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Re: Neon

 

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.?
Re: Spark gap physics.

 

I would dare to suggest that a hot cathode emitter is probably more what the OP is wanting for an ion thruster than a spark gap. I always envisage an ion thruster as being like the cathode end of an oscilloscope tubewithout a phosphor screen on the other end. But then, the OP may well be attempting to use a spark gap in a manner that is more controllable for directing thrust than my imagination can come up with.


On Thu, 13 Jul 2023 at 21:51, John Woodgate <jmw@...> wrote:

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

======================================================================================
Best wishes John Woodgate OOO-Own Opinions Only

Rayleigh, Essex UK

I hear, and I forget. I see, and I remember. I do, and I understand. Xunzi (340 - 245 BC)


On 2023-07-13 21:46, Richard Andrews via wrote:
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.

Re: ISL70444SEH declaration issue?

 

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.
Re: Neon

 

¿ªÔÆÌåÓý

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.

======================================================================================
Best wishes John Woodgate OOO-Own Opinions Only

Rayleigh, Essex UK

I hear, and I forget. I see, and I remember. I do, and I understand. Xunzi (340 - 245 BC)


On 2023-07-13 22:27, Andy I wrote:

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

Re: Neon

 

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
Re: Neon

 

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).



I also remember CFL fluorescents had a significant amount of Neon along with typically Argon (plus small amount of liquid Mercury) in their mix. The older T8 & T12 1"/1.5" linear tubes typically didn't have Neon). I don't know about T5 or CCFL (higher ignition voltage in absence of heater/space charge properties).? I think the Neon suited the current density and shorter length.

That consultant I worked with simply modeled fluorescent lamps by their known (plasma column) voltage vs. the impedances used for voltage dropping. He had other models to handle instant and preheat start and end-of-life current shifts.

No Spice modeling.

I wonder if spark gaps age, based on number of arcs endured and the energy involved (electrode shape change?). I think they have other uses than just as protection devices, but maybe not commonly.

Murray


--
Murray
Re: Spark gap physics.

 

Thanks John.
Re: Spark gap physics.

 

¿ªÔÆÌåÓý

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

======================================================================================
Best wishes John Woodgate OOO-Own Opinions Only

Rayleigh, Essex UK

I hear, and I forget. I see, and I remember. I do, and I understand. Xunzi (340 - 245 BC)


On 2023-07-13 21:46, Richard Andrews via groups.io wrote:

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.

Re: Spark gap physics.

 

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.
Re: Spark gap physics.

 

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.?
Re: Spark gap physics.

 

Dave Bell the formula is Current * sqrt((2*Voltage*Mass)/Ce.
Re: Spark gap physics.

 

¿ªÔÆÌåÓý

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.

======================================================================================
Best wishes John Woodgate OOO-Own Opinions Only

Rayleigh, Essex UK

I hear, and I forget. I see, and I remember. I do, and I understand. Xunzi (340 - 245 BC)


On 2023-07-13 20:45, Richard Andrews via groups.io wrote:

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.

Re: Spark gap physics.

 

¿ªÔÆÌåÓý

This sounds like a very interesting project!

?

Out of curiosity, how do you measure thrust with a spark gap?

?

Dave

?

From: [email protected] <[email protected]> On Behalf Of Richard Andrews via groups.io
Sent: Thursday, July 13, 2023 12:45 PM
To: [email protected]
Subject: EXTERNAL: Re: [LTspice] Spark gap physics.

?

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.

Re: Spark gap physics.

 

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.
Re: Spark gap physics.

 

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.?
Re: Spark gap physics.

 

"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.
Re: POSH (Powershell) tool to manage "user approved" LTspice cmp files

 

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...
Re: Spark gap physics.

 

#1 rule, It is not deterministic.
Every spark gap is unique at some level. There is a distribution curve that can be exploited, in terms of multiple sampling and ratiometric sampling.
Both amplitude and time can be exploited.
the uniqueness can be measured, but not anticipated prior to the event.
and you can have more than one spark gap as well, but one current coupling them all together, i think this would have a tighter bell curve via synchronous, similarity induced averaging. the hot spark get damped by the colder ones, and the cold ones get sped up by the hot ones (think faster)

On Wed, Jul 12, 2023 at 7:45?AM Richard Andrews via <=[email protected]> wrote:

Trying to grasp the resistance in a spark gap I had to write what I know.
If anyone can refute my ideas, let me know.

The voltage and current relationship when a spark gap's gap is increased is as follows:

??? Voltage: The voltage required to initiate a spark across the gap increases
??? as the gap widens. This is because the air in the gap has to be ionized
??? before a spark can occur, and it takes more voltage to ionize the air as
??? the gap widens.

??? Current: The current that flows through the spark gap after it has initiated
??? is relatively constant, regardless of the gap width. This is because the
??? resistance of the ionized air is very low, so a large current can flow even
??? with a small voltage difference.

??? For example, spark gaps are used in spark-ignition engines to ignite the
fuel-air mixture. The spark plug in a spark-ignition engine has a gap of about
0.020 inches, and the voltage required to initiate a spark across this gap is
about 20,000 volts. However, once the spark has initiated, the current that
flows through the spark plug can be as high as 20 amperes.

??? The relationship between voltage and current in a spark gap is not linear.
As the gap widens, the voltage required to initiate a spark increases
exponentially. This means that a small increase in the gap width can result in
a large increase in the voltage required to initiate a spark.

??? The voltage and current relationship in a spark gap is also affected by the
type of gas that is present in the gap. Air is the most common gas used in
spark gaps, but other gases such as argon and helium can also be used.
The breakdown voltage of a gas is the voltage required to ionize the gas,
and it is different for different gases. This means that the voltage required
to initiate a spark in a spark gap will be different depending on the type of
gas that is present in the gap.



--
Ron Davison
principle
Efficient Electronic Solutions
760.505.4380

¡°What I cannot build, I do not understand¡±?Richard Feynman?
Re: Spark gap physics.

 

It's always negative?differential?resistance, whether in an arc, a Gunn diode, the input into a loaded boost converter.? If not ballasted you can make a negative resistance oscillator.?
The term ballast (bare load) is indeed borrowed from the nautical sense - where a top-heavy payload is ballasted by a fixed keel load, lower down.?
The same principle is applied in arc lamps, emitter resistors in paralleled BJTs, shunt loads on LDO's - and anything where a fixed contribution drowns out unwanted variations.?
Re: Spark gap physics.

 

There is an old GE databook on Neon lamps online that discussed adding radioactive gas to certain (apparently not all) lamps and why. Once I downloaded it I lost track of where I found it.

I worked at a small electronic fluorescent ballast company in the mid-90's and my boss contracted a consultant physicist who shared a patent and lawsuit against a magnetic ballast company with two other people.

The consultant told me a plasma is formed in arc lamps, with a negative resistance (as defined by the slope of the v-i curve) being the reason a ballast (resistance or impedance) is required to stabilize the plasma current. He said the association of power being produced by a negative resistance wasn't applicable in that application, just the dynamic v-i curve.

The peculiar choice of the term ballast (I wondered) was an analogy to a nautical ship ballast, which stabilizes the vertical orientation of the ship.

Murray


--
Murray
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