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Mon Dec 3 00:10:42 2007, rana, DAQ, Computer Scripts / Programs, linemon
Mon Dec 3 17:55:39 2007, tobin, HowTo, Computer Scripts / Programs, linemon
Mon Dec 3 19:06:49 2007, rana, DAQ, Computer Scripts / Programs, linemon
Mon Dec 3 19:06:49 2007
In reply to:
Computer Scripts / Programs
I turned up my nose at Matlab's special tools. I modified the linetracker to use the
phase = 2*pi*f*t
to estimate the frequency each minute. The
code uses 'polyfit' to get the mean and trend of the unwrapped phase and then determines
how far the initial frequency estimate was off. It then uses the updated number as the
initial guess for the next minute.
I looked at a couple hours of data before letting it run. It looks like the phase of the
'60 Hz' peak varies at 20 second time scales but not much faster or rather anything faster
would be a glitch and not a monotonic frequency drift.
From the attached snapshot you can see that the amplitude (PZT1_PIT) varies by ~10 %
and the frequency by ~40 mHz in a couple hour span.