Re: Vortex gap loss measurements

["Daniel Boughton" <daniel_boughton-at-yahoo-dot-com> (by way of Terry Fritz <twftesla-at-uswest-dot-net>)]

Bert:

Excellent call to Morecroft (Terman the RF guru of
Stanford defers to his(Morecroft on Spark Telegraphy)
mastery of this subject that's how I discovered the
book) and excellent summary too. Excellent points
(gems)you brought up too:

1. The first current peak is responsible for burning
open the channel and determines its resultant
resistance.

2. Gap resistance is fairly stable for the remainder
of the decrement.

Thanks,

Dan
--- Tesla list <tesla-at-pupman-dot-com> wrote:
> Original poster: "Bert Hickman"
> <bert.hickman-at-aquila-dot-com> 
> 
> Gary, Dan, John, Jim and all.. :^)
> 
> Excellent experiment! 
> 
> It turns out that introducing virtually any spark
> gap into a single
> (uncoupled) RLC circuit will induce
> linearly-decrementing behavior
> instead of the exponential decay seen with a classic
> RLC circuit. It's
> interesting to rediscover this, since it was
> originally reported by Dr.
> J. Zenneck almost 100 years ago (1904!). Because of
> the linear
> decrement, tank circuit energy goes to zero in a
> sharply-defined period
> of time. The waveform on Gary's site clearly shows
> this happening in 295
> uSec for the Vortex Gap. An exponential decline will
> asymptotically
> approach zero but will never quite get there (at
> least in theory).
> 
> The spark gap's nonlinear, arc-like behavior is
> characterized by a
> relatively constant voltage drop (only tens of
> volts) that's pretty much
> independent of gap current. The actual voltage drop
> is mostly a function
> of the geometry, materials used in the gap, gas
> pressure, and the type
> of gas(es) and metal(s) that form the arc. The
> instantaneous energy
> that's lost in the gap is almost directly
> proportional to tank circuit
> current (E = V*I), and it's this characteristic that
> actually drives the
> linear decrement.
> 
> John H. Morecroft devotes a fair section of his book
> to the behavior of
> spark gaps in RLC and coupled circuits in
> "Principles of Radio
> Communication" (in all three editions, but the 1921
> 1st edition is the
> most thorough). Of particular interest is an
> equation, originally
> developed by Zenneck and Stone, which describes the
> linearly
> decrementing tank circuit current as a function of
> the Effective Gap
> Resistance (R):
> 
>          Section A:     Section B:       Section C:
>          ----------     ----------       ----------
>    I = -E*Sqrt(C/L) * (1-(R*t)/(2*L)) *
> sin(t/(Sqrt(LC))
> 
> While Sections A and C of the above equation simply
> describe the peak
> current and sinusoidal oscillations, section B
> represents the linear
> decrementing term that forms the "envelope" of the
> waveform. If the
> spark gap behaved as a pure resistor, section B
> would instead be an
> exponential function of time. The current envelope
> declines to zero when
> (R*t)/(2*L) = 1. 
> 
> This means that, if we know L and measure t, we can
> solve for the
> effective gap resistance R and use it to compare
> different types of
> gaps!  Morecroft suggests that gap resistance was
> actually governed by
> the magnitude of the FIRST current maximum.
> Apparently, the higher the
> first current peak, the larger the initial plasma
> channel, and the lower
> the effective gap resistance for the remainder of
> the decrement. This
> also implied that there was relatively little
> modulation of gap
> resistance by the oscillating RF current inside the
> envelope. 
> 
> Let's re-look at Gary's experiment now in the light
> of the above
> relationship. Gary's primary circuit resonated at
> 138 kHz, and per his
> coil specs, he was using a 0.021 uF tank cap. This
> implies a tank
> inductance of about 63 uH. The Vortex gap
> decremented to zero in about
> 295 uSec, while the vacuum gap did so about 17.5%
> quicker, or in about
> 243 uSec. This implies that the vacuum gap lost
> energy more quickly, and
> thus had a higher effective gap resistance. Solving
> for the effective
> gap resistances of the two gaps styles:
> 
>   RVortex = 2*L/t = (2*63e-6)/(295e-6) = 0.43 ohms 
> (lower = GOOD)
> 
> and
> 
>   RVacuum =  (2*63e-6)/(243e-6) = 0.52 ohms
> 
> Conclusion:
> The Vortex gap has significantly lower gap
> resistance, possibly because
> of the greater number of charge carriers available
> at the higher
> operating pressure. However, gap resistance is only
> one parameter making
> for an efficient gap. Another is its quenching
> capability. Higher
> pressure gaps often take longer to quench. However,
> some of Gary's
> earlier measurements seemed to indicate that the
> vacuum gap was not
> quenching very well, so it remains for another set
> of experiments to
> determine if the Vortex gap has better quenching
> ability. 
> 
> Great job, Gary!
> 
> Safe coilin' to you all!
> 
> -- Bert --
> -- 
> Bert Hickman
> Stoneridge Engineering
> Email:    bert.hickman-at-aquila-dot-com
> Web Site: http://www.teslamania-dot-com
> 
> Tesla list 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
> > 
> 
=== message truncated ===


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