[time-nuts] CSAC Project(was CSAC purchase)
kb8tq at n1k.org
Thu Jan 25 14:04:46 EST 2018
> On Jan 25, 2018, at 12:39 PM, gandalfg8--- via time-nuts <time-nuts at febo.com> wrote:
> 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.
> "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 ….
> 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....
> time-nuts mailing list -- time-nuts at febo.com
> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.
More information about the time-nuts