Re: Variable Capacitance and Inductance

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

Original poster: "Barton B. Anderson by way of Terry Fritz <twftesla-at-qwest-dot-net>" <tesla123-at-pacbell-dot-net>

Hi Dave,

Tesla list wrote:

> Original poster: "David Thomson by way of Terry Fritz
<twftesla-at-qwest-dot-net>" <dave-at-volantis-dot-org>
>
> The coil I used was 4.5" diameter by 9.625" length, sealed with several
> coats of polyurethane, and wound with 21 gage magnet wire.  I'm presently
> bringing the temperature up to 150F degrees in an oven and will measure the
> inductance as it cools to room temperature.

The coil I used was not coated - by choice. I just wanted to see change via
physical movement with
regards to thermal expansion. But, I don't even trust my measurement (it's
so small, it could be in
the meter).

> Temperature alone cannot explain the larger variations in inductance
> measurements reported over the years by various persons, especially since
> temperature variations in the coils are likely rarely to exceed 50F degrees.

I agree. I suspect any reports of large changes in L are speculative. I may
be wrong. I'm no expert
at any of this.

> Essentially what you are saying then is that humidity alters the negative
> ion to positive ion ratio in a given environment?  Obviously the walls are
> not conducting in the sense of current.  But the walls could be conducting
> in the sense that they change to a greater or lesser charge.  This change in
> wall charge is what would affect the capacitance of an object nearby?

All I'm trying to say is when we measure for C, we measure both internal
and external capacitance
at the same time (we don't have choice - the best we can do is get away
from everything and try to
eliminate as much external as possible).

> Variations in inductance measurements can mean the effective (and
> thus real) inductance of the coil is variable.

I'll have to think about that one.

> The environment of the coil is just as crucial to the coil's operation as
> the coil itself.  The same goes for capacitors.  And since the coil and
> capacitor are electromagnetic devices, we should be looking more at the
> electromagnetic and electrostatic environment, not merely the secondary
> environment of temperature and humidity.

Well, yes of course. There are lots of external causes which can be looked
at. I'm not sure how
crucial it all is for coiling. The bottom line for coiling is external
influences are there - tune
accordingly.

Take care,
Bart