How does an electromagnetic relay work?

Update:27-02-2021
It is mainly composed of iron core coil, armature (moving iron core), spring, moving contact, static contact and some terminals. Static contacts include normally closed contacts and normally open contacts. Under normal conditions, the moving contact is closed to the normally closed contact. As long as a certain voltage is applied to the two ends of the line of the relay base assembly, a certain current will flow through the coil, thereby generating electromagnetic effects. The armature will absorb the restoring force of the spring against the spring core under the action of the electromagnetic force suction bow, thereby driving the movement. The contact is separated from the normally closed contact and connected to the normally open contact. When the coil is de-energized, the electromagnetic attraction force also disappears, and the armature returns to the original position under the reaction force of the spring, so that the movable contact and the normally closed contact are restored to close and separated from the normally open contact.
It can be seen that through the energization and de-energization of the electromagnetic relay of the relay coil base assembly, the opening or closing control of the controlled circuit can be easily realized through the contact group. Since there is no electrical connection between the working current through the coil and the contacts, the control circuit is electrically isolated from the controlled circuit.
For each contact of the HOT SALE 120A HIGH POWER GENERAL PURPOSE POWER THREE-PHASE RELAY: when the coil is not energized, the contact in the open state is the "normally open contact", and the contact in the conducting state is the "normally closed contact".
The working principle of the pcb relay can be further illustrated by the experimental circuit shown in the following figure: when the switch SA is off, no current flows through the coil of the electromagnetic relay, no magnetic field is generated in the coil, and the electromagnetic relay is in the "release" state, usually open The contact is open, the normally closed contact is closed, the bulb H1 is off, and H2 is open. When the switch SA is closed, the current flows through the coil of the electromagnetic relay, the coil generates a magnetic field, the internal armature is attracted, and the electromagnetic relay is in the state of "electromagnetic relay" suction meter.
The normally open contact is closed and the normally closed contact is open. As a result, the bulb H1 is turned on and H2 is turned off. It can be seen that an electromagnetic relay is a device that uses electromagnetic principles to control the opening and closing of a contact switch. It usually uses a circuit to control another circuit, which is also the origin of the term "relay".