Emerson Rosemount Oxymitter 4000, Reference Manual, Page: 147 / 198

Figure 8-29: Probe Leakage Paths, Bottom View
A. Corrugated seal
B. Reference air exhaust port
C. Probe head
D. Probe flange gasket
The sensing cell is bolted to the end of the probe and uses a corrugated metallic seal
(Item 25,
Figure 2-18 ).
3. This seal can only be used one time, so always replace this seal when replacing a
cell. Always apply anti-seize compound on both sides of the corrugations.
8.7.2 Probe passes calibration, but still appears to read too
low
Potential cause
The diffusion element at the end of the probe is a passive filter. It plugs very slowly since
there is no active flow being drawn across it. In applications that have a heavy particulate
loading (coal or wood fired boilers, cement and lime kilns, catalyst regeneration, recover
boilers, etc.) the diffusion element will eventually plug. This may cause a calibration shift.
Recommended actions
1. Do not pressurize the sensing cell during calibrations by flowing excessive cal gas
against a plugged diffuser.
2. Only set calibration flow rates when a new diffuser is installed.
3. As the diffuser plugs, do not adjust the flow rates upward.
Detecting a plugged diffuser
When a diffuser is plugged, the O
2
signal's speed of response will degrade. The O
2
trend in
the control room will become smoother. When calibrating, the calibration gas flow rate
will be noted to be lower.
Never readjust this flow upwards. Adjust this flow only when a new diffuser is installed.
Always note the time it takes for the cell to recover to the normal process value after the
cal gas is removed. As the diffuser plugs, this recovery time will get longer and longer. Use
Calibration record .
Reference Manual Troubleshoot
00809-0100-4340 October 2019
Rosemount Oxymitter 4000 147