FWIW - There is a pretty definitive method of measuring an inductor which
will
yield its low freq inductance , its self resonant frequency , and the
distributed capacitance.
It is normally done with a Q meter but can be done with any instrument with
variable freq below the self resoannt freq that will show what capacitance
is required to resonate that inductor at that frequency.
Just measure capacitance to resonate at several freqs well below the self
resonant freq - theoretically two freqs will do but I prefer three or four
as a check that nothing screwy is going on .
Then plot C to resonate on the vertical scale and plot 1/f squared on the
horizontal axis. The points will (or should) fall in a straight line. If
not , an average thru the points will get you very close. The line will
intersect the vertical axis and that point is the distributed capacitance.
The intersection with the horizontal axis is the self resonant frequency
(zero external capacitance to resonate)
The slope of the line is the low frequency or "true" inductance.
Dunno if I can do this equation but here goes.
Basically you take a region of the sloped line and read off a change in 1/(f
squared) for a change in capacitance to resonate (Delta 1/F^2) and (Delta
C)
Then L is 1 /(4 pi squared X Delta C / Delta 1/F^2).
Or , if you want to know the "apparent" inductance at any frequency then
read off C to resonate at that frequency , and using the Co or distributed
capacitance at the intercept the L apparent is L(1+ Co/C)
If you just want the self capacitance - two frequencies , one twice the
other - F1 (C1 to resonate ) and 2F1(C2 to resonate) can be used to
calculate
self capacitance = (C1-4C2)/3 .
If I still had my web site I could put this on it but Qwest in their
infinite customer service wisdom dropped us .
Ancient ancient history when we did not have all the fancy instruments of
today .
Hank K7HP
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