T.C. measurements on precision resistors

[Overspeed]

I guess what seems to be visible as drift is the thermal time lag between copper and resistor. Attached is the final temperature profile, followed by an 8 h stability measurement at lab temperature. As can be seen it takes about 5.5 ... 6 h for the whole thing to equalize.
This time could be reduced by improving the thermal transfer inside the case. I was thinking about filling the case with ceramic balls (3-4 mm in diameter) or ceramic pouder, thermally conductive but electrically insulating.

Edit: Added the initial thermal resistor behaviour for comparison.

-branadic-

Hello
Filling the enclosure with any product will increase the time of temperature equilibrium between the temperature chamber and the part temperature .
In mechanical metrology , parts are let 24H in the lab with controlled temp before measurement time to get stable temp , that the same for chemical testing on energetic material , propellant are let 24H before testing .

Can be interesting to run differential temp measurement with one sensor on the resistor itself ( drill the outside tube ) and the chamber temp

Regards
OS

[branadic]

While verowire (0.2 mm in diameter) perfectly worked for the 100 Ω and 1 kΩ, it didn't for the 10 kΩ. The wire length needed was over 1 m and what I think happened was that this long wire, while wound bifilar around the resistor, introduced a second order term due to thermal expansion. I've now replaced it by 60 µm enamelled copper wire which resulted in way lower wire length and the residual t.c. is now slightly positive and almost linear. I will give it some additional trimming and call it a day afterwards.

-branadic-

[Overspeed]

While verowire (0.2 mm in diameter) perfectly worked for the 100 Ω and 1 kΩ, it didn't for the 10 kΩ. The wire length needed was over 1 m and what I think happened was that this long wire, while wound bifilar around the resistor, introduced a second order term due to thermal expansion. I've now replaced it by 60 µm enamelled copper wire which resulted in way lower wire length and the residual t.c. is now slightly positive and almost linear. I will give it some additional trimming and call it a day afterwards.

-branadic-

Hello
if you wind ( coil winding ) at the temperature reference , your wire dilation shall be negligible IF if the winding core is stable ( no expansion ) and IF you don't strain the wire by too much tension .

Does someone have tried loose winding in epoxy cast ? so a no stress / strain on the wire .

Second parameter is the self heating generate by the electricity power that an interesting as the 10 mW power calibration ( I suppose limited in the aim to limit self heating )  is not a universal value as that directly linked to the size/dims of the tested resistor a S102 is not at all a SPR221 regarding the power which can be handle. I agree that not wire resistor but that an example ratio power vs size .

Some studies demonstrate that resistance value change ( in the last digit ) with current value , a 1 Ohm resistor is a good candidate to check values with 1 mA / 10 mA .

Regards
OS

[branadic]

After trimming, here is what I've ended up with. I'll leave it over here.

-branadic-