[time-nuts] Cs stability

[SAIDJACK at aol.com]

In a message dated 7/16/2007 10:05:51 Pacific Daylight Time,  
Pablo.Alvarez.Sanchez at cern.ch writes:

>My  questions are:

>Are the Allan deviation specs also valid for all the  environmental range, 
including shock and >vibration, or only for lab  conditions?
Hi Pablo,
 
I can only speak from experience on my FTS4050 Cs:
 
First of all the output signal of almost all Rb and Cs units is generated  by 
a quartz OCXO (FTS1200 in my case) so you have all of the shock/vibration and 
 other sensitivites that quartz oscillators have.
 
For example tilting the Cs unit by 90 degrees will typically give an error  
of about 1E-09 or so.
 
It would take some time for the control loops to compensate for this  error.
 
Another observation is that Allan Deviation plots/measurements are usually  
done on units that have fairly constant temperature during the measurement, do  
not get moved, and also have had ample time to settle down (weeks, or even  
months to stabalize for some manufacturers!).
 
The problem is that any other conditions (adding vibration etc) are very  
hard to specify and re-create, it's much simpler to let the unit sit in a  nice 
and stable lab environment, and the measurement results will show very good  
performance.
 
Hope this helps,
bye,
Said
 



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