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Re: Variable Capacitance and Inductance

Original poster: "davep by way of Terry Fritz <twftesla-at-qwest-dot-net>" <davep-at-quik-dot-com>

>>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.

>> 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.
> Temperature alone cannot explain the larger variations in inductance
> measurements reported over the years by various persons,

	Are the reports reliable, and repeatable?
	The first step in investigation is to see if the
	'question' is real.

> especially since temperature variations in the coils are likely

> rarely to exceed 50F degrees.

	1) The change will depend critically on material, notably
	of coil form.

	2) Depending on the application, 50F change is a minimum.

> 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.

	I fail to see why.
	These components have been in use for 100 years.
	Their characteristics are well known and documented.
	There are minimal effects form 'the electrostatic
	and electromagnetic environment'.
	This is a common part of engineering and physics training.
	I don't think its really apropos to go into in depth here.
	cf any text on the subject(s).

	All electronics involves putting caps and inductors in
	'the electrostatic and electromagnetic environment'.  If
	there were significant changes caused by this environment
	it would be noticed.

	There are effects, well understood, from high mag fields

	(eg next to large transformers,) these involve the
	appearance of stray voltages (currents) rather than
	changes in (effective or actual) inductance or
	capacitance.  Analogous events occur with capacitance.

	Such stray currents/voltages can fool meters, if
	incautiously used.