[time-nuts] Z3805 initial behaviour after power up revised

M. Warner Losh imp at bsdimp.com
Thu Jun 18 23:28:03 EDT 2009


In message: <PAEJKNPPIGMNDLMJLENMGEFJHNAA.frledda at verizon.net>
            "Francesco Ledda" <frledda at verizon.net> writes:
: Aging cannot be predicted!  If it could be predicetd, there would be no
: aging.

Actually, if aging could be predicted perfectly, there'd be perfect
holdover (which I think is saying the same thing).  Aging can be
predicted imperfectly in the short term, but the amount of imperfect
grows with the time you're without data...

Warner

: 
: -----Original Message-----
: From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com]On
: Behalf Of Ulrich Bangert
: Sent: Thursday, June 18, 2009 3:04 AM
: To: 'Discussion of precise time and frequency measurement'
: Subject: [time-nuts] Z3805 initial behaviour after power up revised
: 
: 
: 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
: > > >>
: > > >> _______________________________________________
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: > > >
: > > >
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