[time-nuts] Primary Standards...

Poul-Henning Kamp phk at phk.freebsd.dk
Tue Feb 23 22:48:35 UTC 2010

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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