[time-nuts] Primary Standards...

David C. Partridge david.partridge at dsl.pipex.com
Tue Feb 23 23:25:31 UTC 2010


>The "experimental" clocks based on lonely ions and quantum embraces are
very likely primary, once somebody has measured their intrinsic frequency
relative to Cs once.

No they cannot be - yet.  At the point where (e.g.) the second is re-defined
in terms of the aluminium quantum clock, then the aluminium quantum clocks
are then by definition the primary standards of time, and all the Cs clocks
are now secondary standards as the second is no longer defined in terms of
the Cs beam clock.

Dave

-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
Behalf Of Poul-Henning Kamp
Sent: 23 February 2010 22:49
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] Primary Standards...

In message <20100223214204.EAE711174BE at hamburg.alientech.net>, Mike S
writes:
>renamed, since the discussion has shifted.

>"In the time and frequency field, the term primary standard is 
>sometimes used to refer to any cesium oscillator, [...]

That rhymes with and Karls and my perception of the term:

A Cs clock is primary because when you turn it on, it latches onto the
physical phenomenon of a known and invariant frequency subject to no
systematic errors.

The reason the small Rb's do not qualify as primary is that each unit has a
slightly different frequency, due to vapour pressure, isotopemix and other
physical details, and thus you cannot know the frequency of a particular
unit, until you have measured it relative a primary clock.

In other words, Primary and Secondary has nothing to do with which atoms,
but depends a lot on the interogations mechanism used.

So the tiny 1cm^3 Cs standards are secondary, because they are also subject
to all sorts of pulls and offsets.

The "experimental" clocks based on lonely ions and quantum embraces are very
likely primary, once somebody has measured their intrinsic frequency
relative to Cs once.

The way to find out if your new invention has a chance to become a primary
clock, is to build N of them, turn them on, and see if they all find the
same frequency once they are locked, if they do, you're on your way to
become famous.

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

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