An encoder is a device (transducer) that is used to convert rotary or linear motion into useful information. The primary parameters determined are speed, rate, velocity, distance, position, or direction. A typical application will use one or more of these parameters as feedback to the controller in a motion control system.

British Encoder's rugged and reliable encoders are particularly suited to the most challenging applications in process and machine control, motor feedback, factory automation, robotics, web tensioning, etc. In addition to these applications, rotary optical encoders can also provide electronic commutation in brushless servo systems.

An ‘incremental’ encoder accurately records changes in position, but does not power up with a fixed relation between encoder state and physical position. Devices controlled by incremental encoders may have to "go home" to a fixed reference point to initialise the position measurement.

An incremental encoder works by providing an A and a B pulse output that provide no usable count information in their own right. Rather, the counting is done in the external electronics. The point where the counting begins depends on the counter in the external electronics and not on the position of the encoder. To provide useful position information, the encoder position must be referenced to the device to which it is attached, generally using an index pulse. The distinguishing feature of the incremental encoder is that it reports an incremental change in position of the encoder to the counting electronics.