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 <[email protected]> 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" <[email protected]> > To: "Discussion of precise voltage measurement" <[email protected]> > 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 <[email protected]> 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. >>> >>> >>> _______________________________________________ >>> volt-nuts mailing list -- [email protected] >>> To unsubscribe, go to https://www.febo.com/cgi-bin/ >>> mailman/listinfo/volt-nuts >>> and follow the instructions there. >>> >>> _______________________________________________ >> volt-nuts mailing list -- [email protected] >> To unsubscribe, go to https://www.febo.com/cgi-bin/m >> ailman/listinfo/volt-nuts >> and follow the instructions there. >> > > _______________________________________________ > volt-nuts mailing list -- [email protected] > To unsubscribe, go to https://www.febo.com/cgi-bin/m > ailman/listinfo/volt-nuts > and follow the instructions there. > _______________________________________________ volt-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts and follow the instructions there.
