Ultrasonic flowmeter

Abstract

An ultrasonic flowmeter has oscillators, a transmitterfor transmitting burst waves BURST, amplifiersfor amplifying a received signal, a first comparatorfor checking whether the crest of the amplified signal falls within a predetermined range, a second comparatorfor checking whether the amplified signal exceeds a predetermined threshold, a third comparatorfor detecting zero-cross points in the amplified signal, and a controllerincluding a time counter for measuring the propagation time from when the burst waves are transmitted until when the amplified signal reaches a zero-cross point. The time counter has a low-speed clock, a mid-speed clock whose frequency is calibrated with the low-speed clock and whose propagation time is shorter than that of the low-speed clock, and a high-speed clock whose frequency is calibrated with the mid-speed clock and whose propagation time is shorter than that of the mid-speed clock.