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The site is kind of slow lately what with the banning and the election and all. In another thread @gpop was talking about taking out PLCs that turn out to do little or nothing in machines. How about a thread about where you got rid of a PLC?
I have a story about eliminating a PLC, not in a machine but in a convoluted stormwater system. I was subcontracted by a vendor of the engineering company that maintains the site for the owner, a mega-corporation. The companies that designed and installed the system were long gone, little had been done other than routine maintenance for over 15 years, which tells me they did a decent job. The engineers only had a general understanding of how the system worked. They had huge reams of records and documentation, but little of it relevant.
Anyway after a lightning storm the system isn't getting a pond level signal, which it gets from a 4-20ma transducer. They ordered an identical replacement transducer and sent me out to replace it. The I tested the transducer, found it indeed was dead, replaced it, tested the replacement, and it worked on its own not connected to the system. But the system still wasn't operating. I have no idea how to or if I can fix it but they have nobody else so they have me give it a go.
Some wire tugging reveals the 4-20ma level signal goes to a Koyo DirectLogic PLC, which I think is now the Automation Direct Clic. There is no documentation for the PLC and they can't get hold of the contractor that installed it. I have never programmed one of these, don't have any of the necessary cables or software.
But all this PLC has is one 4-20ma input and two 4-20ma outputs. What the hell. But anyway nothing at all was coming out of the outputs, so I declared it fried / dead, figuring the surge got it when it got the transducer. I tell them I am in the dark but it could be who knows how much work to reverse engineer the PLC. They say keep going.
More wire tugging and it turns out the 4-20ma outputs go to two separate 4-20ma inputs on a very nice fancy programmable pump controller. What the hell. Why would a nice fancy controller want the same information twice? I dig into the programming and talk quite a bit to the engineers about what the system is supposed to be doing, what that pump controller is supposed to do.
We determine that due to some limitations in the settings of the controller, for the automation and alerts they need, it needs the pond level on two inputs. There was no scaling or changing of the signal: it was looking for the raw unaltered tranducer output on both inputs. The PLC was being used to take the signal inputs and regenerate it on two outputs. So this won't be so hard to reverse engineer.
Another what the hell at this point - why not just loop the 4-20ma through both inputs? They had it looped through a display and another controller, whoever designed this understood looping 4-20ma. Well, I tried that, and that's when I learned that since those 4-20ma inputs on the pump controller are not isolated, you can't loop through two of them. I suspect the person that designed this learned the same lesson the same way, they planned to loop it through two inputs.
I think they put in that PLC as a kludge to get things going. Rather than saddle the customer with what would probably be another albatross someday, I searched around and discovered a 4-20ma splitter that was made for exactly this kind of task. Still a kludge, and not all that much less expensive than a cheap PLC, but zero maintenance. Hopefully less delicate with surges, but certainly quicker to replace with a surge.
I also installed 4-20ma surge protection on the signal, but it didn't work. Luckily the engineers decided to keep a spare transducer on site, because the transducer was destroyed again the next year and it also zapped the splitter. Luckily the splitter had four outputs, and only the two that were connected to the pump controller got fried, I was able to move to the remaining two outputs of the splitter and keep running. The customer was just happy the system wasn't offline for long the second time. I told them to buy a spare splitter as well, set it right in the DIN rail next to the one that's in production. With the Phoenix style terminals and a little slack it can be switched in about thirty seconds taking your time.
This was all T&E work for me. It was a lot of T and a fair bit of E due to drive time to a remote site. I think I earned their money, I had to do a lot of learning on their clock, but somebody had to do it. It sure isn't my fault that lightning strikes. I improved it a bit over what was there before. As a result of what I learned in the process, I was able to help them cheap and easy with a lot of unrelated issues in the future.
When the engineering company was bought a couple years later, they fired or moved everyone and I stopped getting calls from them, but who knows if I've seen the last of them. I should have pasted a business card sticker inside the control cabinet.
I have a story about eliminating a PLC, not in a machine but in a convoluted stormwater system. I was subcontracted by a vendor of the engineering company that maintains the site for the owner, a mega-corporation. The companies that designed and installed the system were long gone, little had been done other than routine maintenance for over 15 years, which tells me they did a decent job. The engineers only had a general understanding of how the system worked. They had huge reams of records and documentation, but little of it relevant.
Anyway after a lightning storm the system isn't getting a pond level signal, which it gets from a 4-20ma transducer. They ordered an identical replacement transducer and sent me out to replace it. The I tested the transducer, found it indeed was dead, replaced it, tested the replacement, and it worked on its own not connected to the system. But the system still wasn't operating. I have no idea how to or if I can fix it but they have nobody else so they have me give it a go.
Some wire tugging reveals the 4-20ma level signal goes to a Koyo DirectLogic PLC, which I think is now the Automation Direct Clic. There is no documentation for the PLC and they can't get hold of the contractor that installed it. I have never programmed one of these, don't have any of the necessary cables or software.
But all this PLC has is one 4-20ma input and two 4-20ma outputs. What the hell. But anyway nothing at all was coming out of the outputs, so I declared it fried / dead, figuring the surge got it when it got the transducer. I tell them I am in the dark but it could be who knows how much work to reverse engineer the PLC. They say keep going.
More wire tugging and it turns out the 4-20ma outputs go to two separate 4-20ma inputs on a very nice fancy programmable pump controller. What the hell. Why would a nice fancy controller want the same information twice? I dig into the programming and talk quite a bit to the engineers about what the system is supposed to be doing, what that pump controller is supposed to do.
We determine that due to some limitations in the settings of the controller, for the automation and alerts they need, it needs the pond level on two inputs. There was no scaling or changing of the signal: it was looking for the raw unaltered tranducer output on both inputs. The PLC was being used to take the signal inputs and regenerate it on two outputs. So this won't be so hard to reverse engineer.
Another what the hell at this point - why not just loop the 4-20ma through both inputs? They had it looped through a display and another controller, whoever designed this understood looping 4-20ma. Well, I tried that, and that's when I learned that since those 4-20ma inputs on the pump controller are not isolated, you can't loop through two of them. I suspect the person that designed this learned the same lesson the same way, they planned to loop it through two inputs.
I think they put in that PLC as a kludge to get things going. Rather than saddle the customer with what would probably be another albatross someday, I searched around and discovered a 4-20ma splitter that was made for exactly this kind of task. Still a kludge, and not all that much less expensive than a cheap PLC, but zero maintenance. Hopefully less delicate with surges, but certainly quicker to replace with a surge.
I also installed 4-20ma surge protection on the signal, but it didn't work. Luckily the engineers decided to keep a spare transducer on site, because the transducer was destroyed again the next year and it also zapped the splitter. Luckily the splitter had four outputs, and only the two that were connected to the pump controller got fried, I was able to move to the remaining two outputs of the splitter and keep running. The customer was just happy the system wasn't offline for long the second time. I told them to buy a spare splitter as well, set it right in the DIN rail next to the one that's in production. With the Phoenix style terminals and a little slack it can be switched in about thirty seconds taking your time.
This was all T&E work for me. It was a lot of T and a fair bit of E due to drive time to a remote site. I think I earned their money, I had to do a lot of learning on their clock, but somebody had to do it. It sure isn't my fault that lightning strikes. I improved it a bit over what was there before. As a result of what I learned in the process, I was able to help them cheap and easy with a lot of unrelated issues in the future.
When the engineering company was bought a couple years later, they fired or moved everyone and I stopped getting calls from them, but who knows if I've seen the last of them. I should have pasted a business card sticker inside the control cabinet.
