Electromagnetic relays generally consist of an iron core, coil, armature, contact reed and so on. As long as a certain voltage is added to both ends of the coil, a certain current will flow through the coil, resulting in electromagnetic effect. Under the action of electromagnetic force attraction, the armature will overcome the tension of the return spring and draw towards the core, thus driving the moving contact and static contact (normally open contact) to draw. When the coil power, electromagnetic suction also disappeared, the armature will return to the original position in the spring reaction force, so that the moving contact and the original static contact (normally closed contact) suction. This suction, release, so as to achieve the purpose of conduction in the circuit, cut off.