An encoder is a sensor which turns a position into an electronic signal.

There are two forms:

• Absolute encoders give an absolute position value.
• Incremental encoders count movement rather than position. With detection of a datum position and the use of a counter, an absolute position may be derived.

The position may be measured as either linear or angular position

• Linear encoder, converts linear position to an electronic signal
• Rotary encoder, converts rotary position to an electronic signal