[time-nuts] Chronometer contest sponsored by IEEE Spectrum
Jeff Mock
jeff at mock.com
Fri Nov 30 03:05:42 UTC 2007
>> I think that I would start by looking at 32kHz watch crystals, I've
>> often wondered how good a timebase you can make out of one. The tempco
>> is a parabola around 25C with a max slope of something like 0.05 PPM/C,
>> so they are naturally a pretty good timebase with good aging
>> characteristics. The crystals are really tiny, maybe insulating it with
>> a material that has an interesting heat of fusion along with a micro to
>> model the physics of the parabolic shape of the crystal performance.
>>
>> jeff
>>
>>
> Maybe an ensemble of watch crystal clocks and a PIC microprocessor per
> David Allan paper
> of some years ago. After testing you could assign deferent weighting to
> the different clocks.
>
> Bill K7NOM
>
Yes, an ensemble of 32kHz crystals, I like it a lot. Perhaps you can
setup a temperature gradient from hot to cold across a number of
crystals. If the tempco for the crystal is really a parabola, each of
the crystals can be a datapoint along the parabola of crystal
performance. With a little work you might be able to precisely
calculate the maxima of the parabola and precisely set the frequency
independent of temp and aging. Ha!
jeff
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