[time-nuts] Z3805 initial behaviour after power up revised
Ulrich Bangert
df6jb at ulrich-bangert.de
Thu Jun 18 08:04:01 UTC 2009
Gents,
one of the papers suggested by Brian says:
-------------------------------------------
SmartClock monitors the frequency control variable of the internal
oscillator while it is locked to the external reference. This gives a
measure of the frequency difference between the internal oscillator, if it
is free-running, and the external reference over time. The resulting
measurements include the effects of random noise in the oscillator, the
measurement circuitry, and any noise in the external reference as well as
any aging and environmental effects in the oscillator. From this
information, SmartClock makes a continuous prediction of clock error over
time.
-------------------------------------------
The big question is: If the EFC signal includes this all information, how
does the algo manage to extract the individual informations? After having a
look at the PPS TI and the EFC of my Z3805 I am beginning to get a clue of
it (the quirks on the EFC signal heve been removed):
The SmartClock algo seems to set the loop time constants to a large value in
the beginning. In other words: It measures the overall oscillator frequency
influencing effects with a lowpass filter applied that has a very low cutoff
frequency. Only effects which's frequency are sufficient lower then the
cutoff pass the filter. Seems as if the SmartClock uses this filter setting
to exclude any noise related effect and any environmental effect and make
the measurement see ONLY the oscillator's aging.
Once it has learned enough about the aging process it will be able to
predict aging. Having reached this state it will be able to apply his
knowledge about aging to further TI measurements and subtract the "aging
part" of it, leaving mostly the environmental (which is mostly temperature)
part.
Having a model for the aging the Algo can now model the temperature
dependence. However, a precondition for this were that the measurement sees
the temperature effects and that the ambient temperature is measured
independently. For that reason I expect the Algo will reduce its loop time
constant within the next time to make the temperature effect get through the
lowpass. Any bets on that?
Best regards
Ulrich Bangert
> -----Ursprungliche Nachricht-----
> Von: time-nuts-bounces at febo.com
> [mailto:time-nuts-bounces at febo.com] Im Auftrag von Ulrich Bangert
> Gesendet: Donnerstag, 18. Juni 2009 08:29
> An: 'Discussion of precise time and frequency measurement'
> Betreff: Re: [time-nuts] Z3805 initial behaviour after power up
>
>
> Brian,
>
> > You may also want to search for HP An1279, it also goes over HP
> > smartclock operation, and look for a paper titled "the Global
> > Positioning System and HP SmartClock" by John A. Kusters.
>
> In the meantime I have not only found these but also "Smart
> Clock: A New Time" by David Allan et al which shows that
> "Smart Clock" is originally a NIST invention & patent and
> explains very well how it works. Perhaps what I and You have
> seen is a direct consequence of applying the Smart Clock algorithm.
>
> Best regards
> Ulrich
>
>
> > -----Ursprungliche Nachricht-----
> > Von: time-nuts-bounces at febo.com
> > [mailto:time-nuts-bounces at febo.com] Im Auftrag von Brian Kirby
> > Gesendet: Donnerstag, 18. Juni 2009 01:51
> > An: Discussion of precise time and frequency measurement
> > Betreff: Re: [time-nuts] Z3805 initial behaviour after power up
> >
> >
> > They do not talk about driving the frequency off, but they
> > warn to keep
> > the receiver locked the first 24 hours, so it can determine how the
> > oscillator ages. Its in the section on "holdover" (page 52
> > of the PDF ,
> > page 3-8 of the user guide).
> >
> > You may also want to search for HP An1279, it also goes over HP
> > smartclock operation, and look for a paper titled "the Global
> > Positioning System and HP SmartClock" by John A. Kusters.
> >
> > If you have a broadband connection, I can email you each
> one, if that
> > will help.
> >
> > Brian
> >
> > Ulrich Bangert wrote:
> > > Brian,
> > >
> > > thanks for your information!
> > >
> > >
> > >> algorithm. From what I read about the smart clock, it
> takes 5 days
> > >> for it to complete its initial learning cycle and then its
> > >>
> > > continuously
> > >
> > >> refining.
> > >>
> > >
> > > Is that from the Z3801 manual, which I have available, or
> > do you have
> > > any other in depth information source?
> > >
> > > Best regards
> > > Ulrich
> > >
> > >
> > >> -----Ursprungliche Nachricht-----
> > >> Von: time-nuts-bounces at febo.com
> [mailto:time-nuts-bounces at febo.com]
> > >> Im Auftrag von Brian Kirby
> > >> Gesendet: Mittwoch, 17. Juni 2009 16:58
> > >> An: Discussion of precise time and frequency measurement
> > >> Betreff: Re: [time-nuts] Z3805 initial behaviour after power up
> > >>
> > >>
> > >> Ulrich,
> > >>
> > >> I have two Z3801A and both of them act close to what you
> describe
> > >> in the first 24 hours of power up. I believe its part of the
> > disciplining
> > >> algorithm. From what I read about the smart clock, it takes
> > >> 5 days for
> > >> it to complete its initial learning cycle and then its
> > continuously
> > >> refining.
> > >>
> > >> Brian
> > >>
> > >> _______________________________________________
> > >> time-nuts mailing list -- time-nuts at febo.com
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> > >>
> > >
> > >
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>
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