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

Magnus Danielson magnus at rubidium.dyndns.org
Sat Jun 20 07:33:03 EDT 2009


Francesco Ledda wrote:
> Correction...
>
> -----Original Message-----
> From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com]On
> Behalf Of Francesco Ledda
> Sent: Friday, June 19, 2009 9:38 AM
> To: Discussion of precise time and frequency measurement
> Subject: Re: [time-nuts] Z3805 initial behavior after power up revised
>
>
> Variation due to environment are deterministic and are nor part of aging.
> Ageing needs to measured in conditions that remove ambient induced
> perturbations.
Not entierly true, as aging behaviour may be re-started or modified as 
environmental conditions change.
>  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 ;)
>   
Strange, as the aging rate decreases over time, most of its aging and 
shift in frequency occur early. This occurs both in the "green" aging 
period, when it is new, but also after it has been turned off and cooled 
down / low temperature storage.

So what tricks did you use?
> 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 NOT a
> statistical mean, and therefore standard deviation cannot be used.
>   
Standard deviation of frequency isn't used, but rather it is modeled 
thru the frequency drift component, and this is also described for 
different time-spans. Over time it integrates to the drifted frequency 
over that time. In all models it is treated separately from the noise 
components.

The curvature of aging has also been established (see for instance Vig 
on the UFFC site), and with external reference (such as in a GPSDO), the 
parameters for that curve can be established and adjusted over time for 
better prediction of where the aging.

Or is it that we have different concepts or environments in mind when we 
discuss aging? For me, aging is the shift in frequency over time as the 
oscillator is maintained at the same temperature.
> 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.
>   
There are a few others here that was involved with that, and it would be 
fun to have a few discussion on that.

Cheers,
Magnus




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