Emerson Process Management OXYMITTER 4000 Alarms O2 T/C Shorted, Fault 2, Shorted Thermocouple

Instruction Manual

IB-106-340C Rev. 4.1 July 2004

Hazardous Area Oxymitter 4000

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

CALIBRATION RECOMMENDED

b. Fault 2, Shorted Thermocouple

Figure 8-4shows 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

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

the membrane keypad or the LOI module.

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-

age from TP3+ to TP4-. If the reading

is 0 ±0.5 mV, then a shorted thermo-

couple is likely.

2. Remove power and disconnect J1.

KEYPAD

Alarms

O2 T/C Shorted

LOI 37260020

Figure 8-4. Fault 2, Shorted Thermocouple

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

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.

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