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# Re: some proposals for future developments

- To: femm@yahoogroups.com
- Subject: Re: some proposals for future developments
- From: "atreding" <atreding@gwlisk.com>
- Date: Sat, 27 Sep 2003 02:28:23 -0000
- In-reply-to: <5.1.0.14.0.20030926075407.01f9cbb0@staff-mailin.lboro.ac.uk>
- User-agent: eGroups-EW/0.82

    We are pretty good about modeling air gaps, and when we know the
    power draw is low (and hence low saturation) we make very sure the
    gaps are there. Actually, I tend to over estimate the gaps,
    typically I would model a press fit as at least a .002 - .003"
    radial gap, more if we actually expect the gap to cause an issue. As
    for driving the solenoids - we have a few ways. But the most common
    for our group at least is "straight" DC, and that is where we have
    seen the specific problem I'm talking about.

    Also, in answer to Dave's comment, we definitely are aware of how
    treacherous a force measurement can be on a solenoid, especially a
    small one. But the two most common methods we use to measure force
    (deadweight lifting and strain gage) have both shown the same type
    of problems to one degree or another, and we can usually get them to
    agree as long as the side loads aren't too hideous.

    I'm pretty impressed - this question got more of a response than I
    expected. Thank you! By the way, I had a brief correspondence today
    with a company that does B-H analysis on steel samples, and the
    person I spoke with said that machining stresses can increase the Hc
    of a soft steel by a factor of 2 to 5, with a similar change in the
    maximum permiability. Since we are often dealing with thin sections,
    I'm thinking it probably is going largely back to this. I did a
    quick test today where I multiplied the Hc of my 1215 curve by 5 and
    it made quite a difference in the model.

    Andy

    --- In femm@yahoogroups.com, Keith Gregory <k.gregory@l...> wrote:
    > Another thought - how is the solenoid put together? Have you got
    any small
    > parasitic air-gaps that are not being modelled?
    >
    > Keith.

- Follow-Ups:
  - Re: [femm] Re: some proposals for future developments
    - From: Keith Gregory <k.gregory@lboro.ac.uk>

- References:
  - Re: [femm] Re: some proposals for future developments
    - From: Keith Gregory <k.gregory@lboro.ac.uk>

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