| 摘要 |
PROBLEM TO BE SOLVED: To easily discriminate a reflected wave with respect to noise and to expand a measuring range of an approach distance. SOLUTION: A controller 10 is equipped with a microcomputer 20 for outputting an oscillation pulse signal (a) to a signal line 39 via a modulation transistor 18 and inputs the reflected wave signal f', obtained by passing the receiving signal from the sensor part 40A through a detector 33 to detect obstacles or the like. In the sensor part 40A, an ultrasonic microphone 42 is driven by an output circuit 50, to send out an ultrasonic wave and the signal d' obtained through amplification a receiving signal c' by an antilogarithmic amplifier 60 is outputted to the signal line. The input side of the antilogarithmic amplifier is grounded by a prescribed time, containing the drive pulse of the ultrasonic microphone by a transistor 65 to be attenuated. Since reflected waves are amplified to the same level, regardless of the distance up to the obstacle or the like by the antilogarithmic amplifier, even if noise is mixed from the signal line, the discrimination of reflected waves is easy and the reverbration of the ultrasonic microphone is shortened by attenuation duet to the transistor 65 and a detectable distance becomes shorter.
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