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Re: Keeping up with the theory (was is Corum and Corumforbidden topic?)

Original poster: "Ed Phillips by way of Terry Fritz <twftesla-at-qwest-dot-net>" <evp-at-pacbell-dot-net>

Tesla list wrote:
> Original poster: "Ray von Postel by way of Terry Fritz
<twftesla-at-qwest-dot-net>" <vonpostel-at-prodigy-dot-net>
> Terry:
> I agree that the equations and programs being used give practical values,
> but as far as I know they are derived by curve fitting or some other
> method of approximation.
> Because they are based on experimental data, they can only be considered
> reliable over the range of data upon which they are based.

	Not true when it comes to inductance formulae, where exact but messy
solutions have been available for well over 100 years.  The
approximations based on curve-fitting involve best matches to the exact
values, with different approximations designed to give fit within a
certain accuracy over some selected range of length/diameter.  The
closer the fit the smaller the range over which they are valid.  That's
the way all approximations work.  Descriptions of Wheeler's several
approximations usually state the accuracy of fit and the range over
which that applies.  You can get 0.1% accuracy if you want, and better
and not much more complicated formulae are available.  For TC work an
accuracy of 1% is overkill, in my opinion.

	As for self-capacitance, the work that Medhurst did and reported did
involve experimental data.  However, use of Medhurst's methods will give
you results which are more than adequate for TC work, where other
sources of capacitance such as the top terminal loading are equally
important.  I have written some simple programs here to calculate the
self-resonant frequency of solenoids, and find that at a length/diameter
ratio of about 5 the error between calculated and measured SRF is less
than 2%.