What we usually use is an incremental encoder, which can directly input the output pulse signal of the rotary encoder to the PLC, and use the high-speed counter of the PLC to count the pulse signal to obtain the measurement result. Different types of rotary encoders have different phases of output pulses. Some rotary encoders output A, B, and Z three-phase pulses, some only have A and B phases, and the simplest is A phase.