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

noise including radio frequency interference which causes the sensors to indicate a false

higher current reading. If interference does occur than it will be required to move the link

to the AC position. The sensor wiring may have to be moved and it may be necessary to

move the whole sensor to another position to reduce the interference.

The current sensors are calibrated by the manufacturer but occasionally there is one that

has been set wrong or missed. This will mean that field checks and possible re-calibration

may be required.

Each current sensor should have between 50mV and 80mV DC between terminals 1 (C)

and 4 (OUT). If the voltage is outside these levels than field calibration is required.

Field calibration is by the following process:

If the output is less than 500 mVolts. Turn the muti-turn trimpot until the output voltage is

at least 500 mVolts.

Turn the trim-pot until the output voltage just reaches a minimum value.

Now turn the trimpot the other direction until the output voltage is between 5 to 10 mV

higher than the minimum.

Note: Although most current sensor trimpots require anti-clockwise turning to lower the

output voltage some require the trimpot to turn clockwise to lower the output voltage.

The resultant output voltage is typically between 50 mV and 80 mV when no current is

flowing through the circuit being measured.

Workshop calibration is done by passing 5.0 amps through the current sensor and

adjusting the trim-pot until the output voltage is 1.25 volts.

When installing the current sensor ensure that the sense wire is passed through the

sensor in the correct direction. The current sensor has a arrow on it clearly indicating the

direction of positive current flow for the sense wire.

2.3.5 Troubleshooting

It the current sensor is suspected. Then first check the 12 volt supply to it. If this is okay.

Check that when no current is following in the circuit being measured that the output

voltage is about 70 millivolts. If it is significantly more the unit has either failed or needs to

be re-calibrated. Refer to the previous section for details on calibration. If adjustment of

the trimpot from minimum to maximum does not result in the output voltage (terminals 1

and 4) varying than the current sensor is faulty and should be replaced.

If the unit is correctly calibrated, then check the output voltage when the circuit being

measured is drawing current. If the output voltage is as expected, then check the

connections to the level crossing monitor or the Analogue to Digital Converter within the

level crossing monitor.

If it is significantly different to expected then the check that the circuit being measured

does not have any problems. If it does not then replace the current sensor.

If lamps are sometimes detected when the crossing is not operating then change the link

on the current sensors from the DC position to the AC position. This link change will

reduce the Current Sensor’s sensitivity to induction from adjacent circuits. See

section 3.3.4 above for details on interference with the current sensor.

Note that if it is a new installation you must ensure that the wire is threaded through the

measurement aperture in the correct direction otherwise the sensor will not operate. It is

sensitive to the direction of current flow. Refer to drawing M08-854.