Type B Vital Relays - Alstom

Theory of Operation
FRAME
MAGNET
ARMATURE
CORE
Figure 2–37. Polar-Biased Single Armature Relay
The following describes the two position polar-biased assembly. Both cores are
connected by a yoke strap and bolted to the relay frame, forming a U-shaped structure.
The armature is polarized by an alnico permanent magnet, which is mounted directly
above the armature on the relay frame. The frame completes the magnetic circuit to the
cores.
The armature is supported at the center by two springs, which act as a trunnionless
bearing. Vertical armature support springs are fastened at the bottom to the yoke.
Horizontal guide springs are fastened at one end beyond either the right or left pole
faces. In the double armature relay, each armature can be operated independently but
not simultaneously. Contact actuation arms are riveted to the armature at the junction of
the vertical and horizontal support springs. The vertical armature spring supports the
armature and provides a torque bias to return the armature to the de-energized position.
With energy applied to the coils in the direction indicated in Figure 2–38, the armature is
attracted to the right pole piece, overcoming the bias of the armature support spring.
Magnetic flux is now concentrated in the right core. When energy is removed from the
relay, the armature, because of biasing, returns to the left pole piece, Figure 2–39.
P1457, Rev. Nov/07 2–40 Alstom Signaling Inc.