[volt-nuts] Vishay Z-foil resistors

[Frank Stellmach]

Andreas,

I also had some talks with one Frank from Teltow and another Frank (also 
physicist) from Heilbronn .. latter one told me about the background 
stories of this technology, especially before 1989, when this stuff was 
produced in the former GDR, for the Russian military and airspace use.

Today, this also the main market, I assume.

That's also the reason for the -55..+125°C specification range, because, 
no, its definitely much too expensive for automotive use; I must know ;-)

The only option to order 'metrology parts' with a reduced temp. range is 
ordering those 2-chip-matched VHP 101 at the moment.
I ordered the VHP202, without further requirements. Wouldn't have helped 
me, anyhow, as it was explained to me later (and as I was aware before, 
from reading carefully the spec.)

Currently, you'll find again the Z203 on their site, also intended for 
metrology, but no max. values are given either. The attribute "typical" 
is missing by mistake, currently.

Those parts are also a phantom, to my opinion, they really are not able 
to control this technology to a perfect level.

While we are at it, I would like to cite another publication from John 
Pickering, the Britisch engineer who designed the famous Metron/Fluke 
7000 reference, based on the LTZ1000, with hysteresis elimination..

Later in 2002, he designed also a high precision 10mA current source for 
the CERN, for calibrating the huge Tesla-coils (several kA). This is 
based on a 10kOhm resistor, built from 4x 10K VHP202 resistors.
http://cdsweb.cern.ch/record/643294/files/cer-002399331.pdf

Obviously, Vishay then was able to either produce low TCR parts, or they 
could deliver batches with opposing TCR, so a matching could be done. 
Otherwise, this extreme degree of stability could not have been achieved.
The people from German Vishay PG could not give me any background infos 
for that.


A German PhD thesis deals about a 35kV precision divider,  based on VHA 
518 types,(same datasheet as VHP202), but the success is based clearly 
on the selection of several different batches. The final divider was 
positively checked at the PTB:
http://miami.uni-muenster.de/servlets/DerivateServlet/Derivate-4212/diss_thuemmler.pdf

Therefore, if you take a lot of money in your hands, its possible to get 
ultra stable results from those parts.


Btw.: Andreas, I don't know in which area you are living, perhaps we may 
meet some day.

Because, "You got a brand new pair of roller skates, and I got a brand 
new key".

Frank