The encoder code wheel (or disc) defines the transmission code of pulses; it is formed by a support made of plastic, glass or metallic material, on which is engraved a pattern of alternated clear (transparent) and opaque segments.

In incremental encoders transparent segments alternate with opaque ones along a single circular ring on the disc; the number of these segments determines the number of pulses and, therefore, also the resolution of the device. Since there is no absolute position in the incremental measure system, it’s often used an additional segment called “zero pulse” as a univocal reference to determine the starting position.

Incremental code wheel

In absolute encoders transparent segments alternate with opaque ones along several circular rings, according to a pattern that provides the position in a binary code configuration. To avoid encoding errors, a variant of the natural binary code is employed, the Gray code, which has the distinctive characteristic to vary only one binary digit between a code and the following one, ensuring a higher reliability both in code generation and decoding.

2 bit disc with binary code	2 bit disc with Gray code