Emerson Rosemount OCX8800 Instruction Manual page 199

Fault Isolation
April 2017
ADC Failure (Voltage to digital conversion could not complete)
ADC Ref Error (Voltage to digital conversion not accurate)
Probable Cause
Incorrect wiring between electronics and
sensor housings
Electronics package failure
O2 Htr Failure (Oxygen sensor heater could not reach final temperature)
Probable Cause
O heater circuit wiring open
2
O heater open
2
Heater electronics failure
COe Htr Failure (Combustibles sensor heater could not reach final temperature)
Probable Cause
COe heater circuit wiring open
COe heater open
Heater electronics failure
SB Htr Failure (Sample block heater could not reach final temperature)
Probable Cause
Sample block heater circuit wiring open
Sample block heater open
Heater electronics failure
Sensor housing exposed to high wind and/
or extreme cold temperatures
Table continued on next
page
Probable Cause
Calibration gas supply low or gas
connection leaking
O cell degraded or failed:
2
O2 Slope Error (Slope <34.5 mV/Dec or
>57.5 mV/Dec)
O2 Constant Error (Constant not between - indicated, replace O
20 mV to +20 mV)
Table continued on next page
172
Recommended Corrective Action
Check all wiring between the electronics and sensor housings per Figure 8-5.
Correct wiring faults.
Replace electronics package.
Recommended Corrective Action
Check O cell heater circuit for broken wire or loose connection per Figure 8-5
2
and . Repair broken wire or loose connection.
Check resistance of O heater per . Normal O
2
Replace O heater if heater is open or has a large resistance.
2
Check heater fuse F3 in electronics housing per
correct cause of overload. If F3 is not open, or if cause of overload cannot be
found, replace electronics package.
Recommended Corrective Action
Check COe heater circuit for broken wire or loose connection per
. Repair broken wire or loose connection.
Check resistance of COe heater per . Normal COe heater resistance is 97.7 Ohms.
Replace COe heater if heater is open or has a large resistance.
Check heater fuse F3 in electronics housing per
correct cause of overload. If F3 is not open, or if cause of overload cannot be
found, replace electronics package.
Recommended Corrective Action
Check sample block heater circuit for broken wire or loose connection per
Figure 8-5 and . Repair broken wire or loose connection.
Check resistance of sample block heater per . Normal sample block heater
resistance is 36.4 Ohms each (18.2 Ohms with both heaters in parallel). Replace
sample block heater if heater is open or has a large resistance.
Check heater fuse F4 in electronics housing per
correct cause of overload. If F4 is not open, or if cause of overload cannot be
found, replace electronics package.
If above probable causes are not causing the SB heater failure, install flange
insulator (PN 6P00162H01).
Recommended Corrective
Action
Check calibration gas supplies and connections. Adjust gas pressure and flow.
Replenish low calibration gas supplies and tighten or repair loose or leaking
connections. When calibration gas supplies are adequate, recalibrate.
Check O cell impedance by reading the O2 Cell Imped value via the LOI (see
2
Figure 1-5, sheet 2), or the O2 Snsr R value via Foundation Fieldbus menu tree
(see Figure 6-8, sheet 2). If cell impedance is zero, replace O
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
cell.
2
Flow calibration gas to the O
2
millivolt output and the calibration gas O
Figure 8-4
. If the plotted values do not fall on the slope line shown in
8-4, replace the O cell.
2
Instruction Manual
heater resistance is 62.5 Ohms.
2
Figure 8-3. If open, locate and
Figure 8-3. If open, locate and
Figure 8-3. If open, locate and
cell. Read the cell millivolt output. Plot the cell
concentration on the chart shown in
2
IM-106-880C, OI
Figure 8-5 and
cell. If cell
2
Figure
Fault Isolation