| 摘要 |
PURPOSE:To enable measurement even when the ultrasonic wave propagation time is larger than the pulse width of the oscillation frequency, by providing two ultrasonic wave converters and a forward/backward switching circuit. CONSTITUTION:An output frequency (f) continuously oscillated form an oscillation circuit 10 is controlled intermittently through a counter circuit 20 and a gate circuit 30. Ultrasonic wave converters T and R convert an output of the circuit 30 into an ultrasonic wave signal and does the ultrasonic wave signal into an electrical signal respectively. A forward/backward switching circuit K changes over the propagation direction of the ultrasonic signal with respect to flow velocity V by switching the circuit 30 over to the converters T and R. Then, the ultrasonic wave signal is converted into an electrical signal, which is supplied to an up/down circuit 50 through a square wave converting circuit 41, a shift register 42 and an exclusive OR circuit 31 and respective outputs of the circuit 50 the one when the propagating direction of the ultrasonic wave signal is forward with respect to the flow velocity V and the other when it is backward are introduced into a addition circuit SIGMA and a subtraction circuit DELTArespective-to compute. At this point, once an output of the circuit SIGMA is feedback to a circuit 10 through a D/A converter 60 to keep an oscillation frequency output constant, an output of the circuit DELTA is outputted as flow velocity V.
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