General Purpose Relays

Structure and Principle of Relays

A relay consists of an electromagnet that receives an electric signal and converts it to a mechanical action and a switch that open and closes the electric circuit.

Schematic Diagram Showing the Principle of Relays

General Relays

Principle of Operation

In this example, we will turn ON a lamp using switch S₁ and a relay.

1. Press S₁ to turn it ON.

2. Current i flows to the operating coil and magnetizes the core.

3. The armature is drawn to the core by the electromagnetic force.

4. When the armature reaches the core, the moving and fixed contacts make contact and the lamp lights.

5. When S₁ is released to turn it OFF, current no longer flows to the operating coil, the electromagnetic force no longer exists, and the armature returns to its original position by the force of the release spring.

6. When the armature has returned to its original state, the contacts become separated and the lamp turns OFF.