A rotary encoder is a device that can keep track of how much something has turned. This is called its angular position. That information is useful to know how far a motor has turned, for example.
Basic types[change | change source]
Absolute[change | change source]
An absolute encoder always keeps track of what value its on, even if it isn't powered.
Incremental[change | change source]
An incremental encoder only keeps track of changes. It gives off signals if it is turned one way or another.