What is Encoder? An encoder is a device that is used in many industries to provide feedback. In the most basic terms, an encoder, regardless of the type, which we will cover later, senses position, direction, speed, or counts. Encoders will use motion, under a variety of technologies, and translate it into an electrical signal. That signal is then sent back to a controlling device, such as a PLC, and is interpreted, meaning scaled, to represent a value that will then be used within the program.