[time-nuts] Tbolt time constant

[bg at lysator.liu.se]

Hi Bill,

While certainly not beeing Tom...

Damping is used in control theory to describe how the time response of a
second order system behaves. Depending on your feedback regulator you
might create a second order system.

   http://en.wikipedia.org/wiki/Damping_ratio

   http://en.wikipedia.org/wiki/File:2nd_Order_Damping_Ratios.svg

Higher number means slower reaction to a change in the system. Lower
number equals a quicker response but with "ringing" overshoot.

The time constant is related to how quick changes in the error signal the
regulator is capable of following. Long time constant means the regulator
will attenuate high frequency content in the error signal. We can have
longer time constants when we trust the OCXO is very stable at these time
scales.

--

   Björn
> Hi Tom,
>
> Can you explain what is meant by "damping ?"
>
> How is the "damping" related to the time constant ?
>
> I gather from your referenced web page that it seems that a higher number
> was
> better. Is this a correct assumption ?
>
> thanks,
>
> Bill.....WB6BNQ
>
>
> Tom Van Baak wrote:
>
>> > Does the longer time constant actually make a "better" frequency
>> standard, or
>> > does it just push the noise from one frequency region to another?  Has
>> > anybody with gear good enough to measure close in noise looked at the
>> > spectrum for different time constants?
>>
>> Hal,
>>
>> Last I checked - phase noise, as in L(f), is the same for all
>> time constants.
>>
>> Frequency stability, as in sigma(tau), ADEV, etc. typically
>> improves as the TC increases, out to 1000 s. The default of
>> 100 s works pretty well for normal environments. But if your
>> sat visibility and voltages and temperature and air currents and
>> local seismic (vibration, shock, kids playing, doors closing, etc.)
>> environment is unusually stable then you could bump the TC
>> beyond 100, maybe even near 1000. I run my best TBolts
>> closer to 300.
>>
>> For some time constant plots, see:
>>
>> http://www.leapsecond.com/pages/tbolt-tc/
>>
>> /tvb
>>
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