There are a host of things that will cause a JJA to be
off voltage... not the least of which is temperature and
frequency.
Absent other standards to compare with your JJA, you are
really operating in the blind.
The only major advantage to the JJA, and the reason it is
given primary standard status, is it relates voltage, to
frequency. If the pumping frequency is offset for some
reason, the voltage will be wrong by a similar amount.
Do you imagine that NIST uses only one JJA to hold the
nation's standard volt?
-Chuck Harris
Tom Knox wrote:
The physics of a properly run JJA will always produce the same result so you do
not need additional units for comparison. That is the point of a world wide
quantum voltage standard defined as K
J-90 = 483 597.9 GHz/V . Just has the
Hyperfine Transition of Cesium at about 9.192631770GHz is used to define the
second. What is neat about the work NIST has done recently is that it has
automated the System for ease of use and reduced the price to the point that it
should see much wider use in day to day metrology. Having your Agilent 3458A
calibrated on a JJA may not yield much difference over a Fluke 5730A cal, but
once
the meter has been run a few years characterizing the A to D converter and 10VAC
range would only need to be done once and could substantially improve
performance.
I personally think that the face of calibration will change in coming years,
rather then simple time based cal periods, instruments will contain complex
environmental sensor packages that will constantly monitor the instruments
environment . S o calibration will be based more on the instruments exposure to
extreme conditions then simple time. I bet the act of shipping has more effect
on
cal then years sitting in a lab. So if for example a 3458A was put in an
environmental chamber on a shaker table I am sure we find that up to a certain
point enviromental conditions would have little effect on cal but at some point
would have a major effect. Once documented the cals would be based more on
environmental exposure. In addition I am sure some environmental effects on cal
are repeatable and could be documented so if monitored they could be compensated
for extending time between cals. So in the future you would see your instrument
display "environment conditions exceeded" "cal require", with perhaps even a
display of currently instrument uncertainty. This could change the face of
calibration and become a multi-billion dollar industry.
Thomas Knox
Date: Sun, 16 Feb 2014 07:06:18 -0700 From: [email protected] To:
[email protected] Subject: Re: [volt-nuts] JJA progress report
If Earth is subjected to a GRB strong enough to damage ground based
electronics, we are all going to have much more urgent problems than wondering
if a JVS is operating properly. Same for an EMP. Lightning, however, might
pose a more localized and serious threat.
Part of your training as an expert operator will include techniques to dissuade
various critters from considering the JVS for their burial ceremonies.
Carrying your best zener reference to the nearest facility with another JVS
would be less expensive than buying and operating a second or third system.
Joe
On 2/16/2014 12:58 AM, cheater00 . wrote:
How do you know the primary standard is not off? That is, how do you know it's
still "primary"? Maybe a gamma ray burst from a supernova damaged some of the
machinery inside, or a colony of crazy ants crawled in and died inside.
D.
On Sat, Feb 15, 2014 at 10:10 PM, Joe Hobart <[email protected]> wrote:
These devices are primary standards; you don't need three; you probably
don't even need two. If certain conditions are met, conditions you can
check/verify, they will accurately generate the desired voltages.
What you will probably want are at least three good zener type voltage
standards and a constant temperature environment. The three will serve as a
day to day standard and reality check on the JJA. And you need to really
learn how to operate the JJA standard, so you can detect and correct any
problems.
Joe Hobart Flagstaff, Arizona
On 2/15/2014 1:17 PM, Gordon DeWitte wrote:
Clearly need three (or some higher odd number) so they can vote...
Gordon
On Sat, Feb 15, 2014 at 2:51 AM, Poul-Henning Kamp
<[email protected]>wrote:
In message
<[email protected]>, Randy
Evans writes:
We'll all probably want a spare unit also.
Two, how can you know which one fails, if you only have two ?
-- Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 [email protected]
| TCP/IP since RFC 956 FreeBSD committer | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by
incompetence. _______________________________________________
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