Bill, Not quite. The loop filter is a second-order polynomial with damping factor as described in rfc-1305, the web documentation and my book. The coefficients are chosen for a slightly underdamped characteristic yielding an overshoot of about 7 percent at all poll intervals.
Dave Unruh wrote: > "Maarten Wiltink" <[EMAIL PROTECTED]> writes: > > >>"Unruh" <[EMAIL PROTECTED]> wrote in message >>news:[EMAIL PROTECTED] > > >>>[...] (actually since it is >>>a second order critically damped system, this is not really accurate. The >>>correction action goes to zero faster than that, overshots by something >>>like 20% and then comes back to zero). ... > > >>Never thought I'd be picking nits about this, but isn't that a strongly >>damped system? ISTR critical damping being defined as not overshooting. > > > A critically damped system is one whose solution is (A+Bt) e^(-gt) > If B is negative it overshoots. If B is 0 it approaches 0 as rapidly as > possible. If B is positive it may actually increase before it decreases. > My vague recollection is tha tthe parameters were chosen for ntp to be > critically damped, but the initial conditions are in general such that B is > negative. An underdamped system will always have oscillations (infinitely > many but decreasing in amplitude. A critically or overdamped system can > overshoot as well, but has the problem that in general it approaches > equilibrium more slowly than a critically damped one. > > > >>Groetjes, >>Maarten Wiltink > > > _______________________________________________ questions mailing list [email protected] https://lists.ntp.org/mailman/listinfo/questions
