A relay is a device that indirectly controls high-voltage and high-current circuits by using the on-off of weak current circuits and low voltages. An electromagnetic relay is a switch that uses an electromagnet to control a working circuit.
Two basic functions of electromagnetic relays:
1. Electromagnetic relay is an important part of electric bell, telephone and automatic control circuit device. Its essence is a switch controlled by electromagnet, which plays a role similar to a switch in the circuit:
(1). Use low voltage and weak current to control high voltage and strong current;
(2). Realize long-distance manipulation and automatic control.

2, the use of electromagnetic relays can use weak current and low voltage control circuits to control high current and high voltage working circuits, and can realize production automation and remote control. Electromagnetic relays are widely used in automatic control (such as control circuits in automobiles, refrigerators, machine tools, elevators) and communications.