What are the Five PLC programming languages?

The IEC (International Electrotechnical Commission) Section 61131-3 Standard includes 5 languages. This IEC standard specifies some ground rules for standardising PLCs and associated programming languages. Let’s take a closer look at some of the most popular PLC Programming Languages.

The most popular Programming Languages of PLCs are:

  1. Ladder Diagram (LD)

  2. Sequential Function Charts (SFC)

  3. Function Block Diagram (FBD)

  4. Structured Text (ST)

  5. Instruction List (IL)

Ladder Diagram (LD)

Ladder Diagram is a graphical programming language that you use to develop software for programmable logic controllers (PLCs). Ladder Diagram uses internal logic to replace everything except the physical devices that require an electrical signal to be activated.

On relay-logic schematics, a ladder diagram is made up of horizontal rungs with two vertical rails that represent the electrical connection.

All of the necessary input conditions, whether logical or physical, can be programmed to affect the output conditions.

What is a ladder logic and what is ladder logic diagram in PLC

All About Ladder Logic We Need To Know

Advantages and Disadvantages of Ladder Diagram (LD)

Advantages of Ladder Diagram (LD)

  • Ladder Logic is a visual language that provides status confirmations for most instructions. It is simple to implement and troubleshoot. In other words, someone with limited expertise of a certain process can easily go through the programme and comprehend the reasoning.
  • Modular Design | Ladder Logic can be readily adjusted by adding or removing logic. Each rung represents a distinct condition that can be removed or added as needed.
  • Ladder Logic’s resilience and consistency enable the user to implement a wide range of functions. However, the language is strongly standardised and does not provide complete flexibility, resulting in code that is consistent across different implementations.

Disadvantages of Ladder Diagram (LD)

The main disadvantage is that some instructions are not available, which may make programming more complicated, such as motion or batching.

Sequential Function Charts (SFC)

If you’ve worked with flowcharts before, you’ll recognise this PLC Programming language. In Sequential Function Charts, you employ stages and transitions to get to your desired outcome.

Steps play an important role in your programme. These phases contain the actions that take place when you programme them to. This decision can be based on timing, a specific stage of the process, or the physical condition of the equipment.

Transitions are the instructions that you employ to transition from one stage to another by setting true or false conditions.

Advantages and Disadvantages of Sequential Function Charts (SFC)

Advantages of Sequential Function Charts (SFC)

  • Intuitive to Other Programming Languages
  • High Complexity
  • Transferability

Advantages of Sequential Function Charts (SFC)

  • Difficult to Troubleshoot
  • Error-Prone

Function Block Diagram (FBD)

The Function Block Diagram is a graphical language. Function Blocks were created to offer a framework in which you could set up numerous common, recurring operations, such as counters, timers, PID Loops, and so on.

The blocks are programmed onto sheets, and the PLC constantly scans the sheets in numerical order or is decided by links programmed between the blocks.

Advantages and Disadvantages of Function Block Diagram (FBD)

Advantages of Function Block Diagram (FBD)

  • Motion controls work well with the Function Block Diagram.
  • Some users prefer the visual way.
  • The most significant advantage of Function Block Diagram is that it allows you to condense numerous lines of code into one or more function blocks.

Disadvantages of Function Block Diagram (FBD)

  • Hard to Standardize
  • Troublesome at Scale

Structured Text (ST)

Structured Text is a PLC programming language similar to C or assembly. The user enters lines of code that are executed sequentially, evaluates specified functions, performs boolean tests, and activates suitable PLC outputs. For people with an experience in a traditional programming language such as C, C++, Java, or Python, Structured Text enables an easy entry into PLCs. Furthermore, it is easily manipulated in text processors, making it simple to implement without the use of hardware.

Advantages and Disadvantages of Structured Text (ST)

Advantages of Structured Text (ST)

  • It is well-organized and capable of doing big mathematical calculations.
  • It will allow you to cover various instructions not available in other languages, such as the Ladder Diagram.

Disadvantages of Structured Text (ST)

  • The syntax can be challenging.
  • It is difficult to debug.
  • Online editing is challenging.

Instruction List (IL)

This programming language is made up of numerous lines of code, each containing a single instruction. Instruction List is read from top to bottom and from left to right. Because each line is executed consecutively, the Instruction List is very easy to read. Once you’ve mastered the mnemonic codes (Load = LD, Start = ST, and so on), Instruction List is a great language to have in your arsenal since it allows you to write concisely and top time-critical code as needed by your application.

Instruction List, on the other hand, can be more difficult to debug and resolve issues in than some of the other languages. It’s also quite constrained in terms of code structure because “GOTO” is about all you can do to exit the list and run other commands.

Advantages and Disadvantages of Instruction List (IL)

Advantages of Instruction List (IL)

The Instruction List language is useful for applications that require compact and time-critical programming.

Advantages of Instruction List (IL)

  • There are only a few structural options, one of which is the “Goto” command.
  • There may be many errors that are more difficult to deal with than in many of the other languages I have already evaluated.