A relay is an electrical control device. It is an electrical appliance that causes the controlled quantity to undergo a predetermined step change in the electrical output circuit when the input quantity (excitation quantity) changes to meet the specified requirements. 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.

Relay is an automatic switching element with isolation function, which is widely used in remote control, telemetry, communication, automatic control, mechatronics and power electronic equipment, and is one of the most important control elements.

Relays generally have a sensing mechanism (input part) that can reflect certain input variables (such as current, voltage, power, impedance, frequency, temperature, pressure, speed, light, etc.); The actuator (output part) of “off” control; between the input part and output part of the relay, there is also an intermediate mechanism (drive part) for coupling and isolating the input, functional processing and driving the output part.

As a control element, in summary, 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) Integrated 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.