Output signal processing circuit for eddy current sensor and output signal processing method for eddy current sensor

An eddy current sensor output signal processing circuit that processes first and second output signals output by an eddy current sensor including first and second coils that respectively output the first and second output signals, the output signal processing circuit comprising:

• a first mixer circuit that accepts the first output signal and a signal of a predetermined frequency as input, multiplies the two input signals, and outputs an output signal obtained by the multiplication;
• a first low-pass filter that accepts the output signal output by the first mixer circuit as input, cuts a high-frequency signal included in the output signal received as input, and outputs at least a DC signal;
• a second mixer circuit that accepts the second output signal and the signal of the predetermined frequency as input, multiplies the two input signals, and outputs an output signal obtained by the multiplication;
• a second low-pass filter that accepts the output signal output by the second mixer circuit as input, cuts a high-frequency signal included in the output signal received as input, and outputs at least a DC signal;
• and
• a first subtractor circuit that accepts the DC signal output by the first low-pass filter and the DC signal output by the second low-pass filter as input, obtains a difference between the two input DC signals, and outputs the obtained difference.

An eddy current sensor assembly comprising:

• an eddy current sensor including an exciting coil capable of accepting an excitation signal and generating a magnetic field, and a detecting coil capable of detecting the magnetic field and outputting a detection signal;
• and
• an output signal processing circuit that processes the detection signal, wherein
• the output signal processing circuit includes
• a generator circuit capable of generating a noise reduction signal for reducing noise from the excitation signal or the detection signal, and
• an adder circuit capable of adding the noise reduction signal generated in the generator circuit to the detection signal to generate a noise-reduced signal in which noise included in the detection signal is reduced.

An eddy current sensor output signal processing circuit that processes a first detection signal and a first dummy signal output by an eddy current sensor including a first exciting coil capable of accepting an excitation signal as input and generating a first magnetic field, a first detecting coil capable of detecting the first magnetic field and outputting the first detection signal, and a first dummy coil capable of detecting the first magnetic field and outputting the first dummy signal, the output signal processing circuit comprising:

• a first resistance bridge circuit capable of outputting a difference between the first detection signal and the first dummy signal as a first difference signal;
• a first generator circuit capable of generating a first noise reduction signal for reducing noise from any of the excitation signal, the first detection signal, the first dummy signal, and the first difference signal;
• and
• a first adder circuit capable of adding the first noise reduction signal generated in the first generator circuit to the first difference signal to generate a first noise-reduced signal in which noise included in the first difference signal is reduced.

An eddy current sensor output signal processing circuit that processes first and second detection signals and first and second dummy signals output by an eddy current sensor including first and second exciting coils capable of accepting an excitation signal as input and respectively generating first and second magnetic fields, first and second detecting coils capable of detecting the first magnetic field and the second magnetic field, and respectively outputting the first and second detection signals, and first and second dummy coils capable of detecting the first magnetic field and the second magnetic field, and respectively outputting the first and second dummy signals, the output signal processing circuit comprising:

• a first resistance bridge circuit capable of outputting a difference between the first detection signal and the first dummy signal as a first difference signal;
• a second resistance bridge circuit capable of outputting a difference between the second detection signal and the second dummy signal as a second difference signal;
• and
• a third adder circuit capable of adding together the first difference signal and the second difference signal.