From: "Malcolm Watts"
Date: Mon, 9 Oct 2000 09:45:34 +1300
Subject: Re: [TSSP] The Corum's model?
Hi Paul,
I confess you are right. The article is a rant
indeed. It is however the latest in a long string dating back
over a decade, the essence of which has been to push a
transmission line model.
On 8 Oct 00, at 11:55, Paul wrote:
> Thanks Barry and Terry for the pointer to
>
> http://www.ttr.com/corum/index.htm
>
> I *have* seen this one before - but I didn't think it was relevant to
> our discussion - it's not a presentation of a theory, just a poorly
> written, ranting and misleading tutorial.
>
> Malcolm, perhaps this is not the Corum 'theory' you were thinking
> of?
>
> I'll comment on it anyway!
>
> The authors are advocating a transmission line model as a better
> description of a tesla resonator than the lumped model. OK, thats
> fine and obvious. But then in doing so they perpetuate the mistaken
> belief that transmission line resonance represents a different mode of
> operation of a tesla coil, compared with 'lumped operation'.
I think they are clearly trying to refute that truly lumped
circuits exist. One of the papers I've seen points out that
this is true only for a fictional point source. Unfortunately
as Terry points out, the approximations can be quite good. The
problem has been that people have claimed that the circuits
are lumped without really grasping what lumped actually means
in strict physical terms. I do not buy at all the notion that
C&C push of the circuits behaving as lumped-coupled circuits
during gap dwell at typical TC k's. They claim that the
primary has a firm grip over the entire secondary during this
time with a resultant uniformity of current in secondary due
to the coil dimensions being << operating wavelength but this
appears not to be true since no expt shows secondary behaviour
changing once the gap has gone out (they claim there is a
clear difference in secondary base current which rises during
the "coherence time of the secondary". The impication is that
if this does happen, Vtop also changes correspondingly and I
have never seen this happen (which is not to say that it
doesn't but I find it extremely distressing that I cannot see
it).
> Corums wrote:
>
> > If lumped analysis describes your coil, cheer up - modify its
> > operation to an open resonator and you'll see what Tesla called,
> > on July 11, 1899, "a beautiful advance in the art"!
>
> A 'lumped component' is of course a theoretical fiction, approximately
> valid for frequencies where the electrical length of the component is
> small compared to the wavelength in the component. It's convenient
> because it allows us to do circuit theory, it certainly doesn't offer
> an alternative mode of operation!
It is on this exact basis that they claim a different mode of
operation during gap dwell but I think instead that they are
looking at the wrong thing - they should instead be looking at
the degree of coupling between the primary and different
portions of the secondary. I once suggested this to them and
received a slap in the face in return.
> (See my recent attempt to quench this myth, in the list,
> http://www.pupman.com/listarchives/2000/August/msg01119.html)
>
> Most of the rest of the article is spent with a mediocre, incomplete,
> but essentially correct description of transmission line theory as
> applied to the behaviour of tesla secondaries. This is just a
> restatement of conventional understanding. No new theory is offered,
> no predictions, and no testable proposals for improving performance.
Perhaps the worst failing of any of their writings is that
there is not a single example of a coil being designed from
first principles to a stated specification. Instead, an
existing coil is taken and measured after the fact. Even the
approach I outlined in an earlier post does better than this I
think. I agree that pursing their stuff can seem like a huge
waste of time but if they are wrong, I think the results ot
prove it should be made known to the coiling community for all
to see.
> Regards,
> --
> Paul Nicholson,
> Manchester, UK.
> --
Thankyou for putting up with my own rantings. I guess that
flame many years ago made it kind of personal for me.
Regards,
Malcolm
Maintainer Paul Nicholson, paul@abelian.demon.co.uk.