[time-nuts] Digital temperature compensation
alan.melia at btinternet.com
Sat Nov 1 20:10:43 EDT 2014
Mmmm yes you can see the equation evaluation starting to rise in your
"Warmer" plot, as Mark says, which will make a nonsense of the formula if
your summer temps get above 28.
Why not a table and then interpolate between the table data points?. You
might have more points where the changes are greater.
The colder plot looks cubic maybe for a crystal made for 20 deg C ?? But
depending on the oscillator electronics you may have component tempcos
affecting the frequency as well?
I suspect the turnover at 21deg C should be a smooth curve not as your
formula predicts. Which suggests that you have too too high an order of
polynomial I think, but you may not get a good fit with a cubic if other
effects are present.
----- Original Message -----
From: "Dan Drown" <dan-timenuts at drown.org>
To: <time-nuts at febo.com>
Sent: Saturday, November 01, 2014 10:07 PM
Subject: Re: [time-nuts] Digital temperature compensation
>I gave zunzun a try and the one with the lowest root mean squared error
> f(x) = a( x**0.5) + b( x ) + c( sin(x) ) + d( cos(x) )
> It got 0.202 RMSE, so I guess I'll stick with my original function as it
> seems to be closer to what I expect will happen at colder/hotter temps.
> You have a good point about temperatures outside my data samples. Once
> it gets hot again in the summertime, I'm sure I'll have to re-evaluate
> Quoting Mark Sims <holrum at hotmail.com>:
>> You could try submitting your data to zunzun.com It will fit it to
>> around 40,000 different curves and find the best ones.
>> Beware that with all curve fitting formulas, once your live data starts
>> to wander out of the range of your original curve fit data, things can
>> go rather badly...
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