| 摘要 |
To measure flow by means of ultrasonic waves, two ultrasonic transducers, one of which functions as transmitting transducer and the other as a receiving transducer, are arranged at a distance apart in a measurement tube. To determine the flow, the phase shift between the transmitter signal and the receiver signal is measured digitally by counting, in the measurement time-intervals corresponding to the phase shift, the period of a signal with a counting frequency substantially greater than the frequency of the transmitter signal. The starting phase, which incudes the counting frequency signal at the beginning of each counting operation in function of the measurement time-interval, is varied from one measurement time-interval to the next, in a measurement cycle comprising several consecutive measurement time-intervals and the count values obtained during the measurement time-interval are evaluated to obtain a measurement value with a higher resolution. |
