[time-nuts] oscillators

Chuck Harris cfharris at erols.com
Thu Aug 30 00:21:14 EDT 2012


Well, basically the temperature of a wrist watch is very
constant at around 90F.  That and a table lookup that gives
an adjustment for number of cycles per tick vs temperature.

All quartz watches since about 1990 are microprocessor based,
and have a table lookup.  They can only be regulated using
a special computer interface provided by the manufacturer.

-Chuck Harris

Neville Michie wrote:
> Does anyone know about what technology is used in Swiss watches to get much better performance from
> their xtals than you might expect?
> I assumed that they had look up lists to insert extra counts to compensate for ambient variations,
> but I have never heard any details.
> cheers,
> Neville Michie
>
>
>
>
>
>
> On 30/08/2012, at 1:45 PM, Richard (Rick) Karlquist wrote:
>
>>
>> On 8/27/2012 11:45 PM, WB6BNQ wrote:
>>>
>>>
>>> A microprocessor controlled XO is a non oven crystal oscillator system that has
>>> additional computational control providing a bit more than just mere passive
>>> temperature compensation.  The additional computational capability deals with
>>> having coefficients of that particular oscillator's behavior pre coded to
>>> compensate for the nonlinear behavior over a given temperature rang
>>
>> It doesn't use coefficients.  It has a look up table of frequency vs
>> temperature.
>>
>>>
>>> A microprocessor controlled XO system allows for using cheap crystals with
>>> minimum processing time and costs.  Because of limited storage space there is no
>>
>> No it doesn't use a cheap crystal.  It uses a *special* SC cut crystal.
>> This crystal could very easily cost more than an OCXO crystal.
>>
>>> way for the system to have enough data to even try to compete with the quality of
>>> a decent OCXO.  Beyond its initial calibration setup, it has no way of keeping it
>>> tied to a known reference, like the Thunderbolt is doing.
>>>
>>> Bill....WB6BNQ
>>
>> An MCXO is a very good, but expensive TCXO.  Only temperature, not aging is corrected.
>>
>> It has nothing to do with "smart clocks".
>>
>> Rick Karlquist N6RK
>>
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