| 摘要 |
PURPOSE:To prevent malfunctioning due to pulsative noises, by forming a receiving trigger to stop the measurement of time only when a receiving pulse is received with the time range exceeding a fixed value. CONSTITUTION:A probe 11 is driven with a transmission circuit 11 to transmit an ultrasonic wave. The reflected ultrasonic wave is inputted into a pulsative noise removing circuit 20 through a receiving circuit 13 and when a receiving pulse is received with the time range exceeding a fixed value, a receiving trigger is formed to stop the measurement of time with a time measuring circuit 14. Malfunctioning due to a disturbance with the time range more than equal to the envelop of the reflected wave of the ultrasonic wave or that when no received wave is inputted is prevented with the disturbance wave control circuit 40 and a non-received wave input compensation circuit 30. |
