On 09/20/2012 01:55 AM, Jim Lux wrote:
On 9/19/12 4:38 AM, Bob Camp wrote:
Hi
Commonly this sort of thing is done with a sample and hold in the
loop. No reference in / put the loop voltage in hold. You still have a
phase drift and need to cope with the phase offset when the reference
comes back.
or, in our case, we run the loop, but don't have any error signal input
(if you have a second or third order loop, you might as well essentially
predict what is going on)
The phase drift you get repeatedly should integrate up to a frequency
correction. If you want to get fancy, you could separate it and do a
hold-over drift correction such that a secondary integrator compensates
for hold-over drift. Not too hard to do. That was you could reduce the
blurp. Unless you have a very unstable system, it should behave
relatively linear to the amplitude of things, and this on/off pattern
will be more of a 0.5 Hz noise signal in the loop.
Cheers,
Magnus
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