| 摘要 |
PURPOSE:To achieve a high reliability of measurement, by forbidding the sampling of results of measurement when a disturbance wave is detected to remove an abnormal measured value. CONSTITUTION:A probe 11 is driven with a transmission circuit 12 to transmit an ultrasonic wave. The reflected ultrasonic wave is received with the probe 11, the output of which is fed to a time measuring circuit 14 through a receiving circuit 13. A disturbance wave monitoring circuit 41 in a disturbance counter measure circuit 40 detects a disturbance wave with the time range more than equal to the envelop of the reflected wave of the ultrasonic wave before the sampling of the results of measurement of the time measuring circuit 14. When the disturbance wave is detected, a sampling forbidding circuit 42 forbids the sampling of the results of measurement with a sample holding circuit 16. Malfunctioning with no received wave is prevented with a non-received wave input compensation circuit 30.
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