[time-nuts] What cut do I have?

[Bob Camp]

Hi

Any crystal in the vicinity of turnover point is going to be pretty flat. That relates directly to the way turnover is defined. There are some exceptions (10811), but the vast majority of OCXO designs  operate the crystal very near the turnover point. The whole "chill it down" approach was tried quite a while back. The idea at least partially was to reduce aging. The ultimate conclusion was that the added complexity / reduced reliability didn't really get you any benefits.

Bob
   
On Jan 29, 2013, at 3:15 AM, M. Simon <msimon6808 at yahoo.com> wrote:

> Those 32KHz watch crystals are very flat in the vicinity of the turnover. They don't age well. But if all you need is temperature stability and you can correct for aging a nice little electric heat pump (heats and cools) to keep the crystals at around the 25C inflection point might be interesting. The heat pump might not take too much power either. 
> 
> The temp error runs .04 (Tturnover - T)^2 ppm. i.e. .1 deg C from turnover gives .0004 ppm freq change. That is .4ppb. if you can hold .03C (not too difficult) you get 10X better - .04 ppb. Aging of course will be a killer with respect to that. 
> 
> 
> http://www.iqdfrequencyproducts.com/app-notes/timekeeping/
> 
> 
> ======
> 
> Nice page on cuts:
> 
> http://www.4timing.com/techcrystal.htm
> 
> Engineering is the art of making what you want from what you can get at a profit.
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