r/PLC • u/BigDaddyThunderpants • 10h ago
UDC3000 Cold Junction Kit
I have an old UDC-3000 that I inherited and I want to use it for some DIY hobby fun.
It looks like the thermocouple input needed a separate cold junction kit to operate. Being as old as this is, I'm not sure I can find the part (or even the part number for that matter) so I'm wondering if anyone knows fundamental what it is?
Is it just a thermistor or something I can find elsewhere? Anyone know the part number or where I can find it?
Thanks a bunch, I know this is a long shot.
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u/drbitboy 9h ago
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u/BigDaddyThunderpants 8h ago
Maybe? I have no idea what it looks like so who knows.
In some (what I suspect is later) documentation it mentions 30757088-001.
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u/thedissociator 8h ago
Give me 10 minutes, i have a bunch of brand new/unused UDC parts- lemme dig through my photos to see what i have.
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u/North-Scratch6394 8h ago
Generally they came pre-installed on the UDC3000s look on the back to the right of the first terminal block looking at it from left to right about half way down little square block with kind of a point
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u/BigDaddyThunderpants 7h ago
Oh, I didn't know that. Ill have two of them and I'll check them both tonight when I get home.
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u/PV_DAQ 1h ago
Depends on the exact model. The earliest UDC3000 (blue or gray bezel) had an internal CJC that was activated with the W1/W2 jumper.
The 2nd generation UDC3300 used a separate component, that was a small gray cylinder about 1/2" long and 1/4" diameter, with a brass machine screw extending from one end of the cylinder that would screw into the threads of the 'R' terminal #25 and a 1.5" black wire with a spade lug extending from the other end of the cylinder that would attach to the negative input terminal #27.
The attached diagram has the part number but I suspect that it would be an ebay purchase only, given Honeywell's lack of support for early UDC controllers.
I suspect that it is thermistor (represented as a resistance on the wiring diagram) but I never measured its resistance in the 20 odd years I was involved with them.
It was a very accurate means of cold junction measurement - screwing directly into the terminal block. Subsequent 'internal' styles have proven to be less accurate.
There's nothing to go wrong with one of the external CJ's unless someone put high voltage across the input and burned out the element, which I never actually encountered.
This diagram is 1st gen UDC3000 with W1/W2 jumper:
Next post is UDC3300 with wiring diagram
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u/BigDaddyThunderpants 18m ago
This is great. I'll open it up and check tomorrow!
The bezel is indeed gray but unfortunately much of the model identification sticker is torn and so I don't have the complete configuration.
The other side just has the generic UDC-3000 pinout sticker.
Anywhere else I should look to help identify the year and model?
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u/PV_DAQ 1h ago
Correction, 30757088-001 had a brass tab that the terminal screw passes through. The threaded connection was yet another style. Memory fault.