GB1239314A - - Google Patents

Abstract

1,239,314. Ultrasonic fluid flow meters. MITSUBISHI DENKI K.K. 1 Nov., 1968 [1 Nov., 1967; 2 Feb., 1968; 16 July, 1968], No. 51945/68. Heading H4D. In a known ultrasonic fluid flow meter in which the pulse recurrence frequency (p.r.f.) from generator 20 compared with that from generator 21 is a measure of the flow of fluid in pipe 12, each p.r.f. is automatically frequencymultiplied before digital frequency comparison and the digital measurement is converted to an analogue value. Each oscillation loop (" sing- around " loop) may include a time delay circuit to afford a p.r.f. difference for zero flow velocity and to compensate for inaccuracy in transducer pair spacings. For determining the direction of flow the frequency comparator output may be fed via a low-pass filter to a differentiator, a polarity-sensing circuit being connected to the output of the differentiator and feeding a pair of indicators, Figs. 11, 12, 13 (none shown). The frequency multiplication is arranged to automatically produce a predetermined multiplication factor irrespective of any variation in sing-around frequency due to changes in temperature and flow velocity, Figs. 6, 7 (neither shown). Frequency comparator 26 consists of a two-transistor NAND circuit, the output from which (Fig. 2(e), not shown) passes via an adjustable low-pass filter 28 (Fig. 2(f), not shown) and a squarer 30 (Fig. 2(g), not shown), to digital-to-analogue converter comprising a Schmitt trigger circuit (Fig. 2(h), not shown), a one-shot multivibrator to provide pulses of fixed duration (Fig. 2(i), not shown), and a smoothing circuit, Fig. 8 (not shown).