Wow, locating hydrocarbon's!
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I am thinking now I'll have to use e (elementary charge), calculate the number of atoms for the direct path of the gap, use Paschen's voltage and do some magic with them.
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I've had very good luck modeling a spark gap as a switch in series with 20V drop in each direction.? The test case was a parallel tank circuit(about 10uF capacitance at 2.5KV and 10uH inductance) used to create a short AC pulse to excite eddy currents in rock formation strata in the interest of locating hydrocarbon bearing rock for oil exploration.? The current amplitude ramps down linearly instead of decaying linearly as it would with a series resistance.? The gap also quenches realistically.
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I'm not sure what you mean there, I think the arc, or the detection event in a GM tube can be considered 'low' resistance.
I'd like to re-establish credentials as to why we're discussing this on LTSpice's forum.?
1) to show interest in spark gaps, arresters, neons, GM tubes -? what simulation models exist, what's missing and might be nice to have or to develop.?
2) how they are used - I can offer some detail on GM tube drivers, real measurements,?
3) maybe a simplified model for the GM tube as a narrow pulse current sink, enough to discharge its [3pF] capacitance by 50-100V? - in a time that I can confirm by measurement?
4) perhaps evaluate the "quench" circuit mentioned above - is it faster than the tube, does it work, is it any benefit??
5) provide a locus for any future enquiries about this sort of thing.?
6) Ideally, find a poor mans Geiger tube that works well enough and doesn't cost ?300
A basic GM tube spec is here:?https://www.jameco.com/Jameco/Products/ProdDS/2210141.pdf
They recommend 10Meg anode resistance, with their 3pF tube capacitance that's an RC of 30us, which is in keeping with the quoted minimum recovery time of 90us (3xRC).?
I'm guessing the volts drop from V_operating [500V] to V_min [325V] minus a bit, so a swing of 200V, 250V, to guarantee the tube quenches.?
The magnitude and duration of the ionisation current is not specified, but its quick compared to 90us, I'll measure it if I can't find a published figure.?
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Just a thought, I was thinking the resistance drops non-linearly and what ever the source can supply is the current.
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Re: Filters (Butterworth, Chebychev etc.)
Oh sorry. Uploaded again.
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Re: Filters (Butterworth, Chebychev etc.)
Your zip contains filt.sub and filter.asy, but your model is looking for filter.sub
?
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From: [email protected] < [email protected]> On Behalf Of
Christoph
Sent: Wednesday, July 12, 2023 9:07 AM
To: [email protected]
Subject: EXTERNAL: Re: [LTspice] Filters (Butterworth, Chebychev etc.)
?
I uploaded my filter attempt to the file section. Hope all is self contained and it works.
?
Tony wrote, "I didn't have any trouble downloading Filt.zip - must be something in your Firefox setup. ..."
I think the problem is that the LTwiki website uses http: (not secure https:) in many places.? That was a problem for the main LTwiki webpages too.? Currently, for me, the main LTwiki webpage (for information about LTspice) now uses https:, but the branches
for Vlad's and Bordodynov's files still do not.? I don't use Firefox, but I guess Firefox (depending on its settings) might prevent you from downloading anything with an http: URL.? Google Chrome complains mightily, but if you are persistent and ignore all
its warnings about it, you can get it to download from http: URLs.? Bit of a PITA.
Andy
?
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Understood, he's using the neon as a G-M tube, but the common G-M circuit already addresses the issue very simply.? G-M tube capacitance is about 5pF, the neons I've just measured are under 1pF, so the same principles should apply.?
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Re: Filters (Butterworth, Chebychev etc.)
I uploaded my filter attempt to the file section. Hope all is self contained and it works. Anything to correct? ¡ª Christoph
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Tony wrote, "I didn't have any trouble downloading Filt.zip - must be something in your Firefox setup. ..."
I think the problem is that the LTwiki website uses http: (not secure https:) in many places.? That was a problem for the main LTwiki webpages too.? Currently, for me, the main LTwiki webpage (for information about LTspice) now uses https:, but the branches for Vlad's and Bordodynov's files still do not.? I don't use Firefox, but I guess Firefox (depending on its settings) might prevent you from downloading anything with an http: URL.? Google Chrome complains mightily, but if you are persistent and ignore all its warnings about it, you can get it to download from http: URLs.? Bit of a PITA.
Andy
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Bonkers, "It is possible that the high current pulse when the bulb triggers is responsible for some of the chaotic behavior.? In order to remove the effects of the high current spike when the lamp fires, the following quench circuit was constructed:"
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no probs - and yeah, don't know why he's using a couple of transistors, a very high value resistor is all that is used for G-M tubes.?
The high voltage ensures avalanche multiplication, and the low tube capacitance ensures the detection is quickly quenched, minimising recovery time - and its limit on max detection rate.??
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Paschen's Law ({B} * {p} * {d}) / log({A} * {p} * {d}) - log(log(1+(1/1.2)))-{C} has nothing to do with resistance except that I believe you need to know the voltage to find the current.
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Going to this thread and downloading the downloaded file, I was hoping to see the model of the arrester. What I saw had nothing to do with LTspice, except of course the arrester symbol. I am very disappointed. I have not seen a model of the arrester or discharger and apparently there will not be one. This topic is appropriate for another forum. For example on the physics forum.
Bordodynov.
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Thanks Bonkers, I've been to techlib missed that circuit.
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Tor, thank you, I've seen it. Looks over complicated, but I'll keep it in mind.
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Yes, that's true. Right now I am assuming small cylindrical electrodes.
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Interesting topic, relates also to neon bulbs, gas arresters etc.?
I was going to mention that some (all?) neons have some radioactivity - as it bleaches out any variation in striking voltage due to cosmic rays, radiation and photoelectric effects.?
Just checked this on Wikipedia and it also shows a detailed graph of behaviour versus current, well worth a look - the arc you mention is one of a number of possible outcomes, according to gas pressure, voltage, current.
There's also evidence for the electrodes being radioactive (rather than the gas) - but in all cases, they don't seem to make a usable poor man's Geiger-Muller tube.?
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I found an interesting article on the subject:
Seems quite complicated.
br,
Tor
On 12/07/2023 17:45, Richard Andrews
via groups.io wrote:
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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.
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That's it I forgot the pressure even though it's in the equation.
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Bonkers
Christoph
Bell, Dave