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# [TCML] Re: Pratical measurement of voltages and current on TCs

```Hi Joshua,
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There is a lot of information here on such things:
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https://hotstreamer.deanostoybox.com/TeslaCoils/MyPapers/MyPapers.htm
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Terry
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Sent:Â Saturday, December 04, 2021 at 7:53 PM
From:Â "Joshua Thomas" <joshuafthomas@xxxxxxxxx>
To:Â tcml@xxxxxxxxxxxxxxx
Subject:Â [TCML] Pratical measurement of voltages and current on TCs
Hello all,

SGTC. I have experience with measurement of sub-kilovolt equipment, but not
with the higher voltages a tesla coil produces. I would be interested in
hearing about the measurement equipment and connections that other coilers
have used.

Here are options I have thought of or considered.

Primary circuit voltage measurement: A potential transformer in series with
the circuit is likely to be the most accurate, but it is expensive; and I
expect the inductance of the transformer will change the coil resonance
frequency. A high-resistance voltage divider (more than 10 Gigaohm?) would
be simple to implement, should not change the resonance frequency by any
significant amount, and would draw very little current. However I am unsure
about what to use as the ground voltage reference of the divider. I use a
counterpoise system and I would expect it to have transient voltages which
might be large enough to damage voltmeters or scopes connected to it. My
other thought is to put in two dividers, one an each output rail, and
measure the differential voltage between them,

Primary circuit current measurement: The NST current is in the millamp
range. The problem isn't the current, it's still the voltage. I could put a
microamp meter on the voltage divider try to scale it appropriately. The
impediance of the meter might change the divider, but probally not if the
divider impediance is very large. The other option that comes to mind is a
current-sensing transformer, where one of the primary rails runs through a
toroidal transformer which scales the output to the input. I haven't used
these before and I'm not sure on the appropriate use.

Secondary circuit voltage and current measurement: The topload has
something like 300kV or more, and there's not really anywhere to tap into
that doesn't effect the circuit directly. My only guess here is remote
electrostatic sensing. I have absolutely no idea how to implement or
calibrate this. Definately interested in experiences from coilers.

Joshua

--
Joshua Thomas

My new email address is: joshuafthomas@xxxxxxxxx