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.


> 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
> 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
> you want to measure). As it is a CURRENT transformer, you need also a
> to generate a voltage to measure at the secondary of the transformer:
> 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
> measure of secondary voltage. So I used the simple 10:1 probe connected
> 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
> 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...