[volt-nuts] Basic question concerning voltage references

[Russ Ramirez]

My question is partly based on a real situation where I have 3 DMMs of
decent quality Keithley 2000, 34970A (34401A), and 3457A that all agree
with a good quality voltage reference that is exceeding its ppm/degree C
spec as far as I am able to tell. I felt that this was telling me that I
would need a 3458A to know how much closer to 10V the reference was at this
point. A quick calculation of 20 bits of ADC for example told me that I was
looking at 9.5 uV of resolution, or 0.6 uV at 24 bits *noise free*, etc. so
it did not seem to be entirely unreasonable to see the LSD of a 6 1/2 digit
DMM be higher than 1 or 2 counts.

Russ

On Mon, Feb 20, 2017 at 12:57 PM, m k <m1k3k1 at hotmail.com> wrote:

> On 20/02/2017 18:46, Russ Ramirez wrote:
> > I very much enjoy what is shared here. It has led me down the path of
> > learning more about Metrology in general and the pointers to Flukecal
> site
> > from here are appreciated.
> >
> > My question is this. If I measured a 10 volt reference known to be good
> to
> > 8 1/2 digits, but with the LSD being > 0, assuming a transfer standard
> with
> > traceability and documented uncertainties etc, would a 6 1/2 digit
> > voltmeter read 10.00000 volts, or round up to the limits of its AD
> > converter resolution; say X uV over 10.00000 volts?
> >
> > I hope this is not too basic a question.
> >
> > Russ
> > _______________________________________________
> >
> Hi Russ,
>
> some voltmeters will supply extra digits in the output they provide, but
> whether they are of any use depends upon how
> stable the reference is in that particular 6.5 digit dvm, unfortunately it
> needs a dvm with better capability to prove
> if those digits are believable.
>
>
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