From: "Poul-Henning Kamp" <[EMAIL PROTECTED]> Subject: Re: [time-nuts] GPSDO Question Date: Mon, 03 Sep 2007 20:06:03 +0000 Message-ID: <[EMAIL PROTECTED]>
> In message <[EMAIL PROTECTED]>, [EMAIL PROTECTED] writes: > >); SAEximRunCond expanded to false > > >This brings up another question: how good are true PID loops that also make > >use of the differential term (e.g. correcting for rate of change of the > >phase)? The literature talks about the differential term being hardly used > >in the > >industry because it can add noise and instability to a system... > > I tried it and found that you could indeed et faster convergence, but > I did it with a HP5370B as phase comparator to minimize the noise. > > With more realistic phase comparators I don't think it is sensible. > > I personally prefer to start with a very short tempered PLL and then > increase the timeconstant as things get better. You can get improved result in the early phase from adding a D-term too, but once you've acheived lock you can reduce it or totally remove it. Just adds noise when locked. > The hard part is knowing when to stop increasing the time constant, > and I have found that keeping track of phase error zero crossings > is the best indicator: If you don't see any (for too long time), > your PLL has too long timeconstant. This is where the Kalman filter approach has been proven to be better than PLLs since it will automatically tune itself up. The good people at NIST have described it. Cheers, Magnus _______________________________________________ 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.
