Re: secondary waveforms
Tesla List 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
> 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):
> Fr=283khz with 8x26 toroid
> 240 turns 14" x 30"
> primary: 5 turns .375"tubing 18.5" diameter, solenoid wound
> Primary res freq=234khz
> Cap: .021uf
> discharge: 54" to 60" (room limited)
> Thanks in advance for any comments
Sounds like you're seeing some artifacts from the current transformer.
My first "guess" would be capacitive coupling from the voltage component
thats superimposed on the secondary ground line combining with the
current waveform. You may also need to add a "burden" resistor across
the output of the current transformer to reduce ringing.
BTW, make sure you've always got a very solid ground on your secondary
base-lead before attempting to measure this lest your scope (or you)
become toast... :^)
-- Bert H --