Figure 8-4. Fault 2, Shorted Thermocouple - Emerson Rosemount Analytical Oxymitter 4000 Instruction Manual

Instruction Manual
IB-106-340C Rev. 4.1
July 2004
DIAGNOSTIC
ALARMS
CALIBRATION RECOMMENDED
TEST
POINTS
INC INC
HIGH LOW
GAS GAS
DEC DEC
KEYPAD
Alarms
O2 T/C Shorted

Figure 8-4. Fault 2, Shorted Thermocouple

8-6 Troubleshooting
HEATER T/C
HEATER
SW2
O2 CELL
CALIBRATION
O2 CELL mV +
TP1
O2 CELL mv -
TP2
HEATER T/C +
TP3
HEATER T/C -
TP4
CAL
TEST GAS +
TP5
PROCESS -
TP6
% O2
LOI
37260020
Hazardous Area Oxymitter 4000
b. Fault 2, Shorted Thermocouple
Figure 8-4 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.
J1
Membrane Keypad. When Fault 2 is
detected, the HEATER T/C LED flashes
twice, pauses for three seconds, and
repeats.
1. Using a multimeter, measure the volt-
2. Remove power and disconnect J1.
3. Measure the resistance from TP3+
4. If so, the short is not on the PC board.
LOI. When Fault 2 is detected, the LOI
displays the "O2 T/C Shorted" message.
1. Remove power. Unscrew and remove
2. Reconnect power to the Oxymitter
3. Perform the diagnostic steps 1 through
Rosemount Analytical Inc. A Division of Emerson Process Management
age from TP3+ to TP4-. If the reading
is 0 ±0.5 mV, then a shorted thermo-
couple is likely.
to TP4-. The reading should be ap-
proximately 20K ohms.
The thermocouple wiring or the ther-
mocouple is shorted. See paragraph
9-4g, Heater Strut Replacement.
the LOI module from the electronic
assembly.
4000.
4 shown for the membrane keypad.