Abstract: An ultrasonic flowmeter for bidirectionally measuring the rate of flow of a fluid. Two spatially separated ultrasonic transducers alternately transmit and receive bursts of ultrasonic drive pulses through a fluid to be measured. A reference signal generator generates, for said bursts of drive pulses, reference transitions which occur controllable times after the beginnings of the bursts. A sampling signal generator generates sampling signals that define a plurality of sampling windows for use in timing the transitions of the received signal. The timing of the reference transition is dynamically adjusted so that the transitions of the received signal remain within respective sampling windows.

Abstract: In a fluid flow measuring apparatus, a flow of fluid is established through the apparatus at a first known flow rate. For each of two states of the apparatus, electrical drive pulses are applied to transmitting transducers. From the output signals of receiving transducers upcount and downcount values are derived which are indicative of the elapsed times between the drive pulses applied to the transmitting transducers and the zero crossings of the output signals of the receiving transducers, with the values being stored in a form that indicates the frequency of occurrence thereof. At least one test is applied to the stored upcount and downcount values to determine if the values have an acceptable distribution and if so using the stored values to determine a first calibration value for the apparatus. Then a flow of fluid is established through the apparatus at a second known flow rate. Again, for each of two states of the apparatus, electrical drive pulses are applied to transmitting transducers.