CIRCUIT SYSTEM FOR DETECTING PHYSICAL OUANTITY SUCH AS FLOW RATE OF FLOWING MEDIUM BY SUPERSONIC METHOD

摘要

In order to obtain an accurate value of the propagation time of the ultrasonic signal, the arrival of the high-frequency ultrasonic vibration train (S8) at the receiver must be established very accurately. Since the amplitude of the received signal (S8) rises starting from zero, the start of the same is not precisely defined. Consequently, a delayed instant at which the received vibration is at approximately the maximum amplitude is chosen for establishing the accurate arrival time. For this purpose, the ultrasonic signal is used to derive an electric square-wave signal (S12) which is synchronous with said ultrasonic signal, and said square-wave signal is compared in a phase detector (15) with a signal (S14) which is delayed with respect to the start of the vibration train (S8). The signal delivered by the phase detector alters the arrival delay time in such a way that the delay signal coincides precisely with a specific edge of a pulse of the square-wave signal (S12). As a result, the arrival time is accurately defined and the propagation time of the signal can be determined by means of known methods, e.g. counting the pulses of a clock pulse sequence. IMAGE