On 2/27/18 7:28 AM, Carl Noggle wrote:
Has anybody tried putting a many-stage RC ladder voltage divider down the center of the secondary? The E field is uniform (vertical) there, and there's probably not much space charge. I keep thinking about it, but I haven't tried it yet. Maybe a string of 20 M Allen-Bradley 2W resistors with some HV ceramic caps in parallel. The time constant should be at least 10 times the time of one cycle, 10pF or so.
This might work. Say you've got a coil that's a meter/36" tall - You need to pick non-inductive resistors, which might be a challenge, but let's just say that you find them, and they're 1/2" long, so you can fit 75 of them. 75*20 = 1500Meg, with a 15 Meg bottom resistor, that gives you a 100:1 divider
How much current flows in that 1500 Meg resistor at 500kV - ohh about 1/3 mA, which is, I think, a lot. The stack would dissipate 167 watts.
So you need something bigger than 20 Meg to keep the dissipation reasonable.. Say 200 Meg, so now the divider dissipates <20W.
It could be that due to the well-behaved field inside the secondary, that we could dispense with the capacitors and use a long CuSO4 resistor. Be sure to use copper end plugs and measure it often, since chemistry enters into the equation.
Or conductive/dissipative paint - your scope probe should present a 1Meg impedance, and with 1:10,000 ratio, 500kV puts 50V on the scope. That implies the "resistor" should be 10,000 * 1 Meg or 10 Gohms
It's easier to measure the voltage of a Marx, since the output impedance is quite low. Usually some sort of geometrically-calibratable capacitive divider is used.--- Carl On 2/27/2018 6:27 AM, jimlux wrote:On 2/26/18 8:42 PM, Bert Hickman wrote:Chris,It's a very challenging design problem. And, the divider will be quite sensitive to changes in the surrounding E-field. Since TC sparks create shifting space charge regions with corresponding fluctuating E-fields in the surrounding air, accurate direct measurements can be done only if the Tesla coil is not actively creating streamers/leaders.you might look at commercial products made from this: Not a lot of design info, buthttp://www.rossengineeringcorp.com/products/measurement/hv-voltage-dividers.htmlis an example.I'm sure there's stuff out there about designing a divider to work with the output of a Marx at megavolt levels - way above what a TC will put out._______________________________________________ Tesla mailing list Tesla@xxxxxxxxxxxxxxxxxx https://www.pupman.com/mailman/listinfo/tesla_______________________________________________ Tesla mailing list Tesla@xxxxxxxxxxxxxxxxxx https://www.pupman.com/mailman/listinfo/tesla
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