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Incremental Encoders

Incremental shaft encoders also known as Incremental Rotary Shaft Encoders are ideal for monitoring sensing a rotating shaft, or even linear position sensing when used in conjunction with ball screws etc, rollers. When integrated into a control system, they provide speed, position, acceleration & direction feedback data to the system. Incremental encoders produce a series of pulses directly proportional to movement of its shaft. Incremental encoder pulses usually consist of two square-wave signals known as A channel & B channel (also known as 1 channel & 2 channel).

The two digital square-wave signals are identical, but are phase shifted by 90 electrical degrees from each other. One of the square-wave pulses (A or B) could be simply counted measured to provide position and or speed, acceleration etc. However, by using the B signal together with the A signal, with the correct decoding it is possible to determine direction of rotation of the shaft so that pulses can be added in one direct, whilst deducted in the opposite direction. In addition it is possible to use the A & B signals to multiply the resolution by 2x or 4x, again depending on the type of decoding required.

An incremental encoder is also provided with a digital Marker Pulse (also known as a Reference pulse, Z channel, or 0 channel). This is a single pulse per revolution of the shaft. The pulse can be used by the control system counter as a reset, reference, checking pulses, revolution counter as well as many other functions. The Marker channel can usually be supplied in various forms such as, un-gated (of no fixed width), gated with A (only high when A is high), gated with B (only high when B is high), or gated with A & B (only high when A & B are high).

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