Re: Measuring self-capacitance directly (Re: flat secondary)

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Original poster: "Metlicka Marc by way of Terry Fritz <twftesla-at-qwest-dot-net>" <mystuffs-at-orwell-dot-net>



Tesla list wrote:
> 
> Original poster: "Malcolm Watts by way of Terry Fritz
<twftesla-at-qwest-dot-net>" <m.j.watts-at-massey.ac.nz>
> 
> Hi Marc,

Hello Malcolm,
I use aluminum "gutter guard" which is an expanded aluminum screen ,
that i cut three lengths of that equal the height of the coil. I place
these in a star like pattern or three legged cross on the carpet bellow.
I try to put each coil 3" above because this is the usual height that i
start my windings, if less then i use spacers.
  I worried about doing this with the 20" flat coil for just the reason
you mentioned, If a bigger plate is used i might get higher c readings?
Oddly enough I only get higher c readings if i raise the coil, size of
the grid makes very little difference (unless i make it very small).
 I unhook the dedicated earth ground for selfc readings, my thinking was
that i only wanted to measure the c of the effective plate of the
windings, I also thought that even if the grid plate was huge i should
get accurate readings because the effective c of a two plate capacitor
is only as much as the area of the smaller plate? 
 The twisted pair leads have one wire as the test lead and the other is
connected to the bridge chassis ground, unconnected at the other end.
This idea came from reading about some leads used on a fancy l-c-r meter
and as Antonio mentioned, it may not be optimum, i will try with a set
of single wire leads tonight. I do notice that while position of single
wire leads does effect readings, the twisted pair doesn't seem to?
I don't think i would take these readings to heart until some others can
confirm, They are simply something i wished to try, mostly for toploadC
readings?
I hope this helps,
Marc M.


(As a side note:)
The aluminum gutter guard i get a home depot, It seems to work very well
as a toroid covering. I have covered a couple old toroids with it and am
planning on building a wood frame model soon, It stretches, bends,
tweaks, forms and shrinks if rubbed, very nicely. Kinda like chicken
wire for dwarf chickens?
Just thought i would toss this in the ring
 

> 
> Am I to understand that during measurement, the coil is located
> really close to a ground plane of sorts? Unless I'm mistaken, you'll
> be measuring the capacitance of a rather large flat plate capacitor.
> Could you confirm please?
> 
> Thanks,
> Malcolm
> 
> > I have also found that i can get fairly accurate toploadC readings
> > reading without and then with the topload in place, I first tried this
> > last year while getting tssp measurements, mostly because i didn't know
> > it wouldn't work?
> > I'm not quite convinced of the accuracy yet, but i seems good so far.
> > Take care,
> > Marc M.
> >
> >
> >
> >