[time-nuts] Fury - Rubidium - PIS
SAIDJACK at aol.com
SAIDJACK at aol.com
Wed Jul 28 02:16:51 UTC 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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