces a pulse which passes to N#t circuit 14 and also enables gate 12 which allows the next loop B pulse to pass to the N#t circuit 14. This produces pulse of length equal to the time N#t between the Nth pulses in the two loops. The unit 14 output pulse amplitude is controlled by "C-corrector" 13 such that the average output is proportional to t A , t B  being the up- and downstream transit times respectively. The pulse amplitude is controlled by utilizing the discharge of a capacitor (Fig. 6 not shown) modified to approximate to a shape 1/t<SP>2</SP> and thus the unit 14 output pulse varies in amplitude from 1/t A <SP>2</SP> to 1/t B <SP>2</SP> which produces the desired average. Instead of the four transducers, two only may be used in which case, a delay # is introduced between the first pulses in each loop and this is equalized by delaying the counter 15 output pulse. In a second embodiment (Fig. 8, not shown), the time differences between each and every corresponding received pulses are summed to provide a larger output signal. In this case the A and B loop pulses are used to turn a bistable (68) on and off respectively, the output thereof is then averaged and is proportional to If only two transducers are used, a delay # is again introduced into the B loop and a train of pulses of length # is generated, averaged and subtracted from the bi-stable (68) output. The two pulse trains both have their amplitudes controlled by a "C-corrector unit" (66). This produces a D.C. voltage correction for every time difference pulse, proportional to where t s  is the expected mean value of #t. To do this the bi-stable (68) output amplitude is set to the value of the discharge voltage of a capacitor at a time (t A +t S ) after the previous received pulse (Figs. 10-11, not shown). In a third embodiment, Fig. 12, the sing-around loops operate for a predetermined time, t ON , rather than for a predetermined number of pulses. In this case, t ON , is provided by a master multivibrator 112 triggered by the timing circuit 9 and which enables the loop multivibrators 18, 26. The delay # is produced by a monostable 116. The output is formed as in the Fig. 8 embodiment and the description states that for large values of N, the (N+ 1)th pulse in loop A occurs at the same time as the Nth pulse in loop B. Thus, the average output from the subtractor 124 is proportional to where T = total repetition period of the measurement operation, d = spacing of the transducers. All of these are known thus enabling v to be measured without correction for the velocity of sound in the fluid.