Emerson Process Management IM-106-340 Alarms O2 T/C Shorted, Fault 2, Shorted Thermocouple

Oxymitter 4000

Figure 8-4. Fault 2, Shorted Thermocouple

	HEATER T/C
DIAGNOSTIC	HEATER	SW2
ALARMS	O2 CELL	ON
	CALIBRATION

CALIBRATION RECOMMENDED

Instruction Manual

IM-106-340, Rev. 4.0

May 2006

Fault 2, Shorted Thermocouple

Figure 8-4shows 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

TEST

POINTS

INC INC

HIGH LOW GAS GAS

DEC DEC

O2 CELL mV +

O2 CELL mv - HEATER T/C + HEATER T/C -

CAL

TEST GAS + PROCESS - % O2

TP1 TP2 TP3 TP4

TP5

TP6

J1 RED YEL GRN ORG

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

KEYPAD

Alarms

O2 T/C Shorted

LOI 37260020

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 4000.

3.Perform the diagnostic steps 1 through 4 shown for the membrane keypad.

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