Date   : Sun, 12 Mar 2006 17:00:56 -0000
From   : "Mike" <profpep@...>
Subject: Re: Them pesky case stickers (was 1MHZ SCSI/ATA board.)

From: "Jonathan Graham Harston" <jgh@...>
> Pete Turnbull <pete@...> wrote:
> > the rotating disk.  You can also use a clamp meter, a device with a
> > ring-shaped clam on the end instead of cables.  It uses magnetic fields
> > to measure the current, usually via a Hall effect sensor.  Many are
>
> I'm sure they work by transformer effect. The power cable is a
> single loop primary, and the ring clamp forms the secondary.
>
Both right!

The original types were current transformers, and some early type were
moving iron direct loop things, thus AC only. The more modern designs, (IIRC
started by HEME in the UK), use the hall effect and can do vaiable frequency
AC (useful when testing inverter type motor drives), and DC as well. You can
get a very nice one from Mr Fluke that plugs into your testmeter, I daresay
there a plenty cheaper ones around too.

If you are thinking of fitting a current transformer to check your mains
loading, remember that they should never be left with an open circuit
secondary - the voltage goes 'off the clock', similar to a valve amp.....
they can give a very nasty bite! The hall effect ones don't have this habit,
and  you can get an adapter that will clip around an existing cable in two
parts, so you don't have to break the circuit to install it. I used one a
while ago in a maximum demand warning device for a woodworking company.

||\/||ike