FREMGANGSMAADE OG APPARAT TIL STROEMNINGSMAALING VED ULTRALYD

PCT No. PCT/EP89/00775 Sec. 371 Date Feb. 28, 1990 Sec. 102(e) Date Feb. 28, 1990 PCT Filed Jul. 6, 1989 PCT Pub. No. WO90/00723 PCT Pub. Date Jan. 25, 1990.For flow rate measurement by means of ultrasonic waves, on a measuring tube two ultrasonic transducers are arranged spaced apart from each other, one operating as transmitting transducer and the other as receiving transducer. For determining the flow rate the phase shift between the transmission signal and the reception signal is measured digitally in that the measuring time intervals corresponding to the phase shift the periods of a signal are counted with a counting frequency which is substantially greater than the frequency of the transmission signal. The start phase which the counting frequency signal has at the beginning of each counting operation with respect to the measuring time interval is varied from measuring time interval to measuring time interval in a measuring cycle including a plurality of successive measuring time intervals and the counts obtained in the course of the measuring cycle are evaluated to form a measured value with increased measurement resolution.