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PLC programming Languages and its Applications?

Introduction: –

Programming of PLC (Programmable Logic Controller) is a very essential part of industrial automation systems. in this article, I will give you an overview of all PLC programming languages and their applications.

IEC (International Electrotechnical Commission) provided standards for PLC programming languages.

As you know PLC is an industrial-grade computer. And PLC is flexible compared to old relay logic circuits only because of programming capabilities.

For PLC Programing IEC provides some standard languages according to the graphical and textual representation of languages.

IEC 61131-3 Standard

According to IEC standard 61131-3 is all about software architecture and PLC programming languages. There is a list of five PLC programming languages mentioned in the IEC standard.

  • Ladder Logic (LD)
  • Function block diagram (FBD)
  • Sequential Function Charts (SFC)
  • Structured Text (ST)
  • Instruction List (IL)

PLC Programming languages are divided into two parts first is Graphical Programming Languages (GPL) and the second is Textual Programming Languages (TPL).

so, I list out these languages according to their types. Graphical programming languages are easily compared to Textual languages.

Graphical Programming Languages (GPL): –

  • Ladder Logic (LD)
  • Function block diagram (FBD)
  • Sequential Function Charts (SFC)

Textual Programming Languages (TPL): –

  • Structured Text (ST)
  • Instruction List (IL)

Brief about PLC Programming languages and Their applications:

1. Ladders Logic

A short form of Ladders Logic programming language is LLP. It is most commonly used in PLC programming. As the name suggested structure of this language is like a ladder as you can see in this picture.

LLP programming language for PLC

In Ladder logic, you have to create logic between two power lines. In two power lines, one is for supply and one is for ground according to logic PLC reacts with input and gives output according to logic.

Rung is a horizontal connection of two power lines. PLC scans each rung over and over according to its scan time. Usually, the scan time of PLC is in milliseconds.

Applications of Ladders Logic (LD): –

LLP is the most commonly used programming language. By using Ladder logic, you will easily create Timer and Counter-related tasks.

  • Traffic 🚥 Light signal
  • MCC panel
  • DG Panel
  • Industrial Lighting

2. Function Block Diagram

The short form of the Functional Block Diagram is FBD. FBD is another graphical-based programming language used for PLC programming.

In the FBD programming language, there are Different Visual boxes given for sequential, Logical, Timing, and counting tasks. After using these boxes, you will be able to create PLC programs.

FBD Programming Language for PLC

Application of Function Block Diagram (FBD): –

FBD is a very widely used PLC programming language. Using FBD you will be able to create very complex plc tasks. FBD language is mostly used in the following fields.

  • Power Plant
  • Cement Plant
  • Oil Refinery

3. Sequential Function Charts

The short form of the Sequential function chart is SFC. A sequential function chart is also used for the operation of a process sequentially like after some process another process will be started to execute.

SFC programming for PLC

Application of Sequential Function Charts (SFC): –

This programming language is mostly used in Batch processing. SFC programming language is mostly used in this field.

  • Pharma company
  • Automobile production plant
  • Food Processing Plant
  • Dairy Industry
  • Packaging Plant

4. Structured Text

Structured Text Programming language is not most commonly used in industry because of the complexity of this language.

Complex logic development by using ST language becomes more complicated. But for some applications, ST programming language is used. ST languages are related to another programming like C, and C++.

Applications of Structured Text (ST): –

The application of the ST language is very least compared to other languages.

Usually, a Programmer from an IT background is use ST language because of His/her familiarity with the higher-level languages. ST is more popular in complex PLC programs.

5. Instruction List

Instruction List is the replacement for ladder logic language. or you can say it is converting LD program diagrams into word format.

IL language is the most complicated compared to all other languages. you can see the conversion of ladder logic to instruction List as per the given below image.

Instruction List Programming Language for PLC

Application of Instruction List (IL): –

The application of the IL language is very narrow because of the complexity of the IL programming language.

IL language is only used for the replacement of the ladder logic diagram. If somebody will not from an instrumentation background, they will find this language useful.

EndNote: –

We see that Graphical Programming Languages are more popular than Textual based Programming languages.

so, my advice is if you want to start Learning PLC programming then first start with Graphical-based programming languages.

Nowadays Higher-level language is also used for designing more complex in PLC. And Higher-level language supported PLC is now available in the market if you want to know which are then please check my post on PLCnext Technology.

I hope you find this post interesting. You will also check out my previous post on What is MES (Manufacturing Execution System) Software.

Instrumentation and Control Engineer | IAS Member


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