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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
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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
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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.
======================================================================================
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:
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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
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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.?
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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.
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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
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The gas tubes respond in several microseconds. For AC line voltages, they will effectively be a short during each half cycle. If one doesn't have an inline fuse, both wiring and spark gap could suffer damage.
Varistors are the preferred device for use across AC lines but they have their own issues. If the surge event causes catastrophic failure of the varistor, it can catch fire and damage equipment. Varistors should have a thermal fuse in-line to avoid possible fire hazard. Three lead varistors have a built in thermal fuse.?
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Many of the "Neon" bulbs you could buy in the old days aren't readily available anymore. You could buy blue, red, yellow, orange..etc. They are filled with different gas mixtures other than
Neon and some have a radioactive isotope added to lower the ionization voltage. One could buy bulbs screened for voltage/current ranges for use in protection and regulator circuits.
Neon bulbs are still used in AC power strips and as cheap surge protectors for signal and RF lines.?
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In a simulation I have for a power oscillator, I use a green neon bulb as a bias adjustment indicator.
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Tom wrote, "The gas tubes respond in several microseconds."
That's nothing compared to 8.33 milliseconds, unless your definition of "several" differs from mine.? Therefore the arc should extinguish between one half-cycle and the next.? If the next half-cycle also has a large over-voltage event, then of course it would trigger again, and again ... as expected.
All the comments about limiting the current during an over-voltage event are of course valid but that's true for any device that limits an over-voltage condition, whether a gas discharge tube or anything else.? Of course.? It's common sense, but it's unrelated to it being a gas discharge tube.
I still do not see why one should "never use a gas discharge tube across an AC ... line."? I do not believe that is a correct argument.? Once they fire they will self-extinguish before the next half-cycle begins.? Now if it was a DC line, that's another thing.
Andy
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It;s a matter of simple
observation that neon lamps flicker because they go dark at
low voltages. If you attach one to a 1 metre cable and swing
it in a vertical plane you can see the pattern of bright and
dark regions.
You wouldn't put a gas
discharge tube directly across an AC supply because it
would probably explode due to excessive current if it ever
reached striking voltage.
======================================================================================
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 2023-07-16 19:41, Andy I wrote:
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Show quoted text
Tom wrote, "The gas tubes respond in several microseconds."
That's nothing compared to 8.33 milliseconds, unless your
definition of "several" differs from mine.? Therefore the arc
should extinguish between one half-cycle and the next.? If the
next half-cycle also has a large over-voltage event, then of
course it would trigger again, and again ... as expected.
All the comments about limiting the current during an over-voltage
event are of course valid but that's true for any
device that limits an over-voltage condition, whether a gas
discharge tube or anything else.? Of course.? It's common sense,
but it's unrelated to it being a gas discharge tube.
I still do not see why one should "never use a gas discharge tube
across an AC ... line."? I do not believe that is a correct
argument.? Once they fire they will self-extinguish before the
next half-cycle begins.? Now if it was a DC line, that's another
thing.
Andy
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John wrote, "...?because it would probably explode due to excessive current if it ever reached striking voltage."
Interesting point.
But I think it would depend on the impedance of the source of the overvoltage.? If it's a transient overvoltage, presumably the source of that transient does not have the same low impedance as the mains supply itself.? (Unless it was something like the HV wire falling and shorting to the regular mains wire.)
I'm not trying to advocate putting a gas discharge tube directly across an AC mains line without a fuse or breaker.? I'm just playing the "what-if" and wanting to understand what goes on.
Andy
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In testing for immunity to
transients, the transients are really quite energetic, and are
supposed to be representative of transients that occur in real
life.
======================================================================================
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 2023-07-16 21:26, Andy I wrote:
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Show quoted text
John wrote, "...?because it
would probably explode due to excessive current if it ever
reached striking voltage."
Interesting point.
But I think it would depend on the impedance of the source of the
overvoltage.? If it's a transient overvoltage, presumably the
source of that transient does not have the same low impedance as
the mains supply itself.? (Unless it was something like the HV
wire falling and shorting to the regular mains wire.)
I'm not trying to advocate putting a gas discharge tube directly
across an AC mains line without a fuse or breaker.? I'm just
playing the "what-if" and wanting to understand what goes on.
Andy
|
Neon pilot lights were always used with a series resistor.
Le 16/07/2023 à 22:26, Andy I a écrit?:
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John wrote, "...?because it
would probably explode due to excessive current if it ever
reached striking voltage."
Interesting point.
But I think it would depend on the impedance of the source of the
overvoltage.? If it's a transient overvoltage, presumably the
source of that transient does not have the same low impedance as
the mains supply itself.? (Unless it was something like the HV
wire falling and shorting to the regular mains wire.)
I'm not trying to advocate putting a gas discharge tube directly
across an AC mains line without a fuse or breaker.? I'm just
playing the "what-if" and wanting to understand what goes on.
Andy
|
Or with a resistor, capacitor, and a 90V “B” battery, for a relaxation oscillator flasher!
?
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From: [email protected] < [email protected]> On Behalf Of
Jerry Lee Marcel
Sent: Sunday, July 16, 2023 2:08 PM
To: [email protected]
Subject: EXTERNAL: Re: [LTspice] Neon
?
Neon pilot lights were always used with a series resistor.
Le 16/07/2023 à 22:26, Andy I a écrit?:
John wrote, "...?because it would probably explode due to excessive current if it ever reached striking voltage."
Interesting point.
But I think it would depend on the impedance of the source of the overvoltage.? If it's a transient overvoltage, presumably the source of that transient does not have the same low impedance as the mains supply itself.? (Unless it was something like the HV wire
falling and shorting to the regular mains wire.)
I'm not trying to advocate putting a gas discharge tube directly across an AC mains line without a fuse or breaker.? I'm just playing the "what-if" and wanting to understand what goes on.
Andy
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Neon bulbs can be used for receiver or audio amplifier input protection, modem input protection...etc. Neon bulbs?cannot handle the power a ceramic gas tube protector or varistor provides but they have similar capacitance to a ceramic gas tube. Varistors have very high capacitance and are not suitable for RF without say a series choke. The phone/DSL line to your house has a differential ceramic gas tube protector mounted in the NID box provided by the phone company.?
One has to define what surge event could be expected. For an RF receiver/audio amp, one could expect static buildup or discharge by the user or a surge induced into the feedline by a nearby lightning hit. In general a direct lightning hit will destroy almost anything. Goal should be to isolate the damage to a replaceable PCB/module or to an external surge protector.?
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I didn’t follow the discussion, but allow me to throw in that input protection against HF-transients like electrostatic discharge ?sparks“ often can be achieved by ferrite beads put in serial into the input line.
— Christoph
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Neon bulbs can be used for receiver or audio amplifier input protection, modem input protection...etc. Neon bulbs?cannot handle the power a ceramic gas tube protector or varistor provides but they have similar capacitance to a ceramic gas tube. Varistors have very high capacitance and are not suitable for RF without say a series choke. The phone/DSL line to your house has a differential ceramic gas tube protector mounted in the NID box provided by the phone company.?
One has to define what surge event could be expected. For an RF receiver/audio amp, one could expect static buildup or discharge by the user or a surge induced into the feedline by a nearby lightning hit. In general a direct lightning hit will destroy almost anything. Goal should be to isolate the damage to a replaceable PCB/module or to an external surge protector.?
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Most kinds of protection involve both a clamping (shunt) element
and one (in series) that limits current. Inductors (which ferrite
beads are) are just one particular type of series element.
Le 18/07/2023 à 10:59, Christoph a
écrit?:
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I didn’t follow the discussion, but allow me to throw in that
input protection against HF-transients like electrostatic
discharge ?sparks“ often can be achieved by ferrite beads put in
serial into the input line.
—
Christoph
Neon bulbs can be used for receiver or audio
amplifier input protection, modem input protection...etc.
Neon bulbs?cannot handle the power a ceramic gas tube
protector or varistor provides but they have similar
capacitance to a ceramic gas tube. Varistors have very
high capacitance and are not suitable for RF without say a
series choke. The phone/DSL line to your house has a
differential ceramic gas tube protector mounted in the NID
box provided by the phone company.?
One has to define what surge event could be expected. For
an RF receiver/audio amp, one could expect static buildup
or discharge by the user or a surge induced into the
feedline by a nearby lightning hit. In general a direct
lightning hit will destroy almost anything. Goal should be
to isolate the damage to a replaceable PCB/module or to an
external surge protector.?
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murrayatuptown
John Woodgate
Bell, Dave
Christoph