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Re: Tesla simulations vs. scope traces (fwd)
From: Antonio Carlos M. de Queiroz[SMTP:acmq-at-compuland-dot-com.br]
Sent: Wednesday, December 24, 1997 4:03 PM
To: Tesla List
Subject: Re: Tesla simulations vs. scope traces (fwd)
Malcolm Watts wrote:
> I have to disagree....
> I can confirm the results mentioned in the original post. I too have
> done these measurements.
The 4MHz signal can be noise from the spark gap triggering, filtered by
the scope connections, and "created" by the scope sampling ("aliasing").
> > The problem is that the model is wrong. The inter-winding
> > capacitances should be connected across the R-L-R sections, not to the ground.
>
> I disagree especially with that last statement. Even Tesla came around
> to considering the resonator as a cylinder wrt to ground for Cself
> calcs in a latter section of the CSN. If your model is correct, then
> his efforts to reduce Cself by putting in series C's etc should have
> worked. They didn't to his utter torment.
The inter-winding capacitances certainly are there, can't be removed, and must
be present in any valid model. You can add other capacitances to ground to
simulate the effect of different capacitances to ground at different heigths of
the secondary, but they would decrease in size with the height, not increase,
and would be much smaller than the inter-winding capacitances. Add also
corresponding capacitances to the terminal.
These capacitances can really cause the appearance of additional resonances
at higher frequency, as caused in that model, but would probably have
negligible effect in the behavior predicted by the simplest RLC model.
Another problem of that model is that the coupling among all the inductors is
not considered. Remember also that inductances are proportional to the square
of the number of turns, while coil resistances are directly proportional to
the number of turns.
> The problem with that is..... it fails to predict Fr as measured when
> you compare the measurement with the total L and C. Try it. I did,
> and that was how the model was born. Equal sections didn't work at
> all. Only one grading that I tried worked and the one mentioned was
> *it*. This was a built model - no simulation.
What is Fr? When two LRC tanks are coupled, the coupling causes changes in the
resonance frequencies of the tanks isolated. The waveforms at both tanks show
-two- frequencies, one above and other below the original resonances. Maybe
this was what you observed. But that that model is for a magnifier, not
a Tesla coil, as there is no primary tank.
> In real world resonators with a finite Q, one does indeed get
> spurious resonances (at pretty low levels as the Q's go higher of
> course). No spurii = infinite Q which is not real.
The simulation was done with all the resistors in place.
--
Antonio Carlos M. de Queiroz
mailto:acmq-at-compuland-dot-com.br
http://www.coe.ufrj.br/~acmq