| 摘要 |
PURPOSE:To reduce the detection operating time of a proximity switch by always keeping the oscillating state of an LC parallel resonance circuit, that is, its generated voltage nearly constant. CONSTITUTION:A difference detection circuit 30 receives a generated voltage (e) of an LC parallel resonance circuit 10 and a prescribed reference value er to give a difference signal ES representing the difference of the both to a conversion gain adjusting circuit 40, which regulates the conversion gain of a voltage current conversion circuit 20 in a way that the generated voltage (e) is always nearly constant based thereupon. Then a comparator 50 compares a difference signal ES from the difference detection circuit 30 with a threshold value et to output a detection signal DS. Even when an object DBJ approaches an inductor 11 or is parted therefrom, the change in the oscillating state of the LC parallel resonance circuit 10 is very slight and then the operation is very rapid, then the detection time of the proximity switch is decreased by one order or over more than a conventional circuit.
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