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OK - I've compared the actual meter reading to the samples from the hall effect transistor

[ATTACH=full]198867[/ATTACH]

There is fairly close agreement in that I actually used 511L and the above shows 49 transitions (or 490L - rounded to the nearest 10).

However even a small change in the length of the moving average changes that quite a bit: the above is 21 samples long but 20 samples long gives 52 transitions and 24 gives 48 transitions.

I've blown up the section around 2PM (14-00) (21 samples in the moving average):

[ATTACH=full]198866[/ATTACH]

So you can see that there are some transitions that are being missed - and why the shorter moving average picks them up perhaps too well.

So, [USER=6480]@Tony[/USER] - what is the envelope detection filter you were mentioning. (My signal analysis skills are not good but I'm wanting to learn.)

Susan