Patent ID: 8779778

Claim:
A proximity switch comprising an actuator unit to be attached to an object, and a sensor unit for detecting the actuator unit without contact and for outputting a signal indicating said detection, the actuator unit comprising a first antenna coil, and the sensor unit comprising a second antenna coil; wherein the sensor unit comprises a transmitting circuit for driving the second antenna coil to transmit an electromagnetic wave at a constant frequency and a receiving circuit for detecting an external signal received by the second antenna coil, the transmitting circuit and the receiving circuit being connected to the second antenna; the actuator unit comprises a power supply circuit for rectifying an electromotive force generated in the first antenna coil from the first antenna coil to produce power, and a signal processing circuit for frequency-dividing a signal received by the first antenna coil, the frequency-divided signal being transmitted by the first antenna coil and the power supply circuit and the signal processing circuit being connected to the first antenna coil; and the sensor unit comprises a control circuit having a memory for registering a frequency of the frequency-divided signal transmitted from the actuator unit, the control circuit checking the external signal detected by the receiving circuit with operation of the transmitting circuit and the frequency registered in the memory, while controlling the operation of the transmitting circuit, to determine proximity of the actuator unit to the sensor unit.