Emerson Rosemount 5081FG, Reference Manual

Page: 75 / 105

Reference Manual
00809-0100-4882, Rev AB
May 2019
Rosemount 5081FG
5-7
Figure 5-9. Fault 5, O2 Cell Open
Fault 5, O2 Cell Open
The O
2
cell connection is open. The fault
displays as shown in Figure 5-9.
1. Allow adequate time for the oxygen probe
to reach operating temperatures. Probe
temperatures below approximately 500°C
(932°F) may result in this fault.
2. Refer to Figure 5-4 and check the O
2
cell
wiring connections at terminals 7 and 8.
Ensure the wires are properly connected.
NOTE
Check the cell output voltage at the probe
terminals -- not at the electronics.
3. Apply low calibration check gas (0.4% O
2
).
Measure the cell output from the O
2
cell
wires at the probe terminal block. The cell
output should be 100 ±20 mV. If no voltage
can be measured the cell is open.
4. If the O
2
cell is open, replace the oxygen
probe per Oxygen Probe Replacement in
Section 6: Maintenance and Service.
Figure 5-10. Fault 6, Cell Impedance Too High
Fault 6, Cell Impedance Too High
The O
2
cell impedance has exceeded 100 ohms.
The fault displays as shown in Figure 5-10.
1. This fault is usually indicated in conjunction
with Fault 5, Cell Open. Correcting Fault 5
should correct Fault 6.
2. Fault 6 appears independently, the cell has
degraded beyond specification.
3. If the O
2
cell has become too old, replace
the oxygen probe per Oxygen Probe
Replacement in Section 6: Maintenance
and Service.