Emerson Process Management OXYMITTER 4000 - Manual (Page 117)

Instruction Manual
IB-106-340C Rev. 4.1
July 2004
Rosemount Analytical Inc. A Division of Emerson Process Management Troubleshooting 8-21
Hazardous Area Oxymitter 4000
3. 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 the
Calibration Record form provided in
this manual.
Can I calibrate a badly plugged diffuser?
1. It may not be possible to immediately
replace a plugged diffuser while the
process is on line.
2. One can calibrate the probe without
pressurizing the cell by adjusting the
calibration gas flow rate downward
before calibration. For instance, say
the process is at 3%, and the first
calibration gas is 8%. Adjust the flow
of cal gas downward until the reading
begins to migrate from 8% to lower
values, indicating that process gases
are now mixing in with the calibration
gases.
3. Adjust the flow rate back up until this
mixing is just eliminated. Calibrate at
this flow rate. Replace the diffuser at
the first opportunity.
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