Encoder (incremental vs absolute)

Encoders turn motion into a signal a controller can read. Incremental encoders output pulses (usually two channels in quadrature, so direction is known) that the controller counts; after power loss the system must find a reference again, typically by driving to a home switch. Absolute encoders report a unique position everywhere, so the system knows where it is the moment it powers on.

Common technologies are optical (high resolution, sensitive to dust and condensation), magnetic (robust and inexpensive, often less accurate) and inductive or capacitive designs. Resolution, accuracy and repeatability are different specifications; a high-count encoder can still be inaccurate if it is mounted off-center.

Where it bites: homing routines add startup time and failure modes, encoder cables pick up electrical noise near motors, and contamination degrades optical encoders in harsh environments.