Specifications

RailCorp Engineering Manual — Signals — Equipment Manual

Cerberus Level Crossing Monitor Field Equipment Manual TMG E1261

Issued August 2012 UNCONTROLLED WHEN PRINTED Version 2.1

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.

2.2.3.1 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.

2.2.3.2 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

2.2.3.3 Configuration and Set-Up

Their is no configuration and set-up for the power supply.

2.2.3.4 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.

a) 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.

b) 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 output voltages. They should be

(+5 VDC , +12 VDC, -12 VDC). The pin-outs for the PSU are either on the top

or the sides of the PSU.

c) To test remove the power supply connector from the rear of the backplane and

test the power supply using a voltmeter between 0V and +5V, +12V and -12V. If

the +5V rail is less than 4.7V the system will not work.

d) The +5V may be tested in circuit using the test points on the Input or Output

Optoisolator Boards.