Principle of electromagnetic relay

Electromagnetic relay is an electronic control device. It has a control system (also called input loop) and a controlled system (also called output loop). It is usually used in automatic control circuits. It actually uses low voltage and weak current circuits. A kind of "automatic switch" to control high voltage and strong current. Therefore, it plays the role of automatic adjustment, safety protection and conversion circuit in the circuit.

Principle characteristics

The electromagnetic relay is a switch that uses an electromagnet to control the on and off of the working circuit.

(1) Structure: The main components of the electromagnetic relay are electromagnet A, armature B, spring C, moving contact D, and static contact E.

(2) The working circuit can be divided into two parts: a low-voltage control circuit and a high-voltage working circuit. The low-voltage control circuit includes an electromagnetic relay coil (electromagnet A), a low-voltage power supply E1, and a switch S; the high-voltage working circuit includes a high-voltage power supply E2, a motor M, the contact parts D and E of the electromagnetic relay.

(3) Working principle-close the switch S in the low-voltage control circuit, and the current generates a magnetic field through the coil of the electromagnet A, thereby generating attraction to the armature B, making the dynamic and static contacts contact, the working circuit is closed, and the motor works; when it is broken When the low-voltage switch S is opened, the current in the coil disappears, the dynamic and static contacts are disconnected, the working circuit is disconnected, and the motor stops working.

As long as a certain voltage is applied to the two ends of the coil, a certain current will flow through the coil, thereby generating electromagnetic effects, and the armature will attract the iron core against the pulling force of the return spring under the action of electromagnetic force attraction, thereby driving the armature. The moving contact and the static contact (normally open contact) are attracted. When the coil is de-energized, the electromagnetic suction will disappear, and the armature will return to the original position under the reaction force of the spring, releasing the moving contact and the original static contact (normally closed contact). This pulls in and releases, thus achieving the purpose of turning on and off in the circuit. The "normally open, normally closed" contacts of the relay can be distinguished in this way: the static contacts that are off when the relay coil is not energized are called "normally open contacts"; the static contacts that are in the on state are called It is "normally closed contact".

The use of electromagnetic relays can use low voltage and weak current control circuits to control high voltage and strong current working circuits, and can realize remote control and production automation. Electromagnetic relays are widely used in automatic control (such as refrigerators, automobiles, elevators, machine tools Control circuit) and communication field.

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