Specifications

Engineering Standard –NSW
Signalling SMS 02
Cerberus Level Crossing Monitor Equipment
March 2005 Version 1.2 © Australian Rail Track Corporation Page 34 of 118
This document is uncontrolled when printed.
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 500mVolts. Turn the muti-turn trimpot until the
output voltage is at least 500mVolts.
 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 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.
3.3.5 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 recalibrated. 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