Hi Joshua,
A home made resistor voltage divider is not practical, stray capacitance will dominate at ac, so it will be grossly inaccurate. The cheapest HV diff probe that I know of is the Caltec ct4079, but it is still a big investment.
In the case of a pig driven coil, the primary of the pig tracks the secondary voltage very closely and can be measured with a much cheaper HV diff probe, like the Micsig DP10013. But as the ballast is a part of a NST, this method is not feasible for a NST coil.
Current can easily be measured by a current transformer. You can make these yourself using a toroidal ferrite core with a winding, and loading the winding with a resistor. Frequency linearity can be tested with an audio amplifiera loaded with a resistor, fed by a signal generator.
I have some measurements on my web site https://www.sthlmteslacoil.se/measurements.html
You can find information about making you own current transformer on the web. But selet the core for the frequency range, and dont forget to load the winding with a low value resistor.
But voltage measurement is not possible without an expensive HV diff probe. Another NST backwards would be theoretically possible, but I think all the extra inductance would change everything to the extent that it would be meaningless.
Regards,
Jan
Skickat från min iPad
> 5 dec. 2021 kl. 05:18 skrev Joshua Thomas <joshuafthomas@xxxxxxxxx>:
>
> Hello all,
>
> I'm starting to think ahead about connecting measurement equipment to my
> 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.
>
> Thanks in advance,
> Joshua
>
>
> --
> Joshua Thomas
>
> My new email address is: joshuafthomas@xxxxxxxxx
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