Ultra-sonic gas flow meter that uses a pair of transducers to find the time different for a signal to travel with the flow and against the flow

摘要

Disclosed is an ultra-sonic gas flow rate meter comprising a measurement path, a pair of ultra-sonic transducers which, transmit and receive ultra-sonic pulse measurement signals across the measurement path. The meter has an electrical control circuit which determines the time that an ultra-sonic pulse measurement signals take to traverse the measurement path, used to find the rate of gas flow. The control circuit has a pulse signal generator, and a square wave generator to produce signals of duration 2T. The pulse signal causes the first ultra-sonic signal generator to transmit an ultra-sonic pulse, which is received by the second ultra-sonic transducer to provide a receive signal. The timing circuit of the control circuit has a ramp signal generator and a sample and hold circuit such that when an ultra-sonic pulse is received by the second transducer, an interval of time (dt1) is found. The interval dt1 corresponds to the time from transmitting an ultra-sonic pulse to a first occurrence of square wave transition, summed with a whole number (n) of half wave periods (I). The number n is determined by the number of square wave signal transitions further summed with an interval (dt2) of time corresponding to the time taken from the last square wave transition to the time of reception of the ultra-sonic pulse by the second transducer. The period of time (dt1 + dt2) is determined from a value of a characteristic of the partial square wave transition at the time of transmission and at the time of reception, respectively, to enable determination of the time the signal takes to traverse the measurement path (dt1 + nT + dt2).