From: "Terrell W. Fritz"
Date: Sat, 14 Oct 2000 14:15:30 -0600
Subject: Re: [TSSP] Surprising secondary voltage profiles
Hi Paul, Sorry it took awhile to post back on this... At 04:47 PM 10/13/2000 +0100, you wrote: >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. I can't get the URLs of yours to load up here but I remember the graphs. I was sort of stunned at the time that they were so different than mine. I decided to let it go since my measurements may have been wrong. I used a tiny antenna placed very near the coil and measured the RMS voltage at every inch along the coil (my big sonotube coil). The antenna, of course, was tethered by a thin coax wire that I lead straight away from the coil so as to have a little effect as possible. I retuned the coil for maximum signal to sort of compensate for detuning by the antenna. I needed these profiles for E-Tesla5 and this was the best I had. However, I do feel that the "concave" quality of the graphs is correct. Please refer to the following "Malcolm's Ruler Machine" experiments: http://users.better.org/tfritz/site/misc/MalRulMa/ 1st.jpg shows a spring steel wire that is being oscillated by a loosely coupled (rubber band) driving motor (woofer speaker). "I" feel that this is an accurate representation of the voltage profile along a secondary inductor with no top load. If one compares these spring wire harmonics to those of the graph: http://users.better.org/tfritz/VoltDistBare.jpg You will see the similarities given that the wires mass and such is a bit different that the electrostatics of the coil. However, I feel that the basic qualities are the same. > >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 I would submit that the greater voltage at the top of the coil is storing far more energy. This seems to force the voltage to act more like a spring steel wire with the base fixed rather than have the wire's base be able to freely pivot (hope that makes sense). the wire's curve is concave because the wires if fixed in the wood block. I would submit that the lower part of a coil seems to have great capacitance which stores energy (lower voltage) more at the base of the coil near ground. >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? There are many questions about how the measurements was taken and the things that could have gone wrong. That is way I did not worry much when you got a different curve, although, I "worried" about it. One thing that does trouble me is that E-Tesla5 uses the curves I measured and gives very good accuracy for loaded and unloaded coils. I tried your graphs back then as secondary voltage profiles and the program showed significant errors. Not just simple scaling but it appeared the voltage profiles were not working... I was hoping you would figure the curves out then I would figure the program out :-)) Cheers, Terry > >Regards, >-- >Paul Nicholson, >Manchester, UK. >--
Maintainer Paul Nicholson, paul@abelian.demon.co.uk.