----- Original Message -----
From: "Jed Rothwell" <[EMAIL PROTECTED]>
Subject: Re: Battery shapes
jonfli wrote:
Er, what other measurement would you prefer? RMS, Peak...?
I prefer lots and lots of instantaneous power measurements.
Average measurements are equivalent to DC if the relative phase angles are
taken into account and therefore are the most accurate means . . .
No, no, no -- not in the realm of wideband noise as in plasma electrolysis.
Taking phase into account is just a first step. You also have to include
peak factor and the simple instruments can't handle more than about 3:1.
There is a Texas Instrument portable oscilliscope with a 100 Mhz bandwidth
and two totally isolated inputs which can measure instantaneous I and E.
You grab a windows worth of the waveform and the instrument will calculate
the instantnaeous power for each sample and integrate ***not average*** them
to a true power measurement. It will also plot instantaneous power. Naudin
used this some years ago in his studies of the Newman machine. More recent
photos show another instrument whose specs indicate that it has similar
capabilities. The TI scope costs about two kilobucks. These instruments do
what Jed prefers, per his comment above.
Do sophisticated meters usually take these things into account? Or do they
finesse the problem by taking zillions of samples?
Zillions of sampes is not finessing the problem. It is doing it correctly,
fundamentally.
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 calorimetry
is hard but they fall back on it in the end. It is the oldest method of
measuring energy.
That method is an older one, used by Hewlett Packard years ago, and perhaps
by other instrument makers. It is also fundamental but is fussy to use, for
the input signals have to be amplified to drive the heater, and those
ampolifiers have themselves bandwidth and saturation problems. It's not a
slam-dunk. As in many cases, you have to not only understand what you are
trying to measure, but how the measruign device actually works. The hand
held meters are really designed for 60 Hz near sinusoidal measurement and
can give serious errors if used otherwise.
Mike Carrell
