The only down side with the plastic case is the binding posts can be forced to apply mechanical stress on the leads to the resistor, I tried to add some strain relief on the leads.
QuoteThe only down side with the plastic case is the binding posts can be forced to apply mechanical stress on the leads to the resistor, I tried to add some strain relief on the leads.
Maybe an inner steel plate with flattened holes, like the molds from the Pomona plastic bushings?
Nice and compact built!
Your VHP101 seems to be right in the middle between the binding posts.
How did you decide which side to use for sense and which side is force?
I have always placed the resistor as close as possible to the force terminals.
May be it is not needed.
May be even better for mechanical stress to keep the resistor in the middle?
Looks nicely made, possible improovements could be to add a heatsink and a temp sensor
see example from Dr. Frank
https://www.eevblog.com/forum/metrology/t-c-measurements-on-precision-resistors/msg464413/#msg464413
I made a copy using a Vishay 0TC part - much appreciate the idea! Mine's in a metal box with a thermistor. I used the 0.0% TC unit from Digi-Key.
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.
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.
Sorry for stupid question:
Can I buy similar resistors on Ebay?
Can I use some wirewound resistors from old resistance decade?
Sorry to reply at such an ancient post, but was thinking about using a low tempco trimmer to trim a slightly lower 10k resistor to tune it to a perfect 10k.
I wanted to use a standard 71-Z201T10K000VB Vishay resistor with a 0.2ppm, choosing one that measures around 999,995 or so and add something like this: Y005610R0000K0L 10R Trimmer so that I can reach a perfect 10k... the tempco of that trrimmer is 15ppm but on 10 Ohm, and it's really cheap compared to the 10ppm part which is like 60 Euro each. This one goes for around 18 Euro.
And obviously ask the help of some merciful soul here so that it can be tuned to that value on a real voltmeter, 7.5 or even 8.5 digit machine - without spending a fortune.
Nicest machine i own is a 34410A, plus another classic 34401A.
Reasoning behind this and not choosing a single fixed resistor of the correct value, maybe with like 1PPM, to trim the Foil resistor: I dont want to make it hard for whoever is doing me this favour to do a very tedious operation of soldering the tuning resistor(s) or purchasing lots of different and expensive parts to do this. All the friend would have to do is leave it on a bench for a day or so and then tune it with the trimmer noting the temperature at which the calibration was done.
what do you think?