| 摘要 |
PURPOSE:To prevent malfunctioning due to pulsative noises, by forming a reception trigger only when a receiving pulse with the time range exceeding a fixed value is received to stop the measurement of time. CONSTITUTION:A probe 11 is driven with a transmitting circuit 12 to transmit an ultrasonic wave. The reflected ultrasonic wave is received with the probe 11, the output of which is fed into a pulse noise removing circuit 20 through a receiving circuit 13. Only when receiving a receiving pulse with the time range exceeding a fixed value, the pulse noise removing circuit 20 form a receiving trigger to stop the measurement of time with a time measuring circuit 14. When the reflected wave is not received and a disturbance wave is detected with the time range more than equal to the reflected wave of the ultrasonic wave, sampling by a sample holding circuit is forbidden with a non-received wave input compensation circuit 30 and a disturbance counter measure circuit 40 to prevent malfunctioning. |
