[volt-nuts] Bls: 3458A resistance calibration

Anton Moehammad moehanton at yahoo.com
Thu May 21 19:30:46 EDT 2015

Dear Frank,
Could You give me more detail which resistor has C-foil and which K-foil.

     Pada Jumat, 22 Mei 2015 5:44, Frank Stellmach <frank.stellmach at freenet.de> menulis:

 Re To: *Electronics and Books

Dear Frans,

I cant't believe this! Thanks alot!

As you mentioned the VHP101 as a reference resistor in your'98 unit, I 
just opened my HP3458A from 2000, and it's also a VHP101!

According to the actual Vishay PG datasheet, it's really the best type 
they offer currently.
As I learnt from a Vishay representative years ago, they pair two 
resistor elements inside, i.e. a C-foil, and a K-foil, to compensate for 
the T.C.

The VHP101 has 10ppm absolute/max. variation over 15..45°C, i.e. an 
average of 0.3ppm/K, and it's oil filled, giving  2ppm/6year stability.
Both parameters I really can believe in, (I'm otherwise very sceptical 
about Vishays specs) as these are specified as being max. value by this 
window definition, and the annual stability of oil filled, hermetically 
sealed Vishay types, I have checked on 5 EA VHP202Z over > 5 years, 

I was not aware of this ultra stable reference resistor inside my 
instrument, as the 40k resistor in my unit was bent backwards, so I 
could not read the type designator, and did not dare to touch it, up to now!

The old CLIP specifies this resistor as having 1.3ppm/K, so I always 
assumed a Vishay k-foil of the 1989 era, non oil filled type.
Also the datsheet specified 1ppm/K (selected component), and 10ppm/year, 
which also indicated the same type of hermetically sealed Vishay BMF.

So, this is a big surprise, no reason any more to change this reference 
HP did not change the specification, but the T.C. should be < 0.5ppm/K, 
and <1ppm/yr for the Ohm ranges.

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