[volt-nuts] Basic question concerning voltage references

[Russ Ramirez]

Right, and also the 34970 using BenchView, though I could not find where
they claimed that. In the 34970/401 case I was simply seeing a lot of
variation in the LSD, and immediately discounted it as useful in any way. 6
1/2 digits had a close correlation (0.893 I think the number was) to
temperature, but 7 1/2 was all over the place and a relatively low value
for sigma.

Now you know how I spent part of last week and this weekend!

Russ

On Mon, Feb 20, 2017 at 1:33 PM, Tom Miller <tmiller11147 at verizon.net>
wrote:

> I believe you can get 7-1/2 digits out of the 3457A via the HPIB port.
>
> Regards,
> Tom
>
> ----- Original Message ----- From: "Russ Ramirez" <russ.ramirez at gmail.com>
> To: "Discussion of precise voltage measurement" <volt-nuts at febo.com>
> Sent: Monday, February 20, 2017 2:26 PM
> Subject: Re: [volt-nuts] Basic question concerning voltage references
>
>
>
> 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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