When you have a command such as this on a schematic:

? ??.options cshunt=1e-14
? ? + noopiter
it is essential to have all three lines in the same SPICE Directive.? But in the schematic you uploaded, the second and third lines and the first line are in separate SPICE Directives.? You can't control how the lines are ordered in the SPICE Netlist (well, actually you can, but it is not how you'd expect, it depends on the order they were added to the schematic).? As a result, the "+ noopiter" and "+ gminsteps=0" come after and add to your ".tran" line, and that doesn't work.

That causes an error, and your simulation can't be run.

Remedy: put the "+ noopiter" and "+ gminsteps=0" lines in the ".options" line's SPICE Directive.

Andy

Tom wrote, "One should never use a gas tube protector across an AC or DC line. Once they fire they will not shut off unless the voltage/current drop below the sustaining level. "

But with AC, doesn't that happen twice every cycle?? Or does the discharge tube take a few seconds to recover?

Andy

They are basically the same principle except the neon gas both lowers the trigger voltage and makes it predictable. Neon bulbs must operate within power limits while spark gap power is only limited by physical size and material.

Spark gaps are etched into PCBs all the time to provide some protection from surges. Unfortunately PCB and air spark gaps exhibit widely varying breakover voltage dependent on gap, temperature, humidity, contamination and altitude.?Spark gaps should never be placed across an AC or DC line. If the line voltage is high enough, they effectively become a short once triggered.

Spark gaps are widely used for protection. The most common is the ceramic gas tube protectors for Telecom. They come in 2 and 3 lead versions. 3 lead used for balanced lines.

In the old days, the gas could have radioactive isotope added but that is very rare today except for certain military and industrial applications. Waveguide Radar receive protectors back in the day were filled with a radioactive isotope gas and a HV priming voltage.

One should never use a gas tube protector across an AC or DC line. Once they fire they will not shut off unless the voltage/current drop below the sustaining level.?

Thanks so much for the detailed explanation!

I actually ended up switching to the LTC6268-10 and found that I'm able to actually get some semblance of a response from that opamp at my smallest pulse width. I am not trying to exactly duplicate the pulse; I am trying to detect that there is a pulse at all so I am thinking (hoping) that this is a sufficient response.

Here's the circuit?if you are interested in continuing to follow this saga. There shouldn't be any other files required except for the LTSpice circuit itself.

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The difference is gas pressure. Obviously, the spark gap has atmospheric pressure, about 100 000 Pa, but the pressure in a neon lamp is much lower: 100 Pa to 3000 Pa.

One thing I was never clear on, is the difference between a spark gaps and neon discharge lamps.? Are they the same principle?? They seem so widely different.? Spark gap discharge is very hot, leading to eventual destruction of the spark's electrodes.? Neon lamps are "cold" discharge.? Are they the same principle, just orders of magnitude apart?? Or different like night and day, which coincidentally end up with similar electrical properties?

The physics aside, it might end up making a difference for electrical modeling.? Or then again, maybe not.

Andy

Maybe off topic, but there is some discussion of gas mixture in different neon lamps (many no longer made) in the 1965 GE Glow Lamp? manual I mis-named earlier. There is some discussion of purpose of radioactivity (maybe altering ignition/extinction characteristics).

--

Thanks John.

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That law is about hot-cathode diodes and probably doesn't apply at all well to spark gaps.

In my studies I found this:The Child-Langmuir law is a differential equation that describes the current through a spark gap as a function of the voltage and the gap spacing.

Thanks for the further clarification of purpose.?
It's not enough to get any real purchase on the problem, but OK that's your business not mine.
I'm just saying that the tolerances on real spark gaps, and the many unknowns that a good model might erm, model, do suggest that it's not the easiest of approaches.?
You might get 20% repeatability.??
There are many established methods for measuring very small currents at very high voltages -? stick to the path if you can, it avoids solving inessential problems.?

Dave Bell the formula is Current * sqrt((2*Voltage*Mass)/Ce.

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Do you mean that you are using the spark gap as an EHT voltmeter? LTspice will simulate a 1Gohm/volt conventional analogue peak voltmeter, which would seem to be simpler and more accurate.

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The spark gap is important to me because I am simulating an ion thruster I created. A proper spark gap will allow me to measure thrust.

I'm not familiar with the spark gap usage, nor the exploding wire thing.?
As I see it, mainstream electronics does not use spark gaps because they are too variable.?
There are effects due to the small geometry that would be needed to protect against say 8kV.
For instance, pits, or worse, spikes in the electrodes caused by previous discharges.?
Also practical PCB design would try to put the spark gap on a surface, and is then prone to humidity, tracking, cathodic filaments etc etc.

I can see it works for EHV pylons, with at least a foot of gap, but even so, a Spice model would be hugely variable.?

For mainstream
- such as LTSpice would want to focus on -
there are inexpensive sintered ZnO varistors with stable characteristics.?
Actually even EHV mains "switchyards" use similar ZnO devices, about the size of a barrel, because they absorb the energy - whereas a spark gap doesn't, much.?
So, interesting though it is, where are we intending to go with spark gaps?? ?What problem are you intending to solve??

Ultimately, what is the purpose??

For me, the purpose of LTSpice is to prove the intended behaviour, and to validate the design against component variation.?
As a bonus, it normally offers great insight and clarity, allowing further refinement - especially for small discrete circuits (2~6 transistors).?
On the flip side, it can prove that a given circuit is rubbish, doesn't work as intended.
Both good reasons to love it.?

"the uniqueness can be measured, but not anticipated prior to the event."

The limitations of a conventional spark gap? can be reduced somewhat by using an? exploding wire between two electrodes. This allows for a degree of freedom in the operating voltage. I used this technique with a 200uF/10kV capacitor. The wire was exploded with a much smaller capacitor.

On Tue, Jul 11, 2023 at 11:28 PM, eewiz wrote:

Hello All

?

eetech00 wrote: I am looking for someone to help test. Anyone interested?

?

I volunteer.

Proverbially, I find myself standing on the field after the rest of troop took two steps back.

But that's alright, I'll enjoy the opportunity to delve into a working powershell script.

Thank you for all of your programming and modeling efforts.

Contact eewiz@... if you feel the need to communicate directly.

?

All for now

Hello eewiz

I've uploaded a .zip file containing powershell script "DoLTspiceUpdate_ps1_20230713.txt".
You will need to rename this .txt file to "DoLTspiceUpdate.ps1".

To run the script:

1. Open (non-admin) command prompt.
2. Change current directory to script location, then type:
?? ? powershell.exe .\DoLTspiceUpdate.ps1 <enter>

Running the script with no command line args (as shown above) will show "USAGE" information.
?? ?
A logfile will be created "DoLTspiceUpdate.log" containing script screen output.

Comments welcome...