The relay has the following functions: 1) Expand the control range: For example, when the control signal of a multi-contact relay reaches a certain value, multiple circuits can be switched, disconnected, and connected at the same time according to different forms of contact groups. 2) Amplification: For example, sensitive relays, intermediate relays, etc., with a very small control quantity, can control a large power circuit. 3) Comprehensive signal: For example, when multiple control signals are input to a multi-winding relay in a prescribed form, they will be relatively integrated to achieve the predetermined control effect. 4) Automatic, remote control, and monitoring: For example, the relay on the automatic device and other electrical appliances can form a program control circuit to realize automatic operation. A relay is an electrical control device. It has an interactive relationship between the control system (also called the input loop) and the controlled system (also called the output loop). Usually used in automated control circuits, it is actually an "automatic switch" that uses a small current to control the operation of a large current. Therefore, it plays the role of automatic adjustment, safety protection, and conversion circuit in the circuit.