[volt-nuts] Which meter?

Greg Burnett gbusg at comcast.net
Sun Nov 15 01:14:36 UTC 2009


Hi Bram,

I agree that the 8508A and 3458A do seem like good choices. As for 
connectivity, I guess you're stuck with GPIB with either of them.

I have a lot of experience with the 3458A, but none with the 8508A. So it 
would be nice to hear from someone with 8508A experience for comparison.

Based on my personal experience with the 3458A (vs. 34401A), I'd say you 
might typically see approximately these amounts of short-term "noise" (for 
10Vdc range, 100 Power Line Cycles):

    For 3458A: +/- 0.2uV variation from reading-to-reading
    For 34401A: +/- 10uV variation from reading-to-reading

(At 10Vdc this would be +/- 0.02ppm "racking" for the 3458A vs. +/-1ppm 
"racking" for the 34401A.)

I think you might find the 3458A's linearity to be typically < 0.06ppm on 
its 10Vdc range. (Fluke's 720A Kelvin Varley Divider isn't linear enough to 
verify this, so you'd need a JJ-Array to "prove" it.)

As for long-term DC stability of the 3458A: I'd say you might typically see 
< 2ppm drift / 6 months. (I'm currently seeing < 2ppm drift / 12 months on a 
couple old 3458As here. ...New 3458As would likely drift more than this 
until they age for several years.)

For added confidence, you could use a trended Fluke 732B 10Vdc standard (or 
a bank of them) to correct for 3458A long-term drift. (But IMO this would 
require 732Bs with known history and as trended over several years minimum.)

Disclaimer: The above numbers are what I'm actually used to seeing here. 
Published specs are of course greater than these numbers. So, for 
traceability purposes you'd have to use published specs (k = 2) for your DVM 
& Fluke 732B (unless you have several years historical data / trending).

Cheers,
Greg


----- Original Message ----- 
From: "The-al-bundy at home.nl" <the-al-bundy at home.nl>
To: "Discussion of precise voltage measurement" <volt-nuts at febo.com>
Sent: Saturday, November 14, 2009 1:56 PM
Subject: Re: [volt-nuts] Which meter?


Hi Greg,

Well I've made a design with the LTZ1000A and must test it's stability. The
best DVM we have is the 34401, but with the 6.5dig you don't get far with a
LTZ1000 as DUT. So we need something better. As far as I've seen the only
options are the 8508A and the 3458A.

The 8508A is relativly new (2002 I thought), so one would expect better
specifications than the 3485A and more options like other connectivity than
GPIB.
However the 3458A is already around there for >20years and it seems to be
one of the best DVM. The 100k sample rate is a feature which could be handy
in the future.

Money is not so much an issue, just we have to make a good investment for
the next 5+ years or so.
Of course we expect to use the DVM more often for ultra stabile
circuits/sources (in currents as wel as volts).

Thanks,
Bram





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