What is PLC Programming? Types & How It Works?

PLC is the short-form of programmable logic controllers that are used in industrial automation. And the controlling method can vary from switches to complex controlling units or structures. This programming was incorporated in the late 1960s so industrial automation could take power from it. It was mainly developed and formulated to control the manufacturing activities of the factories’ processes.

Thus, if you have an interest in the technical field, then learning about PLC can be an exciting thing. Hence if you want to learn about PLC and how it works in detail, then stay with this post.

What is PLC Programming?

What is PLC Programming

PLC programming or programmable logic controller programming is an industrial control system. It is designed to identify the information about input devices and perform some decision-based tasks to control the customer output machines or devices. And it is an important activity that helps control the output device to get the result based on the customer’s need and demand.

The PLC programming can have a textual or graphical form or interface to represent the logic, so the correct command is implemented. PLC software can be downloaded in the PLC hardware of the manufacturers who allow the given type of PLC programming. Generally, the PLC devices or hardware manufacturer allows the user to enter and install UAC or the user application code in their device.

Nowadays, this programming also allows HMIs, which are the Human Machine Interfaces, to show the variables in the device. When the programming gets downloaded to the PLC machine, then it gets ready to install.

Types of PLC Programming Languages

PLC programming is completed using one of its five major PLC programming languages that are given below.

1. Instruction List

It is a textual-based PLC programming language that works like the assembly language. It uses the codes of AND, OR, LD, and many other codes that work on PLC machines. The primary purpose of this language is to use a device that can process the instructions.

2. Structured Text

Structured text is also a PLC programming language that is used for executing complex tasks. It is one of the high-level programming languages such as Pascal and C. It can utilize the mathematical functions with algorithms with any repetitive activities of the machines. Here the codes can contain statements that semicolons can separate.

3. Function Block Diagrams

Function block diagrams are the graphical-based PLC programming language. Here the diagram is used and represents the relations or the functions of the input and the output commands.

4. Ladder Logic

It was the type of PLC programming language that was modeled based on relay logic. And it is mainly used in the switches and the mechanical relay to control the functions or processes. It uses the internal logic system to replace all other than the physical machines that need electrical signals to stay active.

5. Sequential Function Charts

Sequential function charts use the function chart to perform the given action. And this can be decided based on a time taken basis. It uses the transition to perform the specific task through the predefined scenarios mentioned in the chat form. Here the transition means the set of instructions that comes in use to automate the various processes.

Types of PLCs

The PLC or programmable logic controllers can be of different types because of their size and structure.

  • The PLC can also be compact that is known as the compact PLC. And it has the fixed programs of the I/O unit, and Its user or manufacturer mainly controls it.
  • The modular PLC is the PLC machine that has the many I/O units which the user asked for. And these units can be manufactured together, so they can quickly get a customized machine for input and output monitoring purposes.

Each of the languages has its advantages and disadvantages, and the use scenario depends upon the programmer. Thus, the programmers are more likely to switch any PLC programming languages depending on the customer’s need and project demand.

How Does PLC Work?

The programmable logic controller first gathers the information from the connected devices. And these devices are mostly input devices or sensors; then, they process the given information or command. Once it processes the command, then it triggers the result based on the programmed parameters.

The PLC device can also monitor the temperature, run the program automatically, and can turn on or off the processes. Because of these features, PLC programming has become one of the robust technologies used by industry.

In PLC hardware, the essential components are the CPU, I/O unit, rack, and power unit. The CPU is called the brain of the PLC machine that handles all the heavy tasks to run the system automatically at a fast pace. The I/O unit is the sensors of the PLC that work to gather feedback from the machine.

And here the output work to run the processor performs mechanical motions through the device. Here the rack works as the bridge or the pillar that connects the I/O unit with the CPU, so the communication between this two hardware stays stable.

So, the first scanning process happens, then it conducts an internal check; after that, the scan input occurs. Once this process happens, the EPL or the execution of the program logic starts. Finally, it shows the output in the form of mechanical motion.

Why is PLC Programming Used for Industrial Automation?

PLC programming is industrial programming that installs in the PLC hardware to monitor the input and output processes. So that machine can decide on the preprogrammed code stored in the PLC’s memory unit. With the help of this industrial programming, human decisions can become more efficient and fast. Hence now it is implemented in various industries where these PLC machines place several automatic tasks efficiently.


So, PLC programming is the industrial program that comes in use to automate industrial machines. Thus, I hope it’s clear to you what PLC programming is, how it works, and its programming languages. Here we discussed some other terms that will help you make your knowledge strong about PLC programming.

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