Specifications

Engineering Standard –NSW
Signalling SMS 02
Cerberus Level Crossing Monitor Equipment
March 2005 Version 1.2 © Australian Rail Track Corporation Page 10 of 118
This document is uncontrolled when printed.
Through the use of the configuration data the level crossing monitor
processes a number of mathematical expressions (known as 'Boolean
Expressions') to examine the relationships. Each expression is the
equivalent of a non-vital relay circuit. For more information on Boolean
Expressions consult the section on configuration data.
The pre-programmed relationships are customised for each particular
level crossing. However they are all based on a standard set of
relationships that are discussed in this section. Any specific
expressions for a level crossing are contained in the expression file for
that particular level crossing.
The Level crossing monitor processes Boolean expressions with,
internal intermediate states and timer facilities to one second accuracy.
Appendix A contains a sample set of Boolean expressions that define
the relationships for a standard level crossing.
The Level crossing monitor determines the number of lamps operating
on each lamp circuit. It then checks the number of lamps operating
against the number that should be operating as specified in the
expression file. A lamp fault indication is provided when the number of
lamps detected is more than expected on any particular lamp circuit or
1 or more lamps has failed on any circuit.
In normal operation the level crossing monitor will display two green
LEDs which indicate NO FAULT and NO WARNING. If a maintenance
computer (either locally or remotely via modem) is connected these two
indications are combined to give a status of NORMAL on the
maintenance computer. If a FAULT occurs than the LED (on the level
crossing monitor front panel) for NO FAULT will extinguish, indicating
that a FAULT has occurred. If a WARNING occurs then the LED for NO
WARNING will extinguish, indicating that a WARNING has occurred.
The NO FAULT status indicates that the battery voltage is not low, no
more than 1 lamp is out, more lamps than expected have not been
found, and no other fault detected by the level crossing monitor. The
Fault indication is latched until the fault reset push button is pressed or
the fault reset command with the appropriate pin number is received
from a serial channel.
The NO WARNING status indicates that none of the warning conditions
are present. The Warning indication is latched until the fault reset push
button is pressed or the fault reset command with the appropriate pin
number is received from a serial channel.
The list below indicates what could cause the status indications. This
list is based on the standard set of GENERIC i/o and expression files
dated 18/5/95.
A status indication of WARNING is indicated if one or more of the
following has occurred: