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Re: [Fwd: secondary waveforms]
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> From: Tesla List <tesla-at-poodle.pupman-dot-com>
> To: Tesla-list-subscribers-at-poodle.pupman-dot-com
> Subject: [Fwd: secondary waveforms]
> Date: Friday, February 14, 1997 12:25 AM
>
> secondary waveforms
>
> Subscriber: sgreiner-at-mail.wwnet-dot-com Thu Feb 13 22:10:08 1997
> Date: Thu, 13 Feb 1997 16:04:24 -0800
> From: Skip Greiner <sgreiner-at-mail.wwnet-dot-com>
> To: tesla list <tesla-at-pupman-dot-com>
> Subject: [Fwd: secondary waveforms]
>
> This is an addendum added to my earlier post on this subject.
>
> Using a John Freau probe (ie., a probe dangling from the oscope inputs
> and situated 10' from the operating coil) I was able to look directly at
> the radiated electric field on the scope. It is classical and right out
> of the book...one frequency, sinusoidal, 285khz which is almost the
> exact frequency of the wire length, 279khz. And it is a decaying
> waveform lasting more than 1 msec.
>
> This still does not answer the question of what the current probe on the
> secondary is actually putting on the scope.
>
> Skip
>
> [ Part 2: "Included Message" ]
>
> Date: Thu, 13 Feb 1997 13:53:10 -0800
> From: Skip Greiner <sgreiner-at-mail.wwnet-dot-com>
> To: tesla list <tesla-at-pupman-dot-com>
> Subject: secondary waveforms
>
> Hi All
>
> I have wound a small toroid with a few turns of wire which are connected
> to an oscope. The grounded lead from the TC secondary passes thru the
> toroid and then to ground. Purpose, I thought, was to look at the
> wavfeform of the current in the secondary during operation. I have
> waveforms but not quite what I expected.
>
> The waveform does indeed exhibit a decreasing envelope which is
> synchronized with spark gap. The oscillations within the envelope are
> not pure sine waves. They appear to be a mixture of probably two sine
> waves of about equal amplitude, one being about 2x the frequency of the
> other.
> This gives a waveform which appears to be one sine wave with a major dip
> in each peak which goes almost all of the way to zero. I assume this is
> about what two frequencies, one being 2x the other would end up to look
> like. This implies, if true, that the secondary is ringing at two
> different frequencies. The lowest frequency appears to be about 290khz
> which is approximately the unpowered resonant frequency.
>
> The question: What am I seeing? I assumed that the ring down in the
> secondary would be sinusoidal at a frequency somewhat less than the
> natural resonant frequency in the unpowered state. Should the ring down
> be a single frequency sinusoid in a correctly operating TC? Most
> write-ups seem to imply this. If this is the case, where is the second
> frequency coming from and how does one get rid of it?
>
> Some specs( unpowered):
> Secondary
> Fr=283khz with 8x26 toroid
> Fhigh=301khz
> Flow=227khz
> 240 turns 14" x 30"
>
> primary: 5 turns .375"tubing 18.5" diameter, solenoid wound
> Primary res freq=234khz
> Cap: .021uf
> Neon:15kv-at-120ma
> discharge: 54" to 60" (room limited)
>
> Thanks in advance for any comments
>
> Skip
>
Skip,
A private post so as not to tie up the Tesla list.
The Free hanging scope probe is indeed measuring the radiated electric
field
of the secondary. The Current probe is indeed measuring current through the
secondary. Your head-scratching is, I suppose, because you thought
the current and the voltage should have the same waveform? That kind of
thing is only found in resistive circuits and tuned circuits with
smooth current input. Which ain't my definition of a Tesla coil!
Well, you might say that the current in the secondary consists of *two*
currents. There is the initial current that basically starts the ball
rolling,
and then there is the *resultant* current that is the sum of the currents
flowing *up* and *down* the secondary winding. If you think of the
secondary in terms of a 1/4 wave transmission line, it helps. You are
periodically pushing current INTO the the transmission line. It
periodically *returns* some of this current **out of phase**. That
phase distortion could show up as a dip in the sum of the currents.
Try changing the Toroid to a larger or smaller unit (or putting TWO
Toroids on at once), and you will probably see
that the POINT where the distortion occurs will slide around to a new set
of positions. If that is what you see, then you are simply witnessing the
reflected currents that have been phase shifted.
If the point of distortion
remains basically unchanged, then it means that the secondary is trying to
oscillate at the fundamental and the first harmonic. This is something
like when you blow into a soda bottle and it makes a note. If you blow
into the bottle SUPER hard, you will get a note that is double the
frequency.
In the case of a Tesla coil it would mean that you are dumping in so
much energy that the secondary cannot get rid of it efficiently, so
it gets over-driven and operates at twice the frequency, where the energy
dissipation is twice as much. I don't think that is what is happening
in your case, because the radiated energy shows a properly damped wave.
My guess is that it is reflected current summing in a negative fashion as
outlined above.
Check and see what kind of result you get from these experiments. Then you
can communicate the RESULTS to the Tesla list.
Fr. Tom McGahee