[time-nuts] Re: General discussion of PID algorithms applied to GPSDO control loops (continued 1)

[Pluess, Tobias]

Hi André,
possibly you should also consider contributing to the Kalman filter
approach; I haven't read your entire thread yet, but I would be interested
in filtering the TIC readings with a Kalman filter, using the Kalman filter
as a kind of observer, and feeding the filtered output to the PID
controller.
In my opinion, this approach is missing in your list ;-)
the neural network is of course the really crazy stuff, do you have some
literature about that? So would you use the NN also to filter the TIC
readings and then provide filtered readings to the PID, or is your approach
a totally different one?

anyways, as glen eglish said:
"fantastic discussion going on here. love it."

best
Tobias
HB9FSX



On Sun, Apr 17, 2022 at 6:55 PM André Balsa <andrebalsa at gmail.com> wrote:

> Hello Poul-Henning,
> First let me thank you for your career-long significant contributions to
> the Open Source world and to global internet standards.
> Second, regarding your comment that "You _can_ have hybrid steering, but
> you must assign "weight" to the
> different contributions, so that they will never oscillate."
> That is exactly how I intend to implement the hybrid PLL/FLL control loop
> for the STM32 GPSDO. By December this year I should have implemented
> separate PLL, FLL and hybrid PLL+FLL PID control loops for my STM32 GPSDO
> project and hopefully I'll be able to collect enough data to compare their
> behavior. I would also like to try programming a Neural Network (NN) based
> GPSDO control loop algorithm and again compare its behavior with the
> "classic" PID control loops.
> Many thanks for your comment,
> Andrew
>
> On Sat, Apr 16, 2022 at 4:55 PM Poul-Henning Kamp <phk at phk.freebsd.dk>
> wrote:
>
> > --------
> > Bob kb8tq writes:
> >
> > >>> You mean the FLL and PLL are exclusive of each other ? I guess you
> are
> > >> right, but I am trying to think "outside the box" and see if there are
> > any
> > >> alternatives.
> > >
> > >You will have two people driving the car at the same time. One hits the
> > >accelerator and the other hits the brakes at the same time. They both
> > can’t
> > >be active *and* feed the EFC at the same time. The practical answer is
> to
> > >run each during the warmup phase that it makes sense to do so.
> >
> > You _can_ have hybrid steering, but you must assign "weight" to the
> > different contributions, so that they will never oscillate.  I normally
> > have found it better to have a big switch which decides who gets to
> > control,
> > based on the (external) circumstances.
> >
> > As a general rule of thumb, FLL's only make sense if the product
> > of the rate at which you measure phase difference, and the jitter-noise
> > when you do, ends up way to the right and above the allan-intercept.
> >
> > Prof. Dave's infamous "Call NIST once a day with a modem" mode in
> > NTPD is a good example:  Forget about tracking temperature, XO drift
> > or anything else:  Just try to get the average frequency right on a
> > timescale measured in weeks.
> >
> > Poul-Henning
> >
> > PS: When you implement your PLL:  The way to void "wind-up"
> > durign startup, is to short the integrator, until the phase error
> > has reached its proper sign.  It is surprising how hard it is
> > to write code to spot that, compared to deciding it manually :-)
> >
> > --
> > Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
> > phk at FreeBSD.ORG         | TCP/IP since RFC 956
> > FreeBSD committer       | BSD since 4.3-tahoe
> > Never attribute to malice what can adequately be explained by
> incompetence.
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