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Re: PSpice modeling of spark gaps

Subject: 
             Re: PSpice modeling of spark gaps
  Resent-Date: 
             Thu, 12 Nov 1998 09:07:57 -0700
 Resent-From: 
             tesla-at-pupman-dot-com
        Date: 
             Thu, 12 Nov 1998 08:27:09 -0700
       From: 
             Tesla List 
         To: 
             tesla-at-pupman-dot-com




Original Poster: "Barton B. Anderson"  

Hi Malcolm,

Tesla List wrote:

> Original Poster: "Malcolm Watts" 
>
> Hi Bart,
>
> Closest I've come has been scoping primaries and deducing the basic
> characteristics from the waveforms, then applying a bit of math to it
> to reach some interesting conclusions regarding Q etc.  I have also
> tried using a bank of MOSFETs in place of the gap to investigate
> quench issues and resonator action. Additionally, after forming and
> opinion as to the nature of the real gap model, I did setup a
> benchtop LC circuit and stuck in both back-to-back zeners and anti-
> parallel diodes (low drop relative to the peak cap voltage). The
> zeners were unrepresentative at the low voltages I was working with
> but the diodes did a nice job *provided that the operating point was
> carefully picked*. I found that I could obtain log, linear and
> antilog responses depending on which circuit values I used so it pays
> to be careful when using diodes of any sort as a substitute for the
> real thing.
>      The most amazing finding the math revealed was that Q for a
> tuned circuit with a gap in it couldn't be quantified as a fixed
> value the way it can if there is normal resistance only. The math
> showed that Q climbed with voltage and absolute losses increased with
> current. The reason for this is that Vgap is not proportional to Igap.
> Neither voltage nor current is a fixed quantity but continuously
> varying in normal circuit operation.
>
> Malcolm

Yes, the gap is complex and difficult to model these details.  I remember when
you posted your results sometime ago. It is interesting. I'm not sure I can
grasp Vgap not being proportional to Igap. Even with varying capacitive and/or
inductive loading in the gap, V and I should remain proportional, unless
there's a new physical law I don't know about. If Q climbed with voltage then
it appears to me the "gap" reacts capacitively in nature and the gap
capacitance changes with volts/time as well as with varying current. Wouldn't
Q then follow Vgap? My thinking here is if Cgap = Igap / (dv/dt) = Q/V.

Sorry I didn't reply sooner, I've been in the garage the past couple nights
building a new spark gap.

Bart
The actual phenomenon encountered is probably a plasma production by dielectric breakdown across the gap followed by trans-plasma conductance. The prediction of the rate of plasma production  and resulting change of  concentration of plasma (dC/dt) and the associated decrease in pressure of air and it's dielectric effect (dP/dt) should be modelable. See attached. Note discharge resistance.

http://iyl.ee.titech.ac.jp/res-e97/UV-e.html 

-- BEGIN included message

Original Poster: "Barton B. Anderson" <mopar-at-uswest-dot-net> 

Hi Malcolm,

Tesla List wrote:

> Original Poster: "Malcolm Watts" <MALCOLM-at-directorate.wnp.ac.nz>
>
> Hi Bart,
>
> Closest I've come has been scoping primaries and deducing the basic
> characteristics from the waveforms, then applying a bit of math to it
> to reach some interesting conclusions regarding Q etc.  I have also
> tried using a bank of MOSFETs in place of the gap to investigate
> quench issues and resonator action. Additionally, after forming and
> opinion as to the nature of the real gap model, I did setup a
> benchtop LC circuit and stuck in both back-to-back zeners and anti-
> parallel diodes (low drop relative to the peak cap voltage). The
> zeners were unrepresentative at the low voltages I was working with
> but the diodes did a nice job *provided that the operating point was
> carefully picked*. I found that I could obtain log, linear and
> antilog responses depending on which circuit values I used so it pays
> to be careful when using diodes of any sort as a substitute for the
> real thing.
>      The most amazing finding the math revealed was that Q for a
> tuned circuit with a gap in it couldn't be quantified as a fixed
> value the way it can if there is normal resistance only. The math
> showed that Q climbed with voltage and absolute losses increased with
> current. The reason for this is that Vgap is not proportional to Igap.
> Neither voltage nor current is a fixed quantity but continuously
> varying in normal circuit operation.
>
> Malcolm

Yes, the gap is complex and difficult to model these details.  I remember when
you posted your results sometime ago. It is interesting. I'm not sure I can
grasp Vgap not being proportional to Igap. Even with varying capacitive and/or
inductive loading in the gap, V and I should remain proportional, unless
there's a new physical law I don't know about. If Q climbed with voltage then
it appears to me the "gap" reacts capacitively in nature and the gap
capacitance changes with volts/time as well as with varying current. Wouldn't
Q then follow Vgap? My thinking here is if Cgap = Igap / (dv/dt) = Q/V.

Sorry I didn't reply sooner, I've been in the garage the past couple nights
building a new spark gap.

Bart

-- END included message

References: