A rotary encoder, also called a shaft encoder, is an electro-mechanical device that converts the angular position or motion of a shaft or axle to analog or digital output signals.Rotary encoder is the device which measure the rotate speed and improve the speed quickly with PWM technology. The angle displacement of the angle encoder is increased or decreased by transforming the timing sequence and phase position relation of the angle encoder with two inner Photosensitive acceptor tube.

For rotary encoders, it is specified in arcseconds or arcminutes, and for linear encoders accuracy is typically given in microns.The lower resolution encoder can report a movement of 90 degrees just as accurately as the higher resolution model.