[time-nuts] Primary Standards...

Mike S mikes at flatsurface.com
Tue Feb 23 23:24:53 UTC 2010


At 05:48 PM 2/23/2010, Poul-Henning Kamp wrote...

>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.

There is no difference between Cs and Rb in that regard, except perhaps 
scale.

The frequency of a Cs is subject to gravitational and electromagnetic 
effects. Which is why the definition of the second was clarified in 
1997 by the CIPM to refer "to a caesium atom at rest at a temperature 
of 0 K."

Since absolute rest and absolute zero are impossible conditions for a 
real world clock, Cs clocks do not have a "known and invariant 
frequency." If they did, why would they have a C-Field knob to twiddle, 
and why would TAI be a weighted average of multiple Cs clocks?  I'd 
guess that Cs clocks can also be thrown off by trace gasses in the 
tubes and numerous other effects, impossible to completely remove.

Even if one could obtain absolute zero acceleration and temperature, 
Heisenberg would still be heard. 




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