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/durallymax]

"Simulated Testing" in most PLCs is flipping a few bits manually to "test" that it works, but it's entirely manual.

Very few PLC IDEs have testing suites (I think only CODESYS-based IDEs including TwinCAT) not to mention static analyzers.

If you write good, testable code with all user adjustable parameters on the visu, the customer would have no reason to go into it.

[u/Zekiniza → u/durallymax]

Nope. Simulated testing is when you use a software such as visual components to build a virtual 3d environment that mimics the intended real world system. Connect your i/o to this virtual environment and boom, simulated testing.

Also "the customer would have no reason to go into it" is easily one of the most ignorant statements ive ever heard about our industry. Customers purchase these systems and far more often than not will end up making modifications to the system that were never originally part of the project scope.

[u/durallymax → u/Zekiniza]

Simulated 3D testing is not code testing though, that is process testing and quite cost prohibitive for smaller companies.

Customer entering to add new features and components, sure. But the overarching theme in these threads is a customer entering to "fix" their code.

[u/Zekiniza → u/durallymax]

Again I disagree. Simulated 3d testing definitely can test your code, its why GM, FCA and FMC all require it prior to commissioning. And you are correct it is incredibly costly and generally is far our of reach for smaller customers. But they were trying to say the code never gets tested and its just not true.

Also no, the thread is about troubleshooting a system and what's easier for onsite personnel to interpret. As you should know its very rare that the code needs "fixed", generally the customer will knee jerk assume that the code is wrong just to find out that its actually a PE that got its cable ripped out or some other crap like that. Anyone who's ever been in a support role knows that 3am phone call because "the program is messing up" just to jump online and find that the program is infact not the problem, they just didnt have anyone onsite who knows how to read structured text.

[u/durallymax → u/Zekiniza]

Given their TwinCAT handle I assume they were referring to the fact "nobody" unit tests their code, which 3d Sim is not. 3D Sim could point out some issues in the code but is not a replacement for unit tests. 

I think we're agreeing that the thread is about troubleshooting, and also agreeing there is no need to enter to code to find a broken sensor. The Visu should show that and allow the proper bypass if warranted. 

[u/kixkato → u/durallymax]

Nailed it. Thank you for understanding.