> -----Original Message----- > From: questions-bounces+edward.mischanko=arcelormittal....@lists.ntp.org > [mailto:questions- > bounces+edward.mischanko=arcelormittal....@lists.ntp.org] On Behalf Of > David Woolley > Sent: Saturday, May 25, 2013 4:02 PM > To: questions@lists.ntp.org > Subject: Re: [ntp:questions] Tighter regulation? > > unruh wrote: > > > > > Note that on maxpoll 10, the clock will freerun for about 7000 sec > > between disciplines. 5ms in 7000 sec is about 1PPM. Now if your computer > > The time constant for the proportional correction is 16384 seconds, so > only about 35% of the correction would be made over 7000 seconds. In > terms of correcting a random step phase change some time in that > interval, one is only talking about losing an average about 17% of the > total correction required as a result of the lower effective sampling > rate. > > I think the time for the integral component to remove a frequency step > is even longer (I think it actually rings), except that the rapidly > growing offset will cause the poll interval and time constant to drop. > I suspect, if the poll interval remained constant, the reciprocal of the > loop frequency would be so much longer than 7000 seconds that there > would be little difference between 1024 and 7000 second effective > sampling rates. > [Mischanko, Edward T]
Yes, I agree! > As I said above, the real issue is that of correctly identifying a step > in the frequency, or its first derivative, and rapidly turning down the > time constants. > [Mischanko, Edward T] I tried reducing the Allan Intercept to 7 and the result was wild swings in frequency ppm. I don't know why? Is the FLL broken? Has anyone else observed this behavior? > I am also wondering whether setting a lower Allan Intercept would help. > One problem is that it assumes gaussian behaviour of frequency > errors, but the situations where high offsets actually indicate a bad > time generally involve very non-gaussian statistics. > _______________________________________________ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
