Introduction To Relay

Hi Friends...Today i'm going to post about relay.In this post i will cover What is relay? Its types, parts which a relay consist,and about how a relay is working...

As we all know Relay is a very important device now days.It used in various types of circuits our school project,university project as well as industry projects.And the purpose of this post is many of us have problems of how to use a relay. And in this post i will try to solve this problem.

RELAY :
A relay is an electrical switch actuated by an electromagnetic coil.And the main purpose of relay is switching.

Types of relay

1. Single Pole Single Throw (SPST)- These types of relay provides one contact at a time it may be a normally open or normally close.These relays comprise of 4 terminals. Two terminals are used as coil points and other two can be used to connect or disconnect the circuit (A and B).

2. Single Pole Double Throw (SPDT)- These type of relay provides both a normally open and normally closed contacts.Closed contact set in one unit actuated by the electromagnet coil.

3. Double Pole Single Throw (DPST)- These type of relay provides two sets of SPST relays contact in one unit.

4.DoublePole Double Throw(SPDT)- this design of relay provides two sets of SPDT relays contact in one unit.

Parts of a Relay Switch
There are 5 parts in every relay -
1. Electromagnet- It consists of iron core wounded by coil of wires. When electricity is passed through it become magnetic therefore it is called as electromagnet.
2. Armature-The movable magnetic strip is known as armature. When current flow through them, it energizes the coil and produce magnetic field which is used to make or break the normally open (N/O) or normally close (N/C) points. Armature can be moved with direct current (DC) as well as alternating current (AC).
3. Spring - When no current flow through coil electromagnet, the spring pulls the armature away so that circuit cannot be completed.
4. Set of electrical contacts- There are two contact points :
a. Normally open-In this the device connected to it will work when relay is activated and disconnect it when relay is inactive.
b. Normally close- In this the device connected to it will not work when relay is activated and the circuit is connected when relay is inactive.
5. Molded frame-Relays are covered with plastic or glass so that we can observe its working without opening or removing its cover.

Working of Relay
Working of relay is simple, when power is supplied to relay current start flowing through the control coil as a result electromagnetic starts energizing. Hear points A,B,C are used as control points. When power is applied to input terminal due to electromagnetic effect, B and C are connected thus closes the contacts causing a short circuit for the power to the load. If the relay was already De-energized when the contacts were closed, then the contact move opposite and make an open circuit. When power supply is cut off point A and C are connected. This force is mainly provided by two factors they are spring and gravity.

I hope this post will be very useful for all.in case of any query please leave a comments.

THANKS....:)

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