| 摘要 |
PURPOSE:To prevent a proximity switch device from malfunctioning by repeating the transmission and reception of an ultrasonic wave within a specific time at a specific period. CONSTITUTION:A received signal and a received timing signal from a receiving circuit 10 are inputted to a NAND 16 and a flip-flop FF 17 is set to output a positive potential (a) and a zero potential (b); and a zero-potential signal is inputted to the U/D terminal of an up/down counter 18 and a pulse output from the terminal Q2 of a frequency divider 2 and the output of an FF 21 are passed through a NAND 20 and an inverter 22 to obtain positive-polarity pulses, which are applied to a terminal CK through a NAND 23 to perform adding operation. At this time, the device does not reacts unless the received wave continues by more than specific pulses, so even if a short-time external noise is received, the device does not malfunction. If there is a long-time external noise, the noise signal and a positive pulse Q5 are inputted to a NAND 29 to obtain a negative pulse, which sets the FF 21 to cut off the NAND 20, so that a counter 18 stops counting.
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