A rotary encoder is a sensor for measuring angles of rotation. It delivers digital output signals which are decoded for evaluation.Therefore, rotary encoders are often also referred to as encoders. A distinction of rotary encoders is made between incremental and absolute encoders. There are rotary encoders with and without integral bearing.

Incremental rotary encoders can be evaluated based on the acquisition of a certain number of pulses per revolution, including a repeating zero pulse per revolution as a reference. By evaluating two different tracks that can be distinguished by a quarter pulse, the direction of the rotation can be established in addition to the speed. The acquisition is done via a magnetic wheel, line disk or by means of gear wheel flanks.

Absolute rotary encoders use a coding disk for the acquisition of revolutions and angles of rotation. Since each position on the coding disk is unique, no reference is required. This is unlike the evaluation of incremental rotary encoders. The number of revolutions are counted, for example, by a connected gear or by pulse wire sensors.