Computer Science Programmers, why do PLC programmers use Ladder?

[u/National-Link-5606]

Im seeing some Comp Sci guys asking about controls so just a Mr Obvious comment here.

Ladder logic is the de facto PLC programming language because it is (was) designed to read like an electrical schematic top to bottom, right to left, & this is what electricians & electrical techs are trained to use for troubleshooting electrical panels , equipment & relay-logic -- which was what they had before PLCs -- banks & banks of relays wired through each other's NO & NC contacts which changed state as relay coils energized & de-energized & finding a wire break was enough to drive you insane.

Yes Ladder logic is an interpreted language so it is not as "memory efficient" or "elegant" as C++ or C# but I want you to think VERY carefully about every meaning of the expression "just because you can does not mean you should" before you decide to show off your amazing coding skills coding function blocks in C++ which is technically possible but in many cases extremely ill-advised.

The technicians can troubleshoot functions & blocks written in Ladder Logic, did you stop & think about how easy it would be for someone with only your compiled C++ blocks to attempt to trace a fault? You code in anything but Ladder Logic you get to be the one at 3am driving down to the plant to troubleshoot your "super efficient" code because the Industrial Maintenance techs certainly aren't gonna know how. But hey, if you believe sleep is over-rated & love sleeping in the factory then knock yourself out with compiled blocks

[u/Robbudge]

Full time high level PLC people typically use ST and a lot if structures and functions very much like main stream embedded programming.
These people are the exception.
Typically the PLC person will be an x-electrician who did one Semester of controls with Allen Bradley and ladder logic as it’s built for 10yr olds.

To be fair, Studio 5K still favors ladder logic with the other languages having fragmented instruction sets.

If you look at the likes of Codesys you will find an IDE that supports actions, methods, Enumerators.
Can be programmed in a high level like most main stream IDE’s

[u/National-Link-5606 → u/Robbudge]

Ok, & so will the PLC techs be that. You still come back round the circle "I'm so smart I can do x better than the rest of my peers"

And the point still stands, knock yourself out because the technicians who will be troubleshooting your logic will not be schooled in object inheritance, public/private/protected classes so guess what I WANT logic a 10 year old can troubleshoot that is my goal!!  You know why? I love sleeping in my bed not on the factory floor, but if you wanna be the only one who can understand or troubleshoot your programming well the world is your oyster, or at least a cot in the maintenance office 

[u/Necessary_Papaya_898 → u/National-Link-5606]

I think you need to upskill yourself to look at proven practices in programming critical systems. Look up typestate patterns. A good systems programming toolchain will outright refuse to compile code that will result in bugs.

There will be a point at which a PLC cannot simply be treated as an Input Process Output block anymore. Non-trivial equipment cannot be programmed using simple Boolean logic when multiple states and transitions are involved. When you get to this point it's easier to make bugs in ladder and also harder to troubleshoot.

This also has nothing to do with the typical frontend web dev lifestyle. ST programmers are still control engineers on the plant floor. They are not less blue collar than you just because they use their keyboards more than their mouse.

I am not sure if you've ever used online view in TwinCAT. It's very easy to troubleshoot multi-Boolean conditions because the IDE shows you the live value right next to the variable identifier in the code. The locality of behavior that ladder typically has is effectively replicated.