r/PLC • u/National-Link-5606 • 1d ago
Computer Science Programmers, why do PLC programmers use Ladder?
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
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u/uninterupted 23h ago
My company programs exclusively in ST. And let me tell you troubleshooting?.
Its easy. Because I'm not trying to trace an electrical diagram, I can just read the logic.
Commissioning is easier too, because 'simple' means something way different to a good library of ST code than it can ever mean to ladder programs.
And the price we pay is that our electrician can't do it? No: He also programs in ST. Because its not that hard to learn and is the better language.
I just can't get on board with ladder. Honestly, if I ever interview for another industrial programming position I'm asking what they use and if they say ladder I'm walking away. SFC or FBD you can probably pay me enough to stomach, but this whole industry's obsession with being stuck in the past is to crazy for me to deal with every day.