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The alarms are stored in the alarm log in chronological order. However, it may be seen that the current
alarm number will skip some numbers. These numbers have been reserved for alarm events that are still
current. When the alarm cause has been removed, these alarm events will be transferred to the alarm log.
9.2 Common Alarms
The cause of events that trigger the common alarms are described below, along with some suggestions on
what might be the appropriate response to these alarms. If the alarm cannot be resolved using the directions
below then the fault may be with the transmitter itself. If you believe this is the case, please contact your
supplier to discuss further testing or repair options.
It is assumed that an appropriately qualified technician will carry out the testing, the probes, transmitters and
cabling may contain active mains power. Please disconnect all wiring to the probe before performing any
electrical tests.
1. Probe 1 Heater Fail
2. Probe 2 Heater Fail
Alarm Trigger:
This alarm indicates that the heated oxygen probe has failed to reach the minimum
operational temperature of 650°C (1200°F) within 20 minutes of the heater turning on.
A heated oxygen probe should reach its operating temperature of 720°C in less than 20 minutes from the
time it is switched on. If it does not reach this temperature within this time, this alarm will be triggered. The
most likely causes of this fault are a damaged heater or heater insulation. Sometimes this alarm can also be
triggered if the probe is being cooled down by excessive airflow across the sensor.
Response to Alarm:
Use a digital multimeter to test the probe heater and confirm whether it is open-circuit.
Check the fuses FS2 and FS3 inside the transmitter and confirm neither are open-circuit. Test to see
whether there is significant cooling to the probe caused by the process which may result in the probe
temperature dipping below 650°C (1200°F).
3. Probe 1 High Impedance
4. Probe 2 High Impedance
Alarm Trigger:
Oxygen probe electrode failure. The transmitter monitors the health of the oxygen sensor
by periodically testing the sensor's internal impedance. The impedance will naturally vary from ~0.2kΩ when
new and settle at 2kΩ - 5kΩ during its operational lifetime. As the sensor reaches the end of its operational
lifespan the impedance will begin to increase more rapidly and once it exceeds 8kΩ the response rate of the
sensor will be too slow for use.
Response to Alarm:
Replace the probe. Contact your local distributor to discuss refurbishment options for
your old probe.
5. Probe 1 TC Open Circuit
6. Probe 2 TC Open Circuit
Alarm Trigger:
The Probe thermocouple is reading open-circuit.
NOTE: For heated probes, the heater is switched off when the thermocouple is open circuit.
Response to Alarm:
Use a digital multimeter to test the thermocouple contacts on the probe and confirm
whether it is open-circuit. Check any terminations for the thermocouple wires from the cable inside the
transmitter. Check for any physical damage to the probe cable.
7. Aux TC Open Circuit
Alarm Trigger:
The aux thermocouple is reading open-circuit.
This alarm will only trigger for configurations where the Aux TC is enabled. See chapter 7.2.6 Auxiliary
Thermocouple Type
Response to Alarm:
Use a digital multimeter to test the dryer TC and confirm whether it is open-circuit.
Check any terminations for the Dryer TC cabling inside the transmitter and at any other termination points.
Check for any physical damage to the dryer TC cable.
August 2018
1732 Oxygen Transmitter
Technical Manual
51
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