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
