[time-nuts] GPSDO TC

Björn Gabrielsson bg at lysator.liu.se
Thu Jan 8 16:55:25 EST 2009


On Fri, 2009-01-09 at 10:28 +1300, Bruce Griffiths wrote:
> Richard Moore wrote:
> > On Jan 8, 2009, at 2:58 AM, time-nuts-request at febo.com wrote:
> >
> >   
> >> Message: 6
> >> Date: Thu, 08 Jan 2009 11:51:50 +0100
> >> From: Magnus Danielson <magnus at rubidium.dyndns.org>
> >> Subject: Re: [time-nuts] GPSDO time constant
> >> To: Tom Van Baak <tvb at leapsecond.com>, 	Discussion of precise time and
> >> 	frequency measurement <time-nuts at febo.com>
> >>     
> >> For ThunderBolt owners it is pretty straightforward to adjust the  
> >> TC and
> >> damping, which is very nice. Use this oppertunity!
> >>     
> >
> > So, Magnus (and Tom), what damping factor do you suggest for a TBolt?  
> > I'm running a verrry long TC now. If 1.2 is not actually critically  
> > damped, what value would be? Any guesses? BTW, I really like that  
> > plot of Tom's that tracks the oven and then gets better from the GPS...
> >
> > Dick Moore
> >
> >   
> Richard
> 
> As always, the problem is how do you know that the time constant you are
> using is anywhere near optimum?
> 
> 
> Bruce

So what is optimum... from control theory we learn, that with an even
better model of your system, you can push performance to the edge! But
you always loose robustness in doing that. 

So what is the implication of a to large TC here? Nothing going instable
in the control loop? We are just following the "freerunning" OCXO curve
past the point where GPS goes downhill?

--

   Björn





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