The relay consists of four parts, which are coil, magnetic circuit, reaction spring and contact.

The purpose of the coil is that after electricity, it can produce electromagnetic suction, drive the armature of the magnetic circuit to pull, and make the contact to produce displacement action.

Magnetic circuit consists of iron core, iron choke and armature, its task is to establish a magnetic circuit channel for the magnetic flux generated by the coil.

In the magnetic circuit, the most important is the magnetic circuit air gap, which is a gap between the armature and the iron core. When the coil is not energized, the air gap is the maximum value and the contact is the initial state. After the coil is energized, the air gap is zero, and the contact position is in action state.

The function of the reaction spring is to provide repulsive force to the armature in the opposite direction of its action, which can help the armature and its contacts reset when the coil is disconnected.

The contact is used to execute the external control output, which consists of normally closed contact and normally open contact. After the coil is drawn by the electric relay, the normally closed contact is opened and the normally open contact is closed. After the coil is released from power, the normally closed contact and the normally open contact are reset to the initial state.

There are three kinds of relays, which are voltage relay, current relay and intermediate relay.

Voltage relay, its coil number of thin wire diameter, coil and load in parallel. Voltage relay is the main type of relay we commonly see.

The current relay has a small number of turns and a thick wire diameter. The coil is connected in series with the load, so its working current is the load current.