Emerson OCX 8800 instruction manual Fault Isolation, Probable Cause Recommended Corrective Action

Instruction Manual

IM-106-880, Rev 1.0 January 2007

OCX 8800

FAULT ISOLATION

Faults in the OCX 8800 Transmitter are indicated by messages displayed on the HART communicator or LOI. Fault indications that can appear are listed in Table 8-1, Troubleshooting.

If a fault is indicated on the HART communicator or LOI, locate the fault indication in Table 8-1. For each fault listed, there are related Probable Causes and Recommended Corrective Actions. The Probable Causes are listed in the order of most probable to least probable. Starting with the most probable cause, inspect and test the unit to isolate the actual cause, then use the Recommended Corrective Action listed to correct the problem.

Table 8-1. Troubleshooting

O2 Sensor R High (Oxygen sensor resistance high, > 5000 Ohms) O2 Sensor Open (Oxygen sensor disconnected)

Probable Cause

Recommended Corrective Action

Loose or open O2 cell circuit connection	Check O2 cell circuit wires for breaks or loose connections. Repair lead wire break or
	loose connections.
O2 cell degraded or failed	Check O2 cell impedance by reading the O2 Cell Imped value via the LOI (see
	Figure 4-4, sheet 2), or the O2 Snsr R value via HART (see Figure 5-3, sheet 2). If cell
	impedance is zero, replace O2 cell with cell replacement kit. If cell impedance is less
	than 5000 ohms, check for cell housing ground fault. Repair ground fault. If cell
	impedance is greater than 5000 ohms and no ground fault is indicated, replace O2 cell
	with cell replacement kit.

Ref Current Err (RTD excitation current error)

Probable Cause

Recommended Corrective Action

Loose or open lead or circuit wire connection for COe sensor or CJC sensor current loop

COe sensor grounded

Check all COe and CJC sensor current loop wiring per Figure 8-3 and Figure 7-5. Correct wiring faults.

Check resistance of COe sensor leads to ground per Figure 7-5. Replace COe sensor if resistance is less than 10M Ohms.

COe sensor failed	Check resistance of both COe sensor elements per Figure 7-5. Replace COe sensor if
	resistance of sensor element is not between 100 and 250 Ohms.
CJC sensor grounded	Check resistance of CJC sensor to ground per Figure 7-5. Replace CJC sensor if
	resistance is less than 10M Ohms.
CJC sensor failed	Check resistance of CJC sensor per Figure 7-5. Replace CJC sensor if resistance of
	sensor is not between 100 and 150 Ohms.

O2 Temp Hi (Oxygen sensor heater temperature high, > 750ºC)

Probable Cause

Recommended Corrective Action

High noise in OCX power supply	Check power supply for line noise or voltage fluctuations. Install power line filter kit
	(PN 6A00171G01) or high quality line filter for input power.

COe Temp Hi (Combustion sensor heater temperature high, 310ºC)

Probable Cause

Recommended Corrective Action

High noise in OCX power supply	Check power supply for line noise or voltage fluctuations. Install power line filter kit
	(PN 6A00171G01) or high quality line filter for input power.
	Table continued on next page

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