Re: [time-nuts] Primary Time Standards
Magnus Danielson mag...@rubidium.dyndns.org wrote: If you read the fine-print, the SI second is now defined for sea-level gravity and at 0 K black-body raditation, so compensation for these effects should be done. The definition of the second is independent of your frame of reference, otherwise it wouldn't be a universal unit of measurement. When the SI second is used to create a timescale then it must be referred to a standard frame of reference. In the case of TAI and UTC, the frame of reference is the rotating geoid. Tony. -- f.anthony.n.finch d...@dotat.at http://dotat.at/ South-east Iceland: Northerly or northeasterly 5 to 7, decreasing 4 in west. Moderate or rough. Showers. Moderate or good. ___ 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.
Re: [time-nuts] Primary Time Standards
Absolutely, but you can still pull a new Cs out of the box and it will run at the same frequency as your old Cs. Not quite the same. This is called the re-trace spec which is poorer than the stability spec. Vintage Cs standards like the 5060 or 5061 powered up within about 1e-10 or 1e-11. The 5071A retrace spec (called reproducibility in the data sheet) is 1e-13. /tvb ___ 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.
Re: [time-nuts] Primary Time Standards
In message ac0ea5f6-ddbf-49d4-a576-03bd7f91a...@leapsecond.com, Tom Van Baak (lab/iPad) writes: Absolutely, but you can still pull a new Cs out of the box and it will run at the same frequency as your old Cs. Not quite the same. This is called the re-trace spec which is poorer than the stability spec. Vintage Cs standards like the 5060 or 5061 powered up within about 1e-10 or 1e-11. The 5071A retrace spec (called reproducibility in the data sheet) is 1e-13. Right, but this is again not because of the physical principle used, but because of the implementation of it. The reason Rb's are secondary, is because the physical principle has no nominal frequency, but only an approximate one. -- Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 p...@freebsd.org | TCP/IP since RFC 956 FreeBSD committer | BSD since 4.3-tahoe Never attribute to malice what can adequately be explained by incompetence. ___ 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.
Re: [time-nuts] Primary Time Standards
A primary frequency standard is one that faithfully implements the definition of the SI second. Thus primary standards are based on Cs. But not all Cs-based clocks are primary. CSAC, for example, is not a primary standard. Rubidium, hydrogen, quartz, or pendulum clocks are not primary. The definition spells out zero magnetic field, zero temperature (zero velocity), and zero altitude on the earth's rotating geoid. There are many other practical physics details that need to be addressed. For a good example of what it takes to make a Cs clock a primary standard see: http://tf.nist.gov/general/pdf/1497.pdf http://tf.nist.gov/general/pdf/1846.pdf So strictly speaking no Cs clock actually runs at exactly 9192.631770 MHz since you need a certain amount of magnetic field to isolate the hyperfine transition, you can't run at absolute zero, no labs are actually at sea level, and atoms are not simple toys, etc. A lot of work is required to identify, predict, and quantify a host of factors. Again, please read or glance at those papers to appreciate the work that national metrology labs do to make copies of the SI second for their country. Some day the definition of the SI second will change; optical clocks offer much greater promise than microwave clocks. Note the length of a second won't change, it's just that the definition of a second will be more precise. /tvb ___ 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.
Re: [time-nuts] Primary Time Standards
On 15/07/11 10:24, Tom Van Baak (lab/iPad) wrote: A primary frequency standard is one that faithfully implements the definition of the SI second. Thus primary standards are based on Cs. But not all Cs-based clocks are primary. CSAC, for example, is not a primary standard. Rubidium, hydrogen, quartz, or pendulum clocks are not primary. There is an over-focus om the atom being used rather than the physical apparatus being used. Certain physical apparatuses (physical packages) has severe biases frequency so regardless of which atom used, you will have repeatability issues (build two devices, and they will tick differently). However, for various reasons has different atoms (and isotopes) been chosen for various physical packages due to various reasons. For instance, rubidium has two isotopes which makes it feasable to create an optical pumping due to how the D1 and D2 lines of the isotopes is located. Rubidium was investigated in beam configurations just as cesium. In fact, Cesium wasn't even the most stable one when chosen. It was chosen for its lower frequency was deemed more practical to implement. Still, the early beam devices had severe systematic biases in their frequency and much work has gone into prediciting them, reducing them and compensating them. The definition spells out zero magnetic field, zero temperature (zero velocity), and zero altitude on the earth's rotating geoid. There are many other practical physics details that need to be addressed. For a good example of what it takes to make a Cs clock a primary standard see: http://tf.nist.gov/general/pdf/1497.pdf http://tf.nist.gov/general/pdf/1846.pdf So strictly speaking no Cs clock actually runs at exactly 9192.631770 MHz since you need a certain amount of magnetic field to isolate the hyperfine transition, you can't run at absolute zero, no labs are actually at sea level, and atoms are not simple toys, etc. A lot of work is required to identify, predict, and quantify a host of factors. Again, please read or glance at those papers to appreciate the work that national metrology labs do to make copies of the SI second for their country. The 9192631770 cycles per second thing is the easy poster statement, the unattainable goal so to speak. The real world is quite complex. Today I would say that digital cesium, i.e. the locking of C-field from the side-band Rabi responses is among the key technologies which needs to be in a cesium to compete for systematic error removals. 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.
Re: [time-nuts] Primary Time Standards
Primary Standards are ones which don't have to be calibrated against others. My understanding is that Caesium and Hydrogen masers are Primary Standards (in our field). I don't think it quite works that way. Cesium is the primary standard because it's the definition of a second. Hydrogen and Rubidium and everything else are secondary standards as a result of that definition. Even cesium clocks have lots of quirks. As technology gets better some of the quirks get sorted out and we can measure time more accurately. (The one that I did a double take on was the blue shift correction for the differences in gravity due to the differences in elevation of various national standards labs.) But why is it that Caesium Clocks and Hydrogen Masers have an adjustment facility? For Cesium, it's to correct for those quirks. The idea is not to set the time so this clock matches some better clock, but to set some parameter to some known value. (Sorry, I don't have a good example handy.) If someday, somebody builds a superwonderful clock out of that is more stable than Cesium clocks, the standards bodies will probably redefine the second to use it. Rubidium is interesting because it's long term stability is better than quartz and it's much less expensive than Cesium. Hydrogen Masers have very good short term stability. Unfortunately, they have a big price tag. -- These are my opinions, not necessarily my employer's. I hate spam. ___ 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.
Re: [time-nuts] Primary Time Standards
I am an extreme novice in this field but my understanding is that the C-Field adjustments on the CS standards (5061A, 5061B that I am familiar with) allow for insuring that the appropriate energy state transition of the CS Ion is chosen as the 'reference' for the standard, something that can be accomplished without 'calibrating' against another device. The standard 5061A and 5061B provide a standard set of frequencies (5 MHz, 1 MHz, and 0.1 MHz for both the 5061A and 5061B and also 10 MHz for the 5061B). I have never measured them against each other but I suspect their phase will vary while their frequencies will be exact. It is hard to imagine that all CS ions are 'in phase' world wide. The 5061A and 5061B both offer clock options that provide an indication of time in an Hr:Min:Sec format as well as 1 PPS output. There is also an adjustment on these clocks to allow the 1 PPS to be synchronized with an external 1 PPS such that the clocks can all be set to the same time +/- a small error on the 'phase' of the 1 PPS. If my understanding is incorrect, I would greatly appreciate being corrected/educated. Joe -Original Message- From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On Behalf Of Jim Palfreyman Sent: Wednesday, July 13, 2011 9:26 PM To: Discussion of precise time and frequency measurement Subject: [time-nuts] Primary Time Standards Hi All, I've just realised I don't understand something. Something quite basic. Primary Standards are ones which don't have to be calibrated against others. My understanding is that Caesium and Hydrogen masers are Primary Standards (in our field). Secondary Standards are calibrated against the Primary Standards. My understanding is that Rubidium is an example of a Secondary Standard. So I can calibrate my Rubidium clocks by adjusting the C Field. All good. But why is it that Caesium Clocks and Hydrogen Masers have an adjustment facility? And what about the clocks used to determine UTC around the world? Do they have an adjustment facility? What are they adjusted to? Wouldn't that make them Secondary Standards? Now I'm aware that the average of those clocks is UTC, so are those clocks adjusted regularly to get closer to that average? I'm sure someone can clear this up for me. Regards, Jim ___ 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. ___ 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.
Re: [time-nuts] Primary Time Standards
On 14/07/11 04:26, Jim Palfreyman wrote: Hi All, I've just realised I don't understand something. Something quite basic. Primary Standards are ones which don't have to be calibrated against others. My understanding is that Caesium and Hydrogen masers are Primary Standards (in our field). In the ideal world... Secondary Standards are calibrated against the Primary Standards. My understanding is that Rubidium is an example of a Secondary Standard. So I can calibrate my Rubidium clocks by adjusting the C Field. All good. Concept wise yes... But why is it that Caesium Clocks and Hydrogen Masers have an adjustment facility? OK, let's look at the factors which play in here... We have two issues here... stability and frequency correctness. The rubidium gas cell standards (where the gas cell and not the rubidium vapor is the relevant thing) has several frequency pulling mechanisms such as cavity pull, wall-shift, ligth-shift, buffert-gas-shift etc. etc. This makes the gas cell standard (rubidium or whatever) unsuitable for realization of the SI second, but it is pretty stable for the size and power and has found good use in many applications due to this fact, not the least in telecom situations. The active hydrogen standard (there are passives as well) has wall-shift and cavity pulling among is systematic errors. It doesn't have a buffert gas so that pulling effect isn't there. Automatic cavity tuning has improved cancellation of the cavity effect and the active hydrogen standard has a very high mid-term stability of the classical standards. The cesium beam standard also has systematic shift components, but there is no wall-shift and no real cavity pulling. However, phase errors in the Ramsay resonators can introduce shift in frequency. All these standards also has shifts due to things like black body temperature, doppler effects etc. Another common shift is due to magnetic fields. The ideal frequency of these atoms is with no magnetic field (aka C-field). However, in reality this they always have a C-field. However, modern commerical cesium beams have no manual C-field adjustment as the early beams had, but rather a control-loop which looks at the side-band responses and servo the Rabi-splittings to a stable C-field. For a certain C-field the shift of the Ramsey response for the fine-grained middle is predictable and the shifted frequency is used for reference. Together with a number of other control-loops to help stabilize the frequency shifts and maintain noise sufficiently low the modern cesium is much better as a primary standard. So older commercial cesium beams where not really that good for your ideal primary reference... but good enought to be very useful for many applications. And what about the clocks used to determine UTC around the world? Do they have an adjustment facility? What are they adjusted to? Wouldn't that make them Secondary Standards? You are confusing the time of TAI and realization of SI seconds with the adjusted time-scale of UTC, which when needed jumps a second to maintain the UTC-UT1 difference within bounds. The frequency of the clocks does not change by this, it's the phase for UTC. Now I'm aware that the average of those clocks is UTC, so are those clocks adjusted regularly to get closer to that average? Your 10 MHz can be adjusted to be closer to TAI/GPS if you like. It is the digitis of the display which leap-seconds changes. You want your frequency to follow TAI and your time follow UTC. If you let your frequency adjust to UTC then it will be following coarsely the earth rotation as represented by UT1 rather than atomic time of TAI. I know it sounds confusing, but there it is. I'm sure someone can clear this up for me. ... or confuse further. Let's see. 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.
Re: [time-nuts] Primary Time Standards
In message CALH-g5YuKCDiyGxDf4s-MhHtK=ds7qr8z2st17jrqilwvr0...@mail.gmail.com , Jim Palfreyman writes: Primary Standards are ones which don't have to be calibrated against others. My understanding is that Caesium and Hydrogen masers are Primary Standards (in our field). Secondary Standards are calibrated against the Primary Standards. My understanding is that Rubidium is an example of a Secondary Standard. Almost, but not quite. Primary standards run at an intrinsic freqyency which is determined by the atomic/physical principle used. Secondary standards run at a frequency which is different from unit to unit due to side-effects from the physical principle used. Rule of thumb: If the timekeeping atoms are not in vaccuum, it's not a primary std. But why is it that Caesium Clocks and Hydrogen Masers have an adjustment facility? Because there are external effects that need to be cancelled out, mainly the magnetic field from the earth. -- Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 p...@freebsd.org | TCP/IP since RFC 956 FreeBSD committer | BSD since 4.3-tahoe Never attribute to malice what can adequately be explained by incompetence. ___ 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.
Re: [time-nuts] Primary Time Standards
At 10:26 PM 7/13/2011, Jim Palfreyman wrote... But why is it that Caesium Clocks and Hydrogen Masers have an adjustment facility? Cs defines the second, but only at the physically impossible temperature of absolute zero. Relativistic effects make it so the second is a different length at different altitudes. So, when one wants to track global mean time, individual clocks need adjustment. Which brings up another question - what altitude (=geoid?) is TAI defined for? I don't know enough about general relativity, but think the latitude would make a difference, too? ___ 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.
Re: [time-nuts] Primary Time Standards
Hi If you are running a Cs at high altitude, or worse yet in space - relativistic effects are pretty significant. Bob -Original Message- From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On Behalf Of Poul-Henning Kamp Sent: Thursday, July 14, 2011 10:04 AM To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] Primary Time Standards In message CALH-g5YuKCDiyGxDf4s-MhHtK=ds7qr8z2st17jrqilwvr0...@mail.gmail.com , Jim Palfreyman writes: Primary Standards are ones which don't have to be calibrated against others. My understanding is that Caesium and Hydrogen masers are Primary Standards (in our field). Secondary Standards are calibrated against the Primary Standards. My understanding is that Rubidium is an example of a Secondary Standard. Almost, but not quite. Primary standards run at an intrinsic freqyency which is determined by the atomic/physical principle used. Secondary standards run at a frequency which is different from unit to unit due to side-effects from the physical principle used. Rule of thumb: If the timekeeping atoms are not in vaccuum, it's not a primary std. But why is it that Caesium Clocks and Hydrogen Masers have an adjustment facility? Because there are external effects that need to be cancelled out, mainly the magnetic field from the earth. -- Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 p...@freebsd.org | TCP/IP since RFC 956 FreeBSD committer | BSD since 4.3-tahoe Never attribute to malice what can adequately be explained by incompetence. ___ 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. ___ 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.
Re: [time-nuts] Primary Time Standards
Hi One would assume that mean sea level / 1 G would be the standard reference point for the official Cs transition. I've never seen anybody pull out a gravity meter to set up their Cs though. I suspect that NIST has at least done the math. Bob -Original Message- From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On Behalf Of Mike S Sent: Thursday, July 14, 2011 6:26 AM To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] Primary Time Standards At 10:26 PM 7/13/2011, Jim Palfreyman wrote... But why is it that Caesium Clocks and Hydrogen Masers have an adjustment facility? Cs defines the second, but only at the physically impossible temperature of absolute zero. Relativistic effects make it so the second is a different length at different altitudes. So, when one wants to track global mean time, individual clocks need adjustment. Which brings up another question - what altitude (=geoid?) is TAI defined for? I don't know enough about general relativity, but think the latitude would make a difference, too? ___ 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. ___ 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.
Re: [time-nuts] Primary Time Standards
In message 90cc90599ce94dc980a448a08c7d2...@vectron.com, Bob Camp writes: If you are running a Cs at high altitude, or worse yet in space - relativistic effects are pretty significant. Absolutely, but you can still pull a new Cs out of the box and it will run at the same frequency as your old Cs. The distinction is about the implementation, not its surroundings. -- Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 p...@freebsd.org | TCP/IP since RFC 956 FreeBSD committer | BSD since 4.3-tahoe Never attribute to malice what can adequately be explained by incompetence. ___ 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.
Re: [time-nuts] Primary Time Standards
One would assume that mean sea level / 1 G would be the standard reference point for the official Cs transition. I've never seen anybody pull out a gravity meter to set up their Cs though. I suspect that NIST has at least done the math. You can do much better than just doing the math. In 1971, Hafele and Keating put atomic clocks on airplanes and flew around the Earth in both directions to check relativity. http://en.wikipedia.org/wiki/Hafele%E2%80%93Keating_experiment GPS satellites have to correct for gravity/elevation as well as motion/relativity. It's enormous on the scale of accuracy expected: 38 microseconds per day. http://www.astronomy.ohio-state.edu/~pogge/Ast162/Unit5/gps.html I think the first experimental satellite had the correction turned off for a couple of weeks. It's one of the classic tests of relativity. - This version was more fun: Project GREAT: General Relativity Einstein/Essen Anniversary Test Clocks, Kids, and General Relativity on Mt Rainier http://www.leapsecond.com/great2005/ -- These are my opinions, not necessarily my employer's. I hate spam. ___ 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.
Re: [time-nuts] Primary Time Standards
On 14/07/11 18:56, Bob Camp wrote: Hi One would assume that mean sea level / 1 G would be the standard reference point for the official Cs transition. I've never seen anybody pull out a gravity meter to set up their Cs though. I suspect that NIST has at least done the math. The gravity may be ignored when comparing clocks within the same lab, unless with very stable clocks, in which case they either need to be brought to the same level or compensation needs to be done. However, the gravitational differences is being compensated nowdays as TAI is being calculated. If you read the fine-print, the SI second is now defined for sea-level gravity and at 0 K black-body raditation, so compensation for these effects should be done. 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.
[time-nuts] Primary Time Standards
Hi, I think, the correct definition for a Primary (Time) Standard is not yet given here, yet. And I wonder, if there really exists an official definition, in form of a norm / a standard by BIPM. There should be one, does anybody know? I try to give some characteristics which have to be fulfilled all together, in the order of importance (think so): 1) A Primary Standard has to be accepted and defined by the Metrological Communitiy, i.e. by all the national standards institutes joining the BIPM. For time and frequency, its the CCTF which decides over the definition. A certain value is assigned to the Primary Standard, and an official definition is given. 2) A primary Standard is state of the art, it is currently the best one in terms of reproducibility. It must not be the most stable one (like Cs-beam/fountain compared to H-maser) What is accepted as a Primary Standard today, will be a Secondary one only by tomorrow, like the Rubidium, or even Quartz oscillators, which once were state-of-the-art Primaries. Which standard is better, can be measured and judged by comparing the Primary against the Secondaries, and by comparing an ensemble of Primaries against each other. 3) The known side effects or influence parameters (like magnetic field, pressure, temperature, particle motion, gravity, quantum effects, etc.) have to to be identified theoretically and experimentally, which means they are well known by magnitude and understood by a physical model. Experiment and theory have to fit. These side effects then can be effectively removed by either cancelling the influence parameter (e.g. in a Cs standard to zero the external magnetic field), or by evaluating the disturbance to calculate an upper boundary of the total deviation, or by making precise corrections to the output. 4) The Primary should not be an artefact (as the kilogram, currently), but should be defined and reproduced by basic physical effects, preferrably quantum standards, which can be reproduced everywhere in the universe, simply by a construction recipe, instead of sending an artifact around. So to answer Jims questions: A Rubidium standard is not a primary any more, because - it is less reproducible than Cs, due to the ~100 times higher susceptibility of the inner energy levels to magnetic fields. That means: External magnetic fields can be cancelled in both systems in the same way. But this residual field, produces a much smaller output deviation in the Cs clock. - The metrological community has redefined Cesium as the new primary many years ago, instead of the former Rubidium. The TAI is theoretically defined by the SI definition, whereby the UTC also accounts for the earth rotation by leap seconds. In theory the TAI / SI second is ideal (zero uncertainty) The TAI / SI second is practically realized by the complete ensemble of Cs Primaries in the National Standards Institutes worldwide. This real time scale is not perfect, as side effects on Cs are well known and cannot be eliminated completely. The reproducibility of the ensemble is around 2e-15 only.. But being the Primary Standard for the second, I think, this ensemble is simply defined to have zero practical uncertainty also, at least after the correction table is published. The trimming of the Cs clocks is intended for a controlled cancellation of those side effects, i.e. magnetic fields, but not for a sort of calibration! The different clocks principally cannot be adjusted against anything else, because nothing better exists at the moment. If the members of the ensemble all deviate from the total average in the boundaries of error calculations only, then they are Known Good. The statistical model of the complete ensemble gives an idea about the overall stability and reproducibility of the second, and also detects Bad clocks with systematic failures. On the other hand, it is not a good and accepted metrological practise at all , to tune one or more of those good Cs clock artifically close to the average. This would simply spoil the independance of the ensembles members. Today, the Cs is still the Primary Standard, although there might already exist more reproducible physical systems (e.g. Hg ion clock,???) The H maser is much more stable (short term), but not as reproducible (long term) as Cs clocks. That means, it is obviously not possible to get an ensemble of H-masers that close together by design only as it is the case with Cs. Therefore, H-masers cannot be Primary Standards. Frank ___ 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.
[time-nuts] Primary Time Standards
Hi All, I've just realised I don't understand something. Something quite basic. Primary Standards are ones which don't have to be calibrated against others. My understanding is that Caesium and Hydrogen masers are Primary Standards (in our field). Secondary Standards are calibrated against the Primary Standards. My understanding is that Rubidium is an example of a Secondary Standard. So I can calibrate my Rubidium clocks by adjusting the C Field. All good. But why is it that Caesium Clocks and Hydrogen Masers have an adjustment facility? And what about the clocks used to determine UTC around the world? Do they have an adjustment facility? What are they adjusted to? Wouldn't that make them Secondary Standards? Now I'm aware that the average of those clocks is UTC, so are those clocks adjusted regularly to get closer to that average? I'm sure someone can clear this up for me. Regards, Jim ___ 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.
Re: [time-nuts] Primary Time Standards
Jim, It is my understanding that the government standard offices around the globe, like NIST, calculates time by the earths rotation, I guess you could say, the old way, or using astronomy, but with this, they use things like the decay factors of atomic materials to keep this time. If I recall, things had to be recallibrated after the earthquake at Japan, as it changed the earths rotational speed a very minute amount. Its kind of like, which came first, the chicken or the egg on the standards. Best, Will *** REPLY SEPARATOR *** On 7/14/2011 at 12:26 PM Jim Palfreyman wrote: Hi All, I've just realised I don't understand something. Something quite basic. Primary Standards are ones which don't have to be calibrated against others. My understanding is that Caesium and Hydrogen masers are Primary Standards (in our field). Secondary Standards are calibrated against the Primary Standards. My understanding is that Rubidium is an example of a Secondary Standard. So I can calibrate my Rubidium clocks by adjusting the C Field. All good. But why is it that Caesium Clocks and Hydrogen Masers have an adjustment facility? And what about the clocks used to determine UTC around the world? Do they have an adjustment facility? What are they adjusted to? Wouldn't that make them Secondary Standards? Now I'm aware that the average of those clocks is UTC, so are those clocks adjusted regularly to get closer to that average? I'm sure someone can clear this up for me. Regards, Jim ___ 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. __ Information from ESET Smart Security, version of virus signature database 5851 (20110206) __ The message was checked by ESET Smart Security. http://www.eset.com ___ 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.
Re: [time-nuts] Primary Time Standards
No. The standards of time interval are atomic, not linked to the Earth's rotation. Hence Leap Seconds. -John == Jim, It is my understanding that the government standard offices around the globe, like NIST, calculates time by the earths rotation, I guess you could say, the old way, or using astronomy, but with this, they use things like the decay factors of atomic materials to keep this time. If I recall, things had to be recallibrated after the earthquake at Japan, as it changed the earths rotational speed a very minute amount. Its kind of like, which came first, the chicken or the egg on the standards. Best, Will *** REPLY SEPARATOR *** On 7/14/2011 at 12:26 PM Jim Palfreyman wrote: Hi All, I've just realised I don't understand something. Something quite basic. Primary Standards are ones which don't have to be calibrated against others. My understanding is that Caesium and Hydrogen masers are Primary Standards (in our field). Secondary Standards are calibrated against the Primary Standards. My understanding is that Rubidium is an example of a Secondary Standard. So I can calibrate my Rubidium clocks by adjusting the C Field. All good. But why is it that Caesium Clocks and Hydrogen Masers have an adjustment facility? And what about the clocks used to determine UTC around the world? Do they have an adjustment facility? What are they adjusted to? Wouldn't that make them Secondary Standards? Now I'm aware that the average of those clocks is UTC, so are those clocks adjusted regularly to get closer to that average? I'm sure someone can clear this up for me. Regards, Jim ___ 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. __ Information from ESET Smart Security, version of virus signature database 5851 (20110206) __ The message was checked by ESET Smart Security. http://www.eset.com ___ 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. ___ 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.
