Re: [gentoo-user] Re: [Very OT] - Kill-A-Watt (240V Version) to measure my Gentoo Server Power Usage

[Iain Buchanan]

On Thu, 2006-08-03 at 20:58 -0700, Ow Mun Heng wrote:
> On Fri, 2006-08-04 at 13:20 +0930, Iain Buchanan wrote:

> > They're great devices - you can often
> > buy a multimeter (every geek should have one :) with a current clamp (or
> > transducer) thrown in.  That way you have no wiring, no inline plugs,
> > and you won't even have to turn the PC off to install it!
>
> Dang. I have to kick myself for calling myself a Geek.

yeah, I have sore shins too...

> > Here's one that is just a current clamp [fluke.com.au]:
> > http://www.fluke.com.au/auen/products/Fluke+320.htm?catalog_name=FlukeAustralia
> > but you can buy a normal multimeter with the option too...
>
> Hmm.. How does it work? Perhaps a google search or go through
> howstuffswork.com would help.

how does it work or how do you use it?  You use it by clipping the
"claws" around one wire that you're interested in...

um, I just came across a problem - it won't work with an AC power cord,
because you have active and neutral both going through the clamp in
opposite directions, hence they'll cancel each other out.  You need only
the active going through the clamp...  oh well, it was a nice idea.

But "how it works" (with AC) is something like this:  AC produces a
field around the wire as it "flows".  This field in turn will induce a
current in a wire placed close to it.  Loop a wire (transducer) around
another wire (AC current flow), and you can inference the change in
current in the original wire by measuring the current flow in the loop.

It doesn't work with DC, as DC doesn't create a field (at least, not
when it's steady.  When switching on and off a DC device, you'll still
get a change in current)

IANAE(lectrician), so this might be complete bunkum, but that's how I
remember it anyway.

HTH,
-- 
Iain Buchanan <iaindb at netspace dot net dot au>

Truth is free, but information costs.

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