An optical encoder is an electromechanical device which produces an electrical signal output proportional to the linear displacement of a linear guide or the angular position of an input shaft.

Open encoders are exposed and feature no external integrated enclosure. The advantages of open optical encoders include the effective elimination of backlash, shaft wind-up (torsion) and other mechanical hysteresis errors.

The readhead measures position by optically sensing the regularly spaced scale markings and outputs this information as an analogue or digital signal.

The signal is subsequently converted into a position reading by a digital readout (DRO) or motion controller.