| 摘要 |
<p>PURPOSE:To enable prevention of malfunctioning by comparing duration time of an ultrasonic pulse received with upper and lower limits of pulse width which controlled at transmission side and removing out-of-range pulse as a noise. CONSTITUTION:An ultrasonic detector 100 on the side of a working vehicle transmits 101 an ultrasonic pulse. An ultrasonic detector 200 on the side of workers receives 201 the ultrasonic wave and a received pulse signal is received to be turned to generate (a monostable multivibrator circuit) 202 a lower limit pulse with a shorter pulse width and an upper limit pulse with a longer pulse width than the ultrasonic pulse transmitted from the device 100. Then, when duration time of the ultrasonic pulse received is longer than the duration time of the lower limit pulse and shorter than the duration time of the upper limit pulse, the device 200 outputs (an AND circuit) 203 a detection signal. Therefore, the ultrasonic pulse received is compared with the lower (upper) limit pulse and when the duration time thereof is longer (shorter), the ultrasonic pulse is selected. Thus, an impulse-oriented (durability owing to a broadcast wave or a tranceiver communication wave) noise mixed into a reception amplification circuit is removed.</p> |
