I read in sci.electronics.design that Terry Pinnell terrypinDELETE@dial
..pipexTHIS.com wrote (in )
about 'Winding coils', on Sun, 7 Dec 2003:
John Devereux wrote:

Bill Turner writes:

On 6 Dec 2003 13:39:51 -0800, Winfield Hill
wrote:

We're talking a small air-coil here.

Doesn't matter what kind of coil; all coils have a non-linear plot of
either inductance vs frequency OR reactance vs frequency. ALL coils.

Well, just about anything is "non-linear" if you measure it accurately
enough! But is it really true that the *inductance* of a "small air
coil" is "dramatically" non-linear with frequency as you stated?

Intuitively I'd have thought the answer was plainly No, but I'm
certainly not technically savvy enough to be confident about that. But
I strongly suspect that the thread is already ovedue an unambiguous
definition of 'inductance'. Where's John Woodgate when you really need
him...g.

I'm here today, but I was away all last week. I don't think I can add
much; small air-cored coils have inductance independent of frequency up
to about half the self-resonant frequency, when deviation begins to be
noticeable. Low-frequency iron-cored coils are quite another matter; the
inductance varies with frequency, voltage, temperature, previous history
and the state of the tide on Europa. Also, it comes in two varieties,
series equivalent and shunt equivalent, and you'd better get the right
one for your problem. As the inductor gets 'worse', at lower
frequencies, the shunt equivalent tends to infinity, which puzzles
students no end.
--
Regards, John Woodgate, OOO - Own Opinions Only. http://www.jmwa.demon.co.uk
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