measuring power usage

Jim Lux James.P.Lux at jpl.nasa.gov
Wed Jun 4 00:43:17 EDT 2003


Kill-A-Watt does just this.. measures actual waveforms.  Quite a novel feat,
really, to package it all up and sell it for $40..
What the Fluke gives you that the Kill-A-Watt doesn't is things like an
external interface, calibration manuals, multiple ranges, etc.
The Fluke's probably also potentially calibrateable to a NIST traceable
standard, and is probably more reliable.

----- Original Message -----
From: "Dave Lane" <dlane at ap.stmarys.ca>
To: "Beowulf Mailing list" <beowulf at beowulf.org>
Sent: Tuesday, June 03, 2003 5:00 PM
Subject: Re: measuring power usage


> At 04:35 PM 6/3/2003 -0700, Trent Piepho wrote:
>
> > > There is nothing in the flier that indicates that it measures rms amps
and
> > > hence rms watts. Computers are not resistive loads and they draw
> > current in
> >
> >It measures power factor and frequency, so it should be doing what is
> >necessary to find true rms.
>
> Measuring true rms current depends on measuring in some way the area under
> the curve from the shape of the waveform. Non-rms meters usually rectify
> the voltage to all positive voltage and low pass filter it to convert to a
> DC value, then a fudge factor is used which assumes the waveform is a sine
> wave (which it isn't).
>
> ... Dave
>
> ps. what you really need for an accurate measurement of RMS power and
power
> factor is something like:
>
http://ca.fluke.com/caen/products/features.htm?cs_id=5179(FlukeProducts)&cat
egory=PHASE1(FlukeProducts)
> which unfortunely is about $1900US - ouch! There are likely other
> alternatives that are cheaper.
>
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