Calibrating a Fluke 5500A. The step where in input 0 mV from 5720A using solid copper w/copper TC connector, I have been getting about a +4.3 Deg C offset. I ran the software adjustment. Zeroes in regular DC voltage output are all good. When I use a type J cold junction w/ Hart 9101 Ice Point, I get a good zero. When I measure the 5720A with either Fluke 8508A or HP 3458A, I get good zero reading. I ran fresh zeroes on everything (5720A, HP 3458A AutoCal, 5500A Zero). The OEM procedure even says you can use Type J at -200C, 0C, etc. I get good numbers that way. I've cleaned all the copper contacts with Caig Deoxit.
So I have a good zero output from the 5720A, good zero everywhere, except just the 0 uV/DegC setting on the 5500A.
I even took the copper TC connector apart and scrubbed and cleaned it. The only thing I can still think of is that the connector itself has internal impurities, creating an offset. I may next try putting a different actual connector on the copper/TC cable. And I have done this test many times before.
If anyone has had this problem, love to hear your thoughts.
I've had a similar issue as you with our 5520 and the µV/ºC out @ 0ºC was looking off. I think my issue was when I had set the internal cold junction offset, there was an error. That was my situation however, not sure about yours.
May I ask what kind of copper are you using?
I as using some solid copper twin lead (thermocouple type). I think it was metal impurity in the wire, as I finally switched it out. I am using type R connectors (which are not made with R material, but with copper). I switched to quite a bit thicker gauge solid copper twisted pair, and an R connector. After allowing some warmup time, it stabilized within tolerance.
I've never seen bad copper wire like that. It was causing a +4.7 Deg C thermal offset. After switching out the wire, I finally got in tolerance readings. Go figure, bad wire. I even scrubbed it, and had very good surfaces everywhere.
Simple copper end to end is the way we do it
That's how I have done it as well. I use copper mini TC connectors and solid copper wire in between. What I had found was the solid copper wire I was using had impurities. So even so-called "pure copper" can lie to you. That is the lesson learned for me.