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Re: secondary waveforms
At 10:25 PM 2/13/97 -0700, you wrote:
>Subscriber: sgreiner-at-mail.wwnet-dot-com Thu Feb 13 22:02:04 1997
>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,
The ideal toroid to wind over for HF work would be an air core, like a
closed ring of Tygon hose or something. This is what I do making Rogowski CTs.
The second frequency doubled component you are seeing is bogus or an
artifact, I would think, and certainly not a power producer. Check the self
resonant frequency of the toroidal inductor you are using to measure with!
This is why air toroids work better. They allow a lot high natural
frequency of resonance of the measurement transformer. Thus less
interference of the measurement.
R. Hull, TCBOR