[time-nuts] LPRO 101 ADJUSTMENT

Bruce Griffiths bruce.griffiths at xtra.co.nz
Fri Jul 25 23:32:28 EDT 2008

jshank wrote:
> If I choose to control the frequency via External C-field control I guess it 
> would take a very precise and stable voltage source.  Any thoughts or 
> suggestions?
The range of adjustment for a typical Datum/Efratom rubidium standard is 
only a few parts in1E9.
Thus to achieve a resolution of 1E-13( overkill??) a DAC with ENOB= 16 
bits should suffice.
If the DAC is part of a servo loop it only has to be quiet, have a 
monotonic transfer function and not drift too rapidly.
Thus a string DAC or KV style DAC (eg AD569) are ideally suited.
Sigma delta DACs are also suitable. PWM DACs are less useful.
The DAC response time need not be particularly fast if the loop time 
constant is several seconds or more.
Slow drifts in the DAC gain and offset will be corrected by the servo loop.


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