Optical incremental encoders are a mean for capturing speed and traveled distance on a motor. Counting the pulses tells the application how many revolutions, or fractions of, the motor has turned. Rotation velocity can be determined from the time interval between pulses, or by the number of pulses within a given time period. Because they are digital devices, incremental encoders will measure distance and speed with perfect accuracy.

To count up or down according to motor direction, quadrature encoders have dual channels, A and B, which are electrically phased 90¡ apart. Direction of rotation can be determined by monitoring the phase relationship between the two channels.

The encoder's speed measurement makes it possible to use the controller in closed loop speed mode without the need for calibration and drifting problems that can occur using analog tachometer. The pulse count feature is very useful to measure the actual traveled distance by the robot. It can also be used to perform sophisticated and high precision positioning algorithms.