CSAC Project(was CSAC purchase)
Hi
The CSAC spec sheet calls out an aging rate of 0.9 ppb per month as
“typical”. There is also a temperature spec of 0.4 ppb. If both are correct
for your sample (and aging is linear ) you would be out by roughly 10 ppb
per year. There also is a voltage stability spec that might be impacted depending
on how you manage power.
Taking the 30 ppb = 1 second number, you are at a 1 second / year rate after 3 years.
At that point, you have already drifted by a second, if the assumptions are correct.
This makes a massive assumption that the aging stays at the “typical” rate
for years. It’s a very good guess that it does not. Is it going to be 1/3 or 1/10
of typical over that period? Who knows.
Bottom line, you are going to be pretty far from 1 second per 100 years with
a CSAC based wrist watch, if it runs for years (or even for months). It will
do way better than a TCXO or OCXO based watch over months or years.
It’s still not perfect.
Bob
"if it runs for years (or even months)" sounds like an informed comment:-)
When searching for some data recently I came across a report which might be relevant.
"A Second Look at Chip Scale Atomic Clocks for Long Term Precision Timing", written by
Alan T. Gardner and John A. Collins of the Woods Hole Oceanographic Institution, details their
experience with a number of earlier and more recent CSAC modules and their findings make
for very interesting reading.
At the time of writing a copy is available here....
www.obsip.org/documents/Gardner_IEEE_Oceans_2016.pdf
Nigel
GM8PZR
That's a wonderful paper by those Woods Hole guys.
Their temperature-compensated 5 milliwatt crystal oscillators can be
back-corrected (linear drift model) to a few tens of milliseconds over a
year and they make a convincing case they know how to do this.
Their similar graphs for CSAC oscillators are maybe a factor of three
better.
Tim N3QE
On Thu, Jan 25, 2018 at 12:39 PM, gandalfg8--- via time-nuts <
time-nuts@febo.com> wrote:
Hi
The CSAC spec sheet calls out an aging rate of 0.9 ppb per month as
“typical”. There is also a temperature spec of 0.4 ppb. If both are correct
for your sample (and aging is linear ) you would be out by roughly 10 ppb
per year. There also is a voltage stability spec that might be impacted
depending
on how you manage power.
Taking the 30 ppb = 1 second number, you are at a 1 second / year rate
after 3 years.
At that point, you have already drifted by a second, if the assumptions
are correct.
This makes a massive assumption that the aging stays at the “typical” rate
for years. It’s a very good guess that it does not. Is it going to be 1/3
or 1/10
of typical over that period? Who knows.
Bottom line, you are going to be pretty far from 1 second per 100 years
with
a CSAC based wrist watch, if it runs for years (or even for months). It
will
do way better than a TCXO or OCXO based watch over months or years.
It’s still not perfect.
Bob
"if it runs for years (or even months)" sounds like an informed comment:-)
When searching for some data recently I came across a report which might
be relevant.
"A Second Look at Chip Scale Atomic Clocks for Long Term Precision
Timing", written by
Alan T. Gardner and John A. Collins of the Woods Hole Oceanographic
Institution, details their
experience with a number of earlier and more recent CSAC modules and their
findings make
for very interesting reading.
At the time of writing a copy is available here....
www.obsip.org/documents/Gardner_IEEE_Oceans_2016.pdf
Nigel
GM8PZR
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.
Hi
On Jan 25, 2018, at 12:39 PM, gandalfg8--- via time-nuts time-nuts@febo.com wrote:
Hi
The CSAC spec sheet calls out an aging rate of 0.9 ppb per month as
“typical”. There is also a temperature spec of 0.4 ppb. If both are correct
for your sample (and aging is linear ) you would be out by roughly 10 ppb
per year. There also is a voltage stability spec that might be impacted depending
on how you manage power.
Taking the 30 ppb = 1 second number, you are at a 1 second / year rate after 3 years.
At that point, you have already drifted by a second, if the assumptions are correct.
This makes a massive assumption that the aging stays at the “typical” rate
for years. It’s a very good guess that it does not. Is it going to be 1/3 or 1/10
of typical over that period? Who knows.
Bottom line, you are going to be pretty far from 1 second per 100 years with
a CSAC based wrist watch, if it runs for years (or even for months). It will
do way better than a TCXO or OCXO based watch over months or years.
It’s still not perfect.
Bob
"if it runs for years (or even months)" sounds like an informed comment:-)
Actually it was not quite what it sounded like. What I was trying to say was “free runs”
for years or even months. Any device that is re-calibrated will have the aging drift zeroed
out in that process. As noted in another post, CSAC’s have gone through some growing
pains. The Woods Hole paper came out sort of at a low point in the process. The
current crop of CSAC parts seem to be more reliable than the ones Woods Hole
reported on. I’ve seen failures over the years, but not a lot of them ….
Bob
When searching for some data recently I came across a report which might be relevant.
"A Second Look at Chip Scale Atomic Clocks for Long Term Precision Timing", written by
Alan T. Gardner and John A. Collins of the Woods Hole Oceanographic Institution, details their
experience with a number of earlier and more recent CSAC modules and their findings make
for very interesting reading.
At the time of writing a copy is available here....
www.obsip.org/documents/Gardner_IEEE_Oceans_2016.pdf
Nigel
GM8PZR
time-nuts mailing list -- time-nuts@febo.com
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and follow the instructions there.
Also see the very nice presentation:
"Challenges of precise timing underwater"
http://www.ipgp.fr/~crawford/2017_EuroOBS_workshop/Resources/Gardner_OBS_Timing_ATG_20150427.pdf
/tvb
Hi
One of the unique features of underwater timing is that the sea bottom temperature
(once you get well away from a coastline) is very stable. In some deployments, the “random”
nature of ambient temperature that we fight all the time in the rest of the world, simply is not
present. The device sits at 2.345 C and that’s it …..
Bob
On Jan 25, 2018, at 2:06 PM, Tom Van Baak tvb@LeapSecond.com wrote:
Also see the very nice presentation:
"Challenges of precise timing underwater"
http://www.ipgp.fr/~crawford/2017_EuroOBS_workshop/Resources/Gardner_OBS_Timing_ATG_20150427.pdf
/tvb
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and follow the instructions there.
On 1/25/18 9:39 AM, gandalfg8--- via time-nuts wrote:
At the time of writing a copy is available here....
"While results from an early batch of CSACs have been largely positive,
later units have not performed as well. The CSAC specifications have
changed, reflecting a decrease in reliability and accuracy of more
recent units."
no kidding - there's a well known issue when MicroSemi took over
building CSACs from Symmetricom, these things (like many precision
timing widgets) have a "recipe" and it's easy to "lose the recipe" or
find that there's unexpected and unknown components to the recipe.
Take a look at data sheet revs for the CSAC.. full temp range, then all
of a sudden around rev G or H, temperature range is quoted at 0-35C
operating, 0-40C non-op. I asked the sales rep if they ship them with
icepacks in styrofoam like mail order cheese in the summer - that UPS
truck gets way over 40C inside.
As always, this was discussed on the list and is in the archives.
That being said, I have no complaints about Microsemi being forthcoming
about the issue and helping us to understand the nature of the problem.
And they claim to have fixed the problem.
Hopefully, this summer, I'll have some data from a "narrow temp range"
CSAC against GPS 1pps in an environment where there's no gravitational
effects, and fairly small temperature fluctuations.
Hi
Just to be clear, the current data sheet has the temperature range back to
-10 to +70C. They most certainly had a major headache on their hands for
several years straightening things out. I have not seen any complaints about
the “new” (post rework) version of the part.
Bob
On Jan 25, 2018, at 3:31 PM, jimlux jimlux@earthlink.net wrote:
On 1/25/18 9:39 AM, gandalfg8--- via time-nuts wrote:
At the time of writing a copy is available here....
www.obsip.org/documents/Gardner_IEEE_Oceans_2016.pdf
"While results from an early batch of CSACs have been largely positive, later units have not performed as well. The CSAC specifications have changed, reflecting a decrease in reliability and accuracy of more recent units."
no kidding - there's a well known issue when MicroSemi took over building CSACs from Symmetricom, these things (like many precision timing widgets) have a "recipe" and it's easy to "lose the recipe" or find that there's unexpected and unknown components to the recipe.
Take a look at data sheet revs for the CSAC.. full temp range, then all of a sudden around rev G or H, temperature range is quoted at 0-35C operating, 0-40C non-op. I asked the sales rep if they ship them with icepacks in styrofoam like mail order cheese in the summer - that UPS truck gets way over 40C inside.
As always, this was discussed on the list and is in the archives.
That being said, I have no complaints about Microsemi being forthcoming about the issue and helping us to understand the nature of the problem. And they claim to have fixed the problem.
Hopefully, this summer, I'll have some data from a "narrow temp range" CSAC against GPS 1pps in an environment where there's no gravitational effects, and fairly small temperature fluctuations.
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On 1/25/18 11:20 AM, Bob kb8tq wrote:
Hi
One of the unique features of underwater timing is that the sea bottom temperature
(once you get well away from a coastline) is very stable. In some deployments, the “random”
nature of ambient temperature that we fight all the time in the rest of the world, simply is not
present. The device sits at 2.345 C and that’s it …..
It helps that water density has a maximum at a particular temperature -
water that is warmer or colder tends to float up above it. I was just
looking it up and found apparently that does vary with salinity, too...
oh no, another miniscule factor to account for - is there a "seawater
density nuts" list...
Let's see, the bottom of Lake Tahoe (fresh water, so no salinity
variation) is probably fairly stable at 4C. Or any other freshwater
later that actually gets cold enough, and doesn't freeze to the bottom -
so the deeper Great Lakes would probably work. How warm does the bottom
of Lake Superior get in late summer?
Hi
Things have to get pretty deep to be fully isolated from the seasons down to
the “digits past the decimal” level. It does bring up an interesting place to set
up your temperature stabilized timing lab though. The commute back and forth
might be a bit of a chore :)
Bob
On Jan 25, 2018, at 3:42 PM, jimlux jimlux@earthlink.net wrote:
On 1/25/18 11:20 AM, Bob kb8tq wrote:
Hi
One of the unique features of underwater timing is that the sea bottom temperature
(once you get well away from a coastline) is very stable. In some deployments, the “random”
nature of ambient temperature that we fight all the time in the rest of the world, simply is not
present. The device sits at 2.345 C and that’s it …..
It helps that water density has a maximum at a particular temperature - water that is warmer or colder tends to float up above it. I was just looking it up and found apparently that does vary with salinity, too... oh no, another miniscule factor to account for - is there a "seawater density nuts" list...
Let's see, the bottom of Lake Tahoe (fresh water, so no salinity variation) is probably fairly stable at 4C. Or any other freshwater later that actually gets cold enough, and doesn't freeze to the bottom - so the deeper Great Lakes would probably work. How warm does the bottom of Lake Superior get in late summer?
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