VPG on their case study paper state it's VHA518-7, with having Dipl.-Ing Guido Weckwerth, CEO, wekomm engineering GmbH as author
PTFE insulation is very important for low leakage
I found my notes of that talk, so silver coated wire should be better than pure copper because of thermal voltages.
Actually no, because the insulation resistance of the binding posts dominates. And there is no real need for the the on board PTFE insulators either. The printed circuit board could have been simply divided into two pieces and mounted directly to the binding posts. Air is an excellent insulator. And that way you also get rid of the wire inductance and a number metal-metal connections (source of thermal EMF).
Copper-Copper <0.3 µV/°C, Copper-Silver 0.5 µV/°C. But most important is to minimize the number of joints and make them thermally equal.
I think in this case using exotic materials has been more important than thinking the whole picture and doing the math.
You are right, but these binding posts are also highly insulating, and extremely expensive, as Guido told me.
Also don't forget, that Dave has got a prototype, only WEKOMM knows how the devices were built nowadays.
I'm still collecting information & measurements.
Sorry to say, but when we talk about this specific product you sound more like a business partner rather than the scientist familiar to all of us.
So far this is just a $50 resistor in a box with a $5000 price tag. No data of any kind, just sellers vague promises of the exceptional performance. Somehow reminds me of the high-end audio business.
BMF resistors have been used as transfer standards in primary metrology for decades. Especially in AC/DC metrology because of their excellent AC behaviour compared with wire wound resistors. The 10^-8 short term stability mentioned is achievable using off the self BMF resistors without any special treatment or black magic.
My point is that at the moment I see nothing to justify the astronomical price tag. The metrology business is very conservative and for a reason. The equipment are expensive not because of the material cost, but because someone has done the hard, expensive and time consuming work for you. The scientific proof of performance is what you pay for, not some technology or fancy look. From that perspective I think that Wekomm with their marketing first approach has started from the wrong end.
I don't tolerate that at all, and expect your apologies!
You obviously make some wrong assumptions about WEKOMM and their resistors, even so imputing dubious business behaviour to them. Instead of also bringing them in discredit w/o good reasons, I propose that you contact Guido Weckwerth directly for details.
Please give a valid reference of the MBF standard resistor you mentioned, which is assumed to have 1E-8 stability, on what scale ever.
Maybe some very good SR104 or similar PWW based standards may have this capability, on the order of < 1e-7 maybe, but these are also extremely costly, although their obvious BOM cost may be a fraction of that only.
@Itz2000:
No claims. Just facts.
I attached some documents from our german National Standard Institute PTB. They qualify our resistors as primary transfer standards.
@Theobel:
Long term drift if measured by comparing a resistor directly against the Cryogenic Hall Standard for some days. That tells us the drift with a resolution of 10^-10
Dr. Schumacher from PTB developed main parts of the Cryogenic Hall Standard and some mathematical methods for deriving some quite reliable long term drift from these measurements. We specify a max yearly drift of 1ppm, but up to now all resistors were way better than that.
We did not yet reach the good behaviour of an old SR104, they are extremely good. But we are working on that.
At the time being our resistor is better than most of those of our competitors.
Oh, and for example try to load a Fluke 421A-1? with 1A (makes 1Watt power) and do the same with our resistor. Ours drifts max 10ppm and comes back to it's original value better than 10^-8. That lead to the construction of a second resistor type, being capable of heavy loads. That one drifts about 0.8ppm at this load.
Guido
No claims. Just facts. I attached some documents from our german National Standard Institute PTB.
They qualify our resistors as primary transfer standards.
... off the shelf Vishay hermetic foil resistor which is specified to drift less than 2ppm in 6 years, or .3ppm/year for <100 euros?
A new SR104 costs about the same as the Wekomm.
Why then would Fluke sell their 421A resistors if those off the shelf resistors are way better in all respect ?
And this is the "high load" resistor, being tortured in the PTB lab ....
QuoteA new SR104 costs about the same as the Wekomm.Yes ... and is specified with a drift of 2ppm/year. Have you ever bought one the last five years and verified that drift ?
Do you really think you could start a business in this field just by claiming?
Quote... off the shelf Vishay hermetic foil resistor which is specified to drift less than 2ppm in 6 years, or .3ppm/year for <100 euros?
Have you ever checked that
And this is the "high load" resistor, being tortured in the PTB lab ....Do you also have some pictures of the PTB lab equipment, measuring this reference resistor?
What equipment are they using?