[volt-nuts] Back to voltage was Re: Precision current source

Marv Gozum @ JHN marvin.gozum at jefferson.edu
Mon Aug 23 19:15:52 UTC 2010


Thanks a ton, Greg, for these links.  I couldn't agree with you more, 
this has been lacking in the archives and is a necessary part of 
maintaining a DIY reference.

It seems involved but if volt nut is your savvy, it can be done 
cheaply, what is required is the willingness to collect the data for 
the analysis.

Consider, for a minute something like a Geller or Malone board or one 
you design yourself, such as the Chinese URL site provided.  The per 
unit cost using Geller's as example, its $35 @.

The minimum required is 3, a recommend number is 4.  The reason for 4 
are described for why a Fluke model 734 exists, which is 4x732 in a 
transportable modular housing.  3 is minimum so the 3rd is a tie breaker.

Gathering the data is fairly automatic if you have a good DVM with 
data acquisition capabilities to feed a PC, like an HP 3456 or 3458, 
where after a simple ASCII dump into Excel can analyze basic stats easily.

Although one can control temperature, humidity and barometric 
pressure to hold these constant except for the references intrinsic 
variation, a cheaper approach would be simply collect temperature, 
humidity and barometric pressure data simultaneous with the voltage 
data, and regress the correction factor to include variations that 
are linked to environmental changes.




At 06:18 AM 8/23/2010, Greg Burnett wrote:
>I think, using statistical methods, you might improve your "system"
>short-term and long-term stability by tracking the mean of the outputs of
>your multiple voltage references, plotting control charts, eliminating or
>devaluing individual poor performing references in the group (as determined
>by comparison of individuals to the mean of the group), etc. But, as a
>minimum prerequisite you'd want to characterize the TC of each contributing
>reference - and then monitor and control your environmental temperature so
>as to account for it in your process. This statistical process would be
>ongoing over time, and your "system" uncertainty would be unknown until you
>had collected enough statistical data over time.
>
>For examples, see:
>
>The Calibration of DC Voltage Standards at NIST
>See: Calibration of Working Cell Groups (pg 246)
>http://www.nist.gov/customcf/get_pdf.cfm?pub_id=23594
>
>Metrology - Measurement Assurance Program Guidelines (NASA Ref. 1364)
>http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19950018123_1995118123.pdf
>
>Greg
>
>
>
>----- Original Message -----
>From: "Marvin E. Gozum" <marvin.gozum at jefferson.edu>
>To: "Discussion of precise voltage measurement" <volt-nuts at febo.com>;
><volt-nuts at febo.com>
>Sent: Sunday, August 22, 2010 11:06 AM
>Subject: [volt-nuts] Back to voltage was Re: Precision current source
>
>
>Has anyone tested or have a link describing if averaging the outputs
>of multiple voltage references strung together improve short and/or
>long term stability?  By how much?
>
>I've read of attempts to do this from the volt nuts archives linking
>the Chinese forum, but their good work has no follow up with
>stability data beyond some minutes.
>
>http://translate.googleusercontent.com/translate_c?hl=en&sl=zh-CN&tl=en&u=http://www.hellocq.net/forum/showpost.php%3Fp%3D1616460%26postcount%3D58&rurl=translate.google.com&usg=ALkJrhg3JjvD6sPUtn3T0rQtKv3xWuC5ag
>
>Bob Pease wrote recently ...
>
>http://electronicdesign.com/article/pease-porridge/what_s_all_this_long_term_stability_stuff_anyhow_.aspx
>
>
>  From what I peruse, Flukes multiple zener based references run
>concurrently but independently, and their drift characteristics are
>assigned to each reference, not linked together.
>
>http://translate.googleusercontent.com/translate_c?hl=en&sl=zh-CN&tl=en&u=http://www.hellocq.net/forum/showpost.php%3Fp%3D1892104%26postcount%3D285&rurl=translate.google.com&usg=ALkJrhgjHbjHQWdRXogyU8Z8aKSisWIX0Q
>
>
>
>At 01:48 PM 8/17/2010, Dick Moore wrote:
>
> >I suspect (which means "I don't know") that trying to regulate the
> >399 heaters beyond what is incorporated in their design will be
> >unproductive, and that averaging the outputs of several units in
> >tandem will be better. Providing some thermal isolation for the 399s
> >by protecting them from stray air currents and using thin wires or
> >PCB traces is a good idea.
>
>
>
>Sincerely,
>
>
>
>Marv Gozum
>Philadelphia, PA
>
>
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Best Wishes,


Marv Gozum
Philadelphia 




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