Type B Vital Relays - Alstom

Theory of Operation
2.4.4.3. AC Microchron II Timer Relay
The Alstom AC Microchron II Timer Relay is a vital time element relay unit consisting of
a standard vital neutral relay structure and a solid-state timer. There are two versions of
this unit. One version operates at 60 Hz and the other version operates at 25 Hz. This
relay is referenced as the 25 Hz version in this manual.
• The 60 Hz unit operates from a nominal 110 Volts root mean square (Vrms) AC at
60 Hz power.
• The 25 Hz unit operates from a nominal 55 Volts root mean square (Vrms) AC at 25
Hz power.
NOTE
To assure safe application of the AC Microchron II Timer Relay 60 Hz unit,
all application circuits must be reviewed by Alstom engineering before it
will be approved for use.
For both units, the timing range can be set from 1.0 seconds to 19 minutes 59.9
seconds in 0.1-second increments, with accuracy held to +0.1% of the setting plus a
maximum delay of 0.75 seconds. Normal operating temperature ranges between -40°C
to 70°C (-40°F to 160°F). The primary components of the AC Microchron II Timer Relay
are the same for all B relays, including both the 25 Hz and 60 Hz versions of this relay,
see Figure 2–1.
The timer module contains a microcontroller and Complementary Metal Oxide
Semiconductor (CMOS) technology integrated circuits. The timer and relay structure are
housed in a standard Alstom Type B2 relay enclosure. The unit plugs onto a B2
plugboard.
The vital relay structure of the unit has two series-connected coils. The contacts
available for external use include one front-back 26-25-24 (silver impregnated-carbon to
silver and silver to silver), three fronts 13-14, 15-16, 35-36 (silver impregnated-carbon to
silver), and one back check circuit connected to contacts 11-12 (silver to silver). The
remaining contacts are not available for external use due to the requirement for
backward compatibility with AC Motor Timers and the common registration plate. The
relay contacts are the same for both the 25 Hz and 60 Hz versions of the relay. Figure
2–23 shows a front view of the relay contacts.
P1457, Rev. Nov/07 2–24 Alstom Signaling Inc.