| 摘要 |
PROBLEM TO BE SOLVED: To obtain an ultrasonic sensor by which a measurement can be performed with high accuracy even by ultrasonic waves at a comparatively low frequency. SOLUTION: An ultrasonic sensor detects the rise time of a first wave regarding transmitted waves. In addition, regarding received waves, it detects a plurality of peak points P which appear in their waveform, and it detects a waveform reference point in which the time base coordinates of a virtual envelope connecting the peak points P become a minimum value. Then, a prescribed offset time is added to the time of the waveform reference point for the received waves, the rise time of a first wave in the received waves is computed, and the time which elapses from the rise time of the first waves in the transmitted waves up to the rise time of the first wave in the received waves is computed. On the basis of its computed result, a distance up to an object to be measured is computed. |
