To provide a high frequency electromagnetic induction switch for use in radio water quantity inspection unit which can operate for a long term without requiring maintenance/management, e.g. replacement of battery.
A capacitor C1 having capacity resonant in high frequency induction field is connected across a coil L1 formed by winding a thin insulated wire tubularly. A diode D for converting high frequency voltage into DC current is connected between one terminal of the coil L1 and the gate terminal of a field effect transistor Q1 and a voltage equal to gate cut-off voltage is applied to the field effect transistor Q1 through one terminal of the coil L1. A DC voltage is applied through a resistor to the drain terminal of the field effect transistor having source terminal connected with an earth terminal. A receiving section controls the electric switch of a CMOS integrated circuit IC2 based on the fluctuation of DC current at the drain terminal of the field effect transistor incident to fluctuation of high frequency induction field.
OKINO HIDEAKI
MASUDA YUKIO
KYOWA SUIDO KK
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