Re: [femm] inductance

[David Meeker <dmeeker@xxxxxxxxxxxxxxxxx>]

Tomislav Borzic wrote:

> Hello everybody, I am (again) coming with small
> problem.
> It is about inductance. I am callculating inductance
> of a coil.
> 1. one turn
> 2. four turns.
>
> In case (1) I use formula L= (mi0/pi)*(1/4 + ln(D/r0)
> where is: mi0=4*pi*e-7
> D- diameter of coil ( like this: 0-----D----0, where 0
> is
> conductor and D is space between them)
> r0= radius of conductor
>
> I know this is formula for two paralell conductors and
> inductance
> between them but with some assumptions it can work.
> so in this case, r0=0.05m, D=0.8m,I+ = 1A, I-=-1A,
> my callculations give 1.2 e-6 H/m, FEMM 1.16 e-6 H/m,
> so it is ok.
> I used AJ block integral (A j dV/2 = energy)
> BUT, if I take four turns of wire, inductance should
> be 16 times
> higher because inductance of coil rises with n^2.
> (n = number of turns)
> I can not achieve acceptable solution.
>
> *.fem file is attached.
> plase help
> thanks
> tomislav.
>

I think that the trick here is that you've assigned the same "circuit" property to all four turns.
If you do this, 1/4 of the current is carried by each turn, so the current that you need to use in
your calculation is 0.25A for the four-turn case. If you do this, the answer seems reasonable--not
exactly 16 times the single-wire case, because the geometry is different, but in that ballpark.


>
> P.s. (to david) nearly done with translation.
> how to create *.pdf?
>

Well, there are at least 3 options:

1) Use the TOM Document Conversion Server at
http://wheel.compose.cs.cmu.edu:8001/cgi-bin/browse/objweb It seems to do a good job at converting
just about any file format to pdf for free.

2) Get Ghostscript at http://www.cs.wisc.edu/~ghost/index.html You use a Postscript printer driver
to save a postscript printout of your document to disk; you then use ghostscript to convert the
postscript into pdf. It's possible to set it up so that things act just like the pdfwriter print
driver. The down-side of this approach is that it can be very difficult to get everything set up
right in the first place.

3) Just email your document to me personally. I own the pdfwriter print driver, and I also have
ghostscript installed, so I can do the conversion.

Dave


begin:vcard 
n:Meeker;David
tel;fax:781-890-3489
tel;work:781-684-4070
x-mozilla-html:TRUE
url:http://members.aol.com/_ht_a/dcm3c
org:Foster-Miller, Inc.;Electrical and Electronic Systems Group
version:2.1
email;internet:dmeeker@xxxxxxxxxxxxxxxxx
title:Senior Engineer
adr;quoted-printable:;;350 Second Avenue=0D=0A;Waltham;MA;02451-1196;USA
fn:David Meeker, Ph.D.
end:vcard