[Prev][Next][Index][Thread]

Real vs. MicoSim...

Hi again,

	I followed up last night's experiment (the one I didn't mess up ;-)) by
modeling the same thing in MicoSim.  I measured the output impedance of the
audio signal generator by loading it with a know resistor and found that it
was 696 ohms at 350kHz (the resonant frequency of my coil).  My coil's real
AC resistance at resonance is about 116.9 ohms (33.95 ohms DC) found in a
similar way to the above by measuring the voltage drop at the generator at
resonance (my scope has RMS readout so I can measure these signals with
good accuracy).

The MicroSim prediction is at:
http://users.better-dot-org/tfritz/site/misc/Ken02.jpg

The real measurement is at:
http://users.better-dot-org/tfritz/site/misc/Ken01.jpg

So it would appear that the real system's phase and ring up have waveforms
that can be predicted with lumped element analysis even in the sudden turn
on case.  Even I am a little surprised the lumped element models hold so
well here...

Cheers,

	Terry



>Hi Ken,
>
>At 09:56 AM 04/14/2000 -0700, you wrote:
>snip...
>>Also, in my later posting, I talked about the 1st 1/4 cycle--but I should
>>have said, 1st 1/2 cycle.  At the instant when the 1st 1/2 cycle of
>>"bottom" excitation goes thru its first zero-crossing, the 1st 1/2 cycle
>>of the "top" voltage is right on its maximum.  As to the behavior prior
>>to that, obviously the top voltage cannot instantaneously assume the
>>beginning rate of change of that 1st 1/2 cycle of excitation, which--from
>>my generator--starts right out climbing with the rate of change to be
>>expected at zero-crossing.  Instead, the top wave starts with zero rate
>>of change (naturally) & smoothly assumes the appropriate rate of change
>>within the 1st 1/4 cycle.  And I do hope someone will check me on all
>>this.
>>
>
>I did the following:
>
>I used a Tek TDS210 digital scope to capture 2500 points and read them to 
>disk and then to Excel.  I captured the graphs and converted them to a JPG at:
>
>http://users.better-dot-org/tfritz/site/misc/Ken01.jpg
>
>Basically, a nice way to accurately capture the event.
>
>The blue signal is at the wire feeding the base of the secondary coil (no 
>top terminal).  The generator was a sine generator set precisely at 
>resonance.  As the secondary voltage increased, the added loading on the 600 
>ohm generator caused the blue input signal to decrease.  I shorted the 
>generator's output with a wire and quickly pulled it away to get the sudden 
>sine wave turn on.  With about ten tries, I got a good capture.  The probe 
>was hard connected to insure phase was preserved.
>
>The purple signal is the top of the secondaries voltage measured with plane 
>wave antennas that preserve phase and have +100MHz bandwidth.  The signal is 
>a little fuzzy since they are meant to measure the full secondary running 
>voltage and I had to turn the gain way up.
>
>It appears that the secondary top voltage is always 90 degrees later than 
>the input voltage at the base of the coil during this ringup event.
>
>I hope this is what your were looking for.  I have the raw data file if you 
>want it.
>
>>
>>As to loading of the secondary by the probe, no doubt its input
>>capacitance does that, but I wouldn't expect that to affect significantly
>>the kinds of things I measured.  Correct me if I seem to be wrong.
>
>Be very careful of phase information with bare probe ends.  I recently had a 
>bad experience with that ;-))  I no longer trust the "little wire on the end 
>of a scope probe" for anything!  The tiny capacitance that is coupling to 
>the coil's fields to the probe (~0.03pF) is messed with heavily by the 
>probe's own impedance.
>
>>
>>And once again, someone tell me what it is that's >"slow"<!
>
>It comes from a paper by the Corums where they talk about their "slow-wave 
>helical resonator theory".  Basically, they claim that the Tesla coil 
>secondary is acting like a transmission line with a velocity factor of ~0.1% 
>(yes, they do claim 1/1000 the speed of light!).  So the wave is only 
>traveling 1862.8 miles per second.  Thus the wave is "slow".
>
>See their paper (about 10 paragraphs in but mostly the whole first part) at:
>
>http://www.ttr-dot-com/corum/index.htm
>
>Cheers,
>
>	Terry
>
>
>>
>>Ken Herrick
>>
>snip...