FreeLists / si-list / [SI-LIST] Re: Inductance of wire section

[bpanos <bill.panos@xxxxxxxxxxxxxxx>]

Kim-
Frederick Terman gives some brief background and assumptions about the formula
everyone has been mentioning,
in his book:  Electronic and Radio Engineering (written back in the 40's it is
still applicable today)
-Bill


Kim Flint wrote:

> Hi-
> I'm curious about assumptions made in some of these inductance formulas. I
> understand inductance as requiring a coil of wire, wherein magnetic flux
> would intersect the area of the coil. "Inductance of a wire segment"
> doesn't really mean anything without understanding where the rest of the
> current path forming our coil is located. So I'm guessing these formulas
> are approximations based on some set of assumed conditions, like height
> above ground or something like that? Does anybody know what those
> assumptions are in this case? I'd like to understand where I can expect
> this formula to be reasonably valid.
>
> thanks!
> kim
>
> At 08:57 AM 9/5/2003, Stuart Brorson wrote:
> >Hi Guys --
> >
> >Thanks for all your answers.  I used the following formula from Bart:
> >
> >L  =  K * length * [ ln(4*length/Diam) - 0.75 ]
> >
> >L      = Inductance in nanohenries
> >D      = Diameter of wire in cm
> >length = Length of wire in cm
> >K      = 2
> >
> >stuck it into Gnumeric (Linux-based Excel replacement), and got the
> >following answers:
> >
> >                 Unit    qnty    qnty    qnty
> >K                       2       2       2
> >Length          cm      1       1       1
> >Diam            cm      0.08    0.06    0.04
> >
> >Inductance      nH      6.324   6.899   7.710
> >
> >depending upon the wire diameter.  Using the below figure of 20nH/in,
> >and knowing that 1in = 2.54cm, I get L = 7.87 nH.
> >
> >Therefore, I think we have nailed it: L = 7nH/cm +/- 10% or so.
> >
> >Thanks again for all the answers!
> >
> >Stuart
> >
> > >
> > > Hi Stuart: The ROT I use is 20nH/in.
> > > BTW, I verifed this using a 2D extractor
> > > and increasing the boundary distance far
> > > away from the wire to minimize mutual indutance.
> > >
> > >
> > > Hope this helps
> > >
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