T.O. 33B-1-1
4-22
Figure 4-17. Diagram Showing Relationship of Voltage Drops
across Coil Resistance and Coil Reactance
Z
X
R
L
=
+
2
2
Where:
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 as
follows:
tan q = XL / R
Where:
q
=
Phase angle (degrees)
XL =
Inductive reactance (ohms)
R
=
Resistance (ohms)
4.3.2.5
Impedance Changes.
The impedance of a coil appears to change when it is placed adjacent to an electrically conductive or ferromagnetic
part. The eddy currents induced in the part produce a secondary magnetic field that opposes the primary field. This
opposing field also induces a current flow in the coil in opposition to the primary current. If the part is not
ferromagnetic, the net magnetic field resulting from the combination of the primary and secondary fields is decreased
in magnitude, as is the current flow in the coil. This is equivalent to decreasing the inductance and increasing the
resistance of the coil. If the part is ferromagnetic, the net magnetic field is increased because of the magnifying effect
of the relative magnetic permeability, but the current flow in the coil is decreased because of the opposing effect of the
