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Re: Measuring self-capacitance directly (Re: flat secondary)



Original poster: "Antonio Carlos M. de Queiroz by way of Terry Fritz <twftesla-at-qwest-dot-net>" <acmq-at-compuland-dot-com.br>

Tesla list wrote:
> 
> Original poster: "Paul Nicholson by way of Terry Fritz
<twftesla-at-qwest-dot-net>" <paul-at-abelian.demon.co.uk>
>...
> Oh, and finally, much of the error seen when applying Medhurst C to
> find Fres, comes from using Ldc instead of Les.  A calculated Les
> together with the Medhurst C should do a better job.

I don't see sense in considering an inductance that is different from
the DC inductance, if the objective is to model the coil as a simple
LC parallel circuit. There is then just one inductance in the circuit,
and it must be the DC inductance. The capacitance is that is an
approximation, accounting for just the first resonance of the coil.
Just one possible value too.
You can increase the order of the model, adding an extra inductance,
as shown below. This would explain the different
inductances, allowing an extra degree of freedom for more accurate
modeling of the coil impedance around the first resonance.
The model for the coil seen from the base would then be:

    o-----L1-----+-----L2-----o
                 |
  base           C1           top
                 |
    o------------+------------o ground

C1 would be the Medhurst capacitance, or something similar, L1 would 
be Les, and L2 would be Ldc-Les.
It is also possible to add another capacitor from the top to the
ground, and model the two first resonances. Add other sections for
more resonances. The sum of all the inductances is always Ldc.

Antonio Carlos M. de Queiroz