PLC5 remote I/O expertise!

Ivan86

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Hello. Could anybody with PLC5 networks experience give me some idea what could be wrong with our network?
We have Controller 5/25 with remote I/O racks. ( some are old Uticor PMD 450)
Recently the Communication timeout fault began to show up. I can clear it only by resetting the power switch for Chassis 4.
Why installers used only one 150Ohms resistor on Chassis2 and nothing on Controller or Chassis 4 side?
Can I check network with voltmeter?
The AC voltage reading BLUE-Ground, Clear-Ground fluctuates from 0.6 to 2.2 vac

20210616_070219.jpg
 
A Remote IO network should be daisy-chained from device to device, and with termination resistors at the ends of the daisy-chain.

It looks as if there is a star connection, and what about the termination resistors ?
That it has worked for many years may be down to that Remote IO is relatively forgiving for improper cabling.

I dont think that the above has to do with the problems you are facing. It is chassis 4 that is faulting, and you can clear the fault by cycling power to chassis 4 only.
I am guessing that the 1771-ABS Remote IO adapter in chassis 4 is defective.
If you have a spare, you can try to swap it out.
If you dont have a spare, you can try to swap the two adapters in chassis 2 and chassis 4 and see if the error follows the adapter.

You should seriously consider migrating to a modern PLC and HMI solution. Replacing PLC5 spare parts is expensive and only gives temporary relief.
 
JesperMP said:
A Remote IO network should be daisy-chained from device to device, and with termination resistors at the ends of the daisy-chain.

It looks as if there is a star connection, and what about the termination resistors ?
That it has worked for many years may be down to that Remote IO is relatively forgiving for improper cabling.

I dont think that the above has to do with the problems you are facing. It is chassis 4 that is faulting, and you can clear the fault by cycling power to chassis 4 only.
I am guessing that the 1771-ABS Remote IO adapter in chassis 4 is defective.
If you have a spare, you can try to swap it out.
If you dont have a spare, you can try to swap the two adapters in chassis 2 and chassis 4 and see if the error follows the adapter.

You should seriously consider migrating to a modern PLC and HMI solution. Replacing PLC5 spare parts is expensive and only gives temporary relief.
Click to expand...
Hello. I did replace adapters and even chassis.
Didn't try yet controller and not sure about wiring ( blue hose). On Chassis 4 have "smart" modules like RB and Basic for wireless communication.
I am thinking any voltage fluctuations can cause this? For discrete I/O looks like it is not so critical to have exact voltage.
Did you see attached schematic?
 
One thing that may explain why this happens suddenly and only with chassis 4 is if some kind of EMC-generating equipment has been added, or some device has begun generating EMC. If that is near chassis 4, it can explain why it the only location affected.

If that is the case, tidying up the cabling could make the RIO network more resistant against EMC.
Make a proper daisy-chain and terminations at both ends.
Check equipotential grounding between cabinets.
Connect the shield of the blue hose to ground by a shield clamping terminal (avoid pig-tails if possible).
 
JesperMP said:
A Remote IO network should be daisy-chained from device to device, and with termination resistors at the ends of the daisy-chain.

It looks as if there is a star connection, and what about the termination resistors ?
That it has worked for many years may be down to that Remote IO is relatively forgiving for improper cabling.

I dont think that the above has to do with the problems you are facing. It is chassis 4 that is faulting, and you can clear the fault by cycling power to chassis 4 only.
I am guessing that the 1771-ABS Remote IO adapter in chassis 4 is defective.
If you have a spare, you can try to swap it out.
If you dont have a spare, you can try to swap the two adapters in chassis 2 and chassis 4 and see if the error follows the adapter.

You should seriously consider migrating to a modern PLC and HMI solution. Replacing PLC5 spare parts is expensive and only gives temporary relief.
Click to expand...

JesperMP said:
One thing that may explain why this happens suddenly and only with chassis 4 is if some kind of EMC-generating equipment has been added, or some device has begun generating EMC. If that is near chassis 4, it can explain why it the only location affected.

If that is the case, tidying up the cabling could make the RIO network more resistant against EMC.
Make a proper daisy-chain and terminations at both ends.
Check equipotential grounding between cabinets.
Connect the shield of the blue hose to ground by a shield clamping terminal (avoid pig-tails if possible).
Click to expand...

Actually the programmer was working with the RB module that is located on same rack. He is saying everything is OK with program..
Do you familiar with BTW, BTR instructions? As far as I know It allow to send AND receive 64 words at the same time ( totally 64, but not 64 write and 64 read )
What happens if the queue of RB module is full? Is it clears or it get frozen?
 
99% of the times I have had problems with DH+ or RIO, it was wiring. The shield would barf up one stand, and it would be touching something it shouldn't be.

The other time it was a ground loop being caused by some no-no's in panel design.

Wow, I still remember the old "Blue on 2" saying for DH+.
 
What are your indications of a comm timeout?
When that happens, what is the status of the lights on the front of the module?


JesperMP said:
You should seriously consider migrating to a modern PLC and HMI solution. Replacing PLC5 spare parts is expensive and only gives temporary relief.
Click to expand...

PFFFT! We've dozens, probably over a hundred PLC5 racks left. Thats not ever gonna haunt us, ever...o_O
 

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