Emerson Rosemount 5081FG, Reference Manual

Page: 73 / 105

Reference Manual
00809-0100-4882, Rev AB
May 2019
Rosemount 5081FG
5-5
Figure 5-5. Fault 1, Open Thermocouple
Fault 1, Open Thermocouple
The thermocouple connection is open. The fault
displays as shown in Figure 5-5.
1. Refer to Figure 5-4 and check the
thermocouple wiring connections at
terminals 8 and 10. Ensure the wires are
properly connected.
2. Remove power. Disconnect the
thermocouple wires (gray and red) from
terminals 10 and 8. Measure the continuity
across the gray and red thermocouple
leads. The measurement should read
approximately 1-2 ohms. Larger values
indicate the thermocouple is open.
3. If the thermocouple is open, replace the
oxygen probe per Oxygen Probe
Replacement in Section 6: Maintenance
and Service.
Figure 5-6. Fault 2, Reversed Thermocouple
Fault 2, Reversed Thermocouple Active
The thermocouple connections are reversed.
The fault displays as shown in Figure 5-6.
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. Check the gray (to
terminal 10) and red (to terminal 8) wires
for the proper placement.
3. Using a multimeter, measure between
terminals 8(-) and 10(+). If the reading is
negative, the thermocouple wiring is
reversed. Rewire as necessary.
4. If the wiring is correct and the probe is at
operating temperature, then the transmitter
electronics are bad. Replace the faulty
analog or CPU board per Electronics
Replacement in Section 6: Maintenance
and Service.