[time-nuts] CSAC Project(was CSAC purchase)

Tim Shoppa tshoppa at gmail.com
Thu Jan 25 13:29:59 EST 2018


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 at 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
>
>
>
>
>
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