Specifications

Engineering Standard –NSW
Signalling SMS 02
Cerberus Level Crossing Monitor Equipment
March 2005 Version 1.2 © Australian Rail Track Corporation Page 36 of 118
This document is uncontrolled when printed.
3.4.2 Function
The VIO is used to monitor the state of an intermediate point in a Vital
Signalling circuit when it is not practical to do so by other means.
The VIO provides an isolation of greater than 10 KV between the indication
circuit and the Vital Signalling circuit. It is also designed so that the current
drawn is less than half that required to hold a BRB 930 series Safety Relay
energised.
3.4.3 Operation
Terminals 1 and 2 monitor the Vital Signalling circuit. Terminal 1 is
connected to the more positive voltage than terminal 2.
Terminals 3 and 4 provide the indication of the state of the Vital Signalling
circuit. Terminal 3 is connected to the more positive voltage than terminal 4.
For a 50 volt VIO terminals 3 and 4 conduct when the voltage across
terminals 1 and 2 is greater than 25 volts. Terminals 3 and 4 are high
resistance when the voltage across terminals 1 and 2 is less than 20 volts.
For a 12 volt VIO terminals 3 and 4 conduct when the voltage across
terminals 1 and 2 is greater than 8 volts. Terminals 3 and 4 are high
resistance when the voltage across terminals 1 and 2 is less than 6 volts.
3.4.4 Configuration and Set-up
The is no configuration or set-up except the appropriate volt unit is installed
to the voltage signalling circuit being monitored.
A 12V VIO must never be used on
50 volt Vital Signalling Circuits.
3.4.5 Troubleshooting
When the voltage across terminals 1 and 2 is less than 2 volts then the
voltage across terminals 3 and 4 should be equal to the voltage being
switched on the indication circuit. The indication circuit should be in the off
state.
When the voltage across terminals 1 and 2 is close to the rated operating
voltage (12V or 50V) the voltage across terminals 3 and 4 should be about
1.3 volts. The indication circuit should be in the ON state.
In the case of the Flasher VIOs the circuit for terminals 3 and 4 is a 5 volt
circuit (supplied by the special flasher cable from Input 4 of the
CAUTION