From: Dr Bruce Griffiths <[EMAIL PROTECTED]> Subject: Re: [time-nuts] Watch Crystal Aging Rates Date: Sat, 21 Apr 2007 11:17:05 +1200 Message-ID: <[EMAIL PROTECTED]>
> Brooke Clarke wrote: > > Hi: > > > > I've heard that the aging rate of crystals gets better as the frequency > > gets > > lower. The idea is that the more mass in the crystal the less an atom here > > or > > there will be missed. So the 32768 Hz watch crystals should be very good > > compared to a 10 Mhz crystal. > > > > Does anyone have any data on watch crystal aging? > > > > If there was a known aging rate then it could be backed out in the > > countdown > > circuit resulting in much better accuracy. > > > > Have Fun, > > > > Brooke Clarke > > w/Java http://www.PRC68.com > > w/o Java http://www.pacificsites.com/~brooke/PRC68COM.shtml > > http://www.precisionclock.com > > > > > > > > _______________________________________________ > > time-nuts mailing list > > time-nuts@febo.com > > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > > > > > Brooke Bruce, > 32kHz watch crystals are actually very low mass items as they use a > different vibrational mode to common high frequency crystals. Thanks for pointing this out, it was anoying me. The clock crystals at 32,768 kHz is either of XY or NT cutting, which has second-degree frequency responce with a peak at about 25 degrees C. Compare with the typical AT cut which has a third-degree curve with a sadle point usually set at 85 degrees. Also notice that depending on resonance mode, the way that physical dimensions interact to give frequency vary alot. Length, thickness and width (and for AT cut, overtone number) come together in different forms. Cheers, Magnus _______________________________________________ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
