Electromagnetic relays are generally composed of iron cores, coils, armatures, contact reeds, etc. As long as a certain voltage is applied to both ends of the coil, a certain current will flow in the coil, which will produce electromagnetic effects. Under the action of electromagnetic force, the armature will overcome the pull force of the return spring and attract to the core, thereby driving the armature. The moving contact and the static contact (normally open contact) are pulled together. When the coil is de-energized, the electromagnetic attraction will also disappear, and the armature will return to its original position under the reaction force of the spring, releasing the moving contact and the original static contact (normally closed contact). This pulls in and releases, so as to achieve the purpose of conducting and cutting off in the circuit. For the "normally open and normally closed" contacts of the relay, it can be distinguished as follows: the static contact that is in the off state when the relay coil is not energized is called "normally open contact"; the static contact that is in the on state is called It is a "normally closed contact". Relays generally have two circuits, a low-voltage control circuit and a high-voltage working circuit.