Hi all, I was trying my Heathkit curve tracer on a gas discharge transient suppressor (striking at about 200V) and I've found the following behaviour:
Basicly it seems to heavily ring on the turn-off curve? This kind of devices should just show a two lines curve in theory. My curve tracer appears to work fine on other less exotic devices (BJT, zeners). Can someone explain what is happening? Thanks
Frank IZ8DWF
My guess(tm) is that the unspecified maker and model gas discharge tube might be filled with a gas that exhibits a negative resistance characteristic, similar to a neon lamp, and therefore may be oscillating. Neon, argon, and krypton are common gasses. Some gas discharge tubes include something radioactive to lower the threshold voltage. You might try substituting a common NE-2 neon lamp for the suppressor. If the mess on the screen looks similar, then oscillation is the likely culprit.
-- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558
The impedance of a gas discharge, especially at low current after a discharge event, is negative. So, it can oscillate.
Geiger and proportional counter tubes have a gas fill that includes quench gas (CO, or methane, or somesuch) that is intended to reduce the negative-resistance behavior. Those gasses may be omitted from your device, or they may have been used up (depends on how much 'test' discharge the tube has seen). So, this behavior might not happen on an as-delivered device.
Maybe Barkhausen oscillation (aka the Barkhausen-Kurtz effect). This used to show up in old-fashioned incandescent light bulbs that were evacuated instead of argon-filled.
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 hobbs at electrooptical dot net http://electrooptical.net
according to a wikipedia article, the Barkhausen-Kurz oscillator used triodes. So I'm still puzzled. I'll try to make a test setup with constant current on a GDT and try to measure the frequency of the oscillation.
Frank
Not knowing Barkhausen-Kurz from Berkinstocks, I think Phil means it has to do with the time delay. Enough gain and a time delay leads to oscillations. (hmm just like in thermal control loops.)
George H.
You can get Barkhausen oscillations in light bulbs, as I said. If you have a spectrum analyzer, you can find out pretty fast.
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 hobbs at electrooptical dot net http://electrooptical.net
No, it's a coupled plasma/surface effect. It's really cool. It peaks down around a few tenths of a millitorr, but it's still appreciable at higher pressures.
The light bulb thing was discovered by somebody turning on an incandescent lamp and wiping out his reception.
I don't know if the pressure in the transient suppressor is low enough for Barkhausen--if not, it's probably the neon bulb oscillation as others have said.
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 hobbs at electrooptical dot net http://electrooptical.net
I do have one (of course, I'd say). My radio reception (hamradio bands) has never been disturbed by incandescent lights though (and it's about the only electric thing that doesn't make any RF nowadays). In the next days (as I find time) I'll try to run the transient suppressor with a small dc current and see if it oscillates (and at what frequency).
Thanks Frank IZ8DWF
Could I trouble you to disclose the maker and model of the gas discharge transient suppressor that you're testing, and the model number of the Heathkit curve tracer? I don't have a curve tracer but I do have a high voltage variable power supply that I can manually sweep to see if there are any negative resistance regions.
The manufacturers of gas discharge tubes should have something on the gas discharge tubes and negative resistance. Yep, the graph looks much like a neon lamp. The tube triggers at 75 to 600VDC, and rapidly drops to 15VDC.
I have a different guess(tm). When the gas discharge tube conducts, it effectively shorts the terminals of the device. I don't think your Heathkit curve tracer will not like a short circuit. It should have some kind of short circuit or overcurrent protection circuit which I would guess(tm) is doing the oscillating. Insert a large value resistor in series with the gas discharge tube and try again.
-- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558
According to Wikipedia: the gas pressure in a common light bulb is about 70 kPa or 525 torr. That's quite a bit higher than a few tenths of a millitorr.
I don't quite believe it. In the early daze of light bulb research, it was wrongly assumed that a better vacuum produced a better light bulb. So, early light bulbs had a fairly high vacuum, which might explain the RF interference, except that radio hadn't really become common at the time. Eventually, someone figure out that it was the water in the glass that was killing the filaments. Once the water was baked out of the glass, subsequent light bulbs had a much lower vacuum.
I don't think that the ceramic gas discharge tubes have a vacuum. More like they are under pressure in order to lower the conduction current. However, I'm guessing and don't have time to look it up right now.
-- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558
I don't know, I've pulled them out of a scrap PCB. They are marked as 201M TM4M (on two separate lines).
201 might be the discharge voltage which is in good agreement on what I see on the curve tracer.it's IT-3121, connected to an HP-1801A/180AR as display.
series resistor was already selected to limit the current peak value, it's a knob on the curve tracer. I've tried going from 5K to 50K and oscillation remains, of course peak current varies. Using 100K as series resistor doesn't make the tube ignite at all. Max voltage value on this curve tracer is around 240V. Do you mean I should add an external resistor? I believe it would just go in series with the internal one. Indeed these tubes are meant to adsorb transients, so once fired, their impedance could become very low, that would explain what I'm seeing. Frank
How exactly, if not Barkhausen? Hot wires don't produce a lot of RF IME.
If you read my original post, I pointed out that it was only the old fashioned evacuated bulbs that showed the effect, not the modern argon ones.
You don't want to reduce the conduction current in a gas suppressor tube, though, do you? My guess is that they'd be a torr or two, to get lower breakover voltage, which is on the high side for Barkhausen, for sure.
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 hobbs at electrooptical dot net http://electrooptical.net
Right, the argon-filled ones don't show the effect--the gas pressure is much too high. If the transient suppressor has that much gas in it, it definitely won't be Barkhausen oscillation.
I'll be interested in the results.
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 hobbs at electrooptical dot net http://electrooptical.net
Huh, OK... Get any sort of link? B-K tube,
Is it a surface plasmon thing?
Back to Frank, Can you do an I-V (at DC) to see if there is negative resistance. (i've never looked at a negative resistance so I don't really know if I'm asking the right question.)
George H.
All that I know is that someone allegedly turned on a light bulb which produced enough RF to wipe out their radio reception. My point was that until 1916, when Irving Langmuir invented the gas filled light bulb at GE, light bulbs were made with a sufficiently high vacuum to produce Barkhausen noises. The light would also need a tungsten filament, which was introduced in 1908. So, if the bulb really did produce noise, it would have to have been manufactured between 1908 and 1916. The Barkhausen effect was discovered in 1919, so the person flipping the light switch would have needed a pre-1916 light bulb, in order to call the noise Barkhausen Effect by running the test after
1919.Meanwhile the radio receivers of that era were crude at best consisting of coheres, magnetic detectors, cat whiskers, liquid diodes, and early triodes. Regular entertainment broadcasting didn't begin until 1922. Therefore, whatever was being broadcast between
1908 and 1916 would probable have been amateur radio or military signals. The receive technology lurched forward rapidly, but I suspect there was nothing worth listening to until the 1930's by which time all the light bulbs would probably have been gas filled.If not Barkhousen noise, the light switch could have caused an arc somewhere in the light circuit. It could have turned on something else in the circuit, such as a carbon arc lamp, which generates enough RF noise to clobber even the most deaf receivers of the day.
I'm also having problems believing that the weak paramagnetism of tungsten, can generate enough RF to be heard on the presumably AM LF (low frequency) receiver of the day. Also, I don't see why a high vacuum is required since there are several YouTube videos demonstrating the effect at 1 atm.
So, do I wrap some wire around an incandescent light bulb and feed it to my spectrum analyzer? Or, is this a waste of time with modern gas filled light bulbs?
I read that, which is why I'm questioning the timing. At the time when there were radio receivers sensitive enough to hear Barkhousen Effect noises, the light bulbs were all gas filled. Well, I guess the person flipping the switch might have been using an antique light bulb:
I wish I could xray the ceramic GDT and measure the spark gap spacing. My guess(tm) is that it's fairly wide at perhaps 1 mm, something similar to a common NE-2 neon lamp. I wouldn't need to have a hard vacuum in order to get a lower breakdown voltage when neon breaks down so easily. So, if I don't need a vacuum, and want plenty of ionized neon atoms to provide conduction, I would pressurize the tube with as much neon gas as I could cram into the package.
-- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558
I tried to identify the manufactory from the part numbers supplied. Nothing. I would agree that 201 might mean 200V discharge voltage.
I found one in my junk box inscribed Joslyn M-3 2204-44. I also couldn't find any specs on that device. I was going to try it on my hi-v power supply, but ran into 2 problem. The power supply is dead for no obvious reason. My workbench is currently being used to test my latest Harbor Freight purchase, a 1x30" belt sander suitable for sharpening all my dull kitchen knives. That's a priority project.
Schematic and operating instructions at:
On Pg 62 of the operations manual, it shows various display anomalies. Some are loops which look something like your photo. They suggest using the LOOP control to reduce the effect or lower the power supply voltage. You've probably already tried this, but I thought I would mention it anyway.
Yep. Resistor values from 0 to 1M. Aim towards the higher values here.
You might be too close to the conduction threshold on the tube. Hard to tell without specifications. If the device appears to fail to fire at high series resistances, it might have fired, dropped the voltage to about 15v across the tube, and stayed there. Grab a DVM and measure the voltage across the device. My guess(tm) is that it's about 15v and holding.
For fun, put a capacitor (300v or high) across the tube with a high series resistance and see if you can get it to oscillate as a relaxation oscillator.
For additional entertainment, replace the tube with a common NE-2 neon lamp and see if it does the same thing.
No. I didn't realize that there was a series resistor in the curve tracer. This switchable resistor should be sufficient.
Yep. Good luck.
-- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558
well yes, I could do that probably. I have a 300V DC source but it's not variable. I could try with resistor dividers and measure a few points.
Frank
Yes, I've tried the loop control but it doesn't change much of anything on that display.
the test voltage is a half waveform of the 50 Hz (in this part of the world) coming from a secondary winding and some transistor buffers. The voltage waveform is sent to the test probe and the X axis of the oscilloscope. So if the trace on the scope goes all the way to 240V, I think it's not firing. With 100K series resistor I can't see any vertical (current axis) movement even at 1mA division.
another thing to test, ok.
Frank
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nes.
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People do use old bulbs. A place I stayed in the 80s was still using 200w c arbon filament bulbs in the bathrooms to stop them freezing. Back in 1900is h nothing would have been thrown away. Even here I recently used a lamp tha t look like it was from the 60s or earlier.
ISTR being told 15w lamps stayed vacuum a very long time after 60 & 100w we nt gas filled, I don't know if that's correct or not.
NT
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