# Secondary voltage measurement.

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From: 	terryf-at-verinet-dot-com[SMTP:terryf-at-verinet-dot-com]
Sent: 	Friday, September 19, 1997 2:46 PM
To: 	tesla-at-pupman-dot-com
Subject: 	Secondary voltage measurement.

I seek to measure the voltage, current, and phase angle waveforms of
the output of a Tesla coil in real time while it is arcing and doing its
thing.  (You may all laugh now!)  My present methode of attack is using
voltage and current probes under the top electrode.  These are connected to
the sane world through fiber-optic cables.  Looks like the current probe
will be straight forward.  The voltage probe has that nasty problem of
ground reference.  May need mutiple voltage probes along the secondary
spaced in some mathematical series to get the real top voltage during an
arc.  I am asking for any info, thoughts, comments, ect. on the following
questions:

1.      Any idea of what I might find up there?  Field strengths, current
levels, voltage dv/dt,.......  I am planning on a 100A current probe between
the secondary and the top terminal.  The voltage probe will be an inductive
loop near the top of the secondary.  (maybe 2kV max?) I am worried that
durring an arc, that loop may see really nasty voltages.  It will be
protected against this but it won't be able to measure when this protection
kicks in.  I basicaly just want to design for about the right levels.

2.      Does fiber-optic cable flouresce under high E-feilds?  It is

3.      Any ideas on what might happen to the voltage distribution along the
secondary inductor (during and arc) would be useful (I realize it's not
pretty).  Any ideas on what kinds and frequencies of harmonics would help
when designing for bandwidth.

4.      Any coments or other experinces good or bad would be very welcome.
Anything I should know????

I was working on a more conventional voltage probe but it would add about
15pf to the secondarys internal capacitance.  This would require retuning
and would materially change the coil's true output.  It feel it would work
with these limitations, however and probably give useful information.  For
the time being I have stopped work on this probe.  It also requred about 1.6
gal of oil for insulation (I hate oil!).  I hope the fiber-optic probe will
work.  It would have many many advantages.

If these do end up working I will post the plans and results.  It all costs
about \$75  (not including the test equipment it plugs into).  If anyone is
intersted in the old voltage probe idea, I can also provide details on it.
Someone may want to play with this.  If the fiber-optic probes fry, it will
be me :-)

You can E-mail me at "terryf-at-verinet-dot-com" or reply to the group if of
general interest.

Thanks very much for your help.

Terry

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