[time-nuts] Any guesses as to how Citizen is claiming ±1 second/year with using this AT-cut 8.4MHz XTAL?

Mike Cook michael.cook at sfr.fr
Wed Apr 11 22:03:44 UTC 2018


I have a Citizen A660 movement which was spec’d at +/- 5 secs per year. I monitored it from when I bought it in December 2010 until its battery failed on 03/11/2012. 
It was in spec when both on and off the wrist (off the wrist it was in a drawer at a constant temperature and the accuracy was a stability was lower) . 
The error in the first 18 months gave a yearly rate of +1,2 secs. Not bad. So maybe the new movement is just getting the advantage of higher frequency so that their cycle hops are finer grained.



> Le 11 avr. 2018 à 22:24, Bob kb8tq <kb8tq at n1k.org> a écrit :
> 
> Hi
> 
> 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. 
> 
> Bob
> 
>> 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 don’t seem
>> to depend on the temp stabilization of being attached to a human wrist. 
>> 
>> 
>> 
>> https://www.ablogtowatch.com/wp-content/uploads/2018/03/Citizen-Cal-0100-Eco
>> -Drive-Movement-04.jpg
>> 
>> 
>> 
>> I’ve 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.
>> 
>> 
>> 
>> https://www.ablogtowatch.com/citizen-cal-0100-eco-drive-watch-movement/
>> 
>> ---
>> 
>> 
>> 
>> Is this possible with an MXCO running across this wide temp range? How are
>> they compensating for aging at this level of precision?
>> 
>> 
>> 
>> Thanks!
>> 
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Don’t worry about how powerful the machines are. Worry about who the machines are giving  power to.




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