| Topic: |
Science > Physics |
| User: |
"PD" |
| Date: |
02 Feb 2005 12:31:50 PM |
| Object: |
Kilogram international prototype |
Since the kilogram is the only base SI unit that is exemplified by a
nonreproducible prototype, how is the international prototype *used*,
except as a displayed artifact under glass?
Another way of asking the question is, how is the standard promulgated?
Or alternatively, how is recalibration done?
If anyone knows specifics about handling and procedures, that would be
ideal, but I'll take whatever I can get.
PD
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| User: "CWatters" |
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| Title: Re: Kilogram international prototype |
02 Feb 2005 01:25:03 PM |
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"PD" <pdraper@yahoo.com> wrote in message
news:1107369110.417674.39340@f14g2000cwb.googlegroups.com...
Since the kilogram is the only base SI unit that is exemplified by a
nonreproducible prototype, how is the international prototype *used*,
except as a displayed artifact under glass?
They use it to check copies every 40 years or so...
http://www1.bipm.org/en/scientific/mass/prototype.html
http://www1.bipm.org/en/scientific/mass/verifications.html
Quote:
On three occasions, roughly 40 years apart, the mass of the official copies,
the national prototypes and the working standards of the BIPM have been
compared with the mass of the international prototype. On the last of these
occasions (1988-1992), 34 standards from national laboratories were cleaned
with solvent and then steam-cleaned with double-distilled water before the
definitive mass comparisons.
The results of comparisons between the official copies and the international
prototype show some divergence with time. The graph below shows changes of
about 5 x 10-8 in the mass of the standards since their first calibration.
All measurements are with respect to the international prototype. For this
reason, the mass of the international prototype defines the x-axis of this
graph.
There is no reason to suspect that the mass of the international prototype
of the kilogram is more stable than its official copies. The question of
stability can only be answered definitively by comparison with a fundamental
constant of nature (such as the Planck constant or the mass of an atom of
28Si). Such experiments are being carried out in several national
laboratories. So far, relative uncertainties of about 10-7 have been
achieved.
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| User: "CWatters" |
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| Title: Re: Kilogram international prototype |
02 Feb 2005 01:26:29 PM |
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"CWatters" <colin.watters@pandoraBOX.be> wrote in message
news:jO9Md.1795$4N.182343@phobos.telenet-ops.be...
"PD" <pdraper@yahoo.com> wrote in message
news:1107369110.417674.39340@f14g2000cwb.googlegroups.com...
Since the kilogram is the only base SI unit that is exemplified by a
nonreproducible prototype, how is the international prototype *used*,
except as a displayed artifact under glass?
Two layers of glass as well!...
http://www1.bipm.org/utils/common/img/mass/prototype.jpg
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| User: "Rene Tschaggelar" |
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| Title: Re: Kilogram international prototype |
02 Feb 2005 01:59:24 PM |
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CWatters wrote:
"CWatters" <colin.watters@pandoraBOX.be> wrote in message
news:jO9Md.1795$4N.182343@phobos.telenet-ops.be...
"PD" <pdraper@yahoo.com> wrote in message
news:1107369110.417674.39340@f14g2000cwb.googlegroups.com...
Since the kilogram is the only base SI unit that is exemplified by a
nonreproducible prototype, how is the international prototype *used*,
except as a displayed artifact under glass?
Two layers of glass as well!...
http://www1.bipm.org/utils/common/img/mass/prototype.jpg
Three layers ? Some optical trick ?
Rene
--
Ing.Buero R.Tschaggelar - http://www.ibrtses.com
& commercial newsgroups - http://www.talkto.net
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| User: "tadchem" |
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| Title: Re: Kilogram international prototype |
02 Feb 2005 01:53:24 PM |
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CWatters wrote:
<snip>
The results of comparisons between the official copies and the
international
prototype show some divergence with time. The graph below shows
changes of
about 5 x 10-8 in the mass of the standards since their first
calibration.
All measurements are with respect to the international prototype. For
this
reason, the mass of the international prototype defines the x-axis of
this
graph.
There is no reason to suspect that the mass of the international
prototype
of the kilogram is more stable than its official copies. The question
of
stability can only be answered definitively by comparison with a
fundamental
constant of nature (such as the Planck constant or the mass of an
atom of
28Si). Such experiments are being carried out in several national
laboratories. So far, relative uncertainties of about 10-7 have been
achieved.
Please help me understand how "changes of about 5 x 10-8" can be
reliably quantified using "relative uncertainties of about 10-7".
That is a signal-to-noise (S/N) ratio of 0.5, and as an analytical
chemist I would never try to certify a value with S/N less than 2 (and
*that* at only 95%).
Tom Davidson
Richmond, VA
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| User: "PD" |
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| Title: Re: Kilogram international prototype |
02 Feb 2005 03:30:57 PM |
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tadchem wrote:
CWatters wrote:
<snip>
The results of comparisons between the official copies and the
international
prototype show some divergence with time. The graph below shows
changes of
about 5 x 10-8 in the mass of the standards since their first
calibration.
All measurements are with respect to the international prototype.
For
this
reason, the mass of the international prototype defines the x-axis
of
this
graph.
There is no reason to suspect that the mass of the international
prototype
of the kilogram is more stable than its official copies. The
question
of
stability can only be answered definitively by comparison with a
fundamental
constant of nature (such as the Planck constant or the mass of an
atom of
28Si). Such experiments are being carried out in several national
laboratories. So far, relative uncertainties of about 10-7 have
been
achieved.
Please help me understand how "changes of about 5 x 10-8" can be
reliably quantified using "relative uncertainties of about 10-7".
That is a signal-to-noise (S/N) ratio of 0.5, and as an analytical
chemist I would never try to certify a value with S/N less than 2
(and
*that* at only 95%).
Tom Davidson
Richmond, VA
I think the point was that efforts are underway to *replace* the
artifact standard with another method that is reproducible (not based
on an artifact). The issue is that other candidate methods have only
achieved a precision of 1E-7, while the variance among the artifact
standards is still less than that. So the candidate replacement
standards are not ready for prime time.
PD
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| User: "Ken S. Tucker" |
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| Title: Re: Kilogram international prototype |
03 Feb 2005 03:37:17 AM |
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PD wrote:
tadchem wrote:
CWatters wrote:
<snip>
The results of comparisons between the official copies and the
international
prototype show some divergence with time. The graph below shows
changes of
about 5 x 10-8 in the mass of the standards since their first
calibration.
All measurements are with respect to the international prototype.
For
this
reason, the mass of the international prototype defines the
x-axis
of
this
graph.
There is no reason to suspect that the mass of the international
prototype
of the kilogram is more stable than its official copies. The
question
of
stability can only be answered definitively by comparison with a
fundamental
constant of nature (such as the Planck constant or the mass of an
atom of
28Si). Such experiments are being carried out in several national
laboratories. So far, relative uncertainties of about 10-7 have
been
achieved.
Please help me understand how "changes of about 5 x 10-8" can be
reliably quantified using "relative uncertainties of about 10-7".
That is a signal-to-noise (S/N) ratio of 0.5, and as an analytical
chemist I would never try to certify a value with S/N less than 2
(and
*that* at only 95%).
Tom Davidson
Richmond, VA
I think the point was that efforts are underway to *replace* the
artifact standard with another method that is reproducible (not based
on an artifact). The issue is that other candidate methods have only
achieved a precision of 1E-7, while the variance among the artifact
standards is still less than that. So the candidate replacement
standards are not ready for prime time.
PD
I worked with Johnson Mathey and Mallory for awhile,
they produce items using precious metals.
For Au (gold) and the like they used beam balances,
of meticulous precision but couldn't account for
discrepancies on a monthly basis, sometimes high,
sometimes low.
For fun I'll pose this problem, they were using
brass weights for the counter-balance. Brass has
a different density than Au, what effect does
air-pressure have on the bouyancy of balanced
masses of differing densities?
The density of air varies with humidity and
altitude as well.
So if you're balancing Au in air you need to use
Au calibrated counter-balances. (same density and
bouyancy). Try explaining that to an accountant.
Generally, the exact density of what is being
weighed is impossible to determine accurately
even by assaying, due to casting variables.
So the weigh scale must be in a vacuum, to
eliminate the bouyancy variable for high precision.
I haven't checked to see if the ISU accounted
for that, likely so.
Conception Dynamics employs an *idealized*
definition of mass-energy based on the time
standard, and the invariance of charge, using
the positional energy stored in a rest system
given by q*Q/r where r = ct. That defines a
unit of *rest mass-energy* in the lab. The "c"
is defined in a vacuum, otherwise the standard
would vary with the refractive index, rather
like the mass standard varies with bouyancy.
Relativistically, time is defined by the
contravariant component x^0, hence the
*rest mass* is defined by the momentum component,
p_0 = q*Q/x^0 .
It's important to note each side transforms
the same.
Naturally, the lab time standard x^0 is only true
in that lab, the rest mass standard is only true
in the lab frame too.
The basis for that is the GR equivalent of the
Lorentz transform embodied in the requirement
that the covariant 3 velocity U_i=0 vanish, so
that the absolute motion dx_i dx^i =0 always,
but the relative dx^i is not generally zero.
That's important because the covariant momentum
denoted p_i =0 generally vanishes, so p_0 is
generally the *rest mass*. That idealized
standard, is what the ISU is trying to achieve,
using modern technology.
Regards
Ken S. Tucker
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| User: "Rene Tschaggelar" |
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| Title: Re: Kilogram international prototype |
02 Feb 2005 01:58:31 PM |
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CWatters wrote:
The results of comparisons between the official copies and the international
prototype show some divergence with time. The graph below shows changes of
about 5 x 10-8 in the mass of the standards since their first calibration.
All measurements are with respect to the international prototype. For this
reason, the mass of the international prototype defines the x-axis of this
graph.
There is no reason to suspect that the mass of the international prototype
of the kilogram is more stable than its official copies. The question of
stability can only be answered definitively by comparison with a fundamental
constant of nature (such as the Planck constant or the mass of an atom of
28Si). Such experiments are being carried out in several national
laboratories. So far, relative uncertainties of about 10-7 have been
achieved.
It would be interesting to know why Platinum/Iridium was
choosen as material. To store a cubic meter of hydrogen in it ?
Rene
--
Ing.Buero R.Tschaggelar - http://www.ibrtses.com
& commercial newsgroups - http://www.talkto.net
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| User: "PD" |
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| Title: Re: Kilogram international prototype |
02 Feb 2005 03:08:58 PM |
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Ha! I get it!
But maybe you're thinking of palladium, not platinum.
PD
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| User: "Dirk Van de moortel" |
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| Title: Re: Kilogram international prototype |
02 Feb 2005 01:20:45 PM |
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"PD" <pdraper@yahoo.com> wrote in message news:1107369110.417674.39340@f14g2000cwb.googlegroups.com...
Since the kilogram is the only base SI unit that is exemplified by a
nonreproducible prototype, how is the international prototype *used*,
except as a displayed artifact under glass?
Another way of asking the question is, how is the standard promulgated?
Or alternatively, how is recalibration done?
If anyone knows specifics about handling and procedures, that would be
ideal, but I'll take whatever I can get.
PD
Have you seen this one?
http://www.eeel.nist.gov/811/elec-kilo.html
Dirk Vdm
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