[volt-nuts] Reference Calibration Options - Solartron 7081andFluke 731B and 335A

[gbusg]

Yeah, I'm using a 732A. It's a nice box, as you know.

I'm also using a pair of Koep PN-VTS3005 10Vdc standards. Over an 8 year 
period one Koep drifted +0.104 ppm/year; and the other
Koep drifted +0.701 ppm/year. However the Koep's short-term noise and tempco 
are notably worse than the Fluke 732A, so I like the 732A the best. (Wish I 
had a 732B, but those are pricey indeed!)

I also used to have a 731B, but my particular 731B was drifting something 
like 10ppm/year - that's still well within its 30ppm/year spec, but it 
wasn't to my liking, so I got rid of it.

The Solartron 7081 is spec'd +/- 4.3ppm at 10Vdc/year (2nd year), so based 
on published specs the 7081 uncertainty at 10Vdc is almost 7x better than 
the 731B (spec'd 30ppm/year).

Not having personal experience with the 7081, I can't offer anything 
anecdotal about it. ...So I must rely on what actual owners (of the 7081) 
have experienced. (Have you read anything from any actual users claiming 
that their 7081 did *not* meet the 4.3ppm/year spec at 10Vdc? ...Would like 
to read more about that if you have any web links to comments about it?

Thanks,
Greg



----- Original Message ----- 
From: "Charles P. Steinmetz" <charles_steinmetz at lavabit.com>
To: "Discussion of precise voltage measurement" <volt-nuts at febo.com>
Sent: Friday, September 09, 2011 11:22 PM
Subject: Re: [volt-nuts] Reference Calibration Options - Solartron 
7081andFluke 731B and 335A


Fluke specifies all outputs of the 731B at +/- 30 ppm absolute
accuracy at 1 year, at 23C +/- 1 degree after a 30 minute warmup (+/-
15 ppm/90 days, +/- 10 ppm/30 days).  The 10 V outputs of the three
that I've had were better by more than an order of magnitude -- 
around 2 ppm/year (but note that mine were powered 24/7/365).  The 1
V and 1.018 V outputs are significantly less stable than the 10 V
output, but well within spec.

The 10 V output of the 732A (which I use now) is specified at +/- 6
ppm/year (+/- 3 ppm/6 months, +/- 1.5 ppm/90 days, +/- 0.5 ppm/30
days), for temperatures between 18C and 28C.  The ones I have do
much, much better.  There is an interesting 1999 IEEE paper by
Vujevic and Ilic, "Stability of Some DC Reference Standards," which
discusses he 732A and notes that it is stable to about 0.1 ppm/year,
which is consistent with my observations.

Given a calibration history, one can plot the expected absolute
voltage as a function of time and get even closer.

Meters are specified somewhat differently, since there are several
distinct error mechanisms.  My understanding is that the 7081 is
specified as more stable than an HP3458A (which has a specified total
error at 10 V of a bit more than 10 ppm/year, including calibration
traceability error), but that within the cal lab community they are
not considered to be anywhere near as stable as the HP.

Best regards,

Charles







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