| 摘要 |
An ultrasonic flowmeter includes: a transmitting device for transmitting a continuous ultrasonic wave into a fluid to be measured; a receiving device spaced by a predetermined distance from the transmitting device, for receiving the ultrasonic wave propagating in the fluid; a phase difference detecting circuit for detecting the phase difference between the transmission signal of the transmitting device and the reception signal of the receiving device by converting the phase difference into a time interval enlarged by a frequency mixing means; and a processing circuit for outputting a signal representative of the flow rate of the fluid in response to the output of the phase difference detecting circuit, whereby the flow rate of the fluid is measured with high accuracy by utilizing the phase difference between the signals at the transmission point and the reception point.
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