From: "Terrell W. Fritz"
Date: Wed, 22 Nov 2000 14:26:59 -0700
Subject: [TSSP] Medhurst and E-Tesla thoughts...
Hi All,
I have been looking at E-Tesla6 and Medhurst's data. For a similar set
of H/D ratios, they both predict the following capacitances of a bare coil:
(10cm in diameter)
H/D Medhurst C E-Tesla6.11 C (pF)
1 4.6 5.18765
2 5.0 6.11249
3 6.1 7.07073
4 7.2 8.00478
5 8.1 8.92074
6 9.2 9.82484
The error generally follows a curve of:
error(h/d) = (0.104(h/d) + 0.291) / (0.09274(h/d) + 0.42606)
The error basically starts just below 0.8 for a H/D of 1 and levels off to ~1
at around the H/D of ~7.
I would guess that Medhurst incorrectly thought the C he was measuring was the
only factor. Apparently, the inductance of bare coils is affected and lowered
by the diminishing currents near the top of the coil. So there is a
capacitance involved but also a variation in the coil's inductance that is a
function of the height to diameter ratio.
Obviously, this would be sort of a messy development since it changes some
fundamental ideas that we use to calculate coil values. All the formulas still
work, but there may be some changes needed in the theory behind them...
Cheers,
Terry
Maintainer Paul Nicholson, paul@abelian.demon.co.uk.