Emerson 4000 manual Alarms O2 T/C Shorted, Fault 2, Shorted Thermocouple

Instruction Manual

IB-106-340 Rev. 3.0

December 2003

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

CALIBRATION RECOMMENDED

Oxymitter 4000

b. 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

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

module.
Membrane Keypad. When Fault 2 is de-
tected, the HEATER T/C LED flashes twice,
pauses for three seconds, and repeats.
1.	Using a multimeter, measure across
	TP3+ and TP4-.
2.	If the reading is 0 ±0.5 mV, then a
	shorted thermocouple is likely.
3.	Remove power and disconnect J1.

KEYPAD

Alarms

O2 T/C Shorted

LOI 37260020

Figure 8-4. Fault 2, Shorted Thermocouple

4.	Measure from TP3+ to TP4-. The
	reading should be approximately 20K
	ohms.
5.	If so, the short is not on the PC board.
	The thermocouple wiring or the ther-
	mocouple is shorted. See paragraph 9-
	4h, Heater Strut Replacement.

LOI. When Fault 2 is detected, the LOI dis- plays the “O2 T/C Shorted” 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.

8-6 Troubleshooting Rosemount Analytical Inc. A Division of Emerson Process Management