What is the encoder index mark?
Our quadrature encoders feature two physical tracks, which generate three signals. One track generates two of the signals, A and B. These signals are phased in quadrature and carry both position and direction information. The second track generates the third signal; this signal changes state only once per revolution, and defines a unique point in the rotation. The mark on the second track which generates the state change is called the index mark. The index signal is often used to define a home position when used in conjunction with an external switch wired to one of the I/O.
