Inductive proximity switch and method of operation of an inductive proximity switch

An inductive proximity switch comprising:

• a signal oscillating circuit and a reference oscillating circuit;
• a multiplexer circuit designed to alternately activate the signal oscillating circuit and the reference oscillating circuit;
• a driver circuit having an oscillator designed to operate the activated signal oscillating circuit and the activated reference oscillating circuit with an oscillator frequency, respectively;
• a detection module designed to detect an oscillation parameter of the activated signal oscillating circuit and an oscillation parameter of the activated reference oscillating circuit, respectively;
• and
• an evaluation module designed to determine a difference signal on basis of the oscillation parameter of the activated signal oscillating circuit and the oscillation parameter of the activated reference oscillating circuit and to generate a control signal depending on the difference signal;
• wherein
• the signal oscillating circuit is designed such that the oscillation parameter for the signal oscillating circuit depends on a position of a target in a detection zone;
• the reference oscillating circuit is designed such that the oscillation parameter for the reference oscillating circuit is essentially independent of the position of the target in the detection zone;
• the oscillation parameter relates to an amplitude of the activated oscillating circuit;
• the signal oscillating circuit includes a signal coil and the reference oscillating circuit includes a reference coil;
• the reference coil has a plurality of sub-windings and the sub-windings are designed in a counter-wound manner with respect to one another;
• and
• the reference coil has four sub-windings or a whole-number multiple of four sub-windings.

An inductive proximity switch comprising:

• a signal oscillating circuit and a reference oscillating circuit;
• a multiplexer circuit designed to alternately activate the signal oscillating circuit and the reference oscillating circuit;
• a driver circuit having an oscillator designed to operate the activated signal oscillating circuit and the activated reference oscillating circuit with an oscillator frequency, respectively;
• a detection module designed to detect an oscillation parameter of the activated signal oscillating circuit and an oscillation parameter of the activated reference oscillating circuit, respectively;
• and
• an evaluation module designed to determine a difference signal on basis of the oscillation parameter of the activated signal oscillating circuit and the oscillation parameter of the activated reference oscillating circuit and to generate a control signal depending on the difference signal;
• wherein
• the signal oscillating circuit is designed such that the oscillation parameter for the signal oscillating circuit depends on a position of a target in a detection zone;
• the reference oscillating circuit is designed such that the oscillation parameter for the reference oscillating circuit is essentially independent of the position of the target in the detection zone,
• the signal oscillating circuit includes a signal coil and the reference oscillating circuit includes a reference coil,
• the signal coil and the reference coil have essentially the same inductance,
• the reference coil has four sub-windings or a whole-number multiple of four sub-windings,
• the counter-wound sub-windings are designed such that high frequency fields generated by the sub-windings substantially cancel themselves out in the activated reference oscillating circuit.