Optical Encoder - Fundamentals
The most popular type of encoder is the optical encoder, which consists of a rotating disk, a light source, and a photodetector (light sensor).
The disk, which is mounted on the rotating shaft, has coded patterns of opaque and transparent sectors. As the disk rotates, these patterns interrupt the light emitted onto the photodetector, generating a digital or pulse signal output.
The encoding disk is made from:
Glass, for high-resolution applications (11 to >16 bits)
Plastic (Mylar) or metal, for applications requiring more
rugged construction (resolution of 8 to 10 bits)