From: Paul
Date: Fri, 13 Oct 2000 16:47:00 +0100
Subject: [TSSP] Surprising secondary voltage profiles
I've been looking at the voltage profiles which Terry measured for his big coil, which I found at Bare coil, http://users.better.org/tfritz/VoltDistBare.jpg Toploaded, http://users.better.org/tfritz/VoltDist.jpg and I've been trying to reconcile them with the simulated profile of the same coil from the tsim program, which I've placed in. Bare coil, http://www.abelian.demon.co.uk/tssp-data/tfltr.vi152400.gif Toploaded, http://www.abelian.demon.co.uk/tssp-data/tfltr45.vi97360.gif There's a substantial qualitative difference which I'm unable to account for. The measurements are generally concave in slope whereas the simulated profiles are convex. Terry, I'm not sure whether the system in which you measured the profiles above was in the same configuration as the one described in the results which you sent for simulation, but I'm supposing that its not too different and that we can at least make a qualitative comparison. However, something more worrying - I'm puzzled by the concave V profile measured. If position up the coil is x then the incremental voltage increase dV on moving from x to x + dx has to be dV = w L I(x) dx where L is the effective self inductance per unit length, which we can surely assume reasonably constant. Now I'm wondering how the concave voltage profile can be obtained without assuming a rising current profile over the top 50% of the coil. In other words, a V rising steeper than linear, must have an increasing dV/dx with x and therefore an I(x) which increases with height! This increase of I(x) with height x would seem unlikely since the external capacitance is diminishing over the region in question. The upshot is, if we accept these measurements at face value, we have to explain quite an extraordinary current profile. Even a uniform I(x) would only give a linearly rising V(x). To achieve the concave V(x) you would need a positive dI(x)/dx I'm fishing now for alternative's. Could the presence of the V probe have added sufficient capacitance? No amount of additional C can make the current rise with height without it changing the resonant mode to that of a half wave between two shorted ends. Perhaps the V-probe is responding proportional to V^2 instead - were you on the knee of a diode rectifier? The latter is my preferred option, as it fixes the profile to a suitably more linear-ish rise. Any suggestions? Regards, -- Paul Nicholson, Manchester, UK. --
Maintainer Paul Nicholson, paul@abelian.demon.co.uk.