Type B Vital Relays - Alstom

Theory of Operation
2.4.4.2. Microchron II Timer Relay (DC)
Designed to replace existing DC motor timers, the Microchron II Timer Relay possesses
a delay range from 1 second to 19 minute and 59 seconds. The range is adjustable in 1-
second increments. Delay is initiated once input power is applied.
The timing package consists of two printed circuit boards that perform time select and
voltage regulation/relay driver and delay processing operations. The front edge of the
delay processor provides visual indications of the delay sequencing. Those provided
include ‘DELAY COMPLETE’ and ‘TIMING/POWER ON’. The time selection is
accomplished by removing the cover from in front of the thumbwheel select switch
assembly and placing the thumbwheels in the desired position.
Four wires run external to the timer assembly: two wires for input power, that are
terminated on the relay contact block and two wires that are connected to the B relay
coils on the relay assembly. Connections between the timer and relay assemblies are
accomplished using pin and socket type connectors.
The relay mechanism consists of a B1 neutral relay with two series connected coils
each with a nominal DC resistance of 250 ohms. Contact configuration is 3 fronts (silver
impregnated carbon to silver), 2 backs (silver to silver impregnated carbon), and 2 frontback
(silver impregnated carbon to silver, silver to silver).
The Microchron II Timer is normally de-energized. Once power is applied, the
microprocessor begins the vital program. Initially vital functions are tested and data
memory is checked for failures. Next, the time selected on the thumbwheel switches is
scanned and appropriate delay counters are initialized. The delay sequence then
begins. The ‘TIMING/POWER ON’ indicator flashes at one-second intervals as the
delay proceeds. A signature analysis following completion of the delay is a final check
that all operations have been properly performed. Successful performance of the
signature analysis allows the program to enter the vital output routine that provides a 10
kHz signal needed to energize the B relay. The indicator ‘DELAY COMPLETE’ is
illuminated at that time. Slight illumination of the ‘TIMING/POWER ON’ indicator
provides visual indication that power is being applied to the unit.
2.4.4.2.1. Operating Specifications
• Input voltage (DC) : 8V to 31.5 VDC
• Maximum Current Draw: 0.100 Amps @ 15VDC Input
• Relay Maximum PICKUP and WORKING Current: 0.0121 Amps
• Relay Coil Resistance (series connected coils): 500 ohms (Nominal)
• Operating Temperature: -40°C to +70°C
P1457, Rev. Nov/07 2–22 Alstom Signaling Inc.