Good quartz watches are, indeed, temperature compensated. More info here: http://forums.watchuseek.com/f9/thermocompensation-methods-movements-2087.html#/topics/2087?page=1
Of much greater interest to watch nerds like me is the improvement of accuracy in mechanical watch movements. Serious watch enthusiasts don't spend (many would say waste) a lot of time on quartz technology. Mechanical horology is a corner of time nuttery all to itself. Bill On Sunday, April 9, 2017, Tim Shoppa <tsho...@gmail.com> wrote: > I've had only a few different cars over the past 25 years but I've been > impressed with how accurate their mass-market built-in clocks are, > especially considering the wide and completely uncontrolled temperature > range. In the winter the interior of the car gets down below freezing most > mornings, and in the summer the interior gets way above 120F in sunlight. > > (Contrast the above with the time-nuttery here where folks buy double-oven > OCXO's and then they insist that the OCXO's have to be put in temperature > controlled environments.) > > I only set the car clock twice a year, at daylight savings time changes. > Yet between daylight savings time changes, the car clock never drifts by > more than a minute. > > 60 seconds in half a year is 4ppm. So I went and looked at the specs of a > stock 32kHz crystal, for example > http://www.mouser.com/ds/2/77/CFS-CFV-4402.pdf > > 1: The crystal is speced as having a turnover point of 25C. I understand > that. > 2: Frequency at the turnover point is speced as being +/-20ppm. OK, that's > not bad, most of that can be compensated for with a small trimmer cap at > the factory to the 4ppm range. Or maybe they just program in the clock > divider at the factory appropriate to the crystal. > 3: The temperature coefficient of the tuning fork cut around the turnover > point seems to always be the same: -.034ppm per deg C squared. If the temp > goes down to 5 deg C, then, the frequency changes by 14ppm. If the temp > goes down to -5 deg C, the frequency changes by 30ppm. > > With that temperature coefficient, temperatures like -5C or 5C that are > common every winter would result in a few minutes of drift every winter. > Yet I never observe that drift. > > So my conclusion, is that all these car clocks must be temperature > compensated. And they must've been doing this for several decades at this > point. > > That shouldn't be too surprising - right next to the clock display on the > dashboard is a digital thermometer. Maybe 30 or more years ago the > temperature compensation was done by analog circuitry, but today I'm > guessing there's a digital chip that takes the thermometer reading and > numerically adjusts the divider word for the 32kHz oscillator to > temperature compensate the clock digitally. > > Is there a way to verify my guess at the TCXO method? > > I'm guessing that all the better quartz wristwatches use a similar > technology too. Maybe they have a different crystal cut that is closer to > body temperature for the turnover point. > > Tim N3QE > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com <javascript:;> > To unsubscribe, go to https://www.febo.com/cgi-bin/ > mailman/listinfo/time-nuts > and follow the instructions there. > -- William H Fite, PhD Independent Consultant Statistical Analysis & Research Methods _______________________________________________ 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.