of a north pole, the right side of the same coil will occupy
a position under approximately the center of an adjacent
south pole. The distance between the centers of two
adjacent poles is the pole pitch. The span of one coil
should be equal or nearly equal to one pole pitch. If a
coil spans exactly one pole pitch, the winding is FULL
PITCH (fig. 7-31). If a coil spans less than one pole
pitch, the winding is FRACTIONAL PITCH. COIL
PITCH is recorded and identified by the number of slots
spanned by the coil in the armature (fig. 7-32).
NUMBERING.-- The dc armature windings are
usually two-layer windings in which each slot contains
two coil sides of a single-coil type of winding (fig. 7-30).
One side of the winding element is placed in the top of
a slot and the other side is placed in the bottom of another
Figure 7-32.--Pole pitch.
slot. Either side of the element maybe placed in the top
or bottom of the slot. When you view the armature from
PITCH.-- Both lap and wave windings are placed
the commutator end, the right side of the coil is usually
on the armature core so that the two sides of an element
placed in the bottom of one slot, and the left side is
occupy the slots that are influenced by adjacent poles of
placed in the top of another slot. The coils are arbitrarily
opposite polarity, and the emfs generated in the two
numbered so that all TOP coil sides have odd numbers
sides add together. In other words, if the left side of a
and all BOTTOM coil sides have even numbers (fig.
coil momentarily occupies a position under the center
Figure 7-33.--Meaning of coil pitch in armature winding.
7-26
