Figure 8-3. Fault 1, Open Thermocouple - Emerson Rosemount Analytical Oxymitter 4000 Instruction Manual

Hazardous Area Oxymitter 4000
DIAGNOSTIC
ALARMS
CALIBRATION RECOMMENDED
TEST
POINTS
INC INC
HIGH LOW
GAS GAS
DEC DEC
KEYPAD
Alarms
O2 T/C Open
LOI

Figure 8-3. Fault 1, Open Thermocouple

Rosemount Analytical Inc. A Division of Emerson Process Management
HEATER T/C
HEATER SW2
O2 CELL
CALIBRATION
J1
O2 CELL mV +
TP1
O2 CELL mv -
TP2
HEATER T/C +
TP3
HEATER T/C -
TP4
CAL
TEST GAS +
TP5
PROCESS -
TP6
% O2
37260019
Instruction Manual
a. Fault 1, Open Thermocouple
Figure 8-3 shows the electronic assembly
for a Hazardous Area Oxymitter 4000 with
a membrane keypad (upper view) and a
Hazardous Area 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
detected, 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 the volt-
age from TP3+ to TP4-. If the reading
is 1.2 VDC ±0.1 VDC, the thermocou-
ple is open.
3. Remove power. Disconnect J1. Meas-
ure the resistance across the red and
yellow thermocouple leads. The resis-
tance should be approximately 1 ohm.
4. If the thermocouple is open, see para-
graph 9-4g, Heater Strut Replacement.
LOI. When Fault 1 is detected, the LOI
displays the "O2 T/C Open" message.
1. Remove power. Unscrew and remove
the LOI module from the electronic
assembly.
2. Reconnect power to the Oxymitter
4000.
3. Perform the diagnostic steps 1 through
4 shown for the membrane keypad.
IB-106-340C Rev. 4.1
July 2004
Troubleshooting 8-5
8