On Mon, Mar 14, 2016 at 2:37 PM, Lars Walenius <[email protected]> wrote:
> I read this but couldn´t understand why this is superior to the PI-loop > with a pre-filter? > > > http://ptfinc.com/wp-content/uploads/2016/03/App_37_RubContol-Rubidium-Control-%E2%80%93-A-Different-Approach.pdf > > Anybody can say why? Even if regression is very useful the limitation of > the GPS and ionosphere will be the problem?How much better is it reasonable > to get?? > I think the potential benefit of this approach is that it continuously predicts the long term drift of the oscillator and attempts to compensate for it. If the drift is reasonably linear, this means that you can use a larger time constant in the control loop and thus be less sensitive to short term GPS timing variations, while keeping the phase error close to zero Of course if the oscillator drift is not predictable, this won't help and might even make things worse. I have done some experiments with an OCXO and a controller design similar to the one Lars posted some time ago. I plotted the trend in the 3-hour average DAC values over many days and used Excel to do a least-squares fit to that data. As long as the oscillator is powered on continuously, this gives an R^2 of over 90%, so the linearity of the drift is very good. If I use this slope as a correction factor, i.e. adding X DAC counts per day to the output of the PI control algorithm, it significantly reduces the average TIC error at long time constants -- --Jim Harman _______________________________________________ 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.
