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Re: Variable Capacitance and Inductance / Tempco of Copper

Original poster: "David Sharpe by way of Terry Fritz <twftesla-at-qwest-dot-net>" <sccr4us-at-erols-dot-com>

Barton, Dave

Keep in mind that copper has a tempco (temperature coefficient
of resistance) of +0.3937% per deg C, that is resistance would go
up by a delta upward, and down by a delta downward change
from "baseline"by amount mentioned above.  Would have a bearing
on Q measurements of the coil, in addition to geometry changes

Dave Sharpe, TCBOR
Chesterfield, VA. USA

Tesla list wrote:

> Original poster: "Barton B. Anderson by way of Terry Fritz
<twftesla-at-qwest-dot-net>" <tesla123-at-pacbell-dot-net>
> Hi Dave,
> I made a temperature  test today on a small coil (1" x 5"). Inductance
> measured before any temp
> change was 405uH and unchanging on the meter. Using hair dryer I measured
> 407uH stable. As I let it
> cool, it dropped back down - stable. I then put it in the freezer for a
> little while. Measured
> 411uH. It went back to 405uH at room temp. Capacitance couldn't be measured
> by the meter.
> Thermal expansion as Terry mentioned is all I'm saying. Temp changes both L
> and C because the
> object physically changes - this should be easily understood. Also, the
> amount of changes depends
> on the L and C value based on the objects size and amount of physical
> change. Usually, pretty
> small.
> Humidity affects walls and other objects which can become greatly more
> conductive in humid
> conditions. If the walls or whatever is conductive or significantly changed
> in conductance by water
> saturation, you're not going to see a defining change. As far as that goes,
> the object itself isn't
> what is changing, but the capacitive affects of objects to test object (not
> the test object itself
> unless the environment causes a physical change). The proximity has much to
> do with how much change
> you will measure. A huge coil in a small bath room will show a greater
> change than a small coil in
> the same bathroom (capacitive affects). That's all I'm saying. This is
> known - has been known a
> long time. We see this change occur all the time. If Tesla was discussing
> vibration, then he is
> discussing frequency measurements we know changes with proximity to
> external conductive objects.
> Take care,
> Bart
> Tesla list wrote:
> > Original poster: "David Thomson by way of Terry Fritz
> <twftesla-at-qwest-dot-net>" <dave-at-volantis-dot-org>
> >
> > Hi Bart,
> >
> > Thanks for pointing out the transformer error.  It's important to know
> > errors.  Especially for measurements off by the magnitude you were showing.
> >
> > Have you tried putting a hair dryer to your coil to see if temperature
> > affects it?  Even with a 100 degree temperature variation, I had no
> > inductance variation.  I'm going to put my coil in the shower today to see
> > how humidity affects it.  I'd like to know for sure whether temperature or
> > humidity are directly responsible for variations in coil inductance.
> >
> > Dave