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Instruction Manual
IB-106-340 Rev. 3.0
December 2003
Rosemount Analytical Inc. A Division of Emerson Process Management Troubleshooting 8-5
Oxymitter 4000
Alarms
O2 T/C Open
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
37260019
Figure 8-3. Fault 1, Open Thermocouple
a. Fault 1, Open Thermocouple
Figure 8-3 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 1 is de-
tected, the HEATER T/C LED flashes once,
pauses for three seconds, and repeats.
1. Check connector J1. Ensure the con-
nector is properly seated.
2. Using a multimeter, measure TP3+ to
TP4-. If the reading is 1.2 VDC ±0.1
VDC, the thermocouple is open.
3. Remove power. Disconnect J1. Meas-
ure continuity across the red and yel-
low thermocouple leads.
4. The measurement should read ap-
proximately 1 ohm.
5. If the thermocouple is open, see para-
graph 9-4h, Heater Strut Replacement.
LOI. When Fault 1 is detected, the LOI dis-
plays the “O2 T/C Open” 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.