Hi quarks,
I think that device of Dr. Frank was for TC testing, so high thermal conductivity and low gradient was important. This box is just a reference and not for TC testing use. The enclosure design goals for this project was, remove air drafts, static field and some EMI/RFI protection, and add some additional thermal stability from outside ambient influences (such as the A/C coming on or the shop door opening with a cool air draft). This is why I chose the copper lined plastic enclosure over aluminum. Also, this gives me a true guard path around the resistor. It seems to work well, its not sensitive at all to handling the enclosure while measuring, but if you put your hands near the unshielded test leads you will see the static charge influence.
For TC testing, I have a new thermal box I'm building on my bench now. That WILL have a 4 wire PT100 and other sensors, its a heavy thick wall aluminum box with uniform heating elements, but this will be saved for a separate thread.
Well , my design is indeed intended as a secondary resistor standard, not only for T.C. testing, and temperature balancing and measurement is strictly required for any reference resistors, see esi SR104 box.
Your box has several bugs:
- Too thick copper wires .. these are heat sinks and create temperature imbalance via the measuring cables
Due to 4 wire Kelvin connection, location of soldering does not play a role.
You also should have avoided heating the VHP resistor during soldering, so these thick copper wires are no good.
- missing aluminium or copper block, assembled to case - your setup creates further temperature imbalances between case and resistance element.
The oil filling would also short temperature gradients
- missing thermometer to precisely determine T.C. in first place, and in use would give the opportunity to precisely determine its R(T), again see esi SR104.
The oil filled hermetically sealed Vishay resistors are extremely stable over time, the specification is < 2ppm / 6 years for shelf life, which seems to be correct from my long term monitoring of five VHP202Z.
So it's really a pity that you regard this resistor as being shabby.