RE: Vortex gap loss measurements

["Lau, Gary" <Gary.Lau-at-compaq-dot-com> (by way of Terry Fritz <twftesla-at-uswest-dot-net>)]

Hi Dan:

Comments interspersed:

>Original poster: "Daniel Boughton" <daniel_boughton-at-yahoo-dot-com> 
>
>Gary:
>
>This is a very interesting experiment. First, when you
>measured the slope during the ring down, did you see
>the same size decrement of each succesive oscillation?
>Is this what you mean by linear as oppossed to
>logarithmic? 

Yes, the envelope of the ringdown is precisely triangular.  You can line up
a straight edge on the ramp and it follows the envelope exactly, right down
to zero.

>Traditional wisdom purports that the
>decay is according to V(t)=V(i)e^-rt where V(i) is the
>forced initial potential on the capacitor. Your
>results are very interesting however in that it flies
>in the face of convention. The derived equation must
>be something like V(t)= V(i)*-krt. 

I think the thing wrong with the traditional equation is that it assumes a
constant arc resistance.  I'm guessing that the arc resistance is a function
of arc current, and not a constant.

>I wonder if without
>the secondary it is linear due to resistive losses
>only. Without the secondary the additional absorption
>of energy via the secondary mutual inductance is
>missing which accounts for the linear decay? 

I think all of the losses have to be resistive, it's just a question of
whether it's a constant resistance.

>Also what
>I found interseting was that with the gap distance the
>slope remained constant. I would have expected greater
>gap resistance at further distances but it seems that
>the plasma provides a constant resistance no matter
>how wide the spark gap is set (within reason of
>course-I 'm sure at a foot the resistance would be
>substantial as compared to 300 mil).

Yes indeed!  I also expected the losses to be proportional to arc length.
But with a wider gap, the breakdown voltage is higher with proportionately
higher tank currents, and if my belief that arc resistance diminishes with
higher currents, it may all be a wash.

Here's a thought experiment.  I don't know the answer, perhaps someone else
does.  If one has a 3 foot long neon sign tube and a 6 foot neon sign tube,
the longer one will obviously require a higher voltage to start ionization.
But once started, won't they both draw the same current from the same NST?
If so, this suggests that gap arc resistance is strictly a function of gap
current, not distance.  If not, then I give up!

>Also, does your scope generate a data file? If so, can
>you share it?

It does, but it's in a format native to the Tektronix scope.  I haven't
figured out how to convert it to a GIF or BMP (the scope is borrowed from
work and doesn't have a manual).  I didn't save any of the traces since the
slope measurements were easy to make with the cursors, but I can repeat a
subset of the measurements and just take a picture of the screen with my
digital camera.  [Crude, crude, crude!]  It may take a week or so to find
the time, but I'll post it to my web site with a heads-up to the List when I
do.

>Regards,
>Dan

Regards, Gary Lau
Waltham, MA USA

--- Tesla list <tesla-at-pupman-dot-com> wrote:
> Original poster: "Lau, Gary" <Gary.Lau-at-compaq-dot-com> 
> 
> Today I found some time and performed a comparison
> between the gap losses of
> my single vacuum gap, and my new single vortex gap. 
> To do so, I scoped the
> primary ringdown with no secondary in place.  I used
> a Terry Fritz fiber
> optic voltage probe across the primary coil and a
> digital storage scope to
> record the results.  I have not yet accurately
> calibrated the voltage
> readout, so for now, the results are just relative
> to each other.
> 
> With no secondary in place, the ringdown is a
> linearly decrementing
> waveform, not logarithmic.  As such, the slope of
> the ringdown indicates the
> losses in the circuit and is independent of the gap
> firing voltage.  I
> performed ringdown slope measurements at a variety
> of gap widths to vary the
> initial voltage, but the ringdown slope is a
> constant, independent of Vgap.
> 
> The power to the blower motor is varied through a
> lamp dimmer and I tried
> varying the motor speed to see what effect that had.
>  At very low speed, the
> linearly decrementing waveform became slightly
> logarithmic-looking, but
> still predominantly linear.  The gap breakdown
> voltage appeared to change
> slightly at low speed, but this was hard to measure
> as it was slight and the
> bang-to-bang gap breakdown voltage is not as
> consistent as one might hope.
> 
> The slope decrement figures are assuming that my
> probe is accurately
> calibrated for voltage, though I suspect it may not
> be, so the figures are
> useful only for relative comparison purposes.  
> The pressurized vortex gap decremented at 200V/usec.
> The vacuum gap decremented at 235V/usec (17.5%
> faster).
> The vortex gap breakdown voltage is about 20% higher
> than the vacuum gap at
> the same gap distance.
> 
> Vortex gap web page: 
> 
>
http://people.ne.mediaone-dot-net/lau/tesla/vortexgap.htm
> 
>
<http://people.ne.mediaone-dot-net/lau/tesla/vortexgap.htm>
> 
> Vacuum gap web page: 
> 
> http://people.ne.mediaone-dot-net/lau/tesla/onegap.htm
> 
> <http://people.ne.mediaone-dot-net/lau/tesla/onegap.htm>
> 
> 
> Regards, Gary Lau
> Waltham, MA USA