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

2.2.3.5 Replacement Procedure

For the main box, if the PSU has failed, remove and replace the whole main box. The

PSU can be replaced in the workshop.

The power supply is a PD65-31LC from PowerBox for a V1.0/V2.0 monitor or a NFC25-

12T05-12 from Computer Products - Power Conversion for a V3.0 monitor.

2.2.4 Analogue to Digital Converter (ADC)

2.2.4.1 Function

The analogue to digital converter provides 8 analogue inputs the level crossing monitor

can monitor and log. They are used to measure the Battery voltage, Lamp currents and

Battery Test currents. It is mounted on a connector on top of the I/O board.

2.2.4.2 Operation

This board is connected to the rear panel 8-way connector via a ribbon cable.

Pin 1 of the 8-way connector is internally wired to the incoming +'ve supply. This

connects the Level crossing battery to analogue channel number 1 on the ADC.

Analogue inputs 2 to 8 are available on the rear panel for connection to the lamp and

battery current sensors.

Due to the voltage drop of approximately 0.16 V DC between the level crossing battery

bus and analogue input number 1 of the ADC board the measured voltage will be 0.16V

DC less than the bus voltage. To compensate for this the level crossing monitor software

through the expression file automatically adds 0.16 V DC to the displayed voltage so that

the bus voltage and the voltage detected by the monitor are within 0.1V DC of each other.

The ADC is an 8 bit Analogue to Digital converter. The board has an onboard voltage

reference to provide greater accuracy. The ADC converts the incoming voltage to an 8-bit

digital signal which is then used by the SCADA I/O microprocessor to detect the battery

voltage and the number of operating lamps.

2.2.4.3 Configuration and Set-up

There is no configuration or set-up required for the ADC.

2.2.4.4 Troubleshooting

The Version 1.0 ADC board will fail if reverse polarity is applied to the level crossing

monitor input terminals. The failure will be indicated by the level crossing monitor giving a

system fault and battery low indication. The application of reverse polarity will cause one

of the PC tracks to burn open circuit. If a jumper wire is soldered in place of the burnt out

track it is most likely that the board will be useable. This problem was rectified for the

ADC boards V2.0 or later which are supplied with the Version 3.0 level crossing monitors.

By looking at the analogue inputs it is possible to see if the ADC board is supplying valid

readings. If the all of the inputs read zero then maybe the ribbon cable is not connected

or the board has failed. The board is susceptible to lightning damage and should be

checked carefully if the level crossing monitor has failed after a lightning strike or surge. If

the inputs read full voltage with no current sensors connected then the ADC board is

faulty and should be replaced.

Failure of the ADC board is indicated by the battery voltage to analogue input 1 reading

zero. This will result in a system fault being displayed. Individual failures of the other