[time-nuts] Any guesses as to how Citizen is claiming ±1 second/year with using this AT-cut 8.4MHz XTAL?
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. https://www.ablogtowatch.com/wp-content/uploads/2018/03/Citizen-Cal-0100-Eco -Drive-Movement-04.jpg 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. 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! ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Designing an embedded precision GPS time
>While crystal curves are indeed cubic, there are higher order terms in >the curve. The “why” is something people get to write papers on. If you >are trying to compensate to tight specs, you will see all sorts of >stuff. It is not at all uncommon to see >9th order curves residual curves. >Indeed some of that is from residuals in the compensation circuit as well as >from the crystal. I’ve been trying to research this very topic! Can you point to some of these papers? I am trying to build the most accurate fee running, low power time base I can. I am using an MCU, 32768Khz watch crystals, 0.5C accuracy temp sensor, lots of thermal bringing between them, and mass around them. The idea is to measure the frequency shift at all temps in the range, and even in both directions (hopefully to capture some hysteresis) for each unit and then use that database to compensate in software once the system is free running. I am trying to beat existing products like the Dallas DS3231 and Micro Crystal RV-8803-C7-32.768kHz-3PPM-TA-QC, which use (I think) a similar strategy. I’m hoping I can beat them by using more accurate temp tensing, longer and more exhaustive calibration effort, and anything else possible! Can you give a quick explanation (or point to reference material) covering the fundamental limits to XTAL compensation accuracy, and how to get there? That is, if I had an infinitely precise temp sensor and an infinite amount of time to characterize an XTAL, what would be limits to how accurately I could temp compensate it? Also, what are the limits of characterizing and compensating for aging? What other sources of inaccuracy would I need to consider? Thanks!!! -josh ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
