On Wed, 06 Jun 2012 22:29:35 -0400
I don't think many of us understand exactly what you're looking for?
At least I am a bit confused, if not for others here
OK, it's pretty simple. I can find all manner of equations, formulas,
calculators, etc., that calculate inductance but that use non-SI units
such as inches, feet, pounds (or whatever).
Of course I could just convert the various values into SI units, but...
it's a pain, and I tend to mix things up a bit and reverse the
calculations I should be doing (multiply when I should divide, etc.).
Doing induction calculations seems to be a black art it seems. For
years i've seen a variation of formula's to represent the value of a
coil once all the data is known.
Same here. To my understanding, the actual calculations (accurate
ones) require diffeq's. In order to simplify, accuracy is sacrificed
and they come up with various approximations that work under a certain
set of conditions (long solenoid; coil with thickness << than diameter;
single layer of turns, etc.).
Hmm... your math below came out kind of funny-looking in my reader. I
One equation looks like:
u n^ A
L=-----------
l
I assume the ^ should be indicating that n is squared?
For example..
In a long single coil, a formula of this type is used and there are
others, too.
u n^ A
L =---------
l
L = uH
u = permeability of air, some where around 1.26-05
A = cross section area of the coil in "m"^
l = Length of the coil in "m"
N = number of turns^
And now for the big HOWEVER>
If you were doing magnetic cores..
I don't know what you mean by magnetic cores. Do you mean using cores
that contain iron, that would affect the inductance?
the math changes just a little.
0.012 n^ u A
L =-------------
Lc
In this case, the "u" permeability for air is 1.0
Note the constant 0.012? This was from a formula I got some where, it
was a note slide in one of my books that is so old it's turning
yellow.
and "A" cross section area is now cm^ not "m"
and Lc is your magnetic size of the field, the physical length of it,
which can extend a bit depending on the form you're on.
I also have some math for inches.
Like I said, it's a black art. for the last few months I've been
playing around with a concept that involves using reluctance
alterations to monitor surface changes. This has forced me to dig out
some older references in my library.
It seems the internet is becoming a junk yard and is hard to find a
agreed method of doing certain things, like this for example.
You're right about that. Back in the olden days (when I was learning
this stuff) the problem was a lack of information. You had to either
have it in books at home, or go to the library or school for it.
Now there is an endless amount of information, but so much of it is
crap that you've got to sort through lots of chaff to find the wheat.
Way too much information, often unreliable, and too much to process in
a reasonable time.
Ah, well. Thanks for your ideas. Maybe I'll eventually figure this
out somehow. Or I *could* just wind the stupid coils and measure the
inductance, and try to figure out a relationship myself.