Tracing exploding wire waveform with Tek 2235

[Ignoramus24570]

I have a Tektronix 2235 scope.

http://igor.chudov.com/projects/Homemade-TIG-DC-to-AC-Inverter/01-Prototype-1/dscf0005.jpg

I also have a hell machine for making high voltage discharges.

http://igor.chudov.com/projects/High-Voltage/Hell-Machine-THUMPER/

I also have a Beckman 50kV high voltage divider probe for high voltage
linemen, similar to this.

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=130053095020

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.

thanks

i

 

[Erik Baigar]

I have a Tektronix 2235 scope.
http://igor.chudov.com/projects/Homemade-TIG-DC-to-AC-Inverter/01-Prototype-1/dscf0005.jpg
I also have a hell machine for making high voltage discharges.

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!

I also have a Beckman 50kV high voltage divider probe for high voltage
linemen, similar to this.

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=130053095020

Very helpful in checking whether there is still
dangerous charge present.

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.

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 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.

I think nearly every scope can be triggered externally...

Be careful in your experiments,

best regards,

Erik.

 

[scada]

I have a Tektronix 2235 scope.

http://igor.chudov.com/projects/Homemade-TIG-DC-to-AC-Inverter/01-Prototype-1/dscf0005.jpg

I also have a hell machine for making high voltage discharges.

http://igor.chudov.com/projects/High-Voltage/Hell-Machine-THUMPER/

I also have a Beckman 50kV high voltage divider probe for high voltage
linemen, similar to this.

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=130053095020

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.

thanks

i

If using a CRT scope, it would need to be a storage Scope. Most digital
scopes can also store captures. Your Tek scope does not appear to be either.

 

[Erik Baigar]

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.

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...

Best regards,

Erik.

 

[[email protected]]

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.

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.

 

[Roger_Nickel]

If using a CRT scope, it would need to be a storage Scope. Most digital
scopes can also store captures. Your Tek scope does not appear to be either.

Maybe he can find a oscilliscope camera for his old Tek?. Getting hold of
the polaroid film could be a problem....

 

[Jim Yanik]

Maybe he can find a oscilliscope camera for his old Tek?. Getting hold
of the polaroid film could be a problem....

use a VCR and a small B&W camera,or a camcorder.

 

[krw]

I have a Tektronix 2235 scope.

http://igor.chudov.com/projects/Homemade-TIG-DC-to-AC-Inverter/01-Prototype-1/dscf0005.jpg

I also have a hell machine for making high voltage discharges.

http://igor.chudov.com/projects/High-Voltage/Hell-Machine-THUMPER/

I also have a Beckman 50kV high voltage divider probe for high voltage
linemen, similar to this.

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=130053095020

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.

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.

 

[colin]

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!

I wonder do/could they make 30kv electrolytics ?
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 !

Colin =^.^=

 

[[email protected]]

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).

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.

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

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:
http://hyperphysics.phy-astr.gsu.edu/hbase/electric/lightning2.html
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. .

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...

Best regards,

Erik.

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.