Re: Finding 'mu' for magnetics

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

Original poster: Ed Phillips <evp-at-pacbell-dot-net> 

Tesla list wrote:
 >
 > Original poster: Matthew Smith <matt-at-kbc-dot-net.au>
 >
 > Hi All
 >
 > For those of us who are saving the planet by using re-cycled materials for
 > our coils and apparatus, I have been wondering how we can determine the
 > factor 'mu'
 > for ferrites and other materials that go into gate drive transformers,
 > flyback transformers, etc.
 >
 > My proposed method:
 >
 > 1) Wind a coil on the core, measure the inductance.
 > 2) Take coil of core, measure inductance again.
 > 3) Calculate mu from ratio.
 >
 > Sounds too simple - but is it?
 >
 > Cheers
 >
 > M

	OK, but only accurate at the particular operating flux density your
inductance test creates in the core.  Depending on the material the
permeability may change quite a bit with flux density.  I assume you
plan to test ungapped cores.  If the core is gapped you'll be measuring
the EFFECTIVE permeability with the effect of the air gap included.

Ed