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

2.5 Input Optoisolator

2.5.1 Description

S-2000 D12/2.0 IIO. Dimensions are 315 mm (l) x 76 mm (w). The PCB is held in a

green plastic circuit board module with mounting feet which clip on to TS32 (Klippon) rail

or TS35 (DIN) rail. Identifying features of the board are:

4 x 8 way ( Green ) connectors

2 x 2 way ( Green ) connectors

Integrated circuits have a white coloured casing (4N35)

Row of 32 indicating LEDs

2 x D25 female connectors (labelled 'O/P 1' and 'O/P 2')

Refer to Drawing M08-731 for physical aspects, drawing M08-732 for the schematic

diagram of the input optoisolator, drawing M08-733 for circuit diagram of the input

optoisolator.

Refer to drawing M08-782 for an example of the input optoisolator circuit in operation.

Refer to drawing M08-861 for details of the cable between the main box and the input

optoisolator. Note that the resistor values have been changed for 12V to 15V DC volt

operation.

2.5.2 Function

The 12 volt Input Opto Board allows connection for up to 32 signalling inputs. The inputs

can be from 9 VDC to 20 VDC.

2.5.3 Operation

Inputs 1 to 16 from the signalling side (green 8-way connector side) are connected (via

the optoisolator circuits) to output pins 1 to 16 on the D25 connector labelled 'O/P 1'. A

cable plugs into this D25 connector to connect 16 inputs into the level crossing monitor

on Input 1. Similarly, inputs 17 to 32 are connected to output pins 1 to 16 of the D25

connector, labelled 'O/P 2'. A cable plugs into this D25 connector to connect 16 inputs

into the level crossing monitor on Input 2.

All 32 circuits are identical and have consecutive component numbering. Referring to

Drawing M08-782, the circuit operation is as follows:

When a voltage of between 9 VDC to 20 VDC is applied to input 1 on the 8-way

connector, a current flows across pins 1 & 2 of the 4N35 optoisolator (U1) and illuminates

the internal LED which turns on the internal phototransistor. This causes the LED (LD1)

to illuminate and pin 1 of 'O/P1' to be high (+5 VDC).

Similarly, when the voltage at the input is less than 3 VDC, no current flows across pins 1

& 2 of the 4N35 optoisolator (U1), the internal LED is extinguished and hence the internal

phototransistor is turned off. This causes the LED (LD1) to turn off and the voltage at pin

1 of 'O/P1' will be low (0 VDC).

A +5 VDC voltage is fed to the Optoisolator Board from the level crossing monitor via the

Cables. The Cable that is connected to 'O/P1' connector feeds +5 VDC to circuits 1 to 16

only. The Cable that is connected to 'O/P2' connector feeds +5 VDC to circuits 17 to 32.