----- Original Message ----- From: "Jed Rothwell" <[EMAIL PROTECTED]> To: <[email protected]> Sent: Monday, June 05, 2006 11:46 PM Subject: Re: Battery shapes
> jonfli wrote: > >>Er, what other measurement would you prefer? RMS, Peak...? No, none of those will do. As for the phase angle stuff (cos phi) it is only ok for sinusoidal waveforms. > > I prefer lots and lots of instantaneous power measurements. That's the way! And then averaging those is ok. Average of products is not the same as product of averages :) Note the sampling rate must be adapted to the waveforms frequency content, or reciprocally (if attachments were allowed I would have posted a picture illustrating the latter, I'll have to set up a web site for such things) >>Average measurements are equivalent to DC if the relative phase >>angles are taken into account and therefore are the most accurate means . . . > > Do sophisticated meters usually take these things into account? Or do > they finesse the problem by taking zillions of samples? I do not > know. The meter I read about (that Mizuno uses) fixes the problem by > diverting a tiny fraction of the power into a joule heater and then > measuring the heat. In other words, by calorimetry! People say Never understood how this worked when you explained it before Jed, how does one concretely divert a fraction of the power, please post more details on this if you think it's competitive with the i v sample, multiply and integrate method of modern electronic meters. Michel > calorimetry is hard but they fall back on it in the end. It is the > oldest method of measuring energy. As Fleischmann says, in some ways > it is still the best method of measuring radioactivity, for example. > Microcalorimeters measure the impact of individual cosmic rays. > > - Jed > >
