Incremental rotary encoders emit a specific number of pulses per revolution (PPR) at equal intervals or per inch or millimetre with linear movement.
A single-channel output is used in applications where the direction of movement is irrelevant. If the direction of rotation is of interest, a two-channel, 90° phase-shifted square-wave output signal is used; the phase shift between the signals identifies the direction of rotation. This is important for processes with reversal of the direction of rotation, in which the "net position" is to be determined when the object is at a standstill or subject to mechanical vibrations.
For example: Machine vibrations when an object is at a standstill can cause a unidirectional rotary encoder to produce a stream of pulses which could mistakenly simulate a machine movement. Misleading the control system can be prevented if a quadrature counter is used. If more precise resolution is required, the counter can achieve a doubling (x2) of the number of counted pulses / revolutions or movements in inches by counting the number of rising and falling edges of a pulse train of a channel. Counting both edges (rising and falling edges) for both channels increases the resolution by four times (x4).
The output of an incremental rotary encoder shows the movements of a recorded object. To display the position, the pulses must be recorded using a counter. This number is important in the event of a power failure or interference due to transient responses to vibrations. When restarting, the device must be reset to a reference or starting position (home position) in order to initialise the position counter.
Some incremental rotary encoders produce another signal, also called a "marker," "index," or "Z-channel”. This signal, generated once per revolution by rotary shaft encoders or with linear scales at a precise known point, is often used to determine a specific position. It is used in particular when moving to a starting position (homing sequence).