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# Re: Scaling question

- To: femm@yahoogroups.com
- Subject: Re: Scaling question
- From: rtickle@visi.com
- Date: Fri, 16 Feb 2001 22:37:24 -0000
- In-reply-to: <Pine.SCO.3.96.1010216105629.6264B-100000@catm.cat.ernet.in>
- User-agent: eGroups-EW/0.82

    > (1). Are you scaling down the whole magnet, including the core
    width, core height, pole width, pole gap, Ampere-turns in the coil
    etc?

    The entire design drawing was reduced to 1/4 scale - core width and
    length, air gap, coil wire diameter. The amp-turns are a different
    issue.
    The number of turns are the same, only the wire diameter has been
    scaled. By keeping the current density fixed in the first
    calculation, I was effectively scaling the current down by a factor
    of (1/4)^2, due to the change in the wire cross-sectional area.. I
    think this was the problem.
    Multiplying the current density by 4 in the 2nd calculation had the
    effect of using the original full-scale current value scaled by
    (1/4), i.e. it was like 1/4 scaling the number of amp-turns.
    Apparently this is the correct approach, since this gave the same
    values for fields along the centerline. I don't have an intuitive
    sense of why this is the right parameter to scale, though, which is
    what I would like to understand.

    > (2). Generally while making the quartre scale(or some other scaled)
    > prototype of a magnet only the length of the magnet is scaled down.

    Not sure what you mean by this. Are you saying amp-turns should not
    be scaled down? A smaller magnet with the same number of amp-turns
    would be driven more closely to saturation generally, producing
    larger fields (in a smaller air gap volume). I am interested in a
    prototype which produces the same field magnitudes and distribution
    within the proportionally smaller volume of the scaled airgap as the
    full scale would have in its airgap.

    > (3) If you are even scaling down the coil parameters by 1/4, then
    you are bound to get 1/4 fields as can be seen even by simply using
    the formula for field of a dipole magnet.

    Not sure what you mean by this either. If I look at a current loop,
    the field at the center is k*i/R. If I scale down both the current
    and the radius, I get the same field at the center...

- Follow-Ups:
  - Re: Scaling question
    - From: rtickle@visi.com

- References:
  - Re: [femm] Scaling question
    - From: Renuka Rajput <renuka@cat.ernet.in>

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