IEC Languages - Which language??

[marke]

The IEC 6-1131 programming languages cover a wide range of programming skills.

Instruction List (IL) is a legacy language from early days of PLC programming and is probably the least used language of the suite today.

Ladder Diagram (LD) and Function Block Diagram (FBD) are both graphical programming languages designed to provide a familiar environment for electricians who are used to assembling relay logic circuits, perhaps using additional function blocks such as timers and counters. For pure logic sections of the project, these can provide a simple program to write and to follow, but when the logic moves away from simple contacts and coils, or basic function blocks, the languages become quite clumsy but still workable.

Scripted Text (ST) is a "plain language" programming language that handles data processing, analog values and mathematical functionality in what can be essentially a self documenting program listing. The text format and syntax is very similar to Pascal with similarities to C, C# Python and similar languages.
Computer programmers adapt to ST programming very quickly.

Instruction List is the most basic of the languages and probably the least intuitive. It is essentially the "assembly language" programming of PLCs. -Expect higher programming frustration and reduced readibility from the use of the Instruction List language. It is probably a reasonable way to mask IP and functionality.

Sequential Function Chart (SFC) is perhaps one of the most powerful tools to use in the IEC language suite. I prefer to consider SFC as a multi-dimensional State Machine than a language, providing an environment and tool set that enhances a well structured program design, debugging and ease of augmentation.
Brake the program design into a series of States and rules to move between the states, then program that in SFC.
Code can then be added to each state in either ST or LD. Some Steps (States) can be written in LD while others are in ST. It is not necessary to focus on one language only.

Which language should I use?  that is entirely up to the programmer. Use which ever language performs your task the best. While you can only use one language within a code module, you can use multiple modues and different languages in the modules. For pure relay logic, consider LD. For visual Function block programming, consider FBD and for numeric processing, it is hard to go past ST.

There is not right and Wrong, if it works for you, then it is right for you.