David Lord <[email protected]> wrote: > Rob wrote: >> Terje Mathisen <[email protected]> wrote: >>> Charles Swiger wrote: >>>> On Feb 12, 2015, at 1:56 AM, Rob <[email protected]> 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. > > At least in my case on occasions the rate of change seems to > be faster than the control loop can handle and offsets of my > various pcs rather than being < 300u rise to 10ms. Only a > small reduction in rate of change would be required to > avoid this. Thermostatic temperature control at the crystal > or a stable external clock source would be better but more > difficult to implement.
It is not certain that this problem is caused by temperature, unless maybe you are running at 1024 second poll interval. When you want close tracking of the offset the first thing to do is set the maxpoll to 6. Otherwise the interval over which the excursions happen is much too large, and overshoots of both the original offset and the compensation happen. With maxpoll 6 and local ethernet reference I have no trouble keeping within 50us. With maxpoll 10 this is impossible. The systems with local PPS (which is configured with maxpoll 4 although this seems to be handled differently in recent versions) normally remain within 10us, temperature changes result in wobbles of 4-6 us. When temperature is constant, it is more like 1-2 us. So it should be possible to get better results when temperature changes are taken into account. _______________________________________________ questions mailing list [email protected] http://lists.ntp.org/listinfo/questions
