| 摘要 |
PURPOSE: To make high accuracy measurement even with ultrasonic waves having a relatively low frequency by sensing the zero-cross point where the virtual envelope tying the peak points of the received waveform intersects the zero level of the waveform. CONSTITUTION: For the transmitted waves, the rising time of the first wave is sensed on the basis of the time when the supply of drive pulse to a vibrator is started. The first wave rising time of the received waves is determined by the zero-cross point where the virtual envelope tying together a plurality of peak points appearing on the waveform intersects the zero-level. Because any wave included by the waveform damps with the same damping factor, the virtual envelope tying a plurality of peak points passes the same zero-cross point irrespective of the size of the damping. That is, the time from the zero- cross point to the first wave rising time (offset time) becomes constant regardless of the distance till the object to be measured. Accordingly the elapsed time from the first wave rising time of the transmitted waves to the first wave rising time of the received waves can be measured without involving an error. |
