04.11.08
The position of the deepest notch i
The position of the deepest notch, _i.e._, the selective notch, on the
circumference of the segment at any station depends upon the number of
that station; thus, the segment of Station 4 will have a deep notch in
the sixth position; the segment for Station 9 will have a deep notch
in the eleventh position; the segment for any station will have a deep
notch in the position corresponding to the number of that station plus
two.
From what has been said, therefore, it is evident that the first, or
normal, notch on each segment is of such a depth as to allow the
moving pawl _6_ to fall to such a depth in the segment as to permit
the rocker arm _2_ to close the talking circuit only. All of the other
notches, except one, are comparatively shallow, and while they permit
the moving pawl _6_ under the influence of the rocker arm _2_ to move
the segment _3_, yet they do not permit the rocker arm _2_ to move so
far to the left as to close even the talking circuit. The exception is
the deep notch, or selective notch, which is of such depth as to
permit the pawl _6_ to fall so far into the segment as to allow the
rocker arm _2_ to close both the talking and the ringing circuits.
Besides the moving pawl _6_ there is a detent pawl _7_. This always
holds the segment _3_ in the position to which it has been last moved
by the moving pawl _6_.
The actuating magnet _1_, as has been stated, is polarized and when
energized by currents in one direction, the rocker arm moves the pawl
_6_ so as to step the segment one notch. When this relay is energized
by current in the opposite direction, the operation is such that both
the moving pawl _6_ and the detent pawl _7_ will be pulled away from
the segment, thus allowing the segment to return to its normal position
by gravity. This is accomplished by the following mechanism: An
armature stop is pivoted upon the face of the rocker arm so as to swing
in a plane parallel to the pole faces of the relay, and is adapted,
when the relay is actuated by selective impulses of one polarity, to be
pulled towards one of the pole faces where it acts, through impact with
a plate attached to the pole face of the relay, as a limiting means
for the motion of the rocker arm when the rocker arm is actuated by the
magnet. When, however, the relay is energized by current in the
opposite direction, as on a releasing impulse, the armature stop swings
upon its pivot towards the opposite pole face, in which position the
lug on the end of the armature stop registers with a hole in the plate
on the relay, thus allowing the full motion of the rocker arm when it
is attracted by the magnet. This motion of the rocker arm withdraws the
detent pawl from engagement with the segment as well as the moving
pawl, and thereby permits the segment to return to its normal position.
As will be seen from Fig. 189, each of the relay magnets _1_ is
permanently bridged across the two limbs of the line.
Each station is provided with a push button, not shown, by means of
which the subscriber who makes a call may prevent the rocker arm of
his instrument from being actuated while selective impulses are being
sent over the line. The purpose of this is to enable one party to make
a call for another on the same line, depressing his push button while
the operator is selecting and ringing the called party. The segment at
his own station, therefore, remains in its normal position, in which
position, as we have already seen, his talking circuit is closed; all
of the other segments are, however, stepped up until the ringing and
talking circuits of the desired station are in proper position, at
which time ringing current is sent over the line. The segments in Fig.
189, except at Station C, are shown as having been stepped up to the
sixth position, which corresponds to the ringing position of the
fourth station, or Station D. The condition shown in this figure
corresponds to that in which the subscriber at Station C originated
the call and pressed his button, thus retaining his own segment in its
normal position so that the talking circuits would be established with
Station D.
When the line is in normal position any subscriber may call central by
his magneto generator, not shown in Fig. 189, which will operate the
drop at central, but will not operate any of the subscribers bells,
because all bell circuits are normally open. When a subscriber desires
connection with another line, the operator sends an impulse back on
the line which steps up and locks out all instruments except that of
the calling subscriber.
[Illustration: Fig. 190. K.B. Lock-Out Station]