Cs stability
Hi,
I am curious about the total stability of Cs clocks. Normally producers give you an initial accuracy after 30 minutes of power on and a table with the Allan deviation for different measurement intervals.
After that they give you the environmental and physical specifications. For the hp5071 you have:
General environment
Temperature
Operating 0°C to 55°C
Non-operating -40°C to 70°C
Humidity 0 to 95%RH (45C max)
Magnetic field dc, 55, 60Hz 0 to 2 gauss peak - any orientation Atmospheric pressure £1E-13 change in frequency for pressure down to 19kPa (equivalent to an altitude of 12.2km) Shock and vibration Mil-T-28800D, Type III, class 5 Hammer Blow Shock Test, Mil-S-901C, Grade A, Class 1, Type A Mile-STD, 167-1 (phase noise)
EMI: Conducted and radiated emissions per CISPR 11/EN 55011, Group 1, Class A
EMC: per MIL-STD-461C, Part 7, Class B dc magnetic field up to 7.8 Gauss
My questions are:
Are the Allan deviation specs also valid for all the environmental range, including shock and vibration, or only for lab conditions?
In the article "OBSERVATIONS ON STABILITY MEASUREMENTS OF COMMERCIAL ATOMIC CLOCKS", Pekka Eskelinen claims to have measured a phase temperature coefficient of 100ns/degree for commercial Cs clocks in 1999.
http://ieeexplore.ieee.org/iel5/6762/18075/00840739.pdf (If you cannot read it I can try to send you a copy by email)
Has any of you ever measured such a coefficient?
Cheers
Pablo
Pablo Alvarez Sanchez wrote:
); SAEximRunCond expanded to false
Errors-To: time-nuts-bounces+bruce.griffiths=ra.co.nz+bruce.griffiths=xtra.co.nz@febo.com
Hi,
I am curious about the total stability of Cs clocks. Normally producers give you an initial accuracy after 30 minutes of power on and a table with the Allan deviation for different measurement intervals.
After that they give you the environmental and physical specifications. For the hp5071 you have:
General environment
Temperature
Operating 0°C to 55°C
Non-operating -40°C to 70°C
Humidity 0 to 95%RH (45C max)
Magnetic field dc, 55, 60Hz 0 to 2 gauss peak - any orientation Atmospheric pressure £1E-13 change in frequency for pressure down to 19kPa (equivalent to an altitude of 12.2km) Shock and vibration Mil-T-28800D, Type III, class 5 Hammer Blow Shock Test, Mil-S-901C, Grade A, Class 1, Type A Mile-STD, 167-1 (phase noise)
EMI: Conducted and radiated emissions per CISPR 11/EN 55011, Group 1, Class A
EMC: per MIL-STD-461C, Part 7, Class B dc magnetic field up to 7.8 Gauss
My questions are:
Are the Allan deviation specs also valid for all the environmental range, including shock and vibration, or only for lab conditions?
In the article "OBSERVATIONS ON STABILITY MEASUREMENTS OF COMMERCIAL ATOMIC CLOCKS", Pekka Eskelinen claims to have measured a phase temperature coefficient of 100ns/degree for commercial Cs clocks in 1999.
http://ieeexplore.ieee.org/iel5/6762/18075/00840739.pdf (If you cannot read it I can try to send you a copy by email)
Has any of you ever measured such a coefficient?
Cheers
Pablo
Pablo
A Cs clock uses a frequency lock loop to control the frequency of the
local crystal oscillator, the crystal oscillator phase is arbitrary. The
phase of the output with respect to the crystal depends on the
propagation delay of any intervening electronics including amplifier and
filter phase shifts. The phase shift of tuned circuits and other narrow
bandwidth filters has a relatively high temperature coefficient and this
is perhaps what has been measured. Modern isolation amplifier designs
eschew the use of tuned circuits and other narrow bandwidth filters and
consequently have much lower phase shift temperature coefficients
(typically a few picosec/C).
Bruce
After that they give you the environmental and physical
specifications. For the hp5071 you have:
...
Are the Allan deviation specs also valid for all the environmental
range, including shock and vibration, or only for lab conditions?
The given specs are conservative (in typical HP style) but
I would guess the best ADEV numbers are only for laboratory
conditions. Someone from Agilent/Symmetricom might want
to comment on this.
In the article "OBSERVATIONS ON STABILITY MEASUREMENTS
OF COMMERCIAL ATOMIC CLOCKS", Pekka Eskelinen claims to
have measured a phase temperature coefficient of 100ns/degree
for commercial Cs clocks in 1999.
I'll comment after I read it. But the 100ns/degree value doesn't
make sense because that's phase instead of frequency units.
Did he mean 100 ns per day per degree? Or per 200 hours,
or 2000 hours, etc. If the latter, that represents a per-degree
frequency shift of 100 ns / 2000 h = 1.3e-14 which sounds
about right to me for a cesium tempco. It also depends on the
model: the tempco of a vintage hp 5060A or hp 5061A is likely
worse than a modern 5071A, for example.
Has any of you ever measured such a coefficient?
Yes, I'll take a look over my old data files and see what I have
on cesium. This week I just happen to be measuring the tempco
of an old Russian H-maser (about 2e-14/C). Please see:
http://www.leapsecond.com/pages/phm-temp/
/tvb
Tom Van Baak wrote:
The given specs are conservative (in typical HP style) but
I would guess the best ADEV numbers are only for laboratory
conditions. Someone from Agilent/Symmetricom might want
to comment on this.
In the article "OBSERVATIONS ON STABILITY MEASUREMENTS
OF COMMERCIAL ATOMIC CLOCKS", Pekka Eskelinen claims to
have measured a phase temperature coefficient of 100ns/degree
for commercial Cs clocks in 1999.
I'll comment after I read it. But the 100ns/degree value doesn't
make sense because that's phase instead of frequency units.
Did he mean 100 ns per day per degree? Or per 200 hours,
or 2000 hours, etc. If the latter, that represents a per-degree
frequency shift of 100 ns / 2000 h = 1.3e-14 which sounds
about right to me for a cesium tempco. It also depends on the
model: the tempco of a vintage hp 5060A or hp 5061A is likely
worse than a modern 5071A, for example.
Tom
Yes it can make sense.
Place one Cs clock in a chamber where the ambient temperature can be
adjusted to various fixed temperatures. Compare the phase of its
5/10MHz and/or PPS outputs with respect to those of another Cs standard
held at constant temperature. The observed phase shift sequence may then
be fitted to both frequency shift and a fixed (for a given temperature)
phase shift components. Repeat for a range of temperatures and plot the
(temperature dependent) fixed phase shift component as a function of
temperature.
Bruce
Who was it that said; every clock is a thermometer?
-----Original Message-----
From: time-nuts-bounces@febo.com [mailto:time-nuts-bounces@febo.com] On
Behalf Of Dr Bruce Griffiths
Sent: Monday, July 16, 2007 8:31 PM
To: Tom Van Baak; Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] Cs stability
Tom Van Baak wrote:
The given specs are conservative (in typical HP style) but
I would guess the best ADEV numbers are only for laboratory
conditions. Someone from Agilent/Symmetricom might want
to comment on this.
In the article "OBSERVATIONS ON STABILITY MEASUREMENTS
OF COMMERCIAL ATOMIC CLOCKS", Pekka Eskelinen claims to
have measured a phase temperature coefficient of 100ns/degree
for commercial Cs clocks in 1999.
I'll comment after I read it. But the 100ns/degree value doesn't
make sense because that's phase instead of frequency units.
Did he mean 100 ns per day per degree? Or per 200 hours,
or 2000 hours, etc. If the latter, that represents a per-degree
frequency shift of 100 ns / 2000 h = 1.3e-14 which sounds
about right to me for a cesium tempco. It also depends on the
model: the tempco of a vintage hp 5060A or hp 5061A is likely
worse than a modern 5071A, for example.
Tom
Yes it can make sense.
Place one Cs clock in a chamber where the ambient temperature can be
adjusted to various fixed temperatures. Compare the phase of its
5/10MHz and/or PPS outputs with respect to those of another Cs standard
held at constant temperature. The observed phase shift sequence may then
be fitted to both frequency shift and a fixed (for a given temperature)
phase shift components. Repeat for a range of temperatures and plot the
(temperature dependent) fixed phase shift component as a function of
temperature.
Bruce
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Who was it that said; every clock is a thermometer?
Even a short length of coax is a thermometer if you look
close enough. See the 50 fs / °C tempco at test #6:
http://www.leapsecond.com/pages/tadd-1/
/tvb
From: "Tom Van Baak" tvb@LeapSecond.com
Subject: Re: [time-nuts] Cs stability
Date: Mon, 16 Jul 2007 19:47:10 -0700
Message-ID: 000501c7c81c$c63d63e0$0300a8c0@pc52
); SAEximRunCond expanded to false
Errors-To: time-nuts-bounces+magnus=rubidium.dyndns.org+magnus=rubidium.dyndns.org@febo.com
Who was it that said; every clock is a thermometer?
Even a short length of coax is a thermometer if you look
close enough. See the 50 fs / °C tempco at test #6:
I guess that is why some GPS antenna cables is temperature-stabilized as well
as the cement-pidestal for the GPS antenna as it stands on solid rock. The same
place have controlled environment for the cesiums and hydrogens, together with
UPS and disel-engine that kicks in for longer runs.
Or I could be wrong... :)
Cheers,
Magnus - still have to do some of that fancy stuff with my rig
I guess that is why some GPS antenna cables is temperature-stabilized as well
as the cement-pidestal for the GPS antenna as it stands on solid rock. The same
place have controlled environment for the cesiums and hydrogens, together with
UPS and disel-engine that kicks in for longer runs.
Or I could be wrong... :)
Magnus,
This is true (temperature stabilization) for sites that do mm
level survey and ps level time transfer, using all the tricks
in the GPS book.
On the other hand, I think for most of us that play at the
meter and ns levels with cheap OEM receivers and plastic
L1 antennas the coax cable temperature issue is quite
overblown. Or if I'm wrong, show me the data.
/tvb
Yes it can make sense.
Place one Cs clock in a chamber where the ambient temperature can be
adjusted to various fixed temperatures. Compare the phase of its
5/10MHz and/or PPS outputs with respect to those of another Cs standard
held at constant temperature.
Bruce,
I'm not sure I follow this. Yes, you will see a phase shift but
how can you tell how much of said shift is due to a fixed
phase shift (as if it were cable phase tempco) vs. how much
is due to phase shift due to frequency offset (as if it were
oscillator frequency tempco)? No change in temperature is
instantaneous; during the (slow) change both phase and
frequency (equals phase change over time) may change.
/tvb
In the article "OBSERVATIONS ON STABILITY MEASUREMENTS
OF COMMERCIAL ATOMIC CLOCKS", Pekka Eskelinen claims to
have measured a phase temperature coefficient of 100ns/degree
for commercial Cs clocks in 1999.
Something is wrong with that claim. There's no way a modern
cesium standard exhibits a phase shift of 100 ns for a one
degree change in ambient temperature. I have Cs standards
that often change in temperature by several degrees and still
keep to nanoseconds. I guess I need to decode that paper
and see what's wrong. Does anyone have contact with the
authors (Finland)?
/tvb