Have people published detailed research papers in rebuttal?
I have not researched any of this of course, but putting my skeptical hat on, I find it hard to believe that one of the leaders in the field of precision resistors for many decades produces "laughable and inept" scientific papers.
Mistakes? I'm sure that happens, but "laughable and inept"?
Proof please.
And BTW, proof is not "go read the professional forums" and "Unlike you folks, I've been in the resistor industry for over 4 decades, I have the experience and knowledge which no one else in this forum has an apparent claim to."
/skeptical hat off
Hi Dave,
I'm also a singulary voice only, as I agree in parts what Edwin Pettis is saying.
But I'm also very hard-arsed, concerning reputable specification for components, as myself, I was creating automotive component specifications for a long time.. and have some experience on Vishay, including many of the companies they took over, all were our suppliers..
Beyschlag once was one of the best manufacturers of Thin Film resistors, with the most reputable specs.. until Vishay swallowed them..
So I can really assess the quality of the current Vishay specs, and find the ones about BMF technology exaggerated quite often.
It is very obvious for every engineer, if you only look carefully on the data sheets, that the typical data are much too optimistic, partly advertised in
big letters, compared to the upper limits they specify.
For example, they always claim a typical T.C. of 0.05ppm/K, on top of the spec, even in the headline, but on the left lower part of the page, they specify a T.C. of +/- 0.2ppm/K +/-2ppm/K maximum.
Only that latter specification parameter is reasonable and serious, so they really do not screw the customer, in the end.
My personal experimental experience with my 5 VHP202Z resistors was exactly, what you doubt, that such a reputable manufacturer tries to lead the user astray by these advertising methods.
These components in reality (according to my own measurements, which I also posted in the EEVBLOG forum) all showed a T.C. between -0.3 to -1.0 ppm/K, no sign of a positive parabola shaped R(T), with a typical 25°C minimum point, as the Z-foil technology would imply, according to several scientific papers from Vishay, where even the honourable Dr. Felix Zandman had signed.
After my complaint about this bad performance of the parts, the Vishay representative had to admit that one can not rely on the typical data and on the intended technology characteristics so far, as advertised...and that there is no guarantee from Vishay about these typical characteristics...
So the new standard from Weekom should be observed very critical also..
In the end, the BMF technology is still very good, and beats PWW components in some aspects, but the production variance is much too big.. an indicator, that Vishay is not really able to control this technology in last consequence.
My impression also is, that with the early death of Dr. Zandman, the respectability of Vishay decreased...as the bean counters took over instead, maybe.
I disagree to Mr. Pettis, that all the papers from Vishay are toast..
Some are very interesting, and several claims really reflect reality, for example the long term stability of these oil filled, hermetically sealed types..again from my own measurements on these 5 resistors.
These have drifted less than 1ppm apart in the last 4 years.. so 2ppm/6years as specified TYPICALLY seems to be reasonable.
Well, that's a singulary finding also, but every bits and pieces sum up to a reliable picture.. in negative and in positive aspects.
I append one of the key documents from Vishay about their BMF technology, regarding the characteristics of the different foil types, C, K and Z. (Z like Zandman)
These characteristic shapes also show up in the BMF specification, but Vishay measures the T.C. not by the physics method, T.C. = dR / dT, but by 3 temperature points only, i.e. the butterfly method.
Also some sort of misleading..
Frank