Re: eddy current with secondary coil

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Malcolm Watts" <m.j.watts-at-massey.ac.nz> 

Hi bart,

On 8 Oct 2003, at 18:12, Tesla list wrote:

 > Original poster: Bart Anderson <classi6-at-classictesla-dot-com>
 >
 > Hi Malcolm,
 >
 > I don't believe the test you described is looking at the inductance at
 > resonance, but of the low frequency inductance and the resonant frequency
 > with the resonator/topload changes. Was the inductance measured while the
 > coil was being driven at it's resonant frequency?

No and I know the resonator characteristics in this regard are
different at resonance since it is not a simple lumped system. Given
the more even LF current distribution though, one might have expected
the change to have been even more radical with an LF lumped test.
However, as I said, the resonant frequency when the resonator was
bottom-driven at resonance did not change by much at all with the
modified topload. Ctot shouldn't have changed by the act of simply
slitting the terminal so Leff couldn't have changed much either.

  The test I did in my
 > reply to Antonio maybe isn't the best method to check this even if it did
 > come out so well. I'll perform some more this week, maybe on a larger coil.
 > I know I performed a number of tests on dc measurements, both C and L, and
 > Fres was off. When you consider the affects of current distribution, it
 > should be off to some degree. When we measure Fres, we are measuring
 > everything all thrown into the pot. How can we use a Cdc measurement and
 > Fres measurement, and expect to get a correct L (or vice-versa)? L would be
 > something between Ldc and the real L seen at resonance. This error would be
 > put on the shoulders of C (which would end up just as wrong). We seem to
 > have only one truely known value which makes the other two difficult to 
find.

The answer to what the "correct" L is: "it depends on the measurement
conditions". :)

Malcolm