Eddy current system with interference signal rejection

An eddy current sensor having a coil set with a reference coil and a measuring coil, and a sine generator whose output signal is applied to the reference coil and the measuring coil. The output signals of these coils are subtracted from one another by a first subtracter, whose ouput signal is applied to a first modulator and to a second demodulator through a 90 degree phase shifter. The output signal of the sine generator is provided to the first and second demodulators as an additional signal via a phase shifter having an adjustable phase angle. A phase angle is selected such that the interference signals have a specified direction in the formed signal plane. The output signal from the first demodulator is applied through an amplifier having an adjustable amplifying factor (a) to an input of a second subtracter. Similarly, the output signal of the second demodulator is provided through an amplifier having an adjustable amplifying factor (b) to the second subtracter. The second subtracter output provides an output signal from which a trigger threshold can be formed and an object to be identified measured.