How does PLC Work?

How does PLC Work
How does PLC Work

PLC stands for Programmable Logic Controller. And, it is one kind of complicated and powerful computer it is an industrial controlling system.  And, PLC continuous state and monitors of the input device. So, take a decision depends on the program to control the output or load.

Generally, it consists of input, output system, power supply, CPU. Central Processing Unit (CPU) takes the information from the contributions and performs logic on the data, basically PLC work by its program.

It will use for industrial automation industrial electromechanical processes. Such as,

  1. Assembly lines,
  2. Light fixtures,
  3. Control of machinery on the factory,
  4. Medicine industry,
  5. Food factory,
  6. Garments industries,
  7. And packaging.

The programmable logic controller is a system that can help to know more about industrial control system. However, there are two types of Programmable Logic Controller you will found. Those are,

  1. Modular PLC &,
  2. Compact PLC.

PLC Programming Language

There is five PLC programming language in the world which are all parts of the International Electro-technical Commission (IEC). Therefore, this IEC standard allows someplace rules that prove its language. Moreover, you can also know more and details about PLC form this link. Here are the five most famous PLC programming languages,

  1. Ladder Diagram (LD),
  2. Function Block diagram (FBD),
  3. Sequential Function Charts (SFC),
  4. Instruction List (IL),
  5. Structured Text (ST),
  6. Ladder Diagram (LD).

Let’s go for more details for those languages.

1. Ladder Diagram (LD):

Ladder Diagram utilizes internal logic to replace all. And, except physical devices that need is an electrical signal to active them. Ladder Diagram generally models from relay-logic. And, which usually uses for physical methods. Thus, like a switch and mechanical relays to control processes. Ladder Diagram is manufacture in the form of horizontal rungs with two vertical rails that present the electrical connection on relay-logic schematics.

The Ladder Diagram does most of the PLC program. Because rung allows us to be organized, and it is straightforward to follow. It supports online editing successfully.

2. Function Block Diagram (FBD):

It is also a descriptive type of language the FBD describes a function between input and output that are connected in the block by connection lines. However, it was raised to make a system so that someone can set up many of the repeatable and everyday tasks like timers, counters, and others.

3. Sequential Function Chart (SFC):

It is used steps and transfers to achieve results this language act as a great function in the program. These steps house the activities that occur when the program will do. However, this decision will base on timing, a physical state of equipment, or a certain stage of the process. The process can break into the main steps that can make troubleshooting easier and faster.

4. Instruction List (IL):

Well, this one is also a textual based language. Moreover, this language answer assembly language. When this language become use as the programming language, then memorial codes are used such as LD, OR, etc. The instruction list contains instructions with every instruction on a new line with any comments. It is valuable for application which needs code that is compact and time-critical.

5. Structured Text (ST):

Formal textual based language and it is a high-level language that is Pascal, Basic, and ‘’C’’. Moreover, you can say that it is a potent tool also. Because it can execute difficult tasks to improve mathematical and algorithms functions along with the reputational tasks. Therefore, this code uses statements that are separated by semicolons and then either input or output.

Working Principle of PLC

The working principle of PLC is program is done, and the program is downloading to its CPU. CPU memory card stores the application and sends it to the output. You can say that the  PLC has a brain, that name is CPU! And it can be hexadecimal or octal microprocessor. PLC work with it two systems. Those are,

1. Control Program:

The control program can carry out all the processing relates to the input signals due to control the output signals depends on the control program. The programming device is the station where the program is written; it can be a handled device on the computer. The power supply works on a power supply of about 24VDC or 220VAC used to power input and output devices.

2. Memory Part:

Its memory will divide into two parts. They are program and data memory. Moreover, the program information is stored in the program memory. But the input and output signals, counter signals are stored in the data memory. The input source converts the real-time analogue to digital electric signals. And, these signals will apply to the PLC in the connector rails. The input signals are stored in the external memory, which is called a bit.


PLC is the main component in the industrial automation and control system. It is a specialized used to control industrial machines and processes.  However, it shares standard terms with typical PCs like memory, CPU, software, and communications. It has come in many shapes and sizes.

Dedicated programming software comes from PLC hardware of tangible manufacturer that allows access and development of user application code.


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