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RE: Variable Capacitance and Inductance
Original poster: "Malcolm Watts by way of Terry Fritz <twftesla-at-qwest-dot-net>" <m.j.watts-at-massey.ac.nz>
Hello Terry, Dave, all,
This is my last post on this subject but I
feel bound to reply. It was really my fault that this got started -
my questioning Tesla's conclusions to explain his results. For the
record, I am sending offlist to Dave T., some measurements that took
a painstaking week of labour to produce using the best techniques I
could muster. These have preveiously been posted to the list and were
additionally passed to members of the tssp list for scrutiny
somewhere near the inception of that project.
I have a couple of comments to make regarding a couple of
comments of mine in my last reply to Dave T. I think others have
adequately covered a number of issues raised so I won;t comment
further on those:
On 24 May 2002, at 22:34, Tesla list wrote:
> Original poster: "Terry Fritz" <twftesla-at-qwest-dot-net>
> >>And so it should with the sphere, should it not? Is that not reasonable?
> >Please address this question and show me exactly why my reasoning is in
> You say that as you raise the sphere, the capacitance to ground decreases
> and the frequency goes up. That IS correct according to "me too". But
> Maxwell knew that in 1873... I thought we were worried with "unusual"
> capacitance variations that Maxwell's field theory could not explain?
> There is the big factor of the connecting wire which reverses the
> situation, but still no new science there.
Agreed. But unfortunately, I cannot isolate a sphere if it is to
remain connected to a coil, and raising it up while connected causes
a drop in frequency which is what Tesla observed. I mentioned this as
a method for fine-tuning the secondary in my '95 article. The drop is
due both to the reduction in mutual shading between coil and terminal
(an increase in total structure size if you like) and to additional
parasitic elements (L and C) associated with the wire. In the case of
Tesla's measurements, I infer that the increase in parasitic elements
(not the sphere's capacitance) was the prime cause of his measured
frequency drop since the sphere was already elevated well above the
coil, not just a few inches from it.
What I did not agree with was Tesla's reasoning that the
sphere's capacitance increased as it was raised. I still don't. It is
one plate of a capacitor with ground as the other. Increase the
distance between them, the capacitance drops. QED.
But I can raise a bare resonator up (base fed from a vertical
feedline) and measure an increase in frequency. At least one
measurement of this type (and possibly more - it is now some time
since I last visited the measurement set) is included in the set I
will be sending to Mr Thomson. Perhaps one might dwell on why Fres
increases if the coil's capacitance increases with elevation (while
its measured inductance doesn't change).
> >As I pointed out, you're using static capacitance as a model for a dynamic
> >capacitance. The amount of extra dielectric that can get between the
> >charged bodies increases. And this is precisely why the capacitance in
> >variable. The amount of free flowing dielectric "material" is always in
> In my tests and calculations over the years, the DC, AC, and resonant
> capacitances have all worked out to the same value.
> >>Suppose we had blindly accepted theories that the resonator was a lumped
> >tuned circuit. Where would that have got us?
> Lumped parameter models could be used to accurately predict voltages and
> currents in a Tesla coil. We all knew it was far more complex and knew we
> were learning to crawl before we could walk. Today, Paul's TSSP work has
> pretty much shown the real actions but the lumped models are still used by
> at least me with great success in basic design problems. It got "me" a
> lot!! Rest assured that my paper:
> Got all the errors pointed out in detail!! But "they" were right so no
> harm was done. That paper did launch some great work to follow!! So just
> another stair step... I think it's most important contribution in the long
> run was to show that hard data could finally be made available to all.
> Even if "I" was wrong, the data was suddenly there in plain sight for all
> to see and interpret themselves. Today those graphs looks old and obvious,
> that was not the case in 1998! The lumped models can still do a few tricks
> TSSP can't. However, I see Paul is starting to use my 220k + 1pF streamer
> model and wishes to improve on it. If TSSP can do as much for streamer
> modeling as it has for secondary modeling, the lumped parameter model will
> be left in the dust of history!! Of course, history suggest that someone
> will come along still and...
In my article, I likened the coil to a top-loaded antenna but I used
lumped equations (including Medhurst) to predict resonant
frequencies. In an addendum to the article, I also included the
familiar output voltage equation based on COE arguments. I have taken
pains over the years to point out that while lumped equations are an
excellent recipe for designing a coil to spec, they are not an
accurate description of its internal workings. In saying what I did
above, I was meaning to reinforce that point.
> >I hope research was done before blindly knocking the guys who came up with
> >the lumped tuned circuit? If it wasn't, I'll bet there was a mud slinging
> >contest over that.
> There was :-)))
> "#*-at-&%!! . . . Thor, you dumdum! You CAN't use lumped circuit modeling! .
> I did, and it worked just fine....
> >>Suppose we had accepted theories that the resonator could be modelled as a
> >uniform transmission line. Where would that have got us?
> It was a major stepping stone to the lumped models that were a stepping
> stone to the TSSP models... It's all a long chain of people trying to
> prove the last guy wrong :o))
Every objection I have lodged to any model was based on one of two
things: either the theory failed to match the most careful
measurements I could devise or they were philosophically unsound.
> >I hope research was done before blindly attacking the guys who came up with
> >that theory, too. What could blind mud slinging accomplish? Ultimately all
> >these mud slinging contests are ended with hard core research. So why not
> >do the research first and avoid the mud slinging?
Speaking for myself, it was *never* a case of mud-slinging. I assure
you that the hard yards were well and truly put in before I felt
compelled to wonder publicly whether the proponents of some ideas
were in fact the doyens they appeared to be. Dave T. is making the
assumption that what I have said is based on some wannabe opinion
with no experimentation to back it up. I wish to assure him that has
never been the case. I have been studying some of the problems
mentioned for a very long time. In fact, it was experimental results
which compelled me to go public.
> We like a good fight :o))) And it makes winning sweeter ;-)) However,
> watch your back since every champion has a challenger...
> Of course, the "mud slingers" or not lightweights and they know a heck of a
> lot!! Their punches hit hard and a "new theory" had better be solid as a
> rock or it's gonna get carried out on a stretcher!! However, when a solid
> theory does come along, it knocks them off like flies...
> The problem with the thread here is we have an idea that has no data to
> back it up. It was Tesla's idea so we all respect it but... We don't see
> the data... Tesla tells of it but his calculations are not "good enough"
> by today's standards. The more we look the more holes we find. Also,
> other modern tests that "should" show such unusual things do not. We just
> don't have that "line in the sand" bit of evidence that challenges us to
> explain. If we ALL could take a sphere and measure 20pF tonight and 50pF
> tomorrow, things would explode like wild fire as we rushed to find out
> why!!! But the sphere is 20pF tomorrow too, so we just yawn and go back to
> The paper of mine above came at a time when many people were sure the
> currents between the top and bottom of the coil were 90 degrees out of
> phase. Having some guy claim (rather loudly) that they were in phase and
> then provide nice scope pictures of them in phase was a "big problem" with
> the status quo. It could not be ignored. I happily answered any question
> as to the setup and helped others to reproduce the results and make fiber
> probes so they could do such work too. Rest assured, people searched for
> the error in the data but they didn't find one. However, they did find a
> "few" errors in some of my conclusions ;-) Lumped models followed that in
> short order that also demonstrated that "it worked" and they put the direct
> challenge "if it is not right, where is the error". Those models are just
> a valid today as they were then and they easily defended themselves against
> the challenges of the Corum's paper above. Of course, time marches on and
> far far better models are now coming up. If a new model works, it gain
> acceptance easily. "Too" easily as I and now Paul find. Paul asks again
> and again for challenges or peer review to find errors in TSSP, but no one
> wants to challenge the champ when he's at his best!! However, if an error
> were to pop up, they will be on us like tigers!!
> Getting back to the matter at hand...
> We cannot trust Tesla's original data for sphere elevation vs. capacitance
> in the Colorado Springs notes. There are too many unknowns and unaccounted
> for sources for error. Whatever conclusion we would make from that data,
> could be shot full of holes far far too easily. Previous posts to this
> thread mention many of them and they cannot be defended against. The
> tables like on pages 209/210 would evoke wild laughter from the audience as
> they carried our beaten carcasses out :o))
> However, we are not "defenseless" ;-)) Programs like E-Tesla6, TSSP's
> Tcap, and the new fastTesla can meet the challenge of finding a 30 inch
> sphere's capacitance at various elevations. The testing of that computed
> data can be compared to real modern measurements easily enough:
> But there is one question. What on Earth will we find that is "unusual"?
> Although "I" have never done "this" exact test, all the testing I have ever
> done suggest that we will see nothing unexpected in either the computer
> models or the actual tests. We will see how well the models correlate to
> actual results but I think we will simply discover we are wasting time
> proving the obvious. Tesla's "astonishing phenomenon" is simple physics
> and electrostatics:
> ""Continuing the investigation of this astonishing phenomenon I observed
> that the capacity varied with the elevation of the conducting surface above
> the ground, and I soon ascertained the law of this variation. The capacity
> increased as the conducting surface was elevated, in open space, from
> one-half to three-quarters of 1 per cent per foot of elevation.""
> Of course, the reason the capacity "increased" is because of the connecting
> wire and such. Tesla just did not see or have the tools to see what was
> going on at that time. Today, it seems obvious... Could weather and all
> kinds of other things have affected his original experiment? Obviously,
> yes!! We could eliminate those effects, at least on the computer, and then
> pat ourselves on the back for proving nothing...
> To make a long story short, what on Earth could be proven or what advance
> will this type of testing give us? If it was easy, we could just do it for
> fun. But there is a full day's work there at least. There are far greater
> fights to be fought... Measuring the top terminal voltage of a Tesla coil
> (directly) is the big challenge of the day. Never been done... Big
> payoff... Big challenge... ;-))
And we are working on it.
Thanks for a thoughtful post. I would like to reiterate that this
will be my last on this thread. May peace reign.