Materi Bab 3 Switch n Relay(2)

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Switches and Relays

Switches are crude electro-mechanical devices thatconnect or seperate pieces of metal, controlled by a lever

or knob.

Relays are crude electro-mechanical devices that connect

or seperate pieces of metal, controlled by an

electromagnet.

Chapter 3

The most common types of components found in a

control circuit are contacts, switches, and coils.

Switches : Toggle

Pushbutton

Selector switch

Switches common for power and

signalling.

Available in single or mutiple

contacts (poles).



Switching Networks

This switching network implements a function of its

input voltages

A mapping from the input domain - the set of possible input voltages - to the output range - the set

of possible output voltages

Throw - number of states

Pole - number of connectingmoving parts (number of

individual circuits).

DPSTSPDT

A Switch is a 2-state device that can be toggled



Toggle Switches

Toggle switches are

generally used in 2-wire

control circuits.



Toggle Switches

AC

source

Toggle switch

2-wire control circuit

Manual Control circuits use components that require

human interaction in order to operate.



Toggle Switches

AC

source

Toggle switch


SAFETY TIP!

2-wire control circuits should not be used on mechanical

loads due to restart after a loss of power occurs.





Automatic Control

Automatic control circuits can operate themselveswithout the need for human interaction.

AC

source

Float switch



Automatic Control

Automatic control circuits can operate themselveswithout the need for human interaction.

AC

source

Float switch



Pushbuttons

Pushbuttons are

generally used in 3-wire

control circuits because

of their momentaryoperation.



Pushbuttons

ACsource C

C

StopStart




Pushbuttons

ACsource C

C

StopStart




Pushbuttons

ACsource C

C

StopStart




Pushbuttons

ACsource C

C

StopStart




Pushbuttons

ACsource C

C

StopStart




Selector

Selector switches

allow manual or

automatic operation

of a circuit.



Selector Switch

ACsource

hand

off

auto



Selector Switch

ACsource

hand

off

auto



Selector Switch

ACsource

hand

off

auto



Selector Switch

ACsource

hand

off

auto



Process Actuated

Switches

Manually Actuated

Switches



Relays A relay is a switch built with an electromagnet

controlled current

controlling current





Coils

When coils are energized, any contacts that are controlledby them change from their normal to energized state.

C

NO NC

Contacts can be Normally Open (NO) or Normally Closed (NC).

Contacts

Relays often used for motors.



Coils

When coils are energized, any contacts that are controlledby them change from their normal to energized state.

C

NC NO

Contacts can be Normally Open (NO) or Normally Closed (NC).

Contacts

Relays often used for motors.



CR

Relay coil

R1

R1 NOOutput contact

input

contact

coil

R1 NC

RELAYS

A switch that can be turned on

and off by electricity (instead of by

a person)

Uses magnetic properties of

materials and the magnetic forces

due to electric current flow

A switch whose operation is activated by an electromagnet is called a"relay"

IN

The switch is closed iff a High

voltage is applied to the input



CR

Relay coil

R1

R1 NOOutput contact

input

contact

coil

R1 NC

RELAYS

A switch that can be turned on

and off by electricity (instead of by

a person)

Uses magnetic properties of

materials and the magnetic forces

due to electric current flow

A switch whose operation is activated by an electromagnet is called a"relay"

IN

The switch is closed iff a High

voltage is applied to the input



Inside a Relay Magnetic force deflectsthe lever downward

when the coil is energizedSpring force restoresthe lever when thecoil is not energized

Connections to coil

Normally opencontact

Normally closedcontact

NO

NCCommon contact

Relay Actuated

Contacts

Timer On-Delay

Timer Off-Delay



Inside a Relay Magnetic force deflectsthe lever downward

when the coil is energizedSpring force restoresthe lever when thecoil is not energized

Connections to coil

Normally opencontact

Normally closedcontact

NO

NCCommon contact

Relay Actuated

Contacts

Timer On-Delay

Timer Off-Delay





A simple relay

circuit

In a digital circuit thevoltages can onlytake on one of twodiscrete values: High

and Low

Vcc

G ND

G ND

Switch

Bulb

OUT



The symbols used in a ladder logic diagram are as shown:

The ladder logic diagram is used to represent the logic in a PLC

control program widely in industry. The ladder logic diagram

makes use of representations similar to electrical circuits in which

a series connection represents a logical AND, and a parallelconnection represents a logical OR.

Input Output

Set-Reset Ladder Diagram

AND

OR

NOT



Wiring diagram

Ladder diagram for the circuit

AN EXAMPLE OF

RELAY LOGIC

For a process control, it isdesired to have the processstart (by turning on a motor)five seconds after a part

touched a limit switch.

The process is terminatedautomatically when thefinished part touches asecond limit switch.

An emergency switch willstop the process any timewhen it is pushed.



Jenis-jenis Limit Switch



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Materi Bab 3 Switch n Relay(2)