| 摘要 |
PURPOSE:To make possible highly accurate automatic measurement of the propagation time of ultrasonic wave by controlling the time interval between adjacent received waves to Ice equal to the period of a continuous oscillation wave and then measuring the period of the continuous oscillation wave. CONSTITUTION:An ultrasonic receiver 100 receives a multiple reflection signal which repeats reflection between an oscillation plate 3 and a reflector 4. The signal thus received is then amplified 6 and AGC amplifying sections 7, 8 amplify only the first and second received waves among multiple waves being received for each transmitting wave. The amplified signal is converted 9, 10 into a single pulse digital signal which is received by a continuous oscillation control circuit 27. The circuit 27 delivers a continuous oscillation signal having frequency fOUT and period t3 equal to an ultrasonic wave propagation time tl to a time measuring circuit 24. The circuit 24 measures the multiperiod component of the continuous oscillation wave by means of a counter having open reference clock and determines a single period time t3 based on the average value thereof. This constitution allows more accurate measurement than the frequency of reference clock. The measurement is employed as the propagation time tl for determining an absolute sound velocity. |
