[Explained] PLC Block Diagram | Programmable Logic Controller

Hey, today we are going to discuss the basic PLC Block Diagram. You will understand the working principle of PLC from the block diagram of PLC. PLC stands for Programmable Logic Controller. Nowadays, PLC becomes more and more popular in industries for automation purpose. PLC replaced the analog control system by bringing the digital control system in the industry.

There are many advantages of PLC or Programmable Logic Controller that is why it is widely used. The main advantages of PLC are

1.      Industrial automation using PLC very efficient.
2.      They are very fast in operation.
3.      Additional advanced tasks can be perform using PLC.
4.      Easy to use and very good experience.
5.      Automated control is also a great advantage of PLC

Block Diagram of PLC

Here a typical block diagram of PLC is given below. From the below block diagram you can understand the total concept and working procedure of Programmable Logic Controller.

PLC Block Diagram, Block Diagram of PLC, Programmable Logic Controller

Main Parts of PLC

As you see in the above figure, PLC has main three parts,

1.      CPU or Central Processing Unit
2.      Input Module and Output Module
3.      Programming device

Generally, microcontroller or microprocessor is used in Programmable Logic Controller and they are programmed by an external computer. After installing the appropriate program, PLC works.

PLC Working Procedure

Now, let's discuss each block of the Programmable Logic Control circuits which will help you to understand the working principle of PLC.

CPU(Central Processing Unit)

It is the main part of the PLC. It processes all the instructions required for working of the circuit. First, we store the program or instruction in memory. In the operation time, the CPU takes the commands from the input module and then process and ultimately gives the output to the output module.


It is a storage device which stores all data, programs, and instructions.

Programming Device 

It is the device where the program or instruction is written and then using this device the program or instruction is stored to the PLC Memory. The programming device may be a computer, laptop, etc 

Input and Output Module

The CPU or Microprocessor can work with 5V DC supply and it can deliver very small output current. But the input devices or sensor may not work with the same voltage that is 5V DC. So to interface real-world input devices and sensors with the microprocessor, the input module is used. Here the input module always gives 5V DC input signal to the CPU. 

Another important point is that the microprocessor can work with only the digital signal but all the input devices or sensor may not produce a digital signal. In fact, most of the sensors create an analog signal. So another important function of the input module to convert the analog signal into a digital signal.

Microprocessor or CPU can deliver a very small amount of current(in few mA) at 5V DC as output. So we can not drive the loads directly with the microprocessor. Here the output Module solved this problem.

Power Supply

The power supply circuit provides the power supply to all devices such as CPU, Memory, Input module, and output module. Generally, the PLC works with up to 24V DC supply.

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[Explained] PLC Block Diagram | Programmable Logic Controller [Explained] PLC Block Diagram | Programmable Logic Controller Reviewed by Author on June 03, 2019 Rating: 5
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