ULTRASONIC DISTANCE MEASURING DEVICE AND ULTRASONIC DISTANCE MEASURING METHOD

摘要

Ultrasonic transducers (52a, 52b) receive ultrasonic waves driven by a drive signal the frequency of which changes with time. A cross-correlation function computation unit (57) computes a cross-correlation function between the received ultrasonic waves and the drive signal. An envelope generation unit (58) determines the envelope of the cross-correlation function. A normalizing unit (62) normalizes the envelope. A transmission time calculation unit (60) detects a zero cross point at which a straight line that connects two points on the rising curve of the normalized envelope intersects a zero level, and on the basis of a time obtained by adding a prescribed time to the zero cross point, calculates the transmission time of the ultrasonic waves from when the ultrasonic waves are transmitted from an ultrasonic wave generation device until reception at the ultrasonic transducers (52a, 52b).