T.O. 33B-1-14-22Figure 4-17. Diagram Showing Relationship of Voltage Dropsacross Coil Resistance and Coil ReactanceZ X RL= +2 2Where:Z = Impedance magnitude (ohms)XL = Inductive reactance (ohms)R = Resistance (ohms)The phase angle (q) of the impedance can be calculated from the values of resistance and inductive reactance asfollows:tan q = XL / RWhere:q = Phase angle (degrees)XL = Inductive reactance (ohms)R = Resistance (ohms)4.3.2.5 ImpedanceChanges.The impedance of a coil appears to change when it is placed adjacent to an electrically conductive or ferromagneticpart. The eddy currents induced in the part produce a secondary magnetic field that opposes the primary field. Thisopposing field also induces a current flow in the coil in opposition to the primary current. If the part is notferromagnetic, the net magnetic field resulting from the combination of the primary and secondary fields is decreasedin magnitude, as is the current flow in the coil. This is equivalent to decreasing the inductance and increasing theresistance of the coil. If the part is ferromagnetic, the net magnetic field is increased because of the magnifying effectof the relative magnetic permeability, but the current flow in the coil is decreased because of the opposing effect of the
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