Oh I can tell stories too! Meanwhile these guys often have huge amounts of practical experience as electricians or control technicians/engineers to go with their PLC skills, so you can't just say we should get rid of them either.

Breaking into the industrial market is tricky if you don't have connections too. And if you're hired as the PLC programmer, it's sometimes an afterthought AFTER the plant is already built. "What do you mean it'll take another month? The plant is finished, isn't it?".

Oh, and some projects ban "PC"s to begin with. Which sort of excludes any kind of PC programmer. And it sort of even makes sense. A lot of default PC behaviors (especially commercial software), are no longer user-unfriendly but potentially very expensive or even user-lethal when attached to a physical plant.

Sounds like I could learn some things from you (and maybe vice versa). Poke me on the email in my HN profile!

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aliasxneo 3 hours ago | parent [-]

Yes, I don't mean to poke fun solely on the integrators. I've seen the "software first" type land in the same role and flail just as hard, if not harder. I recall one individual, who was quite proud of his "beautiful" ladder logic code, after about 3 months of being at the company ended up destroying a $100k+ chiller plant by cavitating all of the pumps because they didn't understand head pressure.

I think that's one of the core difficulties with PLC programming. You have to have strong knowledge on traditional science fields like thermal dynamics, material sciences, fluid mechanics, etc., while also understanding the limitations of a 16 bit floating point integer and why overflowing that can be catastrophic.

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amluto 2 hours ago | parent [-]

Sometimes I wonder whether one could design PLC-style software by first expressing the system’s constraints and then writing the actual code and having either (preferably) formal verification that the code will not violate the constraints or (less preferably) enforced assertions that will send the machine into a safe state if the constraints do not hold.

The system I mentioned in my other post controlled some VFDs, and one would occasionally get stuck running at minimum speed forever instead of turning all the off when it should have. Fortunately the only harm done was a stupid waste of power and and nothing was physically damaged. If it had gotten stuck at maximum speed it might have been a different story.

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aliasxneo an hour ago | parent | next [-]

A lot of PLC controllers can certainly be unforgiving. I mentioned overflowing a 16 bit float point because that's exactly what happened at a waste water treatment plant I was called out to and the resulting regulatory fiasco that ensued probably cost the company tens if not hundreds of thousands of dollars.

I'd love to see more formal methods come to the field. Part of me says I'll return one day, maybe if AI kicks me out of my software field, but I'd really want to come back at a position I could healthily influence towards safety and correctness.

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tedd4u an hour ago | parent | prev [-]

Seems like, here in the 21st century, one could reasonably have a model of the plant that tests could be executed against. Anything like that exist?

	▲	Kim_Bruning 39 minutes ago \| parent \| next [-]
		We're often talking about custom plants here, or plants made in very low volume. Making a simulator for that can be prohibitively expensive, since you can't amortize the cost. For particularly important/expensive plants it still sometimes gets done. Though note the simulator might not be able to capture all the nuances of the real world deployment, so it might not be sufficient. Meanwhile having a separate copy of the plant is also not often viable, once the plants get to any kind of size. edit: After having 'someone' fact check and remind me: there are quite a number of simulation tools available that can sometimes partially do the work.
	▲	aliasxneo 34 minutes ago \| parent \| prev [-]
		It can become really complex. As an example, try to predict resonant frequencies on an entire plant full of rotating equipment. It can be done, but it often requires very expensive equipment and skilled technicians capable of using it to profile a plant. And that's just one potential problem you can run into.