TSSP: List Archives

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.