From: mystuffs@orwell.net (Metlicka Marc)
Date: Tue, 26 Dec 2000 15:20:39 -0500
Subject: Re: [TSSP] Capacitance between primary and secondary
wasn't trying to be a smart alic or anything (actually was a little intimidated to
say anything at all?)
"Terrell W. Fritz" wrote:
> Hi Marc,
>
> I was wondering if anyone would notice that ;-)) I played around with
> positioning and wire lengths and it turned out that having the meter on the
> primary with really short wires gave the best readings. It is devilishly
> hard to measure down to the pFs with something like this, but this is the
> best I could come up with. I tried spacing the meter with wood and such
> but it didn't change anything. I think the meter is pretty hollow on the
> bottom with the terminals leading down there.
i'm thinking it's not so much the meter being ON the primary or the fact that it's
hollow on the bottom, but it's the matter of a conductor placed in the area of the
non conductor. adding another plate to a capacitor so to speak.
now that you have an idea of what capacitance ranges you need, how about using a
pico farad cap as a standard and using a cap bridge to read the differences for the
actual?
i'm about ready to set up some of my coils tonight for some of the same
measurements as you have done, i'll do the meter like you did and then check with
another meter to see how much difference the first meter in place makes. then i'll
try the cap bridge using the cap standard test i spoke of. i have a couple real
nice cap bridges. my general radio 1611-as2 is very precise and accurate and i can
tune out any effect of the leads.
>
>
> I suspect the measurements could be like 10% off from the true values but I
> don't have a ways to measure these tiny capacitances more accurately where
> "everything" affects the readings.
i thought about the 10% that paul mentioned last night and now you and it does
bring everything in about right, just not sure how accurate of readings we are
looking for here?
i'm excited about getting started with all this though. did you physically count
the turns on your secondary? did you measure your inductance's or just calculate
them?
marc
>
>
> Cheers,
>
> Terry
>
> At 02:16 AM 12/26/2000 -0500, you wrote:
> >paul, terry, all
> >in the discrepancies between terry's c and Paul's calculated c values i
> noticed
> >in terry's pictures that his meter was setting on the primary itself. could
> >this be causing an added c to the 0 height value, and then also at the 15"
> >height difference, the meter may be pulling c and therefor causing a less then
> >calculated value? maybe a test using two meters, one connected with longer
> >leads and placed away and then trying a measurement with the first meter
> in the
> >field and then out of the field could show something?
> >marc
> >
> >Paul wrote:
> >
> >> Terry Fritz wrote (on tesla list):
> >>
> >> > I retook the physical measurements of my coil and measured the
> >> > capacitance from primary to secondary.
> >> >
> snip...
Maintainer Paul Nicholson, paul@abelian.demon.co.uk.