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Re: Tesla simulations vs. scope traces (fwd)
From: Malcolm Watts[SMTP:MALCOLM-at-directorate.wnp.ac.nz]
Sent: Tuesday, December 23, 1997 10:03 PM
To: Tesla List
Subject: Re: Tesla simulations vs. scope traces (fwd)
I have to disagree....
> From: Antonio Carlos M. de Queiroz[SMTP:acmq-at-compuland-dot-com.br]
> Sent: Sunday, December 21, 1997 11:49 PM
> To: Tesla List
> Subject: Re: Tesla simulations vs. scope traces (fwd)
>
> Tesla List wrote:
>
> > 1) With a digital scope (500mhz) I captured some traces of my 8X6 coil
> > operating and ran the output through a FFT program at work. The scope was
> > triggering on a 4MHz ring-up , followed by a 100KHz sine wave.
>
> Be very careful with digital scopes, specially when analyzing noisy signals (and
> the vicinities of a Tesla coils are certainly very noisy).
> They like to "invent" signals...
I can confirm the results mentioned in the original post. I too have
done these measurements.
> > 4) A distributed ladder network of series inductors simulating the bottom of
> > the coil equal to the total secondary inductance/2 then /4 ,/8, etc..with
> > capacitances to ground starting at the top equal to total secondary self-
> > C/2+Toroid-C then self-C/4,/8, etc...showed a 91.58KHz component for the
> > Inductor L7 at the top of the coil, and also 1,2,3,and 4MHz spikes for the
> > Inductor L1 at the bottom of the coil...simillar to the scope traces from the
> > real coil.
>
> I looked at the model at your site and repeated the analysis with another
> program. That circuit really shows a set of very high Q resonances above 1 MHz, as
> your analysis showed. 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.
> Also, the value of the first capacitor should be 0.140625 pF and the last inductor
> should be 0.578125 mH.
> With this all the sections resonate at the same frequency, and the circuit
> reduces to a single section (this is why inductors with distributed capacitances
> and resistances can be considered as simple LC tanks).
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.
> The transfer function to the output shows a high peak at 121 kHz and a notch
> at 2.15 MHz. Nothing more.
> It is true that nonlinearities (spark gap, sparks) in the primary and secondary
> circuits can generate other frequency components than those of the usual resonances,
> but this is not considered in this analysis.
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.
> --
> Antonio Carlos M. de Queiroz
> mailto:acmq-at-compuland-dot-com.br
> http://www.coe.ufrj.br/~acmq
>
>
>
>
>