Olin Lathrop ha scritto:
> Take a look at the plot I posted a few days ago.  The input to the filter
> was a sine with the whole bottom cut off.  The output of the two pole filter
> looked a lot more sinusoidal.


going to put it in there, then :)


> Dario is looking at the line voltage, which has very low impedence.  That
> means that even with significant harmonics in the current drawn from this
> line, the voltage will have little harmonic content.  The approximation that
> most of the power is in the fundamental is quite reasonable for many line
> voltage measuring purposes.  Remember that Dario only needs 5% accuracy.

More realistically I may want some +-1% (218..222 out of 220) but I seem 
to be pretty close at the moment.


> Yes, the multiplies are the same cost as adds, but you conveniently left out
> the square root at the end.  RMS would require one multiply and one add per
> sample.  The two poles of low pass filtering I showed used 4 adds and 2
> multiplies per sample.  A good chunk of the 80 extra operations per line
> cycle will be offset by the square root operation of RMS.  However, both
> methods will take only a tiny fraction of processor cycles, and Dario made
> it clear that there were plenty of cycles available, so there is no real
> distinction here.


Now I'm wondering how can I save some cycles, i.e. I need one readout 
out of 1-2 seconds, so am wondering if I still have to sample every 1mS 
and do the math for IIR and peak-detect every time...
I may wish to do it only for one or two full sine every 1 second... 
maybe: what do you think about this?


-- 

Ciao, Dario
--
Cyberdyne
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