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

[Charles P. Steinmetz]

Greg wrote:

>What are the 1year 10Vdc specs for the 731B vs 7081?

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