| 摘要 |
PURPOSE:To prevent mutual interference between adjacent ultrasonic wave switches by providing a pulse width discriminating means passing only a reflected wave having a longer pulse width than that of the transmitted ultrasonic wave pulse of a transmission means among received ultrasonic waves. CONSTITUTION:When the ultrasonic wave received by a receiver 21 has a prescribed level or above, the pulse corresponding to it is outputted from a waveform shaping circuit 24. The pulse width discriminating circuit 25 passes an input signal whose pulse width is wider than that of the transmission pulse of a transmission section 20. The output signal of the circuit 25 is inputted to a detection gate circuit 26 and after a time set by a near distance setting circuit 31 is elapsed after an ultrasonic wave pulse is transmitted, only the output signal of the circuit 25 informs it to the detection gate circuit 26 until the end of time set by a remote distance setting circuit 32. Then the reflected wave of the ultrasonic wave pulse sent from other adjacent ultrasonic wave switch is eliminated and no malfunction is caused without taking synchronization.
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