When a certain voltage or current is applied to both ends of the electromagnetic relay coil, the magnetic flux generated by the coil passes through the magnetic circuit composed of the iron core, yoke, armature, and magnetic circuit working air gap. Under the action of the magnetic field, the armature is attracted to the pole surface of the iron core, thereby pushing the normally closed contact of the contact to open and the normally open contact to close; When the voltage or current at both ends of the coil is less than a certain value, and the mechanical reaction force is greater than the electromagnetic attraction force, the armature returns to its initial state, the normally open contact opens, and the normally closed contact closes.

In a relay, there can be multiple normally open contacts, normally closed contacts, and switching contacts. The normally open contact is in the disconnected position when not powered on, the normally closed contact is in the connected position when not powered on, and the switching contact can switch between the normally open and normally closed states.