Re: eddy current with secondary coil

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: Bart Anderson <classi6-at-classictesla-dot-com> 

Hi Antonio,

The plate I used below the coil was on the ground and connected to RF 
ground (just a conductive ground plate). The C measurement was taken with a 
27XT from top of coil to the ground plate (secondary is also tied to the 
plate). I agree, C should not read half sec C, but it is. I went back 
through the measurements again and they reacted just as before. I then 
started to see if was doing anything not stated. I then began messing with 
amplitude input from gen. to low-z amp. When I did this, the meters 
capacitance reading changed. With the righ adjustment of base voltage, I 
can get the meter to react with and without topload as shown, but also, if 
I tweek the amplitude higher or lower, the meter won't react. Apparently an 
impedance condition is met given all the equipment, coil, meter, etc.. I 
didn't mess with the amplitude, so it must be luck that it was adjusted to 
what the meter would react to and that the values changed as they did (odd 
it worked out as it did). It must have been adjusted just to the edge of 
where the meter would barely react with the topload. The removal of the 
topload and the greater meter reaction is also interesting in that it to 
read less capacitance. I just am so use to looking at Ces and Les these 
days I didn't think to give it too much thought. Regardless of numbers I 
found, I have to say the test is completely invalid regardless of the 
agreement that worked out. Anytime we disturb the distribution, especially 
with a direct connection, all bets are off on these measurements. Hard to 
question something when it just appears to come out right and agree on a 
first run.

Well, thankfully Terry did all those base current measurements for Paul 
which helped Paul verify much of the data. That is something I haven't done 
with this little coil but should. Maybe there's an optics approach as well 
which could be done.

Take care,
Bart


Tesla list wrote:

>Original poster: "Antonio Carlos M. de Queiroz" <acmq-at-compuland-dot-com.br>
>Tesla list wrote:
>
> > Original poster: Bart Anderson <classi6-at-classictesla-dot-com>
>
> > I set up a counterpoise under the coil. I leave the coil completely set up
> > and short the gap. I use the planewave for the Fres measurement to the
> > scope. I drive the coil with the generator with the low-z amp (which has
> > just become my typical drive approach).
>
> >From the base of the secondary?
>
> > The generator is adjusted for Fres.
> > C is measured between topload or top of coil and counterpoise.
>
>With the secondary coil removed, or disconnected?
>
> > C will
> > measure 1/2 the capacitance.
>
>Why? Which capacitance? The "self-capacitance" of the secondary can't
>be directly measured with a normal capacitance meter.
>(But a measurement of the capacitance between a coil, suspended high
>above the ground and the ground (counterpoise) measures about twice
>the Medhurst capacitance, what makes sense.)
>A measurement of the capacitance between the coil connected to the
>topload but insulated from the counterpoise and the counterpoise
>would result in a higher capacitance.
>
>L is solved from Fres and C. There is some
> > loading due to the direct C measurement, but the results match the model
> > well and show the affect on L and C.
>
>Ok, but it's not clear how did you measure the effective capacitance
>of the coil+topload.
>
> > Since Javatc can model the change in L and C, I'll show measured and
> > modeled numbers.
> >
> > The coil driven at Fres unloaded w/counterpoise in place:
> > Measured:                   Modeled:
> > 418 kHz                     419.8 kHz
> > 5.3 x 2 = 10.6 pF            9.87 pF
>
>This x 2 is strange.
>
>Antonio Carlos M. de Queiroz
>
>
>
>