Hi Bert,
I also had some doubts about to what extent the lead from the streamer
discharge to the resistor affected the result. It was a rather long lead,
which inevitably has reactance. I will follow your suggestion and use some
sheet metal that I have available for a counterpoise near the TC, and
connect the current sensing resistor to that for a much shorter ground
connection.
I will of course have to screen the resistor, voltage probe and connection
to the scope, when they are moved to within the streamer striking range. I
will also use a smaller value for the resistor, as I realized in retrospect
that I had overvoltaged the voltage probe slightly.
At this moment I am assembling a few current transformers for different
current and frequency ranges, in line with your other suggestion. The
problem with CT:s is the limited bandwidth, so you almost have to know
beforhand what you are about to measure. I can verify the low frequency end
with an audio amplifier, but it is difficult to verify the high end. But I
realized that my monster current impulses will be handy for that, I could
compare CT results to the current sensing resistor results on the two scope
channels.
I also want to measure the "steady state" streamer current, in between the
large impulses. It might not be so easy to detect what perhaps is mA
waveforms in the presence of kA impulses. My HV probe will just show noise
if I amplify the output side for detection of small voltages. Perhaps CT
measurement is a better way, I could perhaps use series resistors and
parallell diodes to clip out the high energy impulses before the scope
input. Or perhaps the impulses will saturate the core and not be
transmitted, if I choose a suitable CT.
I would also like to move on to measuring primary cap discharge current and
secondary bottom current, if that is possible with CT:s.
Thank you for the very useful comments,
Jan
Stockholm, Sweden
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