T.O. 33B-1-1
3-39
Example:
Determine the current needed to longitudinally magnetize a l2 inch long part with a diameter of
4 inches and using a 5 turn, 12 inch diameter coil. (See paragraph 3.3.12.6.2 to determine the
cross-sectional area ratio between the part and the coil). If the part contains hollow portions, D
should be replaced with Deff (see paragraph 3.3.12.6.3.4).
Substituting known values gives:
I
=
-
43000
6
5
6
12
4
5
( (
/
)
)
I = 3969 amperes
3.3.12.6.3.3 Formula for Cable Wrap or High Fill-Factor Coils.
When using a cable wrap or when the cross-sectional area of the part is greater than one-half of the cross-sectional area
of the coil, the following formula SHALL be used for estimating the current required to longitudinally magnetize a part
centered in the coil. If the part has hollow portions, replace D with Deff, in the formula (see paragraph 3.3.12.6.3.4).
I
K
N
L
D
=
+
((
/
)
)
2
Where:
I = Current through the coil (amperes)
K = 35,000, a constant (ampere-turns)
N = Number of coil or cable turns
L = Length of the part (inches)
D = Diameter of the part (inches)
Example:
Determine the required current to longitudinally magnetize a part 12 inches long with a 4 inch
diameter using the cable wrap technique with a 3 turn wrap.
Substituting known values gives:
I
=
+
35000
3
12
4
2
((
/
)
)
I = 35000/3(12/4 + 2)
I = 2333 amperes
3.3.12.6.3.4 Formula for Hollow Parts or Parts Having Hollow Portions.
If a part has hollow portions, replace the diameter (D) with the effective diameter (Deff), which is calculated using:
D
A
A
eff
t
h
=
-
2
1
2
p
Where:
Deff = Effective Diameter (inches)
At = Total cross-sectional area of part (square inches)
Ah = Area of part hollow sections of part (square inches)
p = 3.1416
