On Sun, 20 Feb 2005 21:35:23 +0000, Grunff wrote:

But (and please correct me if I'm wrong) I still need to sample the
output of the multiplier at a reasonably high rate, then integrate the
data over the time of the run, right?

Depends how analogue retro you want to be. You _could_ integrate it in
an analogue stylee, before sampling. Although I wouldn't. I have
done this, but not for about 15 years. A/D and data capture is just
faster these days.


So all the multiplier means is that instead of logging V and I, we log
the power?

The reason for using an analogue multiplier is when the power factor
(i.e. the ratio between the measured values) is all over the place.
This may need to be "sampled" at a high rate, so that appropriate
pairs of values are multiplied together.

Your "spiky" load is probably not that spiky, compared to this
requirement. I'd expect you could easily sample and mulitply
digitally, with a speed well in excess of the experimental variation
(You'll need to actually work this out anyway, to do your error
analysis).

The other option is of course a pair of synchronised analogue
sample-and-holds (dead easy), then digitising their values at leisure.