What are the benefits of using structured text over ladder logic?

Structured text is like regular coding, easier to read and write for those who know programming. It's flexible, letting you use loops, conditions, and functions efficiently. ST code works well across different systems, making it easier to switch between them. Debugging and testing are simpler, and you can easily spot and fix errors. ST encourages modular code, so you can reuse parts in different projects. It's great for handling complex math and data tasks. Learning ST is easier for people with a programming background.

Choosing the correct language is key. I do believe LAD is easier for technicians, and even most programmers, to tune and troubleshoot if they did not develop the code. However, it has its gaps in complex logic operations that can cause it to get busy, difficult to follow, and long. I personally like to create function blocks for heavy mathematics, loops, or repeatable parts of the process using ST, then tie those blocks into the overview of each part of the process written in LAD that more visually ties in variables, values, and set-points to the complex logic written inside the block. This allows the end-users, field techs, and other programmers to more easily tune and troubleshoot issues in the field and still use the power of ST.

Everyone start with ladder so ladder easy to understand and troubleshoot, when it comes to Structure text , we have advantage here we can do indirect addressing. it can avoid multiple networks of ladder

I hate FBD (this is my personal preference) Instruction List (STL in Siemens) is like assembly code - difficult to understand after a time. In my opinion best option is to use - Ladder for typical logic control (and this service engineers will understand) - in advanced controllers like S7-1200/1500 (not S7-300) you can bin STL as SCL is easier to understand - for math use SCL networks (formula written in LAD using basic blocks is not easy to read - in SCL it looks like formula and it is easier to be understood) - for data manipulation (for example recipe handling, communications) use SCL

It depends on the complexity of the application. If it does not involve lot of math, and all that is expected to do is simple sequencing of the controls then it is easier to have it in Ladder as it is a more "visual" tool it is easy to understand at maintenance technician level. "Inefficient" is a little loaded word. Most of the times the hw we choose is pretty fast. So as long as we maintain the required cycle time why bother if it is an efficient code or not. I personally enjoy writing a tight code- but it may be a hangover from those old "resource poor" days and not sure of that requirement in today's world.

Well in 30+ years of programming controllers with several languages to pick from the client has 99% of the time said LADDER LOGIC ONLY because while structured text may have the same functions it is not easy to troubleshoot when something goes wrong. Also, NO LATCHES! And that's because again it's tough to troubleshoot especially if you left off a reset.

Personally I layout my programs in a specific manner to make them easier to fault find on at a later date especially for maintenance technicians who aren't PLC programmers I tend to use structured text inside function blocks with the function blocks sat in ladder code This allows me to use the far superior ST for complex coding in a very efficient manner as you do not have to declare every single variable like you often have to in ladder. If you're dealing with Boolean logic i.e. digital inputs and outputs and latching then keeping them in ladder is far easier to fault find on. If you're dealing with complex structures and arrays then ST is the best way to go about it as it can get very complicated and hard to follow in ladder

I feel "good enough" is the best. So rarely write code in STL. In any case the appropriate commenting of the code is much more important for understanding the logic whether is Ladder or STL. It does not matter whether cat is black or white as long as it catches the mouse! So I insist on writing thorough comments than the language.

Use standard naming convention for tags and local variables. for example I_<AREA>_<DWG_MARK>_<FUNCTION> for physical inputs where area is part of machine (i.e. control desk), DWG_MARK is mark from electrical drawings (for example QA101 - breaker), function is mnemonic for what it does for example HMI_CB and in comment more info. for functions us I_... for inputs / Q_... for outputs etc. (this will be distinguished from physical IQs because of formating - in TIA physical IQs are in double quites ("") and local variables are prefixed with #. This way you can distinguish what is what without looking at interface which makes debugging and commissioning easier. Also tags with DWG marks give you cross reference machine vs PLC vs drawings.

As I mentioned above, creating function blocks for repeatable parts of the process, identical or similar parts of the process, or redundant equipment in the process make it easier and quicker to implement, prove, and tune code. This also allows you to tie functions into the main routine for that part of the process using blocks that give a much more straightforward and simple approach to troubleshoot in the field so long as the logic inside the function blocks is well-developed and proven before it is deployed.

Yes. Modular and reusable code can make your life easy. Something as simple as converting a floating point number to integer it has to go through the same steps - so why not build a simple function and pass on the floating number and collect the result. It reduces the complexity of the main program by reducing number of steps. And is reusable too.