Relay: Relay (Relay) is widely used in industrial automation, household appliances, automotive electronics, communication equipment and other fields. In the field of industrial automation, relays are often used in PLC (programmable logic controller) systems to achieve accurate control of production equipment; In household appliances, such as air conditioners, washing machines, etc., relays are responsible for controlling the switching of different functional modules and protecting circuits; In the field of automotive electronics, relays are involved in the electrical management of key links such as engine starting and lighting control. In the power system, the relay is used for the protection and automatic control of the power grid, such as overload protection, short circuit detection, etc. From the development of traditional electromechanical relays to solid-state relays, magnetic holding relays, photoelectric relays, etc., they have significantly improved in response speed, service life, reliability and so on, and better adapt to the needs of modern science and technology.