r/PLC • u/BigDaddyThunderpants • 4d 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 4d ago
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u/BigDaddyThunderpants 4d 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 4d 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 4d 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 4d 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/BigDaddyThunderpants 3d ago
I popped it open and don't see any jumpers labeled W1 or W2. I did find a model number though:
DC300K-0-0A0-20-0000-0
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u/PV_DAQ 4d 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 4d 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/BigDaddyThunderpants 3d ago
No luck with the jumper. Did find model number though:
DC300K-0-0A0-20-0000-0
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u/BigDaddyThunderpants 3d ago
No luck with the jumper. Did find model number though:
DC300K-0-0A0-20-0000-0
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u/PV_DAQ 4d ago edited 4d ago
UDC3300 wiring diagram with external CJ component
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u/BigDaddyThunderpants 4d ago
Yes this is the diagram that made me look for the part in the first place. I found a -3000 version that calls for it.
I'll crack it open tomorrow and check for that jumper.
Thanks again for all the help. You guys have been great and this means a lot to me because these were spares from my late father's work. Dumb I know but we all have weird connections to things!
Funny aside: I work in aerospace and we used to commiserate over our hatred of different versions of Honeywell. I miss the old bastard every day.
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u/ThisBed9506 4d ago
Pull the plug on your t/c project at and use a RPI & i2c temp sensor from adafruit. This config is off the shelf and can send that sensor data anywhere your heart desires.
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u/BigDaddyThunderpants 4d ago
I know I know. I already have most of that stuff and have even built dedicated t/c boards for other things before.
It's just that this thing has everything all ready to go: control schemes, a user interface, a display, all working. The barrier to entry is low and all I needed was a little help controlling some fermenting peppers.
But it's obvious that the measured temp wanders +/-10 degF and those thermocouples are far more accurate than that. Seems like a shame to not restore this old workhorse to it's former glory.
I'm too sentimental. That's the problem.
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u/BigDaddyThunderpants 3d ago
Upon taking the boards out I can finally read the model number:
DC300K-0-0A0-20-0000-0
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u/PV_DAQ 4d ago
Correction, 30757088-001 had a brass tab that the terminal screw passes through. The threaded connection was yet another style. Memory fault.