[time-nuts] Digital temperature compensation
Dan Drown
dan-timenuts at drown.org
Sat Nov 1 21:09:58 UTC 2014
Ok, I hadn't considered rate of change. This data is currently 3
day's worth and seems to repeat itself on both days at the same
temperature point. Attached is a time based graph to show that. The
ppm axis (on the right) is inverted to make it easier to see the
relationship between the two.
Quoting Bob Camp <kb8tq at n1k.org>:
> 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 <dan-timenuts at drown.org> 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 -- time-nuts at febo.com
>> To unsubscribe, go to
>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
>> and follow the instructions there.
>
> _______________________________________________
> time-nuts mailing list -- time-nuts at febo.com
> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.
>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: temp-vs-clock.png
Type: image/png
Size: 20464 bytes
Desc: not available
URL: <http://febo.com/pipermail/time-nuts_lists.febo.com/attachments/20141101/7acca30a/attachment.png>
More information about the Time-nuts_lists.febo.com
mailing list