The output from incremental optical encoders and from many other types of measurement devices is known as a “quadrature” signal. A quadrature signal consists of two square waves 90° out of phase. The input channel on our encoder interface board counts the square wave transitions and determines direction by comparing whether channel A is leading channel B or vice-versa. The number of revolutions is determined by dividing the count by the number of pulses per revolution: e.g., 100 counts with a 1000 PPR (Pulses Per Revolution) encoder is equal to 36 degrees. Velocity is computed the same way by counting the number of pulses per second.