[volt-nuts] Back to voltage was Re: Precision current source
wb6bnq at cox.net
Sun Aug 22 23:26:07 UTC 2010
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
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
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
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.
"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.
Bob Pease wrote recently ...
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.
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
>by protecting them from stray air currents and using thin wires or
>PCB traces is a good idea.
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