[volt-nuts] Eppley Standard Cell and What Is It?

[Fred Schneider]

Nice info. I made a C program to calculate the voltage, took me a while, now I see he allready made one.
I have a paper downloaded from NIST about the history of standard cells, very good stuff. 
I measure my cells with the meter in manual 1V range. The meters I use for that are > 10 GOhm. I have a bridge, null detector ect but I think it is more safe to measure direct. ( i store the value in my solartron as calibration for the 1 V range, then use the 720, 845 and 332 to set the 332 at 10 V and calibrte the solartron with that. After that I use the solartron as monitor for the 332 to calibrate an other meter)  It takes shorter time totrouble the cells, no chance in connecting someting wrong and safer because a potentiometric setup does not draw current, if both sources are equal, but they are not at the start of the measurement.

I have the history of my cells from new but a gap of about 20 years were they were not used (  but not heated, not calibrated but also and not moved from the lab they were in use)
I measured them ith a brand new 2000 but later found out I have to include he uncertanty from the 2000, the fact the oven is not nulled and the rather big tempco. The meaurement-limmits are so, the cells could still have their original value. 
Would it be realistic to follow the trend line from 1973 to 1988 and use that value as a reference, corrected for temperature. ( i know the calibration temps) that will fall within the 2000 measured range. The cells are still spaced in voltage excact as they were in 1988.

Fred PA4TIM

Op 22 sep. 2011 om 09:16 heeft "gbusg" <gbusg at comcast.net> het volgende geschreven:

> Then again, in his document, Mr. Hoffman says, "This statement obviously 
> does not include solid state scanners meant for the purpose, or 
> "electrometer input" DVMs having input impedances of hundreds of megohms." 
> ...So maybe 10G ohm input resistance DMMs are safe after all? ...Which maybe 
> leads us back to the question as to if their Auto-Zero (or other internal 
> functions) might generate reverse switching noise back into the Weston 
> Standard Cell? (I still would put the DMM in "Manual Range" and "Auto-Zero 
> Off" modes, just to be safe?)
> 
> ...Apology for so many consecutive posts about this as I read further in 
> Conrad Hoffman's document.
> 
> -Greg
> 
> 
> ----- Original Message ----- 
> From: "gbusg" <gbusg at comcast.net>
> To: "Discussion of precise voltage measurement" <volt-nuts at febo.com>
> Sent: Thursday, September 22, 2011 1:05 AM
> Subject: Re: [volt-nuts] Eppley Standard Cell and What Is It?
> 
> 
> P.S. Conrad Hoffman has good info on the topic of Weston saturated and
> un-saturated standard cells.
> 
> According to his info, even high resistance input modern DMMs shouldn't be
> used to directly measure the output of Weston standard cells.
> 
> See:
> http://conradhoffman.com/stdcell.htm
> 
> Greg
> 
> 
> ----- Original Message ----- 
> From: "gbusg" <gbusg at comcast.net>
> To: <jfor at quikus.com>; "Discussion of precise voltage measurement"
> <volt-nuts at febo.com>
> Sent: Wednesday, September 21, 2011 9:58 PM
> Subject: Re: [volt-nuts] Eppley Standard Cell and What Is It?
> 
> 
> John wrote:
>> Some types of cells really do not
>> like being inverted. It is designed to work into an open circuit....  ie:
>> potentiometric comparison.
> 
> From the Solartron 7081 specs I see its DCV input resistance is >10G ohms
> for 0.1 thru 10 V ranges.
> 
> Have any of you Solartron 7081 users looked to see if there are reverse
> switching transients present at its front DCV input jack while in its DCV
> mode?
> 
> In the case of the HP 3458A, you can temporarily turn-off Auto-Zero, which,
> I *think* should minimize if not eliminate any possible switching transients
> present at its front DCV input terminals. By comparison I'm not sure how
> this works with the Solartron 7081?
> 
> Disclaimer: I've not personally characterized any possible reverse switching
> transients present at the 3458A input terminals. But, in theory I think I'd
> temporarily turn-off Auto-Zero immediately prior to connecting to the
> Eppley.
> 
> Admittedly the Eppley was originally designed to work into infinite load
> resistance (potentiometric comparison back in the old days when DCV meter
> input resistance was lower than for the 7081 and 3458A).
> 
> Comments?
> 
> Greg
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