[time-nuts] Any guesses as to how Citizen is claiming ±1 second/year with using this AT-cut 8.4MHz XTAL?
Richard (Rick) Karlquist
richard at karlquist.com
Wed Apr 11 17:38:59 EDT 2018
The aging spec on the 10811 is 5 parts in 10^10 per day.
After 60 days, it could be off 30 ppb. So what we
have here is a non-ovenized AT cut that is better
than an ovenized SC cut. I'm sure.
I am reminded of the old Accutron ads. The headlines
guaranteed so many seconds a day or whatever it was.
The fine print says they don't actually guarantee that.
The only remedy under that guarantee is that they
agree to adjust the watch to be in spec at the
watch repair shop and hand it back to you. Thus,
they didn't have to worry about aging. Just come
into the shop as often as necessary :-)
On 4/11/2018 9:26 AM, tnuts at joshreply.com wrote:
> That comes out to about 30ppb, and this is a pocket watch so they dont seem
> to depend on the temp stabilization of being attached to a human wrist.
> Ive been reading about the new watch that contains this crystal for about a
> month, but just saw some more detail today
> AT-CUT QUARTZ CRYSTAL OSCILLATOR
> While AT-cut quartz crystals have indeed been in production and use since as
> early as 1934, the technology is more common in larger applications and not
> necessarily wristwatches. To address the needs of individuals seeking only
> the most accurate performance in a wristwatch, Citizen sought to apply and
> optimize this available technology in a way that could serve watch consumers
> on a more direct and personal level. When working to reach the accuracy of
> the Cal.0100, Citizen opted for an AT-cut quartz oscillator instead of a
> more traditional tuning fork shape (XY cut). Perhaps most notably, AT-cut
> variations allow for greater temperature tolerances, specifically in the
> range of -40°C to +125°C. Additionally, this configuration allows for
> reduced deviations caused by wearer orientation, which can cause significant
> changes in accuracy that aren't negligible when attempting this kind of
> performance. As a result, wearers will not have to worry about errors caused
> by spatial orientation and positioning becomes less of a concern. The same
> can be said about durability, which Citizen also improved upon in
> conjunction with the AT-cut oscillator. After all, shock experienced in
> day-to-day situations could easily prove detrimental even for quartz
> movements. And when the goal is an annual accuracy of ±1 second, that just
> isn't acceptable.
> Is this possible with an MXCO running across this wide temp range? How are
> they compensating for aging at this level of precision?
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