Potential causes
1. The oxygen cell interface is designed to indicate a very high output if the
cell becomes disconnected from the electronics. It is possible that a wire
connection, either in the probe or at the electronics, is loose or broken. The
cell may also be damaged from mechanical stress. In extreme cases, a very
low oxygen concentration may cause this alarm. Diagnose at the
transmitter. Refer to Diagnostic alarms for details.
2. This problem could be caused by a mechanical failure in the sensor housing
or at the electronics. An open circuit in the combustible sensor could also
cause this alarm. Refer to Diagnostic alarms for details.
Recommended action
Check sensor wires for loose or broken connectoions or replace the cell.
Sensor Degraded
The Sensor Alerts tab displays Transducer block: O
2
Cell Impedance High.
This alert is active when the oxygen sensor indicates that the cell is beyond its
useful life.
Potential cause
Oxygen cells degrade over time due to aging and corrosion. An increasing cell
resistance is a good indicator of reduced cell performance. As the cell impedance
increases, the cell output falls off, and response time increases. Calibrating the
transmitter compensates for the increased cell resistance up to several hundred
ohms, beyond which the cell is no longer functional. Diagnose at the transmitter.
Refer to Diagnostic alarms for details.
Recommended action
Replace the oxygen cell.
Thermocouple Malfunction
The T/C Heater Alerts tab may display one of the following alarms:
1. O
2
T/C Open
2. O
2
T/C Shorted
3. O
2
T/C Reversed
4. Comb T/C Open
5. Comb T/C Shorted
6. Comb T/C Reversed
7. S/B T/C Open
8. S/B T/C Shorted
9. S/B T/C Reversed
This alert indicates a miswired or faulty thermocouple.
Manual
FOUNDATION
™
Fieldbus
00809-0500-4880 December 2022
Rosemount OCX8800A 121
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