PMEL Forum

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.