Re: Gary's inductance measurement Was: Inexpensive LCR-Multime ter

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

Original poster: "by way of Terry Fritz <teslalist-at-qwest-dot-net>" <Mddeming-at-aol-dot-com>

In a message dated 1/9/03 1:37:15 PM Eastern Standard Time, 
tesla-at-pupman-dot-com writes:



>For example, if you tried creating a high frequency choke using a
>non-ferrite core, you might find you have 100mH at
>say 100 Hz, but when measured at 30kHz, the inductance may only be 10uH.
>
>Dan


Hi all,
        I think that the problem may be more one of epistemology than 
measurement. That is to say that we are not measuring what we think we are 
measuring. Every inductor is a "black box" LCR circuit, with XL>>XC or R, 
every capacitor is likewise a "black box" LCR circuit, but with XC>>XL or 
R, and every resistor is a "black box" LCR circuit with R>>XL or XC. IIRC, 
all meters affordable by mere mortals measure the overall effective X 
caused by the component to determine its L or C. It is thus obvious that 
different frequencies will produce different answers, because the meter has 
the built-in assumption that the "net reactance" is based on a pure L or C 
or R. It is also inescapable that the very act of measurement alters that 
which is being measured. Very careful measurements taken at different known 
frequencies might allow for the construction of a solution matrix from 
which one could determine the L,C, and R of each device. IM! O, there 
are  very few applications in which this would be worth the trouble, and 
probably only a handful of coilers who could "do the math".

Matt D.

"When measuring down to the gnat's A**, then it is important to know if 
your gnat is obese, normal, or anorectic." C. E. Nielsen