I also have a hell machine for making high voltage discharges.
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I also have a Beckman 50kV high voltage divider probe for high voltage linemen, similar to this.
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What I would like to do, is capture on the oscilloscope screen, the waveform of the occurring discharge. I want to keep it for a while to be able to get to the scope and take a photograph.
I only used my scope before for watching continuous waveforms, never for one shot.
I guess my main question is does anyone know how to trigger the scope by the discharge and then let it keep the waveform on the screen, is that even possible with 2235.
Looks great - I built something similar 10 years ago by taking
200 electrolytic capacitors used in electronic flash lights,
300uF/300V each. I connected them to give me a 6uF/30000V capacitor which I charged using a Tesla transformer and a diode (took round about 1 minute). With this you are easily able to generate "exploding wire discharges" of 1m length and more with a very nice BANG!
Very helpful in checking whether there is still dangerous charge present.
Hm, you want to monitor the voltage? Is'nt current much more interesting?
From my experience it is not easy even to "define" voltage during the discharge since even 1mm^2 wires have substantial voltage loss due to their resistance and inductivity. I think current can be measured more easy by building a magnetic pickup (thus measuring the magnetic field). In this way there is no need to connect the measurement equipment (and possibly you) to the "hot" wires. Triggering of the oscilloscope should be possible by using a photo diode, monitoring the flash - but in this case your analog scope might miss the first fractions of a us of the discharge.
I think nearly every scope can be triggered externally...
Well, I think a standard current probe will not have high enough current capability since I expect more than 1000A ushing out of the capacitors - at least if no pulse shaping network is used and inductivity is small (i.e. no long cabling).
Regarding lightning discharge (See the book "Lightning Discharge" from Martin A. Uman), there one encounters rise times (0 to peak current) of several us and the current decays in roundabout 50us (Statistical values!). Peak currents of 30000A are regularly observed.
BTW: researchers investigating lightning discharge measure the electric field using a "field mill", the magnetic field using antennas or the lightning flash using photo sensors or streak cameras.
No of them seems to use a shunt resistor ;-)
Ignoramus, please keep us up to date what your measurements revealed...
Or just use a current probe. Now more than a few years ago, I had a problem popping metal fuses on a chip and decided to set up a storage scope and current probe to understand what exactly was happening on the wafer. I was amazed to see the metal fuse pop in around a microsecond. A wire wouldn't pop as fast, but if you told me 100us, I'd believe it. In fact, lightning strikes are faster.
I did similar things with a driver going into secondary breakdown using a Tektronix Transient Digitizer. Under program control I upped the energy until the device failed. I could then read out the results (current and voltage probe) to calculate the energy needed. It would have taken a pile of film since I wanted to edge up on it without destroying the device.
BTW, I proved only one manufacturer's part would go into secondary breakdown without avalanching first. It was the only one for which we had fire-in-the-field too.
Bottom line, I think you're going to need some sort of a digital oscilloscope. Depending on how long the discharge is you may need something like a Transient Digitizer.
500v seem common enough. I gues at such high voltages the techniques to increase surface area/capacitance would not work with such a necesseraly large effective gap distance.
Not to mention the probable explosive effects of catastrophic failure due to localised breakdowns of the gap !
Yes, I think I forgot to scale the task at hand. ;-) However, couldn't you inductively couple the signal to the current probe? That is have a loop near the line being blown and also have it clamped by the current probe. That should step down the current and not significantly effect the timing.
I've read up on lightning a bit, though not that particular book. I've always heard that that lightning goes from the ground up to the sky. However, the initial strike (I forget the technical term) starts from the sky and heads to the ground. It is only 200A versus 200000A of the return strike (the visible one). This initial strike is indeed in the
1uS range with pauses between current flow of 50us.
Might as well dig up the link:
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Stepped leader was the phrase I couldn't recall. I found a NASA paper indicating that the stepped leader is easily detected at around 66Mhz. Now most people think of lightning detection as an issue with MW radio (i.e. AM BCB), but I suppose it is really more of a function of demod (AM versus FM). The next time I'm in the general area of a lightning storm, I'll try tuning around 66MHz with a communications receiver, so I can force AM demod. .
I too want to see Ignoramus' results, but hope he doesn't live up to his moniker.
BTW, I've seen two ground strikes at a reasonably close distance (say under a mile). While lightning has that bluish tint due to the ionization of nitrogen, what you see on the ground is very yellow. I suspect sodium in the ground is being ionized.
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