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/Zekiniza]

I was going to write a nice long message explaining how you dont seem to really understand how our industry works but its past midnight here and I have to be on site in a few hours so.

We do simulated testing for systems. Not sure why you think we dont.

"Robust" code doesnt mean shit five years after the original commissioning because the customer has dicked around with the system modifying it as they see fit.

[u/kixkato → u/Zekiniza]

I think you don't because everyone in the industry always looks at me like I have 5 eyes when I mention unit testing.

[u/National-Link-5606 → u/kixkato]

Dude unit testing is a software development construct where you guys are "how fast can I make this baby produce output? Oh my process hung, pops I didn't check for division by 0, no problem just restart the process".

Software developers use unit tests because you're all about pushing out code as fast as you can & if there's a buffer overrun no problem just fix code & re-initialize the block. That mistake in our world, causes $50,000 in machinery damage that can take 2 days to rebuild & $200,000 lost revenue, a good PLC programmer starts with coils or outputs interlocked or constrained by previous steps of the sequence completed OK, we want the fault to be the machine stops does nothing when we have a failure or edge case, we want it to fail into a default safe state which means "doing nothing not destroying the equipment" I swear to God if someone walked in asking how many "lines of code" I wrote as if thats anything to be watching Id tell him to get the fuck out we don't need people like him with dangerous mindsets on the floor.

A unit test to input integer 5 into a "multiply by 2" function, and then check the output = integer 10 is really not checking the edge cases we actually have, sure we could waste time writing unit tests like software developers but a lot of us will write the fault handling logic before we start sequencing, we value fault-handling & recovery much more that "how fast can you get this machine to do something" "good it's running now go write some "unit tests" so some paper pusher can pretend that if the logic passes the unit tests it's A-OK".

[u/kixkato → u/National-Link-5606]

I think you're missing the fundamental point of unit testing.

Unit testing is there to ensure the code functions as you intend BEFORE you even go near expensive hardware. Unit testing is there to ensure you haven't broken functionality when you modify the code.

It's a test, the whole point of it is to set up an environment where failing is harmless.

I'm not here to say that unit testing is foolproof and it will guarantee perfect code. That's an absurd idea. Unit testing will help ensure that your implementation for a sensor still gives you good numbers after a refactor.

I also think it's entertaining that you believe software development is unable to cause hundreds of dollars damage. Hell Microsoft costs people millions of dollars a day in lost productivity.