An encoder is a device that compiles a signal (such as a bit stream) or data into a signal form that can be used for communication, transmission, and storage. The encoder converts angular displacement or linear displacement into an electrical signal, which is called a code plate, which is called a yardstick. According to the readout Mode encoder can be divided into two types: contact and non-contact; According to working principle, the encoder can be divided into two types: incremental and absolute. The incremental encoder is to convert the displacement into a periodic electrical signal, then turn the electrical signal into a counting pulse, using the number of pulses to indicate the size of the displacement. Each position of an absolute encoder corresponds to a determined number, so its value is only related to the starting and ending position of the measurement, regardless of the intermediate process of measurement.