Emerson Rosemount OCX 8800, Instruction Manual

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