Encoders

Optical and Magnetic Encoders sense position or orientation for use as a reference or active feedback to control position:
A rotary encoder converts rotary position to an analog (e.g., analog quadrature) or digital (e.g., digital quadrature, 32-bit parallel, or USB) electronic signal.
A linear encoder similarly converts linear position to an electronic signal. Potter-GMH Technologies offer a wide variety of encoders.