Ultrasound Flow Sensor with a Modulo-2Pi for a Remaining Part Tracing

The invention relates to a method for determining the running time (t) of an ultrasound flow sensor ( 6 ) ultrasound signal ( 15 ) which is transmitted by an ultrasound transducer (A, B) to a measuring section (S), wherein the phase position (DeltaF) of said ultrasound signal ( 15 ) is determined with respect to a reference clock (8) and a remaining part (r(t)) is determined as a measure of the running time (tmes) of the ultrasound signal ( 15 ). The measurement of the running time can be carried out in a particularly robust manner with a minimum use of hardware, when the phase position (DeltaF) is determined with the aid of a quadrature-demodulation method consisting in inverting the received signal ( 15 ) in a segmented manner with the aid of a clock signal ( 8 ) and the phase of the off-set clock signal ( 9 ) and the remaining part (r(t)) is determined according to a characteristic quantity (ts) of the sound signal ( 15 ).