| 摘要 |
PURPOSE:To calculate the arrival time of a reflected wave with good accuracy, by comparing a threshold value slightly larger than electric noise and smaller than sound noise by several figures with the amplitude of a reflected ultrasonic wave using the arrival time discrimination part of a signal discrimination means. CONSTITUTION:An ultrasonic pulse generating means II generates an ultrasonic pulse in synchronous relation to the timing pulse from a measuring control pulse generating means I to transmit the same to an article 4 to be measured from an ultrasonic transmitter III. The reflected wave received by an ultrasonic receiver IV and a signal processing means V is inputted to a signal discrimination means VI. An arrival time discrimination part compares the amplitude of a signal with a threshold value close to 0 as near as possible, that is, a threshold value E1 slightly larger than electric noise. Then, the time when the amplitude of the signal exceeds the threshold valve E1 is set to the arrival time of the reflected wave to output a discrimination signal.
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