Single layer coil
design charts (aka nomographs) are a dime a dozen on the Internet. This
nomograph appeared in a 1955 issue of Popular Electronics magazine. A
couple examples of usage are included. The textbook Wheeler's formula for a singlelayer
coil with closely wrapped turns (wire diameter << coil diameter) is L = μ_{r} * d^{2} * N^{2} / (18 * d + 40 * l), where l has units of inches and L has units of μH. To verify
one of the examples given in the article: L = μ_{r} * d^{2} * N^{2} / (18 * d + 40 * l),
= 1 * 5^{2} * 19^{2} / (18 * 5 + 40 * 0.52) = 81.45
μH, which is significantly less than the 100 μH given in the article. Another,
more extensive
Wheeler
inductance formula (too long to reproduce here) yields 90.9 μH. Maybe I made
a mistake somewhere, but I don't think so. I also downloaded the Coil64 software
and plugged numbers into it and go similar results. I'm not saying the chart is
wrong, just verify the results before relying on it. These are without regard to
frequency.
Single Layer Coil Design Chart
This chart can be used to find inductance
of a coil when dimensions and number of turns are known, or to find specifications
to give a desired Inductance. Draw a line between either T and L or d and
l/d,
whichever are both known. Draw a second line between remaining known quantity and
point of intersection of first line and unmarked vertical line. Extend second line
to scale for unknown quantity and read answer.
EXAMPLE A: We have a coil 5" in diameter, 19 turns, 37 turns per inch, and wish
to find the inductance.
l = 19/37" = .52";
l/d = .52/5 = .104. Draw
a line between d=5 and
l/d = .104. Draw
a second line from T = 37 through
the intersection point to the L scale. Read the answer, 100 microhenries.
EXAMPLE B: We require the number of turns of a coil 5" in diameter, wound 37
turns per inch, to give 100 microhenries. Draw a line between T = 37 and L = 100. Draw a
second line from d = 5, through
the intersection point, to the
l/d
scale, and read
l/d = .104. Then
l = 5 x .104 = .52 Inches.
The number of turns is .52 x 37 = 19, approximately.
Single Layer Coil Design Chart
Posted January 12, 2023 (updated from original
post on 4/16/2013)
