Type B Vital Relays - Alstom

Theory of Operation
2.4.4. Microchron II Timer Relays
The ‘Microchron II® Timer’ is a timing relay mechanism consisting of a timing package
and a relay assembly housed within a B2 relay enclosure. See Figure 2–22.
abcd
LED LOCATION
(DC TIMER)
Handle
PCB SLOT
LED LOCATION
(AC TIMER)
DC TIMER
THUMBWHEEL CUTOUT
AC TIMER
THUMBWHEEL CUTOUT
Figure 2–22. Microchron II Timer Relay Cover
The Alstom relay identified as "Microchron II Timer Relay" is a DC relay. Alstom also
manufactures the "AC Microchron II Timer Relay," an AC version.
2.4.4.1. Fail-Safe Performance
The Vital design of the Microchron II Timer Relay ensures that a time delay interval
shorter than that selected cannot be performed. Component degradation or failure can
only lead to a longer than selected time delay.
P1457, Rev. Nov/07 2–21 Alstom Signaling Inc.