RE: Spark Gap VI Scope Capture

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Lau, Gary by way of Terry Fritz <teslalist-at-qwest-dot-net>" <Gary.Lau-at-hp-dot-com>

Hi Terry:

Nice stuff, this is the stuff that fascinates me.

The negative and diminishing voltage offset that appears on the gap voltage 
is certainly odd.  One thing that strikes me is that there does not appear 
to be an identical ground shared between the low side of the gap and the HV 
probe.  Any difference between the "RF" ground and the scope signal ground 
would be seen as an offset, although I would have expected it to be more HF 
in nature.  I know, it's probably not a good idea to connect either side of 
a spark gap to the low side of a probe, but could this be affecting the 
reading?  Interesting that the quench coincides with the zero-offset point, 
but perhaps that's because the difference between the RF and scope grounds 
disappear then also?

Regards, Gary Lau
MA, USA


Hi All,

I figured out this way to look at the voltage across and the current
through a spark gap:

http://hot-streamer-dot-com/temp/2003-05-19-01.jpg

It is just a tank circuit charged with a high voltage DC power supply.  One
side of the gap is grounded through an RF ground.  A 100:1 Pearson 101
current monitor and a TEK6015 probe send the voltage and current to a
scope.  The power supply and scope probes and circuits are separately
grounded and well isolated so it is pretty safe for the scope.  It looks
like this:

http://hot-streamer-dot-com/temp/2003-05-19-02.jpg

http://hot-streamer-dot-com/temp/2003-05-19-03.jpg

The capacitor is really 24nF and the coil is 55uH for a resonant frequency
of 138.5kHz.  The firing voltage was set at around 3000 VDC.

The scope waveform looks like this:

http://hot-streamer-dot-com/temp/2003-05-19-04.jpg

If you pull it into Excel it is clearer:

http://hot-streamer-dot-com/temp/2003-05-19-05.jpg