Re: BH data

["mikejhutch" <mhutchings@xxxxxxxxxxxxxxxxxxxxxx>]

Thanks Chris

impedance measurement is a possibility. I will need to be careful 
with saturation effects in deriving the permeability form measurments

Mike 


--- In femm@xxxx, "Chris Holt" <chris.c.holt@xxxx> wrote:
> Hi Michael and David
> 
> The Brms/Hrms suggestion should work OK for high current
> devices; however, for low current devices (such as eddy
> current probes, LVDTs etc.) the changing field will only
> take the material around a subsidiary B-H loop about a
> point on the magnetisation curve. The incremental
> permeabilities associated with such subsidiary loops are
> much lower than the magnetisation curve would suggest.
> 
> The magnetisation curve for a carbon steel will indicate
> relative permeabilities in the 500 - 5000 range, whereas
> the incremental permeabilities that provide reasonable
> results when used in modelling low current devices are
> more like 80 - 300.
> 
> I doubt you'll find incremental permeabilities listed for
> the material in question. If you have (or can borrow) an
> impedance analyser, you could carry out some measurements
> with a test coil and then iteratively use femm to estimate
> the permeability you should be using in your application.
> 
> Chris
> 
> 
> 
> Chris Holt BSc CPhys MInstP Mem. IEEE
> Senior Consultant, Engineering Solutions
> 
> AEA Technology plc, E1 Culham, Abingdon, Oxfordshire OX14 3ED, UK
> Tel: +44 (0)1235 464089 Fax: +44 (0)1235 463799
> Email: chris.c.holt@xxxx
> Web: http://www.solutionsinengineering.com and http://www.aeat.com
> 
> >>> dcm3c@xxxx 22/10/02 21:38:24 >>>
> This is a good question. Traditionally, people have used the 
initial
> magnetization curve as the BH curve in magnetostatic simulations. 
If
> you have this info, it is OK to use it as your BH curve for
> magnetostatic simulations.
> 
> However, it sounds like you are actually interested in AC 
simulations.
> Even though the program accepts a nonlinear BH curve, the nonlinear
> BH curve is ignored for AC simulations and the linear values of
> permeability are used instead. (strictly speaking, harmonic analyses
> are well-defined only in the case of linear materials) In this 
case, a
> good approach would be to pick a characteristic RMS value of H that
> your material would see and then pick the corresponding point on the
> BH curve corresponding to this value, calling it Brms. The
> permeability that you'd use would for your simulation would be 
Brms/Hrms.
> 
> Dave.
> 
> --- In femm@xxxx, "HUTCHINGS Michael" <mhutchings@xxxx> wrote:
> > Hi David (Meeker) and others,
> > 
> > I am trying to include Radiometal in the materials library. I 
have the
> > manufacturers data for d.c. induction but it is in the form of an
> > initial magnetisation curve. This is unlike the mumetal and 
supermalloy
> > materials in the femm library, which show a high initial slope /
> > permeability, declining steadily as saturation is approached. 
These
> > plots ignore hysteresis.
> > 
> > I am tempted to input data from the radiometal d.c. hysteresis 
loops
> > which I also have, shifted to pass through the origin. At least 
then the
> > plot shape is correct. Is this likely to give acceptable results 
for
> > modelling of low frequency fields and inductances?
> > 
> > Perhaps the included BH curves are similarly derived. I feel it 
will be
> > better to do this than use a description with an initially 
increasing
> > permeability with H.
> > 
> > BTW thank you for an excellent free tool, and all the inputs to an
> > interesting discussion group.
> > 
> > Michael J Hutchings
> > Engineer
> > Solartron Metrology
> > 
> 
> 
> 
> 
> 
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http://docs.yahoo.com/info/terms/ 
> 
> 
> 
> 
> 
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