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

[WB6BNQ]

   Hi Marvin,

   I have a friend, Art Rizzi, who was responsible for the Navys DC
   voltage reference.  He worked at the Navys version of NBS at the North
   Island Naval Air Station, San Diego, CA.  His lab was also responsible
   for approval and acceptance of lesser standards used though out the
   Navy.

   In 1970, his lab received around 100 Fluke 731 voltage standards.
   Though out 1970 and 1971 he spent considerable time characterizing
   these devices.  One aspect, performance over temperature, was quite
   important because but for his environmentally controlled laboratory,
   the rest of the Navy saw quite a variation in temperature and humidity.

   Art was the original developer of the idea of paralleling multiple
   Fluke 731 voltage standards to account for temperature coefficients.
   The basic idea is to take multiple units that had the correct mixture
   of temperature coefficients such that they reduce the effects of
   temperature variation as much as possible (within limits of course).
   Arts efforts, along with other improvements he suggested, were the
   basis of, and incorporated into, the development of Flukes 732 voltage
   standard.

   Clearly, each of the voltage standards needs an output stage that can
   sink and source a given amount of current (a few milliamps) without
   affecting its internal reference or the temperature of an individual
   standards internal environment.  Ground paths within this ensemble are
   very important.

   Creating such an ensemble for an experimenter is not an easy task to
   accomplish.  Not withstanding needing expensive test equipment like
   precise temperature and a very stable known reference to compare to, a
   highly controlled lab environment and an environmental chamber are also
   needed.  Then you need a few hundred voltage references to, hopefully,
   find the ones that will accomplish the right mixture.  Finally you will
   need 6 months to a year or more to do the work !  Did I mention money ?

   However, to answer your question, NONE of the above does anything for
   stability.  All it does is help to correct for temperature variation,
   within limits of course.

   Stability is an entirely different animal !  Many factors control
   stability, some you can deal with and others you have no control over,
   like the manufacturing processes.  So, you buy the best diodes or
   reference devices you can afford and hope for the best.  You can take
   it to the bank that Fluke and HP spend much time and money in producing
   their top of the line products.

   Bill....WB6BNQ

   "Marvin E. Gozum" wrote:

     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.

     [1]http://translate.googleusercontent.com/translate_c?hl=en&sl=zh-CN
     &tl=en&u=http://www.hellocq.net/forum/showpost.php%3Fp%3D1616460%26p
     ostcount%3D58&rurl=translate.google.com&usg=ALkJrhg3JjvD6sPUtn3T0rQt
     Kv3xWuC5ag
     Bob Pease wrote recently ...

     [2]http://electronicdesign.com/article/pease-porridge/what_s_all_thi
     s_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.

     [3]http://translate.googleusercontent.com/translate_c?hl=en&sl=zh-CN
     &tl=en&u=http://www.hellocq.net/forum/showpost.php%3Fp%3D1892104%26p
     ostcount%3D285&rurl=translate.google.com&usg=ALkJrhgjHbjHQWdRXogyU8Z
     8aKSisWIX0Q
     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

     _______________________________________________
     volt-nuts mailing list -- volt-nuts at febo.com
     To unsubscribe, go to
     [4]https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts
     and follow the instructions there.

References

   1. 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
   2. http://electronicdesign.com/article/pease-porridge/what_s_all_this_long_term_stability_stuff_anyhow_.aspx
   3. 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
   4. https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts