> Alan,
>
> I'm pretty sure that he is correct. There is no physical law which
> says that the secondary current equals the primary current times the
> inverse of the turns ratio. That is an approximation which is valid
> for a certain range of load impedances. Fundamentally, you are
> producing some changing flux in the secondary. This will produce a
> given open-circuit voltage according to Faraday's Law. As you load it
> down, and allow current to flow in it, that current will act to reduce
> the flux change. As you approach a short-circuit (load impedance much
> less than the reactance of the secondary) in the secondary, the
> current will begin to match the approximation you mention.
>
> Sean
>
>
> On 3/20/07, Alan B. Pearce <
@spam@A.B.PearceKILLspamrl.ac.uk> wrote:
> > >> Umm, I think you have a problem with mixed units.
> > ...
> >
> > >I am talking about measuring the magnetic field produced by current
> > >in a conductor.A voltage will be induced in the terminals of a winding
> > >wounded around the toroid when the magnetic flux is changing in time.
> > >I will process this induced voltage to the project requirements.That
> > >is it.No need to deal with the current coming out of the secondary coil.
> >
> > Umm, wrong. The magnetic field induces a current in the coil, and the
> > voltage you get out of that will depend on what resistor you put across the
> > coil.
> >
> > This resistor will have a temperature co-efficient that will almost
> > certainly not meet the accuracy spec you are being asked for.
> >
> > The various current probes we have around here all suffer from some form of
> > temperature drift, and the best ones talk in terms of accuracy of about 2%,
> > which is 10^2 worse than you are asking for.
> >
> > Then as Vasile points out, you will not get a consistent magnetic field in a
> > clamp on system. The only way to do that is to thread a wire through a
> > permanently closed toroid. The changing air gap will cost you 1-2%, again a
> > couple of orders of magnitude worse than you are wanting.
> >
> > --