On Aug 17, 2010, at 5:00 AM, volt-nuts-request@febo.com 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.

Best,
Dick Moore

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:

Sincerely,

Marv Gozum
Philadelphia, PA

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:

 399s

 Sincerely,

 Marv Gozum
 Philadelphia, PA

 _______________________________________________
 volt-nuts mailing list -- volt-nuts@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

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@jefferson.edu
To: "Discussion of precise voltage measurement" volt-nuts@febo.com;
volt-nuts@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:

Sincerely,

Marv Gozum
Philadelphia, PA

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

I forgot to mention: It would be good to plot your "statistical dcv system"
vs. a known external reference (e.g., JJ-array if your goal merits that
level of reference).

Greg

----- Original Message -----
From: "Greg Burnett" gbusg@comcast.net
To: "Discussion of precise voltage measurement" volt-nuts@febo.com
Sent: Monday, August 23, 2010 4:18 AM
Subject: Re: [volt-nuts] Back to voltage was Re: Precision current source

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@jefferson.edu
To: "Discussion of precise voltage measurement" volt-nuts@febo.com;
volt-nuts@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:

Sincerely,

Marv Gozum
Philadelphia, PA

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

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

Hello Bill,

Thank you so much for these pearls and the details!  I love the way
you reference links.  A good idea!

I think the gist of your post is making a reference is going to be
futile, because we, as individuals, do not have the resources to
build a 732 like device, nor access to calibrate it against a
Josephson Junction, JJ.

I think a reasonable facsimile or approximation can be done, its why
I've joined this forum, to find others who have.  Read on.

But a short answer to the futility question is simple, buy a used
732, put in back into working order, and find a lab willing to
calibrate it against their NIST traceable references, and now,
maintain your 732.  Now you have a reference well characterized by
Fluke on the assumption, the rebuild has put it back into like
original factory condition.

On your anecdote, while temperature drift is a concern, its minimized
by ovens in the 732 to keep a stable temperature for the reference,
regardless of ambient.  I do not know if more than one voltage
reference chip is used inside each Fluke 732 or any equivalent solid
state reference or others matching - or + tempco references, but if
you can find out, I'd love to read of it.  Its common to use
resistors with such characteristics, where they are applied.

What is typically done to most solid state references to improve
their performance is apply a correction factor to the output every so
many months to fix drift, and this can be done on any device based on
a single reference once its characterized over time.  Here is such a
process.  Its another freely available paper that was published in an
IEEE proceeds but copied here, but there are others like it.

http://vmetrix.home.comcast.net/~vmetrix/ZenerP.pdfhttp://vmetrix.home.comcast.net/~vmetrix/ZenerP.pdf

Historical data from Fluke show aged mature 732 model A trends +/- 1
1ppm over a decade, so net over time its stable. Some of this data is
abstracted in the 732 series user and maintenance manual available
from Fluke's website, and it gives the correction equation.  There
may be more recent ones, but this one is free, for those interested:

http://assets.fluke.com/appnotes/Calibration/deaver_msc01.pdf

Regardless, a lot of circuit manipulation and other controls has not
made solid state references as good as a JJ, over 40+ years of using
zener based references.  This conclusion led to the development of
the portable JJ now being studied as improved transfer reference.

http://assets.fluke.com/appnotes/Calibration/Josephson-Voltage-Standard-in-a-working-Calibration-Laboratory.PDF

A question for the user is really, how accurate is your need: e.g.
300, 30, 3, 0.3 ppm?  For most professional production MetCal uses,
the Fluke 732s [ or equivalent] suffices, and for others not.  For
most users, a NIST traceable cal is acceptable, for others one needs
a direct cal from NIST itself.

Thus, if a less stringent 30 ppm or more suffices for one's need, why
won't something like Geller's board work, and thus save the owner a
lot of money?  However, it must be characterized just like Fluke does
for the 732.  Empirically, such a home brew could rival a more
expensive standard up to a ppm per time period, limited circumstances
that a Fluke 732 cannot contend with given its intended use thus
requiring the extra electronics, housings, redundancy and overall,
cost.  Such circumstances may not even be related to stabilizing the
volt, such as passing UL, CSA, IEC safety requirements, which add to
the cost of the device.

Thus, what is missing in this noble and learned group's archived
discussions [ and brought up in later post by Greg ] is collecting
performance measurements of any device designed and used over time to
ascertain stability, regardless of how the standard is constructed,
be it as robust as the Fluke 732 or as spartan as a Geller
SVR.  Thus, one needs to consider basic statistics on the output of
these devices if one is to maintain them as a local reference.

I think electronic engineering uses the metric "reliability" to
reflect stability, which is the combination of a devices' accuracy
and precision over time.

Looking forward to a stimulating and enlightened discussion!  Onward,
to a home based volt reference on the cheap!

Some minor comments below.

At 07:26 PM 8/22/2010, WB6BNQ wrote:

Yes, but generally when testing a voltage reference or standard, its
vital the DUT draw near zero amps.  A null voltmeter is preferred,
but a very high impedance voltmeter can suffice.  So such capacities
to sink/source are not usually necessary of a reference, long term
stability is.

You certainly need time to gather data, but it needn't be expensive,
or as involved as you suggest.  For over 20 years, the references
used inside high end DVM like HP 3458A or 3456A are typically just an
LM399H or an LTZ1000 in a separate board very much like Geller's but,
like wine, chosen, aged and characterized, will work without special
environmental controls.  It will work better with environmental
controls, but its not necessary given such errors are already
accounted for when calculating the frequency of a device's calibration cycle.

Reliability, as a synonym for stability, is subject to many
variables, temp is just one of them.  Humidity, and pressure also
affect solid state references and have been studied too.

Thus, the reliability calculation and variability takes all of these
variables into account as a phenomenon, assuming that time exposes
the DUT to all variations the variables can throw at it in the
measurement cycle, say 90 days, to 1 year.

The same can be done for something as cheap, and as exposed as a
Geller reference.

What I see others perceive is that looking for a single absolute
reference, that is solid as rock, 1.0180000000000 or 10.0000000000
etc., with ~ zero variability over time.  Even the JJ is not
that.  JJ is simply better than zener, but it is subject to
uncertainty too, now ~  1 pp billion, versus a good zener at 0.1 ppm.

So, why not 1 ppm or 10 ppm, or 30 ppm, as you funds or need allow.

Best Wishes,

Marv Gozum
Philadelphia

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:

Best Wishes,

Marv Gozum
Philadelphia

It would be nice, but it likely unnecessary. The calibrations need to
be done only at the start of the data collection and then at the end,
to establish the end points.  The collected data plots how it varies
day to day, and the general trend.

Sorry, last message sent prematurely.

Also, in setting the environment, its not necessary to complicate
calculations and let it swing to extremes.  So keeping the reference
in a temperature controlled room set by an ordinary air conditioner
is enough to reduce swings in relative humidity and temperature, but
not control it.  This leaves barometric pressure as the largest variable.

At 06:40 AM 8/23/2010, Greg Burnett wrote:

Best Wishes,

Marv Gozum
Philadelphia

Sorry folks, my email sent this prematurely.

To clarify this sentence:

At 03:00 PM 8/23/2010, Marv Gozum @ JHN wrote:

It should read as:

Thus, if a less stringent 30 ppm or more suffices for one's need, why
won't something like Geller's board work, and thus save the owner a
lot of money?  However, it must be characterized just like Fluke does
for the 732.

Empirically, such a home brew could rival a more expensive standard
up to a ppm per time period, excluding circumstances that the a Fluke
732 design was built to include.  For example, a home brew need not
require its own dedicated battery backup, lab grade AC supply, or
built to safety standards that would pass UL, CSA or IEC safety
requirements, which add to the cost of the device.

Best Wishes,

Marv Gozum
Philadelphia

Good points Marv. In the past I've participated in MAPs (and trending) that
were structured just like you describe (with external calibrations done only
at the start and end of the data collection period, to establish the end
points - and with environmental controls sufficient for purpose).

Best,
Greg

----- Original Message -----
From: "Marv Gozum @ JHN" marvin.gozum@jefferson.edu
To: "Discussion of precise voltage measurement" volt-nuts@febo.com;
"Discussion of precise voltage measurement" volt-nuts@febo.com
Sent: Monday, August 23, 2010 1:55 PM
Subject: Re: [volt-nuts] Back to voltage was Re: Precision current source

It would be nice, but it likely unnecessary. The calibrations need to
be done only at the start of the data collection and then at the end,
to establish the end points.  The collected data plots how it varies
day to day, and the general trend.

Sorry, last message sent prematurely.

Also, in setting the environment, its not necessary to complicate
calculations and let it swing to extremes.  So keeping the reference
in a temperature controlled room set by an ordinary air conditioner
is enough to reduce swings in relative humidity and temperature, but
not control it.  This leaves barometric pressure as the largest variable.

At 06:40 AM 8/23/2010, Greg Burnett wrote:

Best Wishes,

Marv Gozum
Philadelphia

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