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

gbusg gbusg at comcast.net
Thu Sep 22 07:16:07 UTC 2011


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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