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Chrisk81

Frustrations

9 posts in this topic

Ok so I have a supervisor for our instrumentation group that will not listen to us when we tell him that it is not recommended nor is it guarenteed to work if you hot swap a PLC 5 analog in card. Just the other day he got mad becasue he swapped out five cards before one finally took. I told him that the cards probably was not bad and when I tested it I found this to be true. So what I am wondering is why. I have tried to think of the best way to explain to him why this is the case and how it actually effects the rack but what i come up with does not seem to be enough. Is there anyone who has more technical or design knowledge on this topic that could better explain it so that I can get him on board with the idea of powering down a rack then inserting card and then powering it back up.

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Explain to him that the PLC has built-in error checking routines and hardware health monitoring, and that the PLC will detect the removal as a failure. Then mention the inrush current and shock to the board when it is inserted live, and the fact that not all contacts on the card will make with the rack at the same millisecond, and thereby may create an electrical issue. And then explain to him it's clearly indicated in the manuals that this is the case, and that hot swapping is not recommended. It's nothing you have control over, it's the design and firmware in the PLC. You don't ask Dell why the power button on the PC doesn't let you boot faster do you? Some people do not understand electronics, and even less understand RTFM!!!!

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Yup, show him the manual. See picture below. Not only for above reasons it could be a SAFETY issue. Edited by Mickey

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PLC 5 (1771) Analog modules typically have HARDWARE configuration jumpers, and SOFTWARE Configurations that are written to the card once during PLC first pass power up. Blindly swapping modules without confirmation of hardware jumpers being set to application design, can lead to unsafe machine operation. I also would not expect the module to operate correctly as the configuration file probably won't be written to the module during a HOT SWAP. Tell your boss that you will do it your way, (following the rules and instructions), and if that does not please him, let him do all the "hot-swapping", and he can incur the unhappy results of doing so.

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Thanks for the responses. That is what I am going to try again but this time if he fials to listen then I will tell him and the plant manager that our group will not be responsible or guarentee these actions.

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Chris I read through these posts and they all make sense but you also need to spend a few minutes in the instrumentation supervisors shoes. Just my HO but - If he's been in the instrumentation field any length of time he has worked with instrumentation {note not plcs} for ages. You can hot swap a properly designed wheatstone bridge and the same goes for porperly designed analog amplifier cards based on the good ole chips like the lm317 or lm741. To design cards to tolerate hot swap costs time and material. In this age of minimal margins that kind of robustness has not been built into your average plc i/o card. Ask him if he would hot swap an op amp chip and he'll probably say no way cause if the input voltage arrives before the rails you fry the chip. But Instrument techs don't hot swap the chip they hot swap the amplifier card which has protective R/C circuitry. The maintenance techniques which work on good well designed instrumentation will be ruin for PLC I/O. You wouldn't put a Ford Engine together with a Buick Transmission and a Chrysler Rear End unless you were a glutton for punishment. The same hold true for using "good instrumentation practices" on PLC hardware. He's in a different world and you need to take time and understand his and explain the difference to him.

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well said, Bob ... naturally it's hard to be sure from where we sit, but the guy probably isn't hot swapping the cards just for fun ... more likely his reason is to keep production up and running so that everyone can get paid ... think: $$$ probably the best way to handle this is to convince him that the PLC-5 cards haven't been designed for hot swapping – and that doing it anyway is almost certain to cost MORE money in the long run ... think: $$$$$$ finally – if hot swapping really IS a definite requirement, then you might consider replacing the PLC-5 system with ControlLogix ... those cards ARE designed for hot swapping ... the buzzword is "RIUP" ... (Removal and Insertion Under Power) ... think: $$$$$$$$$$$$ but if that's what you NEED, then the cost of an upgrade might be worth considering ...

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OR investigate why analog cards have to be replaced at all; they should last a very long time if they are commissioned correctly. Some kind of spike knocking them out temporarily? Is so, you may want to invest in some protective signal conditioning, probably less then a new card. Edited by jstolaruk

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Not to disagree, but it was my understanding that you don't really "hot-swap" or "RIUP" a ControlLogix module. The preferred procedure is disable the slot by SSV Command, Swap the now "idle" card and then re-enable the slot by SSV Command. This is still "RIUP" in the strictest sense but no I/O communications are occuring during the RIUP Operation.

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