| 摘要 |
PURPOSE:To eliminate a measuring error caused by amplitude variation and to make it possible to always perform distance measurement with high accuracy, by discriminating a detection output based on an ultrasonic receiving wave through level discriminators or timers different in a threshold value. CONSTITUTION:The output of a detector 7 based on the reflected ultrasonic receiving wave from an object is inputted to discriminators 9, 12 respectively set to a small and a large threshold values in parallel. By the output of the discriminator 9, the counting of a counter 10 is stopped and an object distance calculation output is outputted through a latch circuit 15 while a timer 13 is operated. In addition, a gate 14 is opened during the timing period of the timer 13 and, when the output from the discriminator 12 is absent during this period, the output of the counter 10 is prohibited while the previous distance calculation output held in the circuit 15 is outputted and alarm generation is performed through an alarm output circuit 16. By this constitution, influence such as reflection loss and propagation loss are erased and distance measurement free from a measuring error caused by amplitude variation can be always performed with high accuracy. |
