Emerson 3081FG - Manual (Page 62)

Instruction Manual
IB-106-3081 Rev. 1.5
September 2002
6-4 Troubleshooting Rosemount Analytical Inc. A Division of Emerson Process Management
Model 3081FG
%
26020024
Figure 6-5. Fault 1, Open Thermocouple
a. Fault 1, Open Thermocouple
The thermocouple connection is open. The
fault displays as shown in Figure 6-5.
1. Refer to Figure 6-4 and check the
thermocouple wiring connections at
terminals 8 and 10. Ensure the wires
are properly connected.
2. Remove power. Disconnect the ther-
mocouple wires (gray and red) from
terminals 10 and 8. Measure the conti-
nuity across the gray and red thermo-
couple leads. The measurement
should read approximately 1-2 ohms.
Larger values indicate the thermocou-
ple is open.
3. If the thermocouple is open, replace
the oxygen probe per paragraph 5-2.
%
26020025
Figure 6-6. Fault 2, Reversed Thermocouple
b. Fault 2, Reversed Thermocouple Active
The thermocouple connections are re-
versed. The fault displays as shown in Fig-
ure 6-6.
1. Allow adequate time for the oxygen
probe to reach operating temperatures.
Probe temperatures below approxi-
mately 500
°C (932°F) may result in this
fault.
2. Refer to Figure 6-4. 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. Re-
place the PC board stack assembly per
paragraph 5-1.