[time-nuts] Fury - Rubidium - PIS

SAIDJACK at aol.com SAIDJACK at aol.com
Tue Jul 27 22:16:51 EDT 2010


Hi John, Brian,
 
actually we set D to 0, and use P and I gains.
 
Yes, the DACGAIN is an overall gain of the loop output - to normalize for  
different oscillator voltage/frequency sensitivities.
 
I forgot that the DACGAIN is limited to 10,000, so instead of setting it to 
 20,000 one can set it to 10,000 and multiply the P and I parts both by 2x, 
that  gives pretty much the same effect as setting DACGAIN to 20,000.
 
Please note that aging and tempco compensation may then take a couple of  
days to fully settle again.
 
I have not tried such high gains since we don't have any oscillators  here 
with such small F/V range, please advise what you find out.
 
bye,
Said
 
 
In a message dated 7/27/2010 19:04:36 Pacific Daylight Time, jfor at quik.com  
writes:

>  That part I understand (your drawing), its a basic phase lock loop.
>  What I am having trouble with is the Fury's commands relationship.

OK.  Sorry for the BW.

Basically you tune a loop by starting with the P, I,  and D set to zero.
You slowly crank up the P until it starts to become  unstable. (Put in a
small step perturbation and look at the response for  ringing) Then crank
up the D until it stabilizes, then crank up the P  again. When you have got
a stable fairly well performing loop, you  introduce some I. You may have
to tweek P and D to keep  stability.

It looks like your system has an overall gain (DACG) and a P  and D
controller gain. This is not uncommon to avoid switching a bunch of  caps.




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