Type B Vital Relays - Alstom

Theory of Operation
If coil B is energized in the direction shown in Figures 2–40, the flux through core B
increases greatly.
N
A
B
+
COIL B
-
CORE B
S
COIL A
CORE A
Figure 2–40. VTB Relay, Two Armatures Energized
As a result, the spring bias and permanent magnet flux acting on armature B are
overcome and the armature is attracted to the left-hand pole piece. If, instead, coil A is
energized to produce the proper direction of magnetic flux, armature B remains in its
biased position and armature A is attracted to the right pole piece.
P1457, Rev. Nov/07 2–42 Alstom Signaling Inc.