[time-nuts] Any guesses as to how Citizen is claiming ±1 second/year with using this AT-cut 8.4MHz XTAL?
kb8tq at n1k.org
Wed Apr 11 16:24:19 EDT 2018
Guess at the aging
Cut the crystal so it’s fairly flat at 25 to 35C
Do a basic / simple temperature compensation (TCXO)
…. and count on the errors to average out.
The success of all that will depend a lot on how close your wrist is to the
environment they used for their guesswork. Did they count on you taking
the watch off at night or not? What temperature is the room at? …..
Before you say it can’t be done, the whole “average out” thing is how time
pieces have been done for hundreds of years. The device may swing this
way and that …. done properly it eventually averages out. How well it works
for you … that depends.
> On Apr 11, 2018, at 12:26 PM, 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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