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by sulcate
1204 days ago
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PLCs are often a pain to integrate with multiple systems and are not nearly as versatile and simple as an internet connected pi running python, for certain desired tasks. Please tell me which PLC you can get for $200 that runs python, can query some REST APIs, query and write to some databases, communicate with several other types of PLC and equipment, check a half dozen types of local sensors, and perform complex operations without purchasing a software subscription or having to be programmed in ladder logic. Obviously they are suitable to different tasks, but there's a reason someone might reach for a PI to integrate new functionality, including on top of an existing PLC. They're tremendously handy in this environment, not just used because people don't know better. |
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> without purchasing a software subscription or having to be programmed in ladder logic
I am thinking of cases where a small PLC, some industrial sensors and ladder logic is a good, reliable and easy solution, but someone reaches for a raspberry pi and python scripts because that's what they've been exposed to.
I agree adding something on top of an existing PLC can be great too. In my first job nearly 20 years ago, I did machine automation and we always added an industrial mini ITX PC to our PLC panels. This cheaply added datalogging (an advertised feature for the customer) and remote programming capability (usually an unadvertised feature that made us look really impressive when we could fix something immediately without going to the very remote site). Depending on what was available on site, we could connect remotely by the site's internet, by a modem/landline, or by a cellular radio (configured as a modem, as this predated reasonable prices for data plans). Sometimes the PLCs were from the 80s and none of the competitors would quote anything except tearing everything out and starting over, but would could find a way to add to the old system.
Connecting remotely by some official upgrade from the PLC manufacturer was usually technically possible, but impossible in practice to get authorization to gain access to the network, and get things configured to allow access to the PLC from offsite. But dialing up to our own installed modem bypassed all of that, and since a PC is versatile, there was always some way to bridge the PLC's programming interface to the PC.
I recall that we had to go out of our way to find PCs that didn't look like PCs and were DIN-rail mounted. Anything that looked like a PC would eventually get messed with by someone.