What are the common PLC programming languages and standards for feedback control systems?

In the world of PLC programming, there are a few common languages and standards used for feedback control systems. You've got your classic ladder logic, which looks like old-school circuit diagrams. Then there's Function Block Diagrams (FBD), which is kind of like building blocks for your logic. You might also encounter Structured Text (ST), which is more like traditional programming languages with loops and conditions. These languages help engineers tell the PLC how to control processes based on feedback from sensors and other inputs, keeping everything running smoothly and in check.

If we talk about Graphical Language, it Resembles electrical relay logic diagrams, making it intuitive for electricians and control engineers. Also, the visual representation of logic makes it straightforward to debug and modify. It is widely used PLC programming language, especially in the manufacturing and process industries.

Ladder Logic (LAD): Ladder Logic is one of the most traditional and widely used programming languages in PLCs. It's based on relay logic diagrams and uses graphical representation resembling electrical circuit diagrams.

Yes, ladder logic is indeed a foundational programming language for PLCs, known for its simplicity and direct representation of electrical circuits. While it's great for basic control tasks and easy troubleshooting, its lack of advanced features like variables and functions can make it less suitable for complex systems where more flexibility is needed.

I think it's important to highlight that structured text (ST) is not uniformly implemented across manufacturers, despite the standard's specifications. By 2013, the third edition of the IEC 61131-3 standard had already expanded ST to include object-oriented programming (OOP). This update has been adopted by some manufacturers (such as Codesys and TwinCAT) but, regrettably, not by others (like Siemens and Rockwell). Without OOP, ST is most akin to Pascal. However, with OOP, it becomes more comparable to C++ or Java, as it then allows for more advanced programming techniques. In my opinion, with its IEC 61131-3 enhancements, ST is the language that is most likely to appeal to non-PLC programmers.

most of professional programmer use STL because many command of STL reduce the program like arrey function and many more. But in ladder have not these type of command so in ladder program size is vary large from the STL.

It is appropriate for complicated algorithms and computations because it is comparable to Pascal or C. For people with experience in programming, it is simpler to write and comprehend. Perfect for jobs that need a lot of data processing. sophisticated algorithms for control. data processing and mathematical calculations.

Structured Text (ST): Structured Text is a high-level programming language, similar to Pascal or C, commonly used for complex control algorithms and mathematical computations in PLCs. It allows for more structured and text-based programming.

Absolutely, structured text provides a higher level of flexibility and power compared to ladder logic. Its resemblance to traditional programming languages like Pascal or C allows for more complex calculations, data manipulation, and algorithm implementation. However, it does come with a steeper learning curve and may not be as intuitive for those accustomed to graphical representations like ladder logic.

In feedback control systems, common PLC programming languages and standards include ladder, FBD, ST, and SFC. Ladder logic is widely used and resembles electrical relay logic diagrams, making it intuitive for engineers from an electrical background. FBD break down control processes into interconnected blocks, simplifying complex systems. Structured text offers a more traditional programming language approach, resembling high-level languages like C, providing flexibility for complex algorithms. SFC enable developers to visualize and design complex control strategies using graphical representations. These languages and standards ensure efficient and effective programming of feedback control systems in industrial automation.

Function blocks are easy to troubleshoot. I always prefer Ladder language inside FBD. Troubleshooting FBD is easier than ladder language.

I have come across the Functional Block Diagram programming language recently in one of my projects and I liked how it helped me make sense of the logic better compared to Ladder Logic language. I could see the complete blocks and their input-output parameters. I could see the flow of data by connectors and arrows. I could also force the data easily for simulation, testing, and debugging purposes. I feel that the routine I was checking out was not complex and therefore I was able to make sense of it easily but if there is a programming with high complexity control loops, debugging will be an issue.

I always prefer ladder logic. Easy to use. Make some standard like make a routines For each function and it is easy to troubleshoot for technician.

It represents functions with blocks, which facilitates the visualization of data flow. Also encourages the usage of function blocks in code reuse. Widely utilized in process industries due to its clear representation of complex logic.

Indeed, instruction list (IL) operates at a lower level, akin to assembly language, offering efficiency and compactness. However, its reliance on mnemonic codes and operands can make it challenging for both writing and understanding, particularly for beginners or in scenarios involving complex control systems. IL finds its niche primarily in legacy systems or specialized applications where direct hardware access and maximum efficiency are paramount.

Sequential function chart (SFC) is indeed structured around steps, transitions, and actions, drawing from the Grafcet methodology. It's particularly adept at modeling sequential and parallel processes common in feedback control systems. However, the lack of explicit specifications for action order and timing within steps can introduce ambiguity and make understanding the program flow challenging in some cases. Despite this, SFC remains a valuable tool for visualizing and designing complex control systems with discrete events and states.

Exactly, IEC 61131-3 serves as the backbone for standardizing PLC programming languages, ensuring consistency, interoperability, and portability across different platforms and vendors. By defining syntax, semantics, and common elements like data types, variables, functions, and libraries, it offers a unified framework for PLC programmers to work within. This standardization ultimately enhances collaboration, simplifies maintenance, and promotes compatibility among PLC systems and applications.

Programming a PLC can be done using the mentioned methods, but the main thing to consider is that whatever the program is used, the end user should be comfortable with it. Any further changes, amendments and modifications should be conveniently incorporated by the maintenance staff, so the programming language used should be clear and concise. Understood by all parties using it. This should be the first consideration for any system programming irrespective of the system being operated. PLC normally are used in cases where process are not very complex or sophisticated so the programming should also match the level of performance.

First Point Control Loop whether Feedback or Feedforward they are not dependent on any Programming language and can be written in any of IEC-61131-3 or vendor specific or Application programming language. People from different background uses based on their confidence level. Ladder Logic : Electrical people uses this language as it is near to the SLD Function Block Diagram: Digital Electronics people love to use this. Structured Text: People trained in Application programming use this language to write logic.

Ladder logic is the easiest to understand for majority of the professionals. It is the best choice for programming feedback control systems in my opinion. It lacked the flexibility of supporting variables for complex programming, however recent updates on softwares are getting these problems fixed.

Using the Ladder logic with clear tag and description which represent field device or process conditions result from the expected command