Olin Lathrop ha scritto:
> No, not with the half wave rectified method.

ok, though I don't see an exact... reason. I mean, scaling it 
differently, it should give some good results all the same. But actually 
maybe it is no longer needed.


> If you make the assumption the input is nearly a sine, then you can get away
> with measuring only the peaks.  There are various things you can do to get
> successively more clever, depending on what performance you really need.

ok


> First approximation is simply finding the peak of each period, and low pass
> filtering those a little.  The theoretical error due to missing the peak is
> about 1.2%, which is well under your 5% spec, so maybe you can stop there.

ok, my idea was to make this peak-measurement every 20mS, and average it 
with the previous one. Resimulated the peak method, and it fits in the 
1.2% error indeed.


> If you're worried about spikes and other noise messing up the peak
> measurements, you can apply just a little low pass filtering and then look
> for the peaks.  The next step is to do third order approximation on the
> three nearest samples to the peak to find the true peak.  Such a small part
> of a sine can be approximated quite well with a 3rd order polynomial, so the
> 1.2% error will pretty much vanish.

I also implemented this, storing 20 samples and grabbing the 3 highest, 
and averaging them. Still have to try it on both simulation and 
hardware. What would you suggest, if you can point me to an "algorithm", 
in depth?



> It depends on what characteristics you care about and how much programming
> and CPU time you are willing to spend on it.


As I said, timing is not critical at all, even making one measure out of 
1 second would be more than good (compared to the 50, now). CPU power is 
indeed in excess (apart from the Ethernet part of it).

thx
Dario
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