Offset correction device and position measuring device

An offset correction device comprising:

• a processor configured to adjust an amplitude of a detection signal output from an encoder by adjusting a gain of the detection signal so that the amplitude is within a predetermined range, by increasing the gain when an intensity of the detection signal is less than a first threshold and decreasing the gain when the intensity of the detection signal is greater than a second threshold, and configured to correct an offset of an amplitude center of the detection signal;
• and
• a storage that stores a relationship between the gain and an offset amount in advance,
• wherein the encoder has a transmitter coil configured to generate magnetic flux, a plurality of conductors that are arrayed in a measurement axis direction, are configured to be electromagnetically coupled with the magnetic flux generated by the transmitter coil and generate magnetic flux that fluctuates in a predetermined spatial period in the measurement axis direction, and a receiver coil configured to be electromagnetically coupled with the magnetic flux generated by the plurality of conductors and detect a phase of the magnetic flux,
• wherein the encoder outputs sine wave signals of which phases are different from each other, as the detection signal,
• wherein the processor refers to the relationship stored in the storage when the processor changes the gain, obtains the offset amount corresponding to the changed gain, and corrects the offset based on the obtained offset amount, and
• wherein the processor varies the predetermined range according to a value of the gain, by changing the first threshold and the second threshold according to the gain.