| 摘要 |
PROBLEM TO BE SOLVED: To provide a method and an apparatus for ultrasonic flow velocity measurement, where the arrival timing of received waves can be specified with good accuracy and the flow velocity can be measured with high accuracy. SOLUTION: Ultrasonic waves, which are transmitted from an ultrasonic vibrator 2 and an ultrasonic vibrator 3, are received by the ultrasonic vibrator 3 and the ultrasonic vibrator 2 which are opposed to each other. The gain of their received waves W is adjusted, and their amplitude is changed. Whether the amplitude of the gain-adjusted received waves W agrees with a preset reference, value K is discriminated. This series of operations is repeated, until the peak part P of the maximum half waves of the received waves W agrees with the reference value K while the gain is changed at each discrimination. A point of zero-crossing time after the received waves W whose gain is adjusted, so as to correspond to the reference value reaches a threshold E is regarded as the arrival timing of the received waves W.
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