Re: [time-nuts] What time is it anyway?
Arnold Tibus wrote:
The answer looks to me a bit difficult reading the USNO definition :
INTERNATIONAL TIME SCALES AND THE B.I.P.M.
http://tycho.usno.navy.mil/bipm.html
citing:
"...the U.S. Naval Observatory timescale, UTC(USNO),
and its real-time implementation, Master Clock #2 (MC #2),
are kept within a close but unspecified tolerance of the
international atomic timescale published
by the Bureau International des Poids et Mesures
(International Bureau of Weights and Measures [BIPM])
in Sevres, France."
"...Hence, all these atomic timescales are called
Coordinated Universal Time (UTC), of which USNO's
version is UTC(USNO)."
"...The difference between UTC (computed by BIPM) and any other
timing center's UTC only becomes known after computation and
dissemination of UTC, which occurs about two weeks after the fact.
This difference is presently limited mainly by the long-term frequency
instability of UTC.
UTC(USNO) has been kept within 26 nanoseconds of UTC during
the past year through frequency steering of our Master Clocks to our
extrapolation of UTC."
So I do understand that BIPM is the world's time keeper, but there
may be a difference between the UTCs of up to 26ns?
First of all, that comment related only to USNOs performance, not any
other lab like NIST, PTB or SP. Historically, it may be 100s of ns away
if they fluke it. This is the difference in should and will supply
stability.
"...Since synchronization is never perfect, we provide the latest data
below on the differences between UTC and the UTC of other timing
centers, including USNO,..."
and
"...All of our reference clocks are real-time approximations of UTC(USNO),
and as such are denoted UTC(USNO,MC). Master Clock #2 (MC #2) is
our official reference clock..."
So I understand this as, that the USA do refer to the time reference
of USNO - and the rest of the world to BIPM directly?
No. First of all, you should consider that there is two bodies in the
USA, NIST and USNO. NIST is the primary body for all BIPM stuff, but
USNO is a complementary body in regards to time.
Then, both NIST and USNO refer back to BIPM, just as PTB in Germany
refers back to BIPM and SP in Sweden refers back to BIPM. The national
laboratories represent the first link in the traceability chain down
from BIPM. In this regard NIST and USNO is just that, the US national
laboratories. If I where to get my traceability through my national
laboratory SP and I also follow the calibration and reporting rules, set
forth in ISO 17025 and related, then that measurement is traceable to
BIPM and let's say HP in their Santa Clara lab does the same, they
relate to NIST (not USNO really) then by mutual agreements these
measurements is being recognised and agreed upon.
This aspect of recognised is highly related to trade and trust in trade.
Since dec. 2009 the PTB in Braunschweig, Germany (with the new
CSF2) and the BIPM in Sevre are the only countries running 4 of the
most precise primary Cs fountain clocks, if I am informed correctly.
Together they should run quite close to the time defined by BIPM I think,
and according our law our official time is transmitted by the PTB.
Cesium fountains is not a good measure of lab stability. Only a small
fraction of all the clocks (250 is a number frequently occuring) being
used. Each individual clock is being measured and weighted in. Most of
them is HP (now Symmetricom) 5071A clocks with normal or
high-performance tubes. The stability of these clocks is being compared
and a optimum stable paper-clock called EAL is created. This is then
corrected into TAI and with the decissions of IERS is corrected into UTC.
TAI is being somewhat of a paper-time, but several labs realize their
variant of it, referred to as TA(x) where x is replaced with lab name.
Now, How do I have to interprete the readout of GPSDOs like
Trimble's Thunderbolt and others PPS difference in ns to UTC?
To which UTC? I suppose to the time transmitted by the US GPS SATs.
The traceability of GPS time becomes:
BIPM -> USNO -> GPS-time -> Sat time -> User equipment
USNO provides measurements into BIPM, they then realize UTC(USNO) and
steer it towards the BIPM for long-term stability.
GPS time is separately maintained and is being supervised by USNO, the
UTC(GPS) is then steered towards UTC(USNO). USNO provides the
calibration values being transmitted over GPS such that the
UTC(GPS)-UTC(USNO) difference can be estimated and corrected for by user
equipment. Precision users use other methods.
The satellite time is being measured by the GPS monitoring stations and
the Kalman filters they employ will estimate ephemeris and time errors
and provide the correction values which is then being linked up to the
satellites and then transmitted. The 50 Wing space command will
regularly provide corrections of orbit and steer the onboard clocks. The
user equipment is able to convert the satellite time into GPS system
time, do the navigation part and then correct the GPS time into UTC
being traceable to BIPM... if only the user equipment itself will meet
the standards of a measurement device and also provide means for
completing the traceability.
Is there another difference in UTC to BIPM included?
UTC(USNO)-UTC
What is with Glonass (and will be later perhaps with Galileo)?
Glonass: Refers back to UTC(SU) which is traceable to BIPM.
Galileo: Will work similarly.
In fact the use of GPS is already spreaded all over the world and
in use in many technical applications, meaning that the world does
refer to UTC given by US GPS !?
Nope. It may look like that. From a legal standingpoint, the UTC time
out of any GPS receiver is not provide a traceable time, but for most
practical use, it is good enough if one only ensures that the
installation is good (GPS visibility, good receiver etc).
Does it make sense under this circumstance as Time Nut to go
below the Xns (26ns ?) frontier as absolute measure?
Will this ever be possible? (Everything is relative...)
The 26 ns number is taken out of context and doesn't relate to anything
else.
But excuse me in case I do miss and misunderstand something
fully...
There are several things behind the scene that you didn't look for. I
hope I have given you a few hints.
Two useful links:
http://www.bipm.org/en/publications/guides/vim.html
http://www.bipm.org/en/publications/guides/gum.html
If you look up traceable in VIM and look for related definitions, you
get the terminology right. There is references out from there to all
kinds of material.
Cheers,
Magnus
Hi
I believe that another component that BIPM considers is earth motion data. That data is not quite as common as cesium time scales are. The cesiums keep the agreed upon second tick "right". The earth motion decides when to drop or add a second. It's the drop / add thing that drives all the "we agree with BIPM" language as much as the right time tick stuff.
On a practical basis - my bar is a lot more likely to get busted for having missed a leap second than for being 21 ns off at closing time.
Bob
On Mar 28, 2010, at 8:51 AM, Magnus Danielson wrote:
Arnold Tibus wrote:
The answer looks to me a bit difficult reading the USNO definition :
INTERNATIONAL TIME SCALES AND THE B.I.P.M. http://tycho.usno.navy.mil/bipm.html
citing:
"...the U.S. Naval Observatory timescale, UTC(USNO), and its real-time implementation, Master Clock #2 (MC #2), are kept within a close but unspecified tolerance of the
international atomic timescale published by the Bureau International des Poids et Mesures (International Bureau of Weights and Measures [BIPM])
in Sevres, France."
"...Hence, all these atomic timescales are called Coordinated Universal Time (UTC), of which USNO's version is UTC(USNO)."
"...The difference between UTC (computed by BIPM) and any other timing center's UTC only becomes known after computation and dissemination of UTC, which occurs about two weeks after the fact. This difference is presently limited mainly by the long-term frequency
instability of UTC. UTC(USNO) has been kept within 26 nanoseconds of UTC during the past year through frequency steering of our Master Clocks to our extrapolation of UTC."
So I do understand that BIPM is the world's time keeper, but there may be a difference between the UTCs of up to 26ns?
First of all, that comment related only to USNOs performance, not any other lab like NIST, PTB or SP. Historically, it may be 100s of ns away if they fluke it. This is the difference in should and will supply stability.
"...Since synchronization is never perfect, we provide the latest data below on the differences between UTC and the UTC of other timing centers, including USNO,..."
and
"...All of our reference clocks are real-time approximations of UTC(USNO),
and as such are denoted UTC(USNO,MC). Master Clock #2 (MC #2) is our official reference clock..."
So I understand this as, that the USA do refer to the time reference of USNO - and the rest of the world to BIPM directly?
No. First of all, you should consider that there is two bodies in the USA, NIST and USNO. NIST is the primary body for all BIPM stuff, but USNO is a complementary body in regards to time.
Then, both NIST and USNO refer back to BIPM, just as PTB in Germany refers back to BIPM and SP in Sweden refers back to BIPM. The national laboratories represent the first link in the traceability chain down from BIPM. In this regard NIST and USNO is just that, the US national laboratories. If I where to get my traceability through my national laboratory SP and I also follow the calibration and reporting rules, set forth in ISO 17025 and related, then that measurement is traceable to BIPM and let's say HP in their Santa Clara lab does the same, they relate to NIST (not USNO really) then by mutual agreements these measurements is being recognised and agreed upon.
This aspect of recognised is highly related to trade and trust in trade.
Since dec. 2009 the PTB in Braunschweig, Germany (with the new CSF2) and the BIPM in Sevre are the only countries running 4 of the
most precise primary Cs fountain clocks, if I am informed correctly. Together they should run quite close to the time defined by BIPM I think, and according our law our official time is transmitted by the PTB.
Cesium fountains is not a good measure of lab stability. Only a small fraction of all the clocks (250 is a number frequently occuring) being used. Each individual clock is being measured and weighted in. Most of them is HP (now Symmetricom) 5071A clocks with normal or high-performance tubes. The stability of these clocks is being compared and a optimum stable paper-clock called EAL is created. This is then corrected into TAI and with the decissions of IERS is corrected into UTC.
TAI is being somewhat of a paper-time, but several labs realize their variant of it, referred to as TA(x) where x is replaced with lab name.
Now, How do I have to interprete the readout of GPSDOs like Trimble's Thunderbolt and others PPS difference in ns to UTC?
To which UTC? I suppose to the time transmitted by the US GPS SATs.
The traceability of GPS time becomes:
BIPM -> USNO -> GPS-time -> Sat time -> User equipment
USNO provides measurements into BIPM, they then realize UTC(USNO) and steer it towards the BIPM for long-term stability.
GPS time is separately maintained and is being supervised by USNO, the UTC(GPS) is then steered towards UTC(USNO). USNO provides the calibration values being transmitted over GPS such that the UTC(GPS)-UTC(USNO) difference can be estimated and corrected for by user equipment. Precision users use other methods.
The satellite time is being measured by the GPS monitoring stations and the Kalman filters they employ will estimate ephemeris and time errors and provide the correction values which is then being linked up to the satellites and then transmitted. The 50 Wing space command will regularly provide corrections of orbit and steer the onboard clocks. The user equipment is able to convert the satellite time into GPS system time, do the navigation part and then correct the GPS time into UTC being traceable to BIPM... if only the user equipment itself will meet the standards of a measurement device and also provide means for completing the traceability.
Is there another difference in UTC to BIPM included?
UTC(USNO)-UTC
What is with Glonass (and will be later perhaps with Galileo)?
Glonass: Refers back to UTC(SU) which is traceable to BIPM.
Galileo: Will work similarly.
In fact the use of GPS is already spreaded all over the world and in use in many technical applications, meaning that the world does refer to UTC given by US GPS !?
Nope. It may look like that. From a legal standingpoint, the UTC time out of any GPS receiver is not provide a traceable time, but for most practical use, it is good enough if one only ensures that the installation is good (GPS visibility, good receiver etc).
Does it make sense under this circumstance as Time Nut to go below the Xns (26ns ?) frontier as absolute measure? Will this ever be possible? (Everything is relative...)
The 26 ns number is taken out of context and doesn't relate to anything else.
But excuse me in case I do miss and misunderstand something fully...
There are several things behind the scene that you didn't look for. I hope I have given you a few hints.
Two useful links:
http://www.bipm.org/en/publications/guides/vim.html
http://www.bipm.org/en/publications/guides/gum.html
If you look up traceable in VIM and look for related definitions, you get the terminology right. There is references out from there to all kinds of material.
Cheers,
Magnus
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
Hi Bob,
Bob Camp wrote:
Hi
I believe that another component that BIPM considers is earth motion data. That data is not quite as common as cesium time scales are. The cesiums keep the agreed upon second tick "right". The earth motion decides when to drop or add a second. It's the drop / add thing that drives all the "we agree with BIPM" language as much as the right time tick stuff.
Actually, that's not the BIPM that deals with that, they acknowledge the
authority of IERS for that aspect.
http://www.bipm.org/en/scientific/tai/tai.html
http://www.iers.org
http://hpiers.obspm.fr/
On a practical basis - my bar is a lot more likely to get busted for having missed a leap second than for being 21 ns off at closing time.
.... and the law enforcers are more likely to miss the leap second than
the average time-nut.
The precision needed to be enforced is mostly never clearly stated, but
for many cases several seconds doesn't make a big difference, and for
closing time of a bar, most places would consider 5 min overtime
pointless to figth about when they want to ensure that it is not on the
scale of hours.
If you are down to miliseconds, what do you legally consider as closed?
Last order served? Last customer out the doors and all doors locked? I
think in practice the law enforcer for that case use their judgement on
the local variant of "closed" and the local variant of tolerance. It's
like porn, we recognise it but it is hard to define it in a legally
meaningful way. The exact border is hard to draw. (A point that Vint
Cerf dressed in his normal IETF three piece suite (he is about the only
one allowed to wear it) made very clear.)
Cheers,
Magnus
So there are 250 clocks, presumably, spread around the World and owned
by the member countries of the BIPM. Their time is somehow compared
centrally and an "absolute" time is determined from them. Each clock
will then have a delta to apply to it's own time to provide the BIPM
"absolute" time which then allows each member country to use its own
clock for timing.
This sounds like a logistic and bureaucratic nightmare, I will have
to look further as to how this is achieved. Any pointers gratefully
accepted.
On 29 March 2010 01:51, Magnus Danielson magnus@rubidium.dyndns.org wrote:
Arnold Tibus wrote:
The answer looks to me a bit difficult reading the USNO definition :
INTERNATIONAL TIME SCALES AND THE B.I.P.M.
http://tycho.usno.navy.mil/bipm.html
citing:
"...the U.S. Naval Observatory timescale, UTC(USNO), and its real-time
implementation, Master Clock #2 (MC #2), are kept within a close but
unspecified tolerance of the
international atomic timescale published by the Bureau International des
Poids et Mesures (International Bureau of Weights and Measures [BIPM])
in Sevres, France."
"...Hence, all these atomic timescales are called Coordinated Universal
Time (UTC), of which USNO's version is UTC(USNO)."
"...The difference between UTC (computed by BIPM) and any other timing
center's UTC only becomes known after computation and dissemination of UTC,
which occurs about two weeks after the fact. This difference is presently
limited mainly by the long-term frequency
instability of UTC. UTC(USNO) has been kept within 26 nanoseconds of UTC
during the past year through frequency steering of our Master Clocks to our
extrapolation of UTC."
So I do understand that BIPM is the world's time keeper, but there may be
a difference between the UTCs of up to 26ns?
First of all, that comment related only to USNOs performance, not any other
lab like NIST, PTB or SP. Historically, it may be 100s of ns away if they
fluke it. This is the difference in should and will supply stability.
"...Since synchronization is never perfect, we provide the latest data
below on the differences between UTC and the UTC of other timing centers,
including USNO,..."
and
"...All of our reference clocks are real-time approximations of UTC(USNO),
and as such are denoted UTC(USNO,MC). Master Clock #2 (MC #2) is our
official reference clock..."
So I understand this as, that the USA do refer to the time reference of
USNO - and the rest of the world to BIPM directly?
No. First of all, you should consider that there is two bodies in the USA,
NIST and USNO. NIST is the primary body for all BIPM stuff, but USNO is a
complementary body in regards to time.
Then, both NIST and USNO refer back to BIPM, just as PTB in Germany refers
back to BIPM and SP in Sweden refers back to BIPM. The national laboratories
represent the first link in the traceability chain down from BIPM. In this
regard NIST and USNO is just that, the US national laboratories. If I where
to get my traceability through my national laboratory SP and I also follow
the calibration and reporting rules, set forth in ISO 17025 and related,
then that measurement is traceable to BIPM and let's say HP in their Santa
Clara lab does the same, they relate to NIST (not USNO really) then by
mutual agreements these measurements is being recognised and agreed upon.
This aspect of recognised is highly related to trade and trust in trade.
Since dec. 2009 the PTB in Braunschweig, Germany (with the new CSF2) and
the BIPM in Sevre are the only countries running 4 of the
most precise primary Cs fountain clocks, if I am informed correctly.
Together they should run quite close to the time defined by BIPM I think,
and according our law our official time is transmitted by the PTB.
Cesium fountains is not a good measure of lab stability. Only a small
fraction of all the clocks (250 is a number frequently occuring) being used.
Each individual clock is being measured and weighted in. Most of them is HP
(now Symmetricom) 5071A clocks with normal or high-performance tubes. The
stability of these clocks is being compared and a optimum stable paper-clock
called EAL is created. This is then corrected into TAI and with the
decissions of IERS is corrected into UTC.
TAI is being somewhat of a paper-time, but several labs realize their
variant of it, referred to as TA(x) where x is replaced with lab name.
Now, How do I have to interprete the readout of GPSDOs like Trimble's
Thunderbolt and others PPS difference in ns to UTC?
To which UTC? I suppose to the time transmitted by the US GPS SATs.
The traceability of GPS time becomes:
BIPM -> USNO -> GPS-time -> Sat time -> User equipment
USNO provides measurements into BIPM, they then realize UTC(USNO) and steer
it towards the BIPM for long-term stability.
GPS time is separately maintained and is being supervised by USNO, the
UTC(GPS) is then steered towards UTC(USNO). USNO provides the calibration
values being transmitted over GPS such that the UTC(GPS)-UTC(USNO)
difference can be estimated and corrected for by user equipment. Precision
users use other methods.
The satellite time is being measured by the GPS monitoring stations and the
Kalman filters they employ will estimate ephemeris and time errors and
provide the correction values which is then being linked up to the
satellites and then transmitted. The 50 Wing space command will regularly
provide corrections of orbit and steer the onboard clocks. The user
equipment is able to convert the satellite time into GPS system time, do the
navigation part and then correct the GPS time into UTC being traceable to
BIPM... if only the user equipment itself will meet the standards of a
measurement device and also provide means for completing the traceability.
Is there another difference in UTC to BIPM included?
UTC(USNO)-UTC
What is with Glonass (and will be later perhaps with Galileo)?
Glonass: Refers back to UTC(SU) which is traceable to BIPM.
Galileo: Will work similarly.
In fact the use of GPS is already spreaded all over the world and in use
in many technical applications, meaning that the world does refer to UTC
given by US GPS !?
Nope. It may look like that. From a legal standingpoint, the UTC time out of
any GPS receiver is not provide a traceable time, but for most practical
use, it is good enough if one only ensures that the installation is good
(GPS visibility, good receiver etc).
Does it make sense under this circumstance as Time Nut to go below the Xns
(26ns ?) frontier as absolute measure? Will this ever be possible?
(Everything is relative...)
The 26 ns number is taken out of context and doesn't relate to anything
else.
But excuse me in case I do miss and misunderstand something fully...
There are several things behind the scene that you didn't look for. I hope I
have given you a few hints.
Two useful links:
http://www.bipm.org/en/publications/guides/vim.html
http://www.bipm.org/en/publications/guides/gum.html
If you look up traceable in VIM and look for related definitions, you get
the terminology right. There is references out from there to all kinds of
material.
Cheers,
Magnus
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to
https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
--
Steve Rooke - ZL3TUV & G8KVD
A man with one clock knows what time it is;
A man with two clocks is never quite sure.
Hi
It's pretty much the way any international standard unit is worked out.
The various national labs come up with a "best guess" and then they swap
around to see how the guesses all compare with each other. Ultimately they
come up with a way to agree on what the "average value" is. The math to
compute that is rarely simple.
After watching the magic number for a while (and tweaking the math) they
conclude that it's the best guess at what's correct.
Bob
-----Original Message-----
From: time-nuts-bounces@febo.com [mailto:time-nuts-bounces@febo.com] On
Behalf Of Steve Rooke
Sent: Monday, March 29, 2010 8:10 AM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] What time is it anyway?
So there are 250 clocks, presumably, spread around the World and owned
by the member countries of the BIPM. Their time is somehow compared
centrally and an "absolute" time is determined from them. Each clock
will then have a delta to apply to it's own time to provide the BIPM
"absolute" time which then allows each member country to use its own
clock for timing.
This sounds like a logistic and bureaucratic nightmare, I will have
to look further as to how this is achieved. Any pointers gratefully
accepted.
On 29 March 2010 01:51, Magnus Danielson magnus@rubidium.dyndns.org wrote:
Arnold Tibus wrote:
The answer looks to me a bit difficult reading the USNO definition :
INTERNATIONAL TIME SCALES AND THE B.I.P.M.
http://tycho.usno.navy.mil/bipm.html
citing:
"...the U.S. Naval Observatory timescale, UTC(USNO), and its real-time
implementation, Master Clock #2 (MC #2), are kept within a close but
unspecified tolerance of the
international atomic timescale published by the Bureau International
des
Poids et Mesures (International Bureau of Weights and Measures [BIPM])
in Sevres, France."
"...Hence, all these atomic timescales are called Coordinated Universal
Time (UTC), of which USNO's version is UTC(USNO)."
"...The difference between UTC (computed by BIPM) and any other timing
center's UTC only becomes known after computation and dissemination of
UTC,
which occurs about two weeks after the fact. This difference is presently
limited mainly by the long-term frequency
instability of UTC. UTC(USNO) has been kept within 26 nanoseconds of UTC
during the past year through frequency steering of our Master Clocks to
our
extrapolation of UTC."
So I do understand that BIPM is the world's time keeper, but there may be
a difference between the UTCs of up to 26ns?
First of all, that comment related only to USNOs performance, not any
other
lab like NIST, PTB or SP. Historically, it may be 100s of ns away if they
fluke it. This is the difference in should and will supply stability.
"...Since synchronization is never perfect, we provide the latest data
below on the differences between UTC and the UTC of other timing centers,
including USNO,..."
and
"...All of our reference clocks are real-time approximations of
UTC(USNO),
and as such are denoted UTC(USNO,MC). Master Clock #2 (MC #2) is our
official reference clock..."
So I understand this as, that the USA do refer to the time reference of
USNO - and the rest of the world to BIPM directly?
No. First of all, you should consider that there is two bodies in the USA,
NIST and USNO. NIST is the primary body for all BIPM stuff, but USNO is a
complementary body in regards to time.
Then, both NIST and USNO refer back to BIPM, just as PTB in Germany refers
back to BIPM and SP in Sweden refers back to BIPM. The national
laboratories
represent the first link in the traceability chain down from BIPM. In this
regard NIST and USNO is just that, the US national laboratories. If I
where
to get my traceability through my national laboratory SP and I also follow
the calibration and reporting rules, set forth in ISO 17025 and related,
then that measurement is traceable to BIPM and let's say HP in their Santa
Clara lab does the same, they relate to NIST (not USNO really) then by
mutual agreements these measurements is being recognised and agreed upon.
This aspect of recognised is highly related to trade and trust in trade.
Since dec. 2009 the PTB in Braunschweig, Germany (with the new CSF2) and
the BIPM in Sevre are the only countries running 4 of the
most precise primary Cs fountain clocks, if I am informed correctly.
Together they should run quite close to the time defined by BIPM I think,
and according our law our official time is transmitted by the PTB.
Cesium fountains is not a good measure of lab stability. Only a small
fraction of all the clocks (250 is a number frequently occuring) being
used.
Each individual clock is being measured and weighted in. Most of them is
HP
(now Symmetricom) 5071A clocks with normal or high-performance tubes. The
stability of these clocks is being compared and a optimum stable
paper-clock
called EAL is created. This is then corrected into TAI and with the
decissions of IERS is corrected into UTC.
TAI is being somewhat of a paper-time, but several labs realize their
variant of it, referred to as TA(x) where x is replaced with lab name.
Now, How do I have to interprete the readout of GPSDOs like Trimble's
Thunderbolt and others PPS difference in ns to UTC?
To which UTC? I suppose to the time transmitted by the US GPS SATs.
The traceability of GPS time becomes:
BIPM -> USNO -> GPS-time -> Sat time -> User equipment
USNO provides measurements into BIPM, they then realize UTC(USNO) and
steer
it towards the BIPM for long-term stability.
GPS time is separately maintained and is being supervised by USNO, the
UTC(GPS) is then steered towards UTC(USNO). USNO provides the calibration
values being transmitted over GPS such that the UTC(GPS)-UTC(USNO)
difference can be estimated and corrected for by user equipment. Precision
users use other methods.
The satellite time is being measured by the GPS monitoring stations and
the
Kalman filters they employ will estimate ephemeris and time errors and
provide the correction values which is then being linked up to the
satellites and then transmitted. The 50 Wing space command will regularly
provide corrections of orbit and steer the onboard clocks. The user
equipment is able to convert the satellite time into GPS system time, do
the
navigation part and then correct the GPS time into UTC being traceable to
BIPM... if only the user equipment itself will meet the standards of a
measurement device and also provide means for completing the traceability.
Is there another difference in UTC to BIPM included?
UTC(USNO)-UTC
What is with Glonass (and will be later perhaps with Galileo)?
Glonass: Refers back to UTC(SU) which is traceable to BIPM.
Galileo: Will work similarly.
In fact the use of GPS is already spreaded all over the world and in use
in many technical applications, meaning that the world does refer to UTC
given by US GPS !?
Nope. It may look like that. From a legal standingpoint, the UTC time out
of
any GPS receiver is not provide a traceable time, but for most practical
use, it is good enough if one only ensures that the installation is good
(GPS visibility, good receiver etc).
Does it make sense under this circumstance as Time Nut to go below the
Xns
(26ns ?) frontier as absolute measure? Will this ever be possible?
(Everything is relative...)
The 26 ns number is taken out of context and doesn't relate to anything
else.
But excuse me in case I do miss and misunderstand something fully...
There are several things behind the scene that you didn't look for. I hope
I
have given you a few hints.
Two useful links:
http://www.bipm.org/en/publications/guides/vim.html
http://www.bipm.org/en/publications/guides/gum.html
If you look up traceable in VIM and look for related definitions, you get
the terminology right. There is references out from there to all kinds of
material.
Cheers,
Magnus
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Steve Rooke - ZL3TUV & G8KVD
A man with one clock knows what time it is;
A man with two clocks is never quite sure.
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Below is a nice description of how UTC is generated including
a chart showing how individual timing laboratories, BIPM and
IERS are connected:
http://www.npl.co.uk/science-technology/time-frequency/time/research/the-world-time-system
/tvb
Steve Rooke wrote:
So there are 250 clocks, presumably, spread around the World and owned
by the member countries of the BIPM.
There is a fair spread geographically, yes. See map:
Their time is somehow compared centrally and an "absolute" time is determined from them.
They are compared by various methods in a network style of operation.
The sites are compared against each other and the clocks of each site is
compared against the clock driving the network comparison. Hence,
through these steps phase differences can be cranked out.
http://www.bipm.org/en/scientific/tai/clock_comparisons.html
Equipment calibrations:
http://www.bipm.org/jsp/en/TimeCalibrations.jsp
Each clock will then have a delta to apply to it's own time to provide the BIPM
"absolute" time which then allows each member country to use its own
clock for timing.
Yes, out comes the delta of each individual clock as well as the
individual labs. These are reported upon regularly to be found in BIPM
circular T:
http://www.bipm.org/jsp/en/kcdb_data.jsp
ftp://ftp2.bipm.org/pub/tai/publication/cirt.266
Useful resource:
http://www.bipm.org/jsp/en/TimeFtp.jsp?TypePub=publication
This sounds like a logistic and bureaucratic nightmare, I will have
to look further as to how this is achieved. Any pointers gratefully
accepted.
I hope the above pointers get you started.
They have spent some time cooking this up, yes.
Toss into that, we have not really spoken too much about how they
process things. I can't tell you too much about it, except that I know
that their tool is called ALGOS. If someone could give me the
appropriate articles I would be greatful.
Cheers,
Magnus
On 30 March 2010 07:46, Tom Van Baak tvb@leapsecond.com wrote:
Below is a nice description of how UTC is generated including
a chart showing how individual timing laboratories, BIPM and
IERS are connected:
http://www.npl.co.uk/science-technology/time-frequency/time/research/the-world-time-system
Thanks for that Tom.
/tvb
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--
Steve Rooke - ZL3TUV & G8KVD
A man with one clock knows what time it is;
A man with two clocks is never quite sure.
Magnus,
Excellent links, as always, many thanks. Much to digest. Clock
comparison looks an interesting area.
Steve
On 30 March 2010 13:12, Magnus Danielson magnus@rubidium.dyndns.org wrote:
Steve Rooke wrote:
So there are 250 clocks, presumably, spread around the World and owned
by the member countries of the BIPM.
There is a fair spread geographically, yes. See map:
Their time is somehow compared centrally and an "absolute" time is
determined from them.
They are compared by various methods in a network style of operation. The
sites are compared against each other and the clocks of each site is
compared against the clock driving the network comparison. Hence, through
these steps phase differences can be cranked out.
http://www.bipm.org/en/scientific/tai/clock_comparisons.html
Equipment calibrations:
http://www.bipm.org/jsp/en/TimeCalibrations.jsp
Each clock will then have a delta to apply to it's own time to provide the
BIPM
"absolute" time which then allows each member country to use its own
clock for timing.
Yes, out comes the delta of each individual clock as well as the individual
labs. These are reported upon regularly to be found in BIPM circular T:
http://www.bipm.org/jsp/en/kcdb_data.jsp
ftp://ftp2.bipm.org/pub/tai/publication/cirt.266
Useful resource:
http://www.bipm.org/jsp/en/TimeFtp.jsp?TypePub=publication
This sounds like a logistic and bureaucratic nightmare, I will have
to look further as to how this is achieved. Any pointers gratefully
accepted.
I hope the above pointers get you started.
They have spent some time cooking this up, yes.
Toss into that, we have not really spoken too much about how they process
things. I can't tell you too much about it, except that I know that their
tool is called ALGOS. If someone could give me the appropriate articles I
would be greatful.
Cheers,
Magnus
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to
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and follow the instructions there.
--
Steve Rooke - ZL3TUV & G8KVD
A man with one clock knows what time it is;
A man with two clocks is never quite sure.