On Sun, 6 Jun 2004 13:23:28 +1000, "Phil Allison"
wrote:

The turns ratio and the (unloaded) voltage ratio you measure are in exact
proportion.


As long as the same flux traverses all the turns.


** That is not a very helpful remark.


But it's true. There's not a lot of sense pretending you can measure
something if you can't.

The suggestion was that the overwind be around the existing coil of the
inductor * PLUS * there is no load on the overwind so leakage inductance
is irrelevant.

Leakage inductance means exactly that the same flux does *not* thread
all turns. So the unloaded voltage induced into the sense winding will
be less volts/turn than the main coil. This is the likely situation
for a drum core with a large air return path; some of the return flux
will sneak back *inside* the sense coil.

As the sense winding gets bigger in diameter, its signal level tends
to zero, loaded or not.

John