Terje Mathisen <terje.mathi...@tmsw.no> wrote: > Charles Swiger wrote: >> On Feb 12, 2015, at 1:56 AM, Rob <nom...@example.com> wrote: >> >>> However, what I observe is that the plots of the offset show the derivative >>> of the environment temperature, which unfortunately cannot be controlled >>> any better. I am considering to locate the crystal that is responsible >>> for the timing and see if it could be ovenized or replaced by a more > > I've considered packing some insulation around the crystal, this would > tend to stabilize (while also increasing) the temperature, but this > would also be likely to reduce its lifetime, and the motherboard would > probably conduct heat too well.
That will only slow down the rate of change, and probably not much. We tend to have temperature cycles over 24h and this will not help. >>> temperature-stable oscillator. However, one can argue that it could be >>> fixed in software as well. ntpd could sense a changing drift and >>> extrapolate >>> it, if necessary helped by input from a temperature sensor. >> >> You're describing a TCXO; using a temperature sensor to compensate for >> thermal >> drift would gain perhaps a factor of 5 accuracy. > > It should be noted that this experiment has been tried out in real life > a few times: It has always helped! Depending upon the (temperature) > offset between the selected sensor and the crystal, you can see an order > of magnitude improvement. > > We don't have any code like that in the ntpd reference code base, simply > because it would be _very_ unportable. :-( I see in chrony there is a command to add temperature compensation, and it has a couple of parameters like the pseudo-file to read and the offset and gain. When just reading a file it is not very unportable, it may be that some systems do not provide that functionality but it will still compile. A more portable solution could extend this with the option of reading data from an external program or script. Linux provides access to onboard temperature sensors via files in /sys or /proc that can just be read by any file access function. _______________________________________________ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
