An incremental rotary encoder, also known as a quadrature encoder or a relative rotary encoder, is a sensor used for the sensing rotary position or speed of a shaft. They can be either mechanical or optical. The mechanical type has two contacts that are actuated by cams on the rotating shaft. The mechanical type has less number of contacts make/break in each revolution as compared to the optical type. Also the contacts requires debouncing of the signals to get rid of the contact noise. Mechanical type encoders are typically used as digital potentiometers on equipment such as lab equipment and consumer devices.

In the optical type there are two gray coded tracks besides an optional indexing Track, on a glass or metal disc. It has two optical sensors to output the quadrature signal. The fact that incremental encoders use only two sensors does not compromise their accuracy. One can find in the market incremental encoders with up to 2,000 counts per revolution, or more. one example is omron's E6B2-CWZ6C 2000P/R 2M. The indexing or reference output activates once on each turn and is used for positioning alignment. The optical type is used when higher RPMs or a higher degree of precision is required.

Incremental encoders are used to track motion and can be used to determine position and velocity. This can be either linear or rotary motion. Very accurate measurements of position, velocity and direction can be made using the incremental encoders.

Figure 2: Track and Signal pattern

Signal Pattern

Signal can be Seen either
1. Series of Levels
2. Series of Edges

depending on the way the designer want to decode it. If a polling scheme is used, the signal can be considered as series of Levels. On the other hand if the interrupt Based system, it can be considered as series of Edges.

For a CW rotation, the series of Levels are  A B  0 0  1 0  1 1  0 1  0 0	For a CCW rotation, the series of Levels are  A B  0 0  0 1  1 1  1 0  0 0
For a CW rotation, the series of Edges are  A B  ^ 0 1 ^  v 1  0 v  ^ 0	For a CCW rotation, the series of Edges are  A B  0 ^  ^ 1  1 v  v 0  0 ^

Mechanical Encoder

The inside view is given below

Another view of the Cover and knob