The incremental encoder is so defined since it tracks the increase (variation) in relation to a position taken as a reference point, independently from the direction of rotation. The incremental encoder senses rotation, speed and acceleration by counting the number of pulses sent by the output circuit, although the zero point of the machine must be reset at every new start.

Incremental encoders can have 3 channels (A, B, Z) or integrated commutation signals (Hall effect phases).

3-channel incremental encoder

The incremental encoder usually provides two types of squared waves, out-of-phase of 90° electrical degrees, which are usually called channel A and B. Channel A gives information only about the rotation speed (number of pulses in a certain unit of time), while channel B provides data regarding the direction of rotation, according to the sequence produced by the two signals. Another signal, called Z or zero channel, is also available; it gives the absolute “zero” position of the encoder shaft and is used as a reference point. 

Integrated commutation phases (Hall effect phases)

There are other encoders that integrate additional electrical output signals called incremental encoders with integrated commutation signals, normally used as motor feedback. These additional signals simulate the Hall phases, which are usually employed in brushless motors and are generally formed by magnetic sensors.
In Eltra’s encoders these commutation signals are optically generated and are represented as 3 squared waves, shifted by 120° electrical degrees. These signals are used by the driver that controls the motor to generate the correct voltage phases needed to determine the rotation.

These commutation pulses can be repeated many times within one mechanical revolution, since they depend directly on the number of poles of the connected motor.

For further information, please check the complete PDF on-line.