[time-nuts] Sensitivity to g in atomic clocks

John Ackermann N8UR jra at febo.com
Tue Jan 11 13:58:27 EST 2011


FWIW, I have an FTS militarized Cesium that has an accelerometer as part of the OCXO assembly to reduce vibration sensitivity.  I'm told -- but can't document -- that it was for the Navy and the idea was to counteract the effects of the ship's guns.  FTS engineers had a couple of PTTI articles describing their accelerometer research.

John

On Jan 11, 2011, at 1:37 PM, "Tom Van Baak" <tvb at LeapSecond.com> wrote:

>> While sensitivity to g is an usually specified parameter for crystal
>> oscillators, I've been unable to find any indications for atomic clocks, say
>> 5071A, or more modestly LPRO. Can anybody point me to any source of info on the
>> subject?
>> Thanks,
>> Antonio I8IOV
> 
> Hi Antonio,
> 
> You may find some information on g-sensitivity of rubidium
> in old FCS or PTTI papers. There are high-rel rubidium for
> the military and space applications, so practical issues of
> acceleration and jerk sensitivity have been well researched.
> 
> The other thing you could do is quickly and/or very slowly
> turn over a running LPRO and report what happens. Like
> what we do with quartz, try it on all three axis. It would be
> a fun experiment.
> 
> For a 5071A the frequency shift is gh/c². Earth tides cause
> a couple of ten cm change during the day; this change in
> local g affects the output by parts in 10^17; way too low to
> be detected with a 5071A but getting near to the capabilities
> of ion clocks. See:
> http://www.nist.gov/pml/div688/clocks_092810.cfm
> 
> For some info on g, tides, and clocks see:
> http://www.leapsecond.com/hsn2006/
> 
> To detect changes in g with a 5071A you can raise the clock
> by many meters. For example, g is about 9.808 m/s² at sea
> level in Seattle but 1 km up it's closer to 9.805 m/s². A 5071A
> runs about 1e-13 faster at 1 km elevation compared to one
> at sea level. This is large enough to be measurable. See:
> http://www.leapsecond.com/great2005/
> 
> /tvb
> 
> 
> 
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