[time-nuts] Sensitivity to g in atomic clocks

Rob Kimberley rk at timing-consultants.com
Wed Jan 12 22:43:40 UTC 2011


I've got some data that FEI released on g sensitivity enhancements in their OCXOs. 

I'll dig it out.

Rob Kimberley

-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On Behalf Of John Ackermann N8UR
Sent: 11 January 2011 6:58 PM
To: Tom Van Baak; Discussion of precise time and frequency measurement
Cc: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] Sensitivity to g in atomic clocks

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/c . 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/s  at sea level in Seattle but 
> 1 km up it's closer to 9.805 m/s . 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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