From: Finn Hammer
Date: Tue, 05 Jun 2001 22:03:09 +0200
Subject: Re: [TSSP] Interesting article on Medhurst, Wheeler, modeling,etc.
Paul wrote: snip > We need > to be able to show, without a shadow of a doubt, that the correct > dispersion cannot be reproduced without Cint, and that when Cint is > introduced, the correct mode frequencies come out. This should be done > for a short coil, say h/d = 1 or less, so that the effect is largest. > As it happens, these are the hardest to model, and I need to smarten up > the Cint calculation in order to tackle it. I plan to introduce a short > range approximation using pieces of an elliptic integral, stitched > together and normalised to match the longer range Cint as presently > calculated using the boundary element method. This will give us a > reliable and justifiable short range interpolation to improve the > accuracy at small h/d, but it's at least a month or two's work. > Paul Nicholson, > Manchester, UK. > -- I took this to mean that too few measure, and that there is a lack of measurements on short coils, so I wound a 500 turns coil, 160 mm in diametre and 146 mm long. It measures 29.4mH on my handheld LCR meter. Tried to take resonant measurements of it, but probably violating all known rules of how to do it. Sine generator to base of coil, sitting one metre up from the floor on a 160 mm sewer pipe (pvc), scope probe dangling 1/2 meter from the coil, with a cliplead as an antenna clipped to the tip of the probe. I was close to the coil too, about one meter, but long enough to not make a difference if I moved around. Frequences at which the scope trace roze high: 340 kHz (measured with fluke 87 as counter, it will not measure beyond 650kHz) 725 kHz 1100 kHz 1450 kHz Sorry guys, perhaps there is a description of a good measurement procedure I could follow? I`m here to learn, and to help provide some of that experimental evidence. Cheers, Finn Hammer
Maintainer Paul Nicholson, paul@abelian.demon.co.uk.