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 D_eff (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 D_eff, 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 (D_eff), which is calculated using: D A A eff t h = - 2 1 2 p Where: D_eff = Effective Diameter (inches) A_t = Total cross-sectional area of part (square inches) A_h = Area of part hollow sections of part (square inches) p = 3.1416