Re: Re: DMM with PC interface reduced @ maplin

[Kim Wall <kim@xxxxxxxxxxxxxxxxxx>]

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.