The structure of the electromagnetic relay is composed of electromagnet, armature, reed, contact (static contact, moving contact) and its working circuit is composed of low voltage control circuit and high voltage working circuit. Low voltage control circuit is composed of electromagnet, low voltage power supply and switch; The working circuit is composed of the machine (motor, etc.), the high voltage power supply and the contact part of the electromagnetic relay. The working principle of the electromagnetic relay when the smaller current through the terminal D, E into the coil, the electromagnet to the armature suction, the moving contact to the high voltage working circuit of the two terminals connected by the circuit, the larger current can drive the machine to work when the power off, the electromagnet magnetic disappeared, the spring to the armature spring, cut off the working circuit. 1. Through the electromagnetic relay can realize the use of low voltage, weak current circuit indirectly control high voltage, strong current circuit, to ensure the operator's personal safety, convenient control. 2, the workplace temperature is high or the environment is not good, can use electromagnetic relay to achieve remote operation and control, improve the operator's working environment, convenient control. 3. When the power is on, the magnetism disappears when the power is off, which is convenient for control.