Thanks downloaded the paper. I assume the hyper fine transition happened to
be the one nearest that frequency? You can tune to either side of the peak
and get a lock on the next transition.
Regards
Paul.

On Tue, May 8, 2012 at 9:14 PM, David C. Partridge <
david.partridge@perdrix.co.uk> wrote:

It is my understanding that they actually got it a bit wrong, which is
why we seem to have a lot of leap seconds.

David

On 5/8/12 9:19 PM, paul swed wrote:

No, leap seconds have to do with the gradual slowing of the Earth's
rotation, and nothing to do with Cesium.

73, Eric Lemmon WB6FLY

-----Original Message-----
From: time-nuts-bounces@febo.com [mailto:time-nuts-bounces@febo.com] On
Behalf Of David McGaw
Sent: Tuesday, May 08, 2012 6:29 PM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] Why 9,192,631,770 ??

It is my understanding that they actually got it a bit wrong, which is
why we seem to have a lot of leap seconds.

David

On 5/8/12 9:19 PM, paul swed wrote:

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On Tue, May 08, 2012 at 09:28:33PM -0400, David McGaw wrote:

The atom is a much better timekeeper than the Earth.  They

could have chosen differently for convenience, but there's nothing really
wrong with the choice as it was made.

The issue is what to do with it over time as the Earth continues

to slow.

--msa

In message F621A5241A5E4ACF82E70AA8CC48B714@self6a5awnhg2m, "Eric Lemmon" wri
tes:

Not quite true.

When they decided the 9,192,631,770 they did so with astronomical
observations which were half a century old.  If they had used a
more up to date astronomical result, we would have had a lower
rate of leap seconds, essentially getting rid of the "one leap
second every 18 months" average value.

In the long term it doesn't make a difference of course, there
earths slowing down will dominate.

--
Poul-Henning Kamp      | UNIX since Zilog Zeus 3.20
phk@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.

In message 4EBB3F0321D24025B6BA3F4AA81B5134@pc52, "Tom Van Baak" writes:

See also:
http://phk.freebsd.dk/raga/sneak/

--
Poul-Henning Kamp      | UNIX since Zilog Zeus 3.20
phk@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.

Hi Paul,

The definition is the second specifies which hyperfine transition to use; it also requires zero temperature and zero magnetic field. Since you can't actually achieve the latter two in a beam tube, good cesium standards accurately compensate for the slight frequency shift with synthesizers.

Yes, when you apply the magnetic field you do get multiple peaks. You'll see this in most technical descriptions of how cesium clocks work; see this old one by hp:
http://leapsecond.com/museum/hp5062c/theory.htm

The center peak is the one to use because it's most immune from changes in magnetic field and also the tallest, sharpest peak. This is clear in the energy level diagram. You can also see each of the 7 peaks in detail here:
http://leapsecond.com/pages/cspeak/
Or the tall wall-poster(!) version:
http://leapsecond.com/pages/cspeak/image002.gif
John Miles joined the 9192631770 club:
http://www.ke5fx.com/cs.htm

Yes, older cesium standards would allow you to deliberately (or accidentally) lock to the wrong peak. In that case the clock runs many ppm fast or slow. Easy to detect.

The difference between the peaks is the "Zeeman frequency"; it allows one to cleverly indirectly calibrate the C-field so that the cesium standard more accurately ticks SI seconds. Modern cesium standards (e.g., 5071A) do this automatically. Here is a tall plot showing how much the other 6 peaks shift when the magnetic field is manually changed (e.g., hp 5061A):
http://leapsecond.com/images/cfield.gif
For more information on the Zeeman frequency and cesium beam tubes goggle: zeeman frequency site:febo.com

/tvb