Sensitivity to g in atomic clocks
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
There are three things people refer to as G sensitivity on a crystal
oscillator:
- 2 g tip sensitivity (flip it 180 degrees on the bench).
- Vibration sensitivity (vibration translates into phase noise)
- Relativistic effects (take the oscillator to the moon and it's frequency
changes).
The first does not apply to an atomic clock. Since (unlike quartz) they are
sensitive to magnetic field, they will change when you flip them around, but
for other reasons. That would make actually proving a "no sensitivity" spec
difficult.
The second will not impact the atomic transition in an atomic clock
directly. Since they have narrow loops in them, it will impact the quartz
oscillators in the atomic clock. You will indeed see vibration translate
into phase noise at a ~ 2x10^-9/g sort of rate.
The third does indeed apply to atomic clocks. Change the gravity and time
changes. Change time and there goes frequency. This is a very real part of
the spec process on space flight atomic clocks. I've never seen it worried
about on crystal oscillators for space applications.
Bob
-----Original Message-----
From: time-nuts-bounces@febo.com [mailto:time-nuts-bounces@febo.com] On
Behalf Of iovane@inwind.it
Sent: Tuesday, January 11, 2011 8:49 AM
To: time-nuts@febo.com
Subject: [time-nuts] Sensitivity to g in atomic clocks
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
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to
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and follow the instructions there.
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
Bob Camp wrote:
Hi
There are three things people refer to as G sensitivity on a crystal
oscillator:
- 2 g tip sensitivity (flip it 180 degrees on the bench).
- Vibration sensitivity (vibration translates into phase noise)
- Relativistic effects (take the oscillator to the moon and it's
frequency
changes).
The first does not apply to an atomic clock. Since (unlike quartz) they
are
sensitive to magnetic field, they will change when you flip them around,
but
for other reasons. That would make actually proving a "no sensitivity"
spec
difficult.
Actually, some cesium beam tubes are sensitive to acceleration
because of beam ballistics. The 5071 CBT is specifically engineered
to make this effect negligible. In Rb standards, inverting the
clock might change the temperature distribution and affect the
frequency that way (after a delay).
Regarding relativity: the state of the art clocks at NIST supposedly
are so precise that they could detect the relativistic shift between
the 1st and 2nd floors of the building. Not that they fit in a
elevator...
Rick Karlquist N6RK
Hi Antonio:
Atomic clocks don't have a sensitivity to the direction of the
acceleration like a crystal. That's to say a crystal has "planes" and
the direction of the acceleration changes the crystal frequency. See
the plot at:
http://www.prc68.com/I/PRS10.shtml#Accel
The PRS10 was rotated so different faces were sitting on the bench and
the Electronic Frequency Control signal to the crystal oscillator were
plotted, see:
http://www.prc68.com/I/Images/FC_ROT.jpg
But atomic frequency standards have a sensitivity to the magnitude of
the gravitational field they are in. See:
Project GREAT: General Relativity Einstein/Essen Anniversary Test
Clocks, Kids, and General Relativity on Mt Rainier
http://www.leapsecond.com/great2005/
Have Fun,
Brooke Clarke
http://www.PRC68.com
iovane@inwind.it 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
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
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@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
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
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@febo.com [mailto:time-nuts-bounces@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@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
time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to
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and follow the instructions there.
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and follow the instructions there.