Slc 500 1746-nt8

nmhandberg

Member
Join Date
Feb 2019
Location
Minnesota
Posts
1
So i have a 1746-NT8 thermocouple for a conveyor furnace that is causing some problems. When the CPU is in run mode the channel 6 LED flashes, but the other channels are fine. When looking at the HMI it gives good temp readings on everything except for Zone 7 (which would relate to the flashing channel 6 LED due to there being a 0 channel) which is reading ~6000 degrees Celsius. We tried to replace with another 1746-NT8 thermocouple but the same exact problem persisted but this time with channel 0 and 1 flashing and the HMI showing Zone 1 and 2 temps ~6000 degrees Celsius. I am positive the wiring is correct on both.

When running online i get the error shown on the attached image (the thermocouple is in Slot 7 as the error reads).

I would like to note that the thermocouple with the two flashing channels may have experienced water damage from a leak in our cooling process in the furnace. The one with the one flashing channel has experienced no damage as far as i am aware as it was pulled from a spare SLC 500 chassis we had in our store room.

From what it seems to me it is a hardware error of the thermocouple modules but wanted to post here to see if anyone can give me their opinion.

I have attached the .rss file we are using in case it would come in handy.

Thanks,
Nick

Capture.PNG
 

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  • FURNACE 1 101304.zip
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Hi Nick,

Was this a running system or is it a new system you are just now installing?

Have you tried moving channels around? just to see if you get the same error on your system? it maybe wired correct but you may have a sensor failure
 
Hi Nick and Welcome to the Forum.

Not saying this is your problem but just wanted to pass on an experience I had trying to trouble shoot a similar error. I changed, cards, power supplies even the CPU. Ended up being the back plane.
As I say this may not be your problem but just throwing it out there.
 
Oh "back plane"!...a memory shoots to the front of my brain...

...now where is it?...

...Ah, here you go...

39281 - Causes and Troubleshooting Error code 55 on SLC500 PLC
Access Level: Everyone

...&...

40614 - SLC-5/xx: Error S:6=xx55h, I/O module in slot XX which is required for the user program is detected as having the wrong I/O count
Access Level: TechConnect

Among other things, a backplane issue is a very likely candidate here.

Regards,
George
 

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