Relay is essentially a switch controlled by an electromagnet, which controls the high voltage and strong current by the low voltage and weak current, so as to realize automatic control.

It is a typical application of electromagnetics. The electromagnetization phenomenon was discovered by Oster. Oster’s experimental phenomenon showed two problems. First, there is a magnetic field around the conducting wire, and the magnetic field is related to the direction of current. The north and south poles of the magnetic field are known by the Ampere rule.

Common relays are electromagnetic relays. From the perspective of structure, they are mainly contact systems, electromagnetic mechanisms and transmission mechanisms. The electromagnetic mechanism is the multi-core component of the relay, mainly the coil and the iron core.

The relay coil is energized to realize the electromagnetization process, while the magnetization of the iron core attracts the armature and resists the spring reaction force and finally pulls. When the armature is drawn and closed, it drives the transmission mechanism to make the contact system work, making the corresponding contacts of the relay turn over logically.

When the relay coil loses power, the electromagnetic phenomenon disappears, the armature is released again under the spring reaction force, and the corresponding contact logic of the contact system is reset again.

There are two types of relay contacts, normally open contacts and normally closed contacts. With the usual household switch wiring is not much different, usually contact wiring connected to the control circuit of the fire line.

For example, the application of intermediate relay, which is characterized by many contacts, can expand the number of circuit contacts, so that a master signal can realize multiple circuit responses. In the same way, its contacts and those of other low-voltage appliances can be used to realize AND/OR logic circuits.

In addition, the intermediate relay can realize capacity expansion, substitution, intermediate conversion, process control state memory and so on.

The normally open and normally closed relay can be distinguished by the wiring diagram on its shell. The normally open and normally closed label is very clear. Secondly, the multimeter can be used to measure the on-off of each contact when the coil is not energized, and the type of contact can also be determined.