Probe Passes Calibration, But Still Appears To Read Too Low - Emerson Rosemount Oxymitter DR Reference Manual

Reference Manual
00809-0100-4880
3. This seal can only be used one time, so always replace this seal when replacing a
5.7 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
2. Only set calibration flow rates when a new diffuser is installed.
3. As the diffuser plugs, do not adjust the flow rates upward.
Rosemount Oxymitter DR
Figure 5-1: 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 1).
cell. Always apply anti-seize compound on both sides of the corrugations.
against a plugged diffuser.
Troubleshoot
October 2019
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