[time-nuts] quartz drift rates, linear or log
kb8tq at n1k.org
Sun Nov 13 11:44:47 EST 2016
> On Nov 13, 2016, at 9:34 AM, Artek Manuals <Manuals at ArtekManuals.com> wrote:
> Tom et all
> While our instinct based on some "pre- knowledge" of the aging and drift processes is to try and fit these to linear or logarithmic curves there is a third possibility . That is, in fact the aging is not exactly either and may be better represented in fact be some kind of polynomial curve. The fact that there may be more than one drift and aging process at play here would also fit this hypothesis. Ii makes my head hurt to think about how one would derive the polynomial. Following this thread further ( and not to discourage your endeavor) but the entire history of each Xtal may be more of a factor than we initially surmised as well. Each xtal is at a different point in its journey through TIME and its history may have as much or more to do with how it behaves at this point in TIME than we can characterize
Having fit a few (quite a few) OCXO’s and TCXO's to various curves … the log curve in 55310 is about as good as any you can use. Polynomial curves will (in general) give you a real mess … The most common outcome is that your time interval is to short / your data to noisy / your aging to low to get a real fit with a good confidence estimate. The statement “as good as” should be taken in that context. The only real way to validate the fit is to go ahead and run the parts for another month or year to see what happens over various time periods. Because of the inevitable noise in the data, the curve fit is a bit tricky….
> Statistically it is also advisable to throw out (from the curve fitting exercise anyway) unusual units that are clearly not like all the other kids since they are clearly marching to a different drummer and for the purpose of this exercise are adding to the NOISE of the analysis 8^)
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