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# Re: BH data

- To: femm@yahoogroups.com
- Subject: Re: BH data
- From: "mikejhutch" <mhutchings@solartronmetrology.com>
- Date: Thu, 24 Oct 2002 15:19:01 -0000
- In-reply-to: <sdb672df.076@a-hgwd3.harwell.aeat.co.uk>
- User-agent: eGroups-EW/0.82

    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@y..., "Chris Holt" <chris.c.holt@a...> 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@a...
    > Web: http://www.solutionsinengineering.com and http://www.aeat.com
    >
    > >>> dcm3c@e... 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@y..., "HUTCHINGS Michael" <mhutchings@s...> 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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    >
    >
    >
    >
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- References:
  - [femm] Re: BH data
    - From: "Chris Holt" <chris.c.holt@aeat.co.uk>

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