> It's true, the shape of the signal is known ( sinusoidal ) and I will use > a peack detector. OK, for a pure sine Vrms = Vpeak / sqrt(2) > There is no modulation, Of course there is. If there wasn't you could make a single measurement and be done forever. > but could be distorsions which will mess the whole measurement. Then you don't know the shape of the waveform after all. Is the power in the harmonics significant, or can it be ignored for your purposes. > On the other hand distorsions will increase the current into the load so > measuring this one can gave me some informations about how clean is the > signal. That's all specific to you system, so I can't comment on that. However, you've got to stop playing fast and loose with the theory. You can't have a changing signal and have no modulation. You can't have the signal be a sineusoid but still have harmonics. You should be sure to look at this problem in both the time domain and the frequency domain, and make sure all your assumptions and analisys makes sense in both. There's no place in engineering for sloppy thinking. Leave that to your manager or the marketing department . ***************************************************************** Embed Inc, embedded system specialists in Littleton Massachusetts (978) 742-9014, http://www.embedinc.com -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.