[time-nuts] Car Clock drift - the lowly 32kHz tuning fork crystal specs

[Bob kb8tq]

Hi

The compensation process either for a clock or a watch has been embedded
in the IC for a lot of years now. They do a pulse add / pulse drop approach 
to “level out” the 1 pps drive to the display. Temperature does not move fast
enough that averaging things over a minute is an issue. That gives them < 
1 ppm resolution which is better than what they know about temperature. It
is also good enough to set it on “at the factory” to run at whatever rate they
decide on. In most cases the nominal target is for the watch or car clock to 
run a bit fast (= it’s never slow) rather than try to set it dead on. Most people 
yell at watches when they are late ….

Bob

> On Apr 9, 2017, at 4:11 PM, Bill Hawkins <bill.iaxs at pobox.com> wrote:
> 
> Nice article in Wikipedia. Didn't see any familiar names in the
> reference list, though.
> 
> Seems to me inhibition compensation is useful for compensating for the
> variation in purchased crystal frequencies, but not for temperature
> compensation.
> 
> Also seems to me that a watch spends 2/3 of a day at wrist temperature
> and 1/3 at bedroom temperature, which varies with the seasons.
> 
> Would a ceramic capacitor crafted for a certain temperature coefficient
> work? Can the fork have a crafted tempco?
> 
> Bill Hawkins
> 
> 
> -----Original Message-----
> From: time-nuts [mailto:time-nuts-bounces at febo.com] On Behalf Of Ron
> Bean
> Sent: Sunday, April 09, 2017 12:05 PM
> To: Discussion of precise time and frequency measurement
> Subject: Re: [time-nuts] Car Clock drift - the lowly 32kHz tuning fork
> crystal specs
> 
>> In your case, the car sits in an environment that matches their test 
>> setup well. In my case ?\200? not so much.
> 
> FWIW, mine drifts pretty badly. It's in an aftermarket stereo, and I
> don't remember when I bought it (I moved it from my previous car).
> 
> I assume that all quartz clocks and watches these days use "inhibition
> conpensation".
> 
> https://en.wikipedia.org/wiki/Quartz_clock#Inhibition_compensation
> 
> 
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