Programmable Logic Controllers (PLCs) are advanced control systems replacing traditional hard-wired logic relays in industrial automation, programmed to manage electromechanical processes. They consist of key components like a processor, input/output assemblies, and power supply, allowing for flexibility and ease of reprogramming as production needs change. PLCs enhance functionality, save space, and simplify troubleshooting, making them cost-effective for controlling complex systems.

1. Programmable Logic
Controllers (PLCs)

2. Introduction
• PLC stands for Programmable Logic Controllers.
• They are basically used to control automated systems in industries.
• They are one of the most advanced and simplest forms of control systems
which are now replacing hard-wired logic relays at a large scale.
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3. • The biggest differences are that a PLC can perform discrete and
continuous functions that a PC cannot do.
• A PLC is much better suited to rough industrial environments.
• A PLC can be thought of as a ‘ruggedized’ digital computer that manages
the electromechanical processes of an industrial environment.
• PLCs play a crucial role in the field of automation.
• A PLC can be programmed according to the operational requirement of
the process.
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4. • In the manufacturing industry, there will be a need for reprogramming
due to the change in the nature of production.
• To overcome this difficulty, PLC-based control systems were introduced.
• We’ll first discuss PLC basics before looking at various applications of
PLCs.
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5. Example
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6. How Does a PLC
work?
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7. A PLC Scan Process
• 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.
• 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.
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8. Physical Structure of PLC
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9. 5 Common components of a PLC unit
• Processor
• Rack/Mounting
• Input Assembly
• Output Assembly
• Power Supply
• Programming Device/Unit
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10. Processor
• Processor which is also called the CPU which means central
processing unit.
• It is the most important component of a PLC.
• Similarly, processor is the core component in PC.
• Without a processor a PLC cannot perform its action.
• If the processor of PLC stops working, then the PLC is of no use
anymore.
• Different techniques are used to fully utilize a PLC processor.
• If the processor of PLC remains idle than the efficiency of the
PLC is compromised which is not bearable in large industries.
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11. • Different PLCs comes with different processor.
• If the PLC is being used at a big scale than a PLC with a big processor is
used and if the processor is being used at a small domestic level or in a
small processing unit than a PLC with small processor is purchased.
• The CPU or the processor of the PLC is used to determine the different
aspects of a PLC like memory available, different programing functions
available, processing speed and the size of the application logic available.
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12. Rack/Mounting
• A PLC unit is formed by combining a
number of components.
• Sometimes two or more components are
combined together to form a working
block.
• All the components used to form a block
needs to be attached with each other as per
the designed mechanism.
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13. • A rack is used to assemble different components of a PLC at a one place.
• The racks of a PLC are also called housing as it provides space for
different components of a PLC.
• In smaller PLCs, if there is only one component then it is also called a
brick or a shoebox.
• The rack of the PLC is designed carefully as it handles the different
components of PLC.
• The rack should be strong enough to hold various bricks of a PLC.
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14. Input Assembly
• Input assembly is used to transmit the input signals from processor of
the PLC to the controller of the PLC.
• Input assembly includes various switches, operator inputs and pressure
sensors.
• This assembly can be termed as the senses of the PLC which is used to
sense different inputs.
• Different kind of inputs can be provided to the PLC as per the
programming of the PLC.
• The input of the PLC can be also divided into the analog and digital
categorizes. Each category is handled by its own specific class.
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15. Output Assembly
• Output assembly is used to transmit the executed data from the PLC to
the outside world.
• The outside world can be any application of the PLC.
• This assembly is called the actuator of the PLC.
• Outputs from the PLC are received in different form at the receiving
end.
• The output can be also of analog or digital type depending upon the
input type.
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16. Power Supply
• A power supply is used to provide the essential power to the PLC.
• Different kind of power supplies are used in different PLCs.
• The power supply provides the enough current to PLC in order to
operate different components of the PLC.
• The different power supplies used in the PLC ranges from 24V DC to
120V AC.
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17. Programming Device/Unit
• The programming device of unit is the device which is used to program
a PLC.
• Each PLC comes with its own programming software and code.
• The programmer programs the PLC with the help of the programming
unit.
• The different logics for the PLC are made by the programmer and then
implemented to different units.
• The PLCs are programmed using personal computers or laptops with the
help of provided software for the programming.
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18. Types of PLCs-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.
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19. 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.
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20. Why should I use a PLC?
• PLCs eliminate the need for rewiring and adding additional hardware
for each new logical configuration.
• These devices increase the functionality of controls and do not take up
much physical space.
• Since PLCs are sectional, they can be mixed and matched, so you can
choose the best combination of input and output devices for your
specific operation.
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21. • PLCs can perform relay-switching tasks, as well as count, calculate, and
compare analog process values.
• A PLC’s flexibility makes it easy to modify control logic at any time.
• PLCs are cost-effective for controlling complex systems.
• PLCs provide easy trouble-shooting capabilities.
• PLCs can work seamlessly with Human-Machine Interface computers.
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22. PLC Programming
• When using a PLC, it’s important to design and implement concepts
depending on your particular use case.
• To do this we first need to know more about the specifics of 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.
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23. • https://conceptsystemsinc.com/the-basics-of-programmable-logic-
controllers-plc/?v=a284e24d5f46
• https://www.electrical4u.com/programmable-logic-controllers/
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24. B.Varun
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