Relay

What is RELAY?

Relay can be defined as electrically operated switch.They mostly use electromagnet to operate a switch.They are used to control a circuit by low power signal or where several circuits must be controlled by one signal.During initial phase relays were extensively used in telephone exchanges and early computers to perform logical operations.

As shown in figure above a simple electromagnetic relay consists of a coil wrapped upon a soft iron core,a iron yoke that provides low reluctance path for magnetic flux,movable armature made up of ferromagnetic material and one or more sets of contacts.The armature is hinged to yoke and is mechanically linked with contacts.Armature is held by spring such that when relay is d energized,there is an air gap in magnetic circuit.In this case one set of contacts is opened where as other set is closed.

Working

When electric current passes through the coil a magnetic field is generated which activates armature and consequent movement of movable contacts with fixed contacts(makes/breaks).

In industry Normally Open/Closed (NO/NC) term is used to define working of relay.