1. Presented by SARAVANA KUMAR . M (EEE III Year) SBM CET
Switches & Relays
Presented by
SARAVANA KUMAR . M
(EEE III Year)
SBM CET

2. Demo
What is a Switch?
A switch is a device that allows you to stop the flow of current entirely. These are usually mechanical devices that separates two bits of metal (contacts). When the metal doesn't touch, current doesn't flow. When the metal touches, is called a closed circuit. When the metal doesn't touch, is called an open circuit. (closed = ON, open = OFF)
Basic Switch Schematic Symbol S1

3. SWITCH TYPES Single Pole, Single Throw = SPST
Single Pole, Double Throw = SPDT
Double Pole, Single Throw = DPST
Double Pole, Double Throw = DPDT
Push Button Switches (NO/NC)

4. Single Pole, Single Throw = SPST
A simple on-off switch. This type can be used
to switch the power supply to a circuit.
Example
Circuit Symbol
SPST toggle switch

5. Single Pole, Double Throw = SPDT
This switch can be on in both positions, switching on a separate device in each case. It is often called a changeover switch. For example, a SPDT switch can be used to switch on a red lamp in one position and a green lamp in the other position.
Example
Circuit Symbol
SPDT rocker switch

6. Double Pole, Single Throw = DPST
A pair of on-off switches which operate together (shown by the dotted line in the circuit symbol).
Example
Circuit Symbol
DPST rocker switch

7. Double Pole, Double Throw = DPDT
A pair of on-on switches which operate together (shown by the dotted line in the circuit symbol).
Example
Circuit Symbol
DPDT slide switch

8. Push Button Switches (NO/NC)
A Normally Open (NO) switch returns to its normally open (off) position when you release the button.
A Normally Closed (NC) switch returns to its normally closed (on) position when you release the button.
Circuit Symbol
Example
Push-to-make switch
Circuit Symbol
Example
Push-to-break switch

9. What is a Relay?
A Relay is an electromechanical switch, operated by passing current through a coil of wire wound around a steel core, which acts as an electromagnet, pulling the switch contact down to make or break a circuit.

10. Relay

12. Electrically controlled switch Current through coil
RELAY OPERATION
Electrically controlled switch
Current through coil
Magnetises soft iron core
Soft iron armature moves
Contacts join to closed

13. RELAY OPERATION Each relay has two mechanical parts inside.
The two terminals operates as a switch
The contacts operates similarly to the contacts of a simple switch or pushbutton.

14. Relay contacts Normally Open vs. Normally Closed
The Normally Open: contacts are not in contact with the armature when the relay is not activated
The Normally Closed: set of contacts are in contact with the contact on the armature when the relay is not activated.

15. EXAMPLE:
The animation shows how a NO contact
operates by lighting a light bulb:

16. The NC contacts, it works exactly opposite as the NO contacts:

17. A combination of contacts:
The NO and NC contacts are referred to the COMMON terminal.

18. Examples of Common Relays
This is a simple single pole single throw relay. You can see that there is no normally closed contact. The only time that this relay will pass current through its contacts is when the coil is energized.
This is a single pole double throw relay. This is the standard Bosch type relay. This one is made by Tyco.
This is a three pole double throw relay. The terminals on this one require that it be used in a socket.
This is a four pole, double-throw relay.

19. Last part of the relay operation.
The device that forces the terminal to move, is actually an electromagnet.
A coil is placed right under the contact.
when current is flown through this coil, a magnetism is created.

20. A load-Relay should be used for this application.

21. Relays are essential for automation systems and for controlling loads.
Why are they used?
Relays are essential for automation systems and for controlling loads.
Relays are the best way for galvanic insulation between high and low voltage portions of a circuit.

22. Why are they used? Safety Remote control
Starter Motor, Head Lights, Horn, Door Bells
Industrial Machinery
Remote Lighting Systems
Etc…

24. THANK YOU