| 摘要 |
PURPOSE:To raise the accuracy of a range finding by an ultrasonic wave, by compensating a variation of a propagation characteristic of the ultrasonic wave in accordance with a characteristic of the atmosphere. CONSTITUTION:Comparison with reference voltage is executed in a comparator 7 of a comparing circuit 6, an ultrasonic receiving signal exceeding a prescribed level is outputted, and a range finding based on the time between transmission and reception is executed. This reference voltage is varied in accordance with a temperature, etc. by a reference value setting circuit 11 responding to a detecting atmospheric characteristic of a temperature, etc. by a thermistor 14. Accordingly, an ultrasonic receiving signal 1 whose variation of a propagation speed, etc. of an ultrasonic propagation characteristic by a temperature, etc. is outputted from the comparator 7. As a result, an error due to a variation of the atmospheric characteristic can be reduced and the accuracy of a range finding by an ultrasonic wave can be raised. |
