[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.
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
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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