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What is PLC ? How does it works? The Functions & types of applications?

What is PLC?

PLC is used for industrial automation. PLC stands for the programmable logic controller. This is used to control the different electromechanical processes, product processes.

PLCs are very important in the automation industry. PLCs are in different sizes and components. small and the large. small are flexible. but large is require heavy racks.  Some PLCs are customized with rare panels and functional modules to fit into different industrial application types.

PLCs are very fast, easy to operate, and easy to program. This is the reason, the PLCs are used in different industries. PLCs can be programmed in different ways, from ladder logic, which is based on electromechanical relays, to specially transformed programming languages.

Types of PLCs

  • Integrated or compact PLC
  • Modular PLC
  • Small PLC
  • Medium PLC
  • Large PLC

PLC Programing Languages

  • Ladder Diagram
  • Structured text
  • Function block diagram
  • Instruction list
  • sequential flow chart

Advantages of PLC

  1. Easy to program and Modify.
  2. Reliability
  3. Easy to erection and Commissioning
  4. Regulate accessories make programming easier and bring down the downtime
  5. Easy to Change Logic
  6. Low power consumption
  7. Good Documentation
  8. Capable of handling complicated logic operations
  9. Counter, timer, and comparator can be programmed

Applications of PLC

At first, PLCs are designed for industrial control replacing. But now these are used in so many other applications. The application of PLCs is the benefit of future expansions.

The communication tools merged into the PLCs, to improve the possibility and its applications to consolidated manufacturing and production systems.

To create applications, PLCs have several languages. The ladder diagram’s language is the most familiar to those who are involved in operations with PLCs.

Components of PLC

CPU Module

This is the central processor. Memory is required to store the information and accomplish the tasks. Here, data figuring and processing through receiving inputs and producing the outputs.

Power supply

All factors of the PLC anticipate the power supply. The PLCs are designed to receive AC and convert to DC.

Programming device

PLC is used for software programming. This establishes the control logic to the system. Here, users can create, transfer, and make changes.

Input/Output modules

The Input and the output factors collect data from sensors, and feed into the PLC system, and then make readable information. These modules can be either digital or analog.

How does a PLC work?

PLC is worked by the cyclic scanning method. It can be easily understood.

PLC scan process includes the following steps

  • The operating system starts the cycling and monitoring time.
  • The CPU starts reading the data from the input and checks that data.
  • The CPU starts executing the application program written in ladder programming or any other programming language.
  • Next, the CPU performs all the internal detection and communication tasks.
  • As claimed by the program results, to update the outputs, it writes the data into the output module.
  • This process continues till the PLC is in execute mode.


Basic Functions of PLC

  • Sequential Control

Here, PLC processes the binary input signal into output used for systematically processing of techniques. PLC maintains all steps in sequential processes.

  • Monitoring Plant

PLC monitors the position of a system and takes the major actions in connection with the process is controlled the message to the operators.

  • PLC Operation

The main and the important parts of PLC are the Input, output modules, and the CPU

  • Input Modules

Input modules accept different types of analog or digital signals from different sensors and converted them to logic signals by the CPU.

  • Output modules

Output modules convert the control command from the CPU into signals. These are used to control the different field devices.

  • CPU (Central Processing Unit)

The CPU will make decisions and perform the control instructions based on the program and its memory.

Programming Device

A programming device is used to install the instructions that control responding to specific inputs.

Operator module

The operator module allows the process information to be displayed and new managing parameters to be entered.

Control panels are

  • PLC panels
  • MCC panel
  • PCC panels
  • APFC Panels
  • LT Panels
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