A programmable logic controller (PLC) is an industrial computer system that monitors inputs and controls outputs to automate a process. The document discusses PLC systems, including their components, programming, and applications. PLCs are used to control industrial processes like manufacturing plants, processing facilities, and wastewater treatment. They have inputs that monitor data, a CPU that runs logic programs, and outputs that control devices. PLCs are programmed using ladder logic, function block, or sequential function chart languages. They are widely used across industries like mining, oil and gas, and manufacturing due to their reliability in harsh conditions.

1. CONTENT
• WHAT IS PLC SYSTEM?
• COMPONENTS OF PLC SYSTEM
• DESCRIPTION OF COMPONENTS
• BLOCK DIAGRAM
• WORKING
• TYPES OF PLC
• PLC PROGRAMMING
• APPLICATIONS

2. PLC SYSTEMS
A PROGRAMMABLE LOGIC CONTROLLER IS A TYPE OF TINY COMPUTER THAT CAN
RECEIVE DATA THROUGH ITS INPUTS AND SEND OPERATING INSTRUCTIONS
THROUGH ITS OUTPUTS. FUNDAMENTALLY, A PLC’S JOB IS TO CONTROL A
SYSTEM’S FUNCTIONS USING THE INTERNAL LOGIC PROGRAMMED INTO IT.
A PLC IS A COMPUTER SPECIALLY DESIGNED TO OPERATE RELIABLY UNDER HARSH
INDUSTRIAL ENVIRONMENTS – SUCH AS EXTREME TEMPERATURES, WET, DRY,
AND/OR DUSTY CONDITIONS. PLCS ARE USED TO AUTOMATE INDUSTRIAL
PROCESSES SUCH AS A MANUFACTURING PLANT’S ASSEMBLY LINE, AN ORE
PROCESSING PLANT, OR A WASTEWATER TREATMENT PLANT.

3. PLC SYSTEM COMPONENTS
INPUT MONITORING: THE PLC MONITORS RELEVANT DATA INPUTS AND SENDS THE DATA TO THE
CPU. SOME PLCS ONLY USE DATA INPUTS WITH DISCRETE (ON/OFF) INPUTS, BUT PLCS WITH
ANALOG CAPABILITIES CAN ACCEPT ANALOG INPUTS FOR CONTINUOUS VARIABLES. INPUTS MAY
COME FROM IOT DEVICES, ROBOTS, SAFETY SENSORS, HUMAN-MACHINE INTERFACES, OR ALMOST
ANY OTHER TYPE OF DATA ENTRY POINT.
LOGIC PROGRAMMING: EVERY PLC IS BUILT WITH A MICROPROCESSOR CPU, EITHER 16-BIT OR 32-
BIT. ENGINEERS AND TECHNICIANS PROGRAM THE PLC CPU TO RECOGNIZE CERTAIN CONDITIONS
AND VALUES AND TO MAKE CHANGES IN THE OUTPUTS BASED ON ITS PROGRAMMED RULES. THE
CPU IS CONSTANTLY CHECKING THE STATE OF VARIABLES AND MAKING DECISIONS BASED ON
PROGRAMMED CONDITIONS. THIS SIMPLE PREMISE ALLOWS A WIDE VARIETY OF DESIGNS AND
FUNCTIONS.
OUTPUT CONTROL: BASED ON THE PROGRAMMED LOGIC, THE PLC CONTROLS VARIOUS
SWITCHES, MOTOR STARTERS, RELAYS, AND OTHER DEVICES CONNECTED TO ITS OUTPUTS. THIS
ALLOWS THE PLCS TO TAKE CONTROL OF MECHANICAL PROCESSES SUCH AS THE OPERATION OF A
MACHINE. ENGINEERS CAN ALSO LINK MULTIPLE SYSTEM PARTS BY PROGRAMMING PLCS TO
SEND THEIR OUTPUT SIGNAL TO ANOTHER PLC IN A CHAIN.

4. PLC BLOCK DIAGRAM

5. WORKING
THE WORKING OF A PROGRAMMABLE LOGIC CONTROLLER CAN BE EASILY
UNDERSTOOD AS A CYCLIC SCANNING METHOD KNOWN AS THE SCAN CYCLE.
A PLC SCAN PROCESS INCLUDES THE FOLLOWING STEPS
THE OPERATING SYSTEM STARTS CYCLING AND MONITORING OF TIME.
THE CPU STARTS READING THE DATA FROM THE INPUT MODULE AND CHECKS
THE STATUS OF ALL THE INPUTS.
THE CPU STARTS EXECUTING THE USER OR APPLICATION PROGRAM WRITTEN IN
RELAY-LADDER LOGIC OR ANY OTHER PLC-PROGRAMMING LANGUAGE.
NEXT, THE CPU PERFORMS ALL THE INTERNAL DIAGNOSIS AND COMMUNICATION
TASKS.
ACCORDING TO THE PROGRAM RESULTS, IT WRITES THE DATA INTO THE OUTPUT
MODULE SO THAT ALL OUTPUTS ARE UPDATED.
THIS PROCESS CONTINUES AS LONG AS THE PLC IS IN RUN MODE.

6. BLOCK DIAGRAM OF HOW A PLC WORKS

7. TYPES OF PLCS
THE TWO MAIN TYPES OF PLC ARE FIXED / COMPACT PLC AND MODULAR PLC.
COMPACT PLC
WITHIN A SINGLE CASE, THERE WOULD BE MANY MODULES. IT HAS A FIXED
NUMBER OF I/O MODULES AND EXTERNAL I/O CARDS. SO, IT DOES NOT HAVE THE
CAPABILITY TO EXPAND THE MODULES. EVERY INPUT AND OUTPUT WOULD BE
DECIDED BY THE MANUFACTURER.
MODULAR PLC
THIS TYPE OF PLC PERMITS MULTIPLE EXPANSION THROUGH “MODULES”, HENCE
REFERRED TO AS MODULAR PLC. I/O COMPONENTS CAN BE INCREASED. IT IS EASIER
TO USE BECAUSE EACH COMPONENT IS INDEPENDENT OF EACH OTHER.

8. PLC PROGRAMMING
A PLC PROGRAM CONSISTS OF A SET OF INSTRUCTIONS EITHER IN TEXTUAL OR
GRAPHICAL FORM, WHICH REPRESENTS THE LOGIC THAT GOVERNS THE PROCESS
THE PLC IS CONTROLLING. THERE ARE TWO MAIN CLASSIFICATIONS OF PLC
PROGRAMMING LANGUAGES, WHICH ARE FURTHER DIVIDED INTO MANY SUB-
CLASSIFIED TYPES.
1. TEXTUAL LANGUAGE
1. INSTRUCTION LIST
2. STRUCTURED TEXT
2. GRAPHICAL FORM
1. LADDER DIAGRAMS (LD) (I.E. LADDER LOGIC)
2. FUNCTIONAL BLOCK DIAGRAM (FBD)
3. SEQUENTIAL FUNCTION CHART (SFC)

9. PLC APPLICATIONS
PLCS HAVE A VARIETY OF APPLICATIONS AND USES, INCLUDING:
1.PROCESS AUTOMATION PLANTS (E.G. MINING, OIL &GAS)
2.GLASS INDUSTRY
3.PAPER INDUSTRY
4.CEMENT MANUFACTURING
5.IN BOILERS – THERMAL POWER PLANTS

10. APPLICATIONS OF PLC
A PROGRAMMABLE LOGIC CONTROLLER (PLC) IS AN ELECTRONIC DEVICE USED IN
MANY INDUSTRIES TO MONITOR AND CONTROL CONSTRUCTION SYSTEMS AND
PRODUCTION PROCESSES.
UNLIKE PCS AND SMARTPHONES, WHICH ARE DESIGNED TO PERFORM ANY NUMBER
OF ROLES, A PLC IS DESIGNED TO PERFORM A SINGLE SET OF TASKS, EXCEPT IN THE
CASE OF LIMITATIONS IN REAL TIME AND WITH SUPERIOR RELIABILITY AND
PERFORMANCE.
TO MEET THE DEMANDS OF RIGOROUS INDUSTRIAL ENVIRONMENTS, PLCS ARE
DESIGNED TO BE EXTREMELY ROBUST, OFTEN CAPABLE OF WITHSTANDING EXTREME
TEMPERATURES, HUMIDITY, VIBRATION AND ELECTRICAL NOISE. THE LOGICAL
CONTROLLERS ARE COMMONLY RESPONSIBLE FOR MONITORING AND CONTROLLING
A LARGE NUMBER OF SENSORS AND ACTUATORS, AND THEREFORE ARE DIFFERENT
FROM OTHER COMPUTER SYSTEMS IN THEIR EXTENSIVE INPUT / OUTPUT (I / O)
ARRANGEMENTS.
PLC 'S ARE USED IN SEVERAL INDUSTRIES LIKE PETROCHEMICAL ,BIOMEDICAL,
CEMENT MANUFACTURING, OIL AND GAS SECTOR ETC.

11. APPLICATIONS IN OUR EVERYDAY LIVES
ROAD TRAFFIC SIGNALS
IT’S DIFFICULT TO PICTURE OUR MODERN WORLD WITHOUT TRAFFIC SIGNALS. THOSE THREE
COLORED STREETLIGHTS ARE USED AND UNDERSTOOD BY PEOPLE ALLAROUND THE WORLD.
THIS SIMPLE BUT INGENIOUS APPLICATION OF THE PLC HAS A LONG HISTORY IN MAJOR CITIES
AND SMALL TOWNS ALL AROUND THE WORLD, SINCE THEIR FIRST APPLICATION TRAFFIC CONTROL
IN 1926 IN LONDON, ENGLAND. THESE TRAFFIC LIGHTS, THAT WE TAKE FOR GRANTED EVERY DAY
ARE MONITORED AND CONTROLLED BY PLC HARDWARE AND SOFTWARE, RUNNING DEPENDABLY
AND WITHOUT FUSS 24/7/365 DAYS A YEAR.

12. SMART 4 WAY TRAFFIC SIGNAL CONTROL WITH
VARIABLE DELAY