Re:

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: Ed Phillips <evp@xxxxxxxxxxx>

Tesla list wrote:

> Original poster: "Gav D" <gdingley@xxxxxxxxx>
>
> Hi all,
> I've been writing some MATLAB code to explore the use of current
> filament analysis to calculate the inductance of the standard coil
> geometries: flat-disk, helical and conical. The results I've been
> getting have been interesting when compared to the traditional
> formulae used in calculating inductance. Assuming my code works, this
> is what I have found:-
>
> Helical: Wheeler works fine as long as the diameter/radius is greater
> than about 5, beyond this the error is small but still present. Below
> this it can get quite way-off.
>
> Flat-Disk: The code generates values of the right magnitude to the
> standard "Wheeler-variation" formula for this coil geometry, but the
> figures are quite different.
>
> Conical: Have not looked at this one yet.
>
> I was wondering if anyone else has looked into this, perhaps have a
> program by which I can compare my own code? Has anyone else noticed
> how inaccurate the standard formulae can be? Perhaps my code is just
> wrong.
>
> Thanks,
>
> Gavin

   I have used an Excel spread sheet to compare Wheeler's formulae 
for helical coils (the two in the Radiotron Designer's Handbook - 
there are more) with the "classical" method using Nagaoka's constant 
and also with Lundgren's approximation to the same.  I just found the 
sheet comparing Wheeler to Lundgren and will send it to you 
directly.  Bottom line is that by using both the "long" and "short" 
approximations in RDH you get results good enough for most purposes 
(surely for TC's) for all coils with length greater than 0.1 diameter.

Ed