PROGRAMMABLE LOGIC PROGRAMMABLE LOGIC CONTROLLER(PLC)CONTROLLER(PLC)

CONTENTSCONTENTS

• RLCRLC• Ladder logicLadder logic• Disadvantages of RLCDisadvantages of RLC• PLC PLC • Its components Its components • Operation cycle Operation cycle • Information Flow Information Flow • Types Types • ManufacturersManufacturers

RELAY LOGIC CONTROLRELAY LOGIC CONTROL

• Before the invention of the Programmable Logic Controller (PLC), most industrial control was done using relay control panels.

• Relay logic is a method of controlling industrial electronic circuits by using relays and contacts..

• Switches and relays can be arranged in circuits to make logical decisions.

• It uses ladder logic.

LADDER LOGIC USING LINE LADDER LOGIC USING LINE DIAGRAM-1DIAGRAM-1

AND Logic

( )

X Y Z

( )

X

Y

Z

OR Logic

Problems with relay control panels

• Mechanical Relays and switches failed regularly (coil failure, contact wear and contamination, etc.)

• Difficult to diagnose problems and replace relays and switches

• Difficult to change hardwired logic (example: changing an “OR” circuit to “XOR”)

• Consumed a lot of power.

Architecture of PLCArchitecture of PLCProgramming

Device

Input/OutputSystem

OutputDevices

InputDevices

UserProgram

Data Storage

OutputTable

InputTable

What are What are PLC’s componentPLC’s component??

CR???????

Optical IsolationBarrier

Optical IsolationBarrier

CentralProcessor

MEMORYprogram data

Low Voltage

POWER SUPPLY

Output

Circuits

Input

Circuits

Programming / Communication Devices

Based on the data inthe output image filethe PLC energises or de-energises it’s outputcircuits,controllingexternal devices.

What' happens in an operating What' happens in an operating cycle?cycle?

1.Input Scan

2. ProgramScan

3. OutputScan

START

-- -

-

PLCOPERATING CYCLETYPICALLY 1 to 25 ms.

During the input scan PLC examines the external input devices -On or Off. The status of the inputs is temporarily stored in an input image memory file.

The PLC scans the instructions in the ladder logic program,uses the input status from the input image file & determines if an output willbe energised.The resulting status of the outputsis written to the output image memory file.

Information Flow…Information Flow…In

form

atio

nC

on

tro

l

InternetInternet

Modbus ASi

Ethernet TCP/IP

Ethernet TCP/IP

ServerWeb Server

&

Firewall

Switch/Router

BusX BusX

!!

!

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PLC-1FailureReport

Webcast

MANUFACTURERS-MANUFACTURERS-

• ModiconModicon

• Schneider ElectricSchneider Electric

• General ElectricGeneral Electric

• MitsubishiMitsubishi

• Allen BredleyAllen Bredley

• SeimensSeimens

Thank youThank you

BY-BY-

MUSTAHID MUSTAHID ALIALI