Regardless of the difference in the action principle and structure of the relay, they are composed of three parts: an induction mechanism (accepting input signals), a transmission mechanism (providing a comparative amount) and an actuator (output circuit).
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, the yoke, the armature, and the working air gap of the magnetic circuit. Under the action of the magnetic field, the armature attracts the pole face of the iron core. As a result, the normally closed contact of the contact is opened, and the normally open contact is closed; 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 the initial state, and the normally open contact is opened. The normally closed contact is closed.