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Re: Scope pictures of my TC: how I did it
to: Marco
For sec Hv measuring as follows:
Use a reasonable large sphere (20-60 cm dia). Apply a piece of insulating
tape to an area of the sphere. Attach some aluminum foil or piece of metal
to this tape leaving a 1 inch margin all around. Area required approx 20
cm squared. Hook a shielded pickup wire to the piece of metal and the
ground side to the large sphere. Run this shielded cable back to your
scope and thru a 5 ohm resistor. This forms a nice capacitive pickup that
can be calibrated against another source for peak HV readings. Sphere is
of course grounded.
Dr.Resonance-at-next-wave-dot-net
----------
> From: Tesla List <tesla-at-pupman-dot-com>
> To: tesla-at-pupman-dot-com
> Subject: Scope pictures of my TC: how I did it
> Date: Tuesday, January 26, 1999 5:08 AM
>
> Original Poster: "Marco Denicolai" <Marco.Denicolai-at-tellabs.fi>
>
> Last saturday I measured my TC with a scope. I got:
>
> - primary current
> - primary voltage
> - secondary voltage
> - secondary base current
>
> A great simplification was that at the laboratory were I performed the
> measurements they had a really huge ground (it's the Helsinki High
Voltage
> Institute). This means I could use the same ground for everything,
> including secondary, tank and oscilloscope.
>
> Primary and secondary (base) currents I measured with a "current
> transformer" (a toroid you just pass through the wire carrying the
current
> you want to measure). As it is a CURRENT transformer, you need also a
shunt
> to generate a voltage to measure at the secondary of the transformer:
note,
> you are galvanically isolated from the circuit you are measuring.
>
> The primary voltage I measured directly with a HV probe (10 kV,
> Tektroniks).
>
> For the secondary voltage, even if they had plenty of capacitive and
> resistive dividers they were all in use that time and the target of my
> measure was more to find out about power consumption than to have an
exact
> measure of secondary voltage. So I used the simple 10:1 probe connected
to
> nowhere and hanging at about 180 cm from the toroid: I was reading there
> about 50 V (!). That gave a measure of the electric field (I guess)
> magnitude and, thus, indirectly of the secondary voltage.
> This seemed to be true only if there were no streamers: if a streamer was
> born, the secondary current would oscillate down as expected but the
> "electric field" would drop down suddenly to zero. I guess that the
> explanation could be that the streamer loading dumps the electric field
(or
> RF emission?) so that you can't measure it anymore with the flying probe
> (you need to really go and touch the toroid).
>
> But more in the near future...
>
>
>
>