In message <[email protected]>, Magnus Danielson writes:
>> What I did instead was to (badly) reinvent Shewarts ideas for testing >> if the phase residual is under "statistical process control": >> >> I increase the timeconstant if the phase residual has too frequent >> zero-crossings and loosen it if they happen too seldom. >> >> Having read a lot more about statistical process control, since I >> built those NTP servers for the Air Traffic Control 10 years ago, >> I would leverage more of the theory and heuristics developed in >> process control. (3sigma violations, length of monotonic direction >> etc. etc.) > >It's a complex field, and things like temperature dependencies helps to >confuse you. No, not really. The reason I went with the "statistical control" approach was exactly to not be confused or mislead by environmental or other factors: I wanted a PLL which on its own would adapt to circumstances on its own, while still maximizing the hold-over time in case of GPS loss, and all in all it has worked very well. So far I have seen it cope admirably with an OCXO which went from indoors to outdoors environment in the middle of winter, a PRS10 which gradually ran out of steam and only locked 40% of the time and various other odd-ball events, so I think I'm justified in saying that it does a pretty good job for autonomous and even unattended operation. It's certainly not perfect, but it is painfully obvious that the adaptive PLL based on statical control heuristics is much more resilient than a fixed or hand-tuned PLL. I've been trying to find an excuse for giving NTPns an overhaul, (PTP is a leading candidate for this) to get a chance to iron out the kinks I have spotted over the last 10 years, but so far life keeps me busy with other interesting stuff. -- Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 [email protected] | TCP/IP since RFC 956 FreeBSD committer | BSD since 4.3-tahoe Never attribute to malice what can adequately be explained by incompetence. _______________________________________________ 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.
