[volt-nuts] Basic question concerning voltage references

[Tom Miller]

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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