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

Francesco Ledda frledda at verizon.net
Fri Jun 19 10:38:04 EDT 2009


Variation due to environment are deterministic and are nor part of aging.
Ageing needs to measured in conditions that remove ambient induced
perturbations. I used to put crystal oscillators in high quality
environmental chambers that kept temp, humidity and pressure constant and
measure the ageing.  There are tricks that can be done to increase the aging
rate, so that we did not have to wait 20 years ;)

We know that ageing happens, but the direction of ageing cannot be
determined.
A coin toss can yield face or tail.  If the coin is perfect, the
distribution will be uniform.  If a face is 1 and a tail is -1, we can add
successive tosses and track the total number.  Even is the distribution of
tosses is uniform, the sum will walk away from 0 (random walk),cameback to 0
and then move away from 0 again.  This is a good way to model and explain
ageing. Nature is perfect, but things do not follow our math perfectly.  A
better simulation would include a "leaky integral".

The statistical analysis of ageing is tricky, since ageing doeas have a
statistical mean, and therefore standard deviation cannot be used.

This discussion brings lots of good memories back.  The good old days when
SONET synchronization was a new thing, and we were creating new technology.



-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com]On
Behalf Of Magnus Danielson
Sent: Friday, June 19, 2009 7:59 AM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] Z3805 initial behaviour after power up revised


Francesco Ledda wrote:
> Aging cannot be predicted!  If it could be predicetd, there would be no
> aging.
>
Not entierly true. Even with a perfectly known aging, only a few
oscillators would bother to estimate and correct it. This can never be
perfectly done anyway, and there is only so many things you can bring
into the model while keeping it economical. There is fairly good clues
around. If all was included and handled, it would reduce the effects.

Cheers,
Magnus
> -----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
>>>>>
>>>>> _______________________________________________
>>>>> time-nuts mailing list -- time-nuts at febo.com
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>>>>>
>>>>>
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>
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