Specifications

Engineering Standard –NSW
Signalling SMS 02
Cerberus Level Crossing Monitor Equipment
March 2005 Version 1.2 © Australian Rail Track Corporation Page 29 of 118
This document is uncontrolled when printed.
is +5 VDC @ 6.0 A maximum. Output voltage two is +12 VDC @ 3 A
maximum. Output voltage 3 is -12 VDC @ 0.5 A maximum.
Maximum total output power is 65 Watts.
Other features of the PSU are:
 overcurrent protection
 overvoltage protection on the 5 volt output.
3.2.3.1 Function
The Power Supply Units function is to a supply a regulated and stable
DC voltage (+5, +12, -12 VDC) for the I/O Boards, a 5 VDC supply for
the Optoisolators, +12 VDC for the current sensor, and a +12 VDC
supply for the non-vital timer.
3.2.3.2 Operation
The PSU is based on a high frequency DC-DC switchmode
operation. The DC input supply from the Level Crossing Battery is
first converted to a high frequency AC voltage and then converted to
a DC rectified voltage. The DC voltage is then 'chopped' to form a
pulsed DC voltage. The pulsed DC is then transformed to different
voltages and the output rectified and regulated to provide the correct
DC output voltages.
Switchmode DC-DC converters are small, light and consume less
power than conventional linear supplies. They provide very accurate
and stable outputs and are thus favoured for electronic applications
3.2.3.3 Configuration and Set-Up
Their is no configuration and set-up for the power supply.
3.2.3.4 Troubleshooting
This section is aimed at identifying a failed power supply unit.
(a)Check the status of the three indicating LEDs and the power
switch lamp. This should indicate if the problem is with the input
supply voltage or the output voltage.
(b)If the power switch lamp is 'off', measure the input voltage. It
should be between 12 and 18 volts.
Also check the supply fuses.
(c)If there are no LEDs alight on the I/O Boards or Opto Boards, the
+5V has most likely failed. If the maintenance terminal fails to
respond when plugged into the diagnostic port, the +12V and -
12V may have failed.
(d)If any of the indicating LEDs are 'off', the PSU has most-likely
failed and thus the main box requires replacement. However, to
confirm that the PSU has failed, remove the top cover and
measure the