The relay consists of four parts, which are coils, magnetic circuits, reaction springs and contacts. The purpose of the coil is to generate electromagnetic attraction when it is energized, which drives the armature of the magnetic circuit to attract and make the contacts produce displacement actions. The magnetic circuit consists of an iron core, an iron choke and an armature. Its task is to establish a magnetic path for the magnetic flux generated by the coil. In the magnetic circuit, the most important thing 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 in the initial state; after the coil is energized, the air gap is zero, and the contact is in the action state. The function of the counter-force spring is to provide the armature with a repulsive force opposite to the direction of action. When the coil is de-energized, it can help the armature and contacts to reset. The contact is used for external execution control output, which is composed of normally closed contact and normally open contact. After the coil is energized, the relay is closed, the normally closed contact is opened and the normally open contact is closed. After the coil is de-energized and released, both the normally closed contact and the normally open contact are reset to the initial state. There are three types of relays, namely voltage relays, current relays and intermediate relays. Voltage relays have multiple coil turns and thin wire diameters, and the coil is connected in parallel with the load. Voltage relay is the main type of our common relay. 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.
As we can see from the current relay, its coil is short and fat, and its wire diameter is very thick. This is a characteristic of current relays.
The intermediate relay is actually a voltage relay. The reason why intermediate relays are regarded as independent varieties is that the number of contact pairs of intermediate relays is relatively large. Intermediate relays generally have 2 pairs of contacts, even more than 4 pairs.