PLC-5 "hot" swapping of cards

alan_505

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I know you can change out ControlLogix cards with the rack powered.
And I thought that you could not do it with a PLC-5, but a colleague at work did it the other day and it does not seem to have affected it.

So is it advisable to turn off the Chassis power when swapping out PLC-5 cards or not?

Alan.
 
based on personal experience:

it's a random thing ... you're supposed to turn off the power - but I've seen it work OK many times even with the power left running ...

but ...

sometimes (at random) you'll get something like a "stuck run-time error" and the processor will fault out ... you'll have to restart it to get things going again ...

so as Dirty Harry would say: "Do you feel lucky?" ...
 
I know you can change out ControlLogix cards with the rack powered.
And I thought that you could not do it with a PLC-5, but a colleague at work did it the other day and it does not seem to have affected it.

So is it advisable to turn off the Chassis power when swapping out PLC-5 cards or not?

Alan.

Just because you CAN do a thing, does not mean you SHOULD do a thing.
 
I saw a customer pull an analog card out of a running SLC rack and hot swap it. As far as I knew the PLC should have immediately faulted because of a missing IO card, but it worked fine.


As far as the PLC5 - if the card is in a secondary rack through BlueHose the PLC will not know the card was removed, (or even care too much if the rack went offline) but if you pull a card out of the main rack with the CPU in it it 'should' fault the PLC.



I still remember back in early game cartridge computers that trying to insert a cartridge in a Radio Shack Color Computer with the computer on would wipe the cards EEPROM immediately.
 
I know you can change out ControlLogix cards with the rack powered.
And I thought that you could not do it with a PLC-5, but a colleague at work did it the other day and it does not seem to have affected it.

So is it advisable to turn off the Chassis power when swapping out PLC-5 cards or not?

Alan.

Hi Alan

Back two decades ago we had some funny issues with a PLC 5, having randomly analog out card flashing red. Sometimes the CPU came into fault or it was still Running with no faults. Every single time a pop up window appeared on HMI saying ''HMI Loss of communication'' no matter if the CPU was in fault or not (bizarre!!). That PLC has two identical analog out cards so we swapped the cards between them (as no spare card available...lol) even warm or cold but to get the PLC up and running we should toggle the switch from Run to Prog and back to Run but this procedure didn't always worked for us...but was always successful after PLC power cycle.
So I would suggest better power off the chassis before replace/ swap any card maybe avoiding some other issues.
By the way, that Loss Comm problem (nothing to do with the analog cards) has been eradicated by upgrading into a SLC500 plc after a while :)
 
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The advice I was always given was for the 1771 cards, power down the rack first, before removal. I seem to recall that 16 and 32 channel cards were not such an issue as the 4 or 8 channel cards, but memory is a bit hazy on that. I tend to always power down a 1771 rack in any case.
 
The danger you are faced with in removing modules from a PLC-5 chassis is potentially damaging or degrading a module. Also, damaging the chassis/slot.

I've done it successfully, I've also fried a module. I wouldn't do it again. I actually pulled a CPU once under power and scared myself that I had toasted an expensive CPU, but it was OK.

I saw a customer pull an analog card out of a running SLC rack and hot swap it. As far as I knew the PLC should have immediately faulted because of a missing IO card, but it worked fine.

The SLC cannot check modules located in a chassis connected via remote I/O. The remote ASB module does have an ability to store the connected modules in it's own memory, but I think it might only check that on power-up. Either way, that would be a rack fault, not a CPU fault.

As far as the PLC5 - if the card is in a secondary rack through BlueHose the PLC will not know the card was removed, (or even care too much if the rack went offline) but if you pull a card out of the main rack with the CPU in it it 'should' fault the PLC.

What is described here is how the SLC 500 works. PLC-5's do not check for cards in the local or the remote chassis. They have no idea if the module is present or not. However, if you are using remote Flex I/O modules, the logic modules on those units can be hot-swapped even on the PLC-5.


OG
 
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The SLC cannot check modules located in a chassis connected via remote I/O. The remote ASB module does have an ability to store the connected modules in it's own memory, but I think it might only check that on power-up. Either way, that would be a rack fault, not a CPU fault.
OG

The hot swap I saw was a SLC in a single rack, no remote rack, -C9 or ASB. To me that should have faulted the CPU on a missing card.
 
In the SLC's you can disable a slot in the status table. It takes the slot off scan. I have never tried it, but if you disable, you may be able to hot swap without faulting the CPU.
 
In the SLC's you can disable a slot in the status table. It takes the slot off scan. I have never tried it, but if you disable, you may be able to hot swap without faulting the CPU.

That also disables the IO from working. I was testing a CPU in a rack missing a couple needed cards and when I got the cards they would not work until I re-enabled them.
 
The remote ASB module does have an ability to store the connected modules in it's own memory, but I think it might only check that on power-up.

This was my experience on an old RIO rack. Had troubles with modules in a very dirty environment not fully seating and coming loose -- ASB would show as faulted, would just go down the modules pushing on each one, one would *click* into place and faults would clear.

If power had been cycled before I got there, after the modules were all seated the ASB would show faulted and you'd need to cycle power to it again.

Eventually convinced them spend the time to clean it up, and finally upgraded with a much better design.
 
That also disables the IO from working. I was testing a CPU in a rack missing a couple needed cards and when I got the cards they would not work until I re-enabled them.

Yeah, I have disabled an SLC slot and then removed a module. That is back to the issue of damaging the slot or the module, but I didn't have to power down.
Other than that, I have never seen a previously working I/O module removed from the local chassis under power without it causing a CPU fault.

OG
 

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