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Re: high voltage probes



Original poster: "Jim Lux" <jimlux-at-earthlink-dot-net> 

A water resistor makes a good load/probe for a Marx.  You can stand the pipe
vertically, and put  the probe in at the side.. Make the water resistor
something like 50:1 (i.e. if it's 50 inches tall, put the probe 1" from the
bottom) and then use a normal HV probe to get it in range for your scope.

You can capacitively couple out of the resistor too.. a splotch of copper
foil tape stuck to the outside of the water resistor works dandy.
Calibration and compensation's not too hot, but if what you're interested is
rough stuff like rise/fall time and voltage, it'll work ok.

----- Original Message -----
From: "Tesla list" <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Saturday, September 27, 2003 4:05 PM
Subject: Re: high voltage probes


 > Original poster: Terry Fritz <teslalist-at-twfpowerelectronics-dot-com>
 >
 > Hi Mark,
 >
 > Consider "water resistors".  Or, plane wave antenna.  Just make a little
 > flat "transmitter" antenna to get a better signal off what you want to
read.
 >
 > Directly connecting the Marx is scarry since the voltages and currents are
 > so high that no ground can be trusted. Use a cheapo E-bay scope with lots
 > of big MOVs on the power and stuff ;-))  I would simply "plan" on it going
 > bad...  But once you get it going, it will seem easy ;-))  If the scope
 > eats the output, it will also go right into the AC wiring as it happily
 > cremates the scope.  So work on protecting the AC line stuff real
 > well.  Might even consider running off a cheap old UPS power source....
 >
 > Cheers,
 >
 >          Terry
 >
 >
 > At 05:44 PM 9/27/2003 -0500, you wrote:
 > >I have a desire to hook our small Marx Generator up to an oscilloscope to
 > >view the waveform across the rectifier during the discharge event.  A
 > >while back we overvolted a 32kV rectifier we were using at "low voltage"
 > >with only a little over 10kV cap charge.  In theory, only 20kVmax should
 > >have existed across the rectifier.  I don't want a similar event with the
 > >final 55kV rectifier when we run it at full voltage off a 15/30 NST.
 > >
 > >I was thinking of just making a 1000:1 resistive divider, which would
work
 > >for low frequency/DC, but I don't know how well that would work with the
 > >MHz hash in the discharge.  Any opinions from the crowd?  I don't expect
 > >the need to measure more than 25kV.
 > >
 > >Thanks!
 > >
 > >Mark Broker
 > >Chief Engineer, The Geek Group
 >
 >