Hi Attila,
I got to thinking some more about the DUT, and what's inside, and the
parasitics. I found ref [2] that you showed in the OP, about the HP
resistance standards. It's very informative, covering a lot of the
construction details. One thing that struck me is the discussion of
transient performance beginning on page 12, noting that chemical
contamination in older (non-HP) types is known to cause an
electro-chemical cell effect that can last for many seconds. I think you
said your resistor is an old type, similar to the HP ones. I wonder if
maybe this is the cause of trouble.
To eliminate all possible DUT problems, I'd suggest setting it up with
just a regular, medium precision 10 K resistor, like a T9 with wire
leads. For quick, temporary use, you can scrape off the lead plating
down to bare copper, then tightly twist the lead and copper wires to the
3458A, then crimp a splice lug on to crush them together for a gas-tight
seal. Even a (steel-insert) wire nut will do to hold it together for a
while, as long as there's good Cu-Cu contact between all the parts. Then
you can suspend the little DUT up away from everything, and mostly
eliminate the parasitics, packaging, and other issues. If it works with
this, but not the original DUT, you'll know what the deal is.
Ed
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