Hi This sort of thing is normally done with a precisely controlled temperature chamber and multi day temperature ramp runs. Even then there is a bit of “wonder what that was, let’s try it again”.
If you are looking at a crystal oscillator, what you have is a perturbation in the frequency / temperature curve. The response you get will be temperature rate of change dependent. Bob > On Nov 1, 2014, at 4:40 PM, Dan Drown <[email protected]> wrote: > > I'm experimenting with using a temperature sensor to estimate local > oscillator frequency changes. My goal is to have a decent holdover clock for > a NTP server with not so great GPS antenna placement. > > I've been sampling temperature every minute, measured by a DS18B20. I've > been measuring local clock frequency differences, using chronyd's logs from > the GPS's PPS. At 28C through 21C, I get a pretty good result that fits a > quadratic polynomial decently (0.117 ppm stddev). I've attached the graph of > that as "temp-clock-warmer.png". > > With the colder temperatures, there's a sudden drop off in frequency that I'm > having a hard time finding a equation that fits as nicely. All the examples > I can find on the web look like third degree polynomials, while my data > doesn't seem to fit that exactly. The best result I've had so far (0.198 ppm > stddev) is attached as "temp-clock.png" and uses the function: > > f(x) = -abs(a * (x - 20.88)) + b * ((x - 20.88)**2) + c * ((x - 20.88)**3) > a = 0.888582 > b = 0.113806 > c = -0.00445763 > > Does anyone have any advice on how to better model this? Has anyone seen > this behavior? > > I can provide the raw data if that would help any. > <temp-clock-warmer.png><temp-clock.png>_______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
