[volt-nuts] Vishay Z-foil

Andreas Jahn Andreas_-_Jahn at t-online.de
Mon Nov 21 21:54:59 UTC 2011

Hello Frank,

>He could not give me a hint, how to get such "typical" / perfect parts from 
>Z-foil resistors, as those obviously can not be produced on order.
>Instead, a combination of a C- and a K foil resistor is recommended, -i.e. 
>VHP 101/103, which give +/- 10 ppm over 15..45°C, i.e. these resistors 
>really are defined by a box method specification. But thats also not better 
>than 0.3ppm/K.

I recently talked with the FAE from Teltow.
He gave me info about the history of Vishay.
Formerly the only field of operation was in strain gages.
(today most of the turn around is still made in strain gages at precision 
The idea was to use the temperature compensation scheme
of strain gages for precision resistors.
They attach (cement) a metal foil to a ceramic substrate. So the tempco
of the metal foil will be compensated by the expansion coefficient of the 

The following thoughts are only my guesses:
- I would not be surprised if the "typical part" was a 350 Ohms resistor 
since it could be part of a typical strain gage bridge.
   (usually 350 Ohms sometimes 120 Ohms or 1000 Ohms).
- The tempco may be affected by metal foil thickness. (for higher 
resistances they will need a thinner foil).
- I do not think they change substrate thickness when they use a other foil 
thickness to compensate the different forces

So it would be interesting if through different resistor values (foil 
thickness) there are systematic changes in tempco.
I have now here the magic values of a LTZ1000 reference as Z201. That would 
be a point of start for a experiment.
But unfortunately I have not the measurement equipment for a 4 wire 
measurement over temperature.

By the way: did you specify operation from 0..60 degrees with your order. Or 
is this no option when placing a order?
I am wondering why they measure/specify at -55 and +125 degrees for a 
metrology part.

With best regards


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