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

[Ted Ozolins <ted1@telus.net>]

Remy Blank wrote:

>Iain Buchanan wrote:
>  
>
>>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...
>>    
>>
>
>Or only the neutral. It doesn't matter, actually.
>
>  
>
>>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.
>>    
>>
>
>You almost got it. Actually, it's not necessary that the current be AC:
>even a DC current produces a magnetic field around the conductor (albeit
>a DC field). The clamp is a ferromagnetic ring that "concentrates" the
>magnetic field, and it is interrupted at one location by a hall-effect
>sensor that measures the magnetic field. The current can be calculated
>from the magnetic field intensity and the diameter of the clamp ring.
>
>-- Remy
>
>
>Remove underscore and suffix in reply address for a timely response.
>
>  
>
Well you almost got it right.  The clamp is just a basic transformer
being the secondary winding. Since AC current flow changes both in
amplitude and direction, induces a current flow in the secondary
winding, "the clamp". The current is then rectified and the measurement
then is displayed on a meter.  I've used high voltage transformers from
old monitors to monitor and trigger alarms signaling excessive current
change. Basically just a home made clamp.

Cheers.

-- 
Ted Ozolins(VE7TVO)
Westbank, B. C

-- 
gentoo-user@gentoo.org mailing list