Emerson Rosemount OCX8800A - Page 229

Potential cause
O
2
cell degraded or failed.
O
2
slope error (Slope < 34.5 mV/Dec or > 57.2 mV/Dec).
Recommended actions
Check O
2
cell impedance by reading the O2 Cell Imped value via the local
operator interface (LOI) (see Figure 4-4) or the O2 Snsr R value via the HART
®
menu tree (see Figure 5-3).
• If cell impedance is zero, replace the O
2
cell.
• 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 O
2
cell.
Potential cause
O
2
constant error (constant not between -20 mV and +20 mV).
Recommended actions
1. Flow calibration gas to the O
2
cell.
2. Read the cell millivolt output.
3. Plot the cell millivolt output and the calibration gas O
2
concentration on
the chart shown in Figure 9-3.
4. If the plotted values do not fall on the slope line shown in Figure 9-3,
replace the O
2
cell.
Potential cause
COe sensor degraded.
COe slope error (slope not between 200 ppm/Ohm and 4,500 ppm/Ohm).
COe constant error (constant not between -100 Ohms and +100 Ohms.
Recommended action
Replace COe sensor or increase warning level (SYSTEM, CALIB SETUP, or COe
Slope Warn via HART
®
).
Potential cause
Low sample gas flow in sensor housing due to flow path plugging.
Recommended action
Check the following portions of the flow path for plugging:
• Blowback filter
• In-situ filter
• Eductor outlet path
Manual
Troubleshoot
00809-0500-4880 December 2022
Rosemount OCX8800A 229