Patent ID: 7612557

Claim:
An eddy current type sensor for detecting a conductor comprising: a LC circuit including a detection coil for generating alternating magnetic field and a capacitor connected in parallel with the detection coil; an oscillator for supplying an alternating current of a predetermined oscillation frequency to the LC circuit; and a signal processing circuit for determining position of the conductor relative to the detection coil based on a signal voltage outputted from the LC circuit, wherein the signal voltage has a first voltage value when the detection coil is separated from the conductor by a first distance and has a second voltage value when the detection coil is separated from the conductor by a second distance less than the first distance, a voltage difference between the first and second voltage values has a first difference value at a first temperature and has a second difference value at a second temperature less than the first temperature, the first and second difference values become equal to each other at a first frequency and a second frequency less than the first frequency, and the oscillation frequency is set close to the first frequency or the second frequency.