[volt-nuts] 3458A Questions - The Sequel

J. L. Trantham jltran at att.net
Sat Oct 29 19:23:02 UTC 2011


Thanks for the data.  Before I can make any intelligent comments about the
stability of my 'system', I am going to have to solve the HPIB issue and
find a way to communicate with the 3458A.  I solved RS232 with the 7081.
Too bad the 3458A doesn't have RS232.


-----Original Message-----
From: volt-nuts-bounces at febo.com [mailto:volt-nuts-bounces at febo.com] On
Behalf Of Charles Black
Sent: Saturday, October 29, 2011 2:13 PM
To: Discussion of precise voltage measurement
Subject: Re: [volt-nuts] 3458A Questions - The Sequel

Hi Joe,

Your noise and drift on your 731B is more than I see on my Datron 4910. 
I have no experience with the 731B but my 4910 is very similar in 
specifications to a 732B. My major drift with my 3458a measuring a 4910 
cell is the room temperature. It is about 10 microvolt per degree C. My 
peak to peak noise is dependent on NPLC settings up to 200 where it 
becomes very usable with only a minor improvement at NPLC = 1000. NPLC 
1000 is useful to get the ultimate accuracy on my system since it 
integrates out some of the lowest frequency noise in the 4910. I use 
shielded #24 cable with no connectors.  The wire is tin plated Tefzel 
STP but that seems to only cause 0 to 10 nv errors and reaches thermal 
stability much faster than my otherwise identical #22 STP. I have 
included two recent plots of one of my Datron 4910 Cells (it has four 
cells which perform similarly) to illustrate NPLC settings. Notice the 
downward drift in both plots that is caused by changes in room 
temperature and the peak ti peak noise which I assume is 4910 noise. The 
4910 noise spec is 0.04 PPM RMS and my cells are well within that.

I tried using connectors but only the gold plated spade lugs were af any 
use to me. Most of my issues had to to do with thermal mass. To use 
banana plugs I had to wait and wait. Dual gold plated banana plugs  
(about 1mv thermal offset at first) never stabilize on my 3458A. I have 
too many air currents I guess. Fortunately no connectors works perfectly 
here and is the cheapest too.

Enjoy your new (to you) 3458A.


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