Emerson Oxymitter 5000 Instruction Manual page 102

Oxymitter 5000
Figure 8-4. Fault 2, Shorted Thermocouple
DIAGNOSTIC
ALARMS
CALIBRATION RECOMMENDED
TEST
POINTS
INC
HIGH
GAS
DEC
Alarms
O2 T/C Shorted
8-8
HEATER T/C
HEATER SW2
O2 CELL
CALIBRATION
O2 CELL mV +
TP1
O2 CELL mv -
TP2
HEATER T/C +
TP3
HEATER T/C -
TP4
INC
CAL
LOW
GAS
TEST GAS + TP5
DEC
PROCESS -
TP6
% O2
KEYPAD
LOI
Fault 2, Shorted Thermocouple
Figure 8-4 shows the electronic assembly for an
Oxymitter 5000 with a membrane keypad (upper
view) and an Oxymitter 5000 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
J1
When Fault 2 is detected, the HEATER T/C LED
flashes twice, pauses for three seconds, and
repeats.
1. Using a multimeter, measure the voltage
from TP3+ to TP4-. If the reading is 0 ±0.5
mV, then a shorted thermocouple is likely.
2. Remove power and disconnect J1.
3. Measure the resistance from TP3+ to TP4-.
The reading should be approximately 20K
ohms.
4. If so, the short is not on the PC board. The
thermocouple wiring or the thermocouple is
shorted. See "Heater Strut Replacement" in
Section 9: Maintenance and Service.
LOI
When Fault 2 is detected, the LOI displays the
"O2 T/C Shorted" message.
1. Remove power. Unscrew and remove the
LOI module from the electronic assembly.
2. Reconnect power to the Oxymitter 5000.
3. Perform the diagnostic steps 1 through 4
shown for the membrane keypad.
Instruction Manual
IM-106-350, Rev 2.2
July 2008