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Instruction Manual
IB-106-340 Rev. 3.0
December 2003
8-6 Troubleshooting Rosemount Analytical Inc. A Division of Emerson Process Management
Oxymitter 4000
Alarms
O2 T/C Shorted
LOI
KEYPAD
DIAGNOSTIC
ALARMS
TEST
POINTS
HEATER T/C
HEATER
O2 CELL
CALIBRATION
CALIBRATION RECOMMENDED
O2 CELL mV +
O2 CELL mv -
HEATER T/C +
HEATER T/C -
INC INC
DEC DEC
HIGH
GAS
LOW
GAS
CAL
TEST GAS +
PROCESS -
% O2
SW2
TP1
J1
TP2
TP3
RED
YEL
GRN
ORG
TP4
TP5
TP6
ON
37260020
Figure 8-4. Fault 2, Shorted Thermocouple
b. Fault 2, Shorted Thermocouple
Figure 8-4 shows the electronic assembly
for an Oxymitter 4000 with a membrane
keypad (upper view) and an Oxymitter 4000
with an LOI (lower view). The upper view
also shows J1 and test points TP1 through
TP6, located on the microprocessor board,
below the membrane keypad or the LOI
module.
Membrane Keypad. When Fault 2 is de-
tected, the HEATER T/C LED flashes twice,
pauses for three seconds, and repeats.
1. Using a multimeter, measure across
TP3+ and TP4-.
2. If the reading is 0 ±0.5 mV, then a
shorted thermocouple is likely.
3. Remove power and disconnect J1.
4. Measure from TP3+ to TP4-. The
reading should be approximately 20K
ohms.
5. If so, the short is not on the PC board.
The thermocouple wiring or the ther-
mocouple is shorted. See paragraph 9-
4h, Heater Strut Replacement.
LOI. When Fault 2 is detected, the LOI dis-
plays the “O2 T/C Shorted” message.
1. Remove power. Unscrew and remove
the LOI module from the electronic as-
sembly.
2. Reconnect power to the Oxymitter
4000.
3. Perform the diagnostic steps 1 through
5 shown for the membrane keypad.