Re: Re: DMM with PC interface reduced @ maplin

[Chris Hunter <cjhunter@xxxxxxxxxxxx>]

Aha ... thanks ... sounds plausible !   And. 'could be a good way of
monitoring things ... ie: a clamp meter by the consumer unit could
provide a good wa, amongst others, y of verifying HA instructions have
been obeyed - as I see it, the HA system should always look for feedback !

Chris



Kim Wall wrote:

> Chris Hunter wrote:
> > Interesting ... I've not used a clamp meter before, but I somehow
> > imagined a closer & more symmetric fit to the cable to be
measured, and
> > a less-close proximity to other cables ... !
> >
> > 'maybe it depends on the magnitudes of the currents ?
>
> Check a physics textbook.  AIUI the field from any cable outside the
> ring of the clamp cancels itself out, as it induces current on both
> sides of the clamp, where the winding goes in opposite directions, as
it
> were (the same principle that allows twisted pair cable to avoid
picking
> up crosstalk).  Likewise, the clamp diameter and positioning of the
> cable within the clamp aren't critical, as the total field passing
> through the clamp will always be the same for a cable within it (being
> nearer to one point makes the field stronger there, but weaker
> everywhere else).
>
> Deviously cunning things, clamp-meters.
>
>
> Kim