Ultrasonic rangefinder.

摘要

An ultrasonic rangefinder which measures distance to the ground by transmitting ultrasonic waves toward the ground and measuring the time which elapses until the reflected wave is received is shown. In order to reliably prevent erroneous measurement due to ultrasonic waves which travel to the receiver directly without striking the ground, the distance calculation is based on the time which elapses after transmission of the ultrasonic wave until the rate of change of the envelope of the received ultrasonic wave signal exceeds a prescribed value.