5-8 Chapter 5: Testing SHB_U14
Sample cell
Visual check
Since the sample gas flows throughout the sample cell’s sample chamber, the
optical properties of its inner surface can change.
Disassemble the cell for a visual check.
Hold the cell up to a light and look through it.
Both chambers must have equal and uniform surfaces with a bright metallic sheen
and no dark spots.
The windows must be clear and clean.
When? • Offset too high
• Zero drift
• Loss of sensitivity
Causes of staining
and contamination
• Sample chamber
• Process (sample gas composition)
• Incomplete or improper sample gas preparation
• Inadequate maintenance
• Reference chamber/extension chambers
• Loose chambers
Other measures • Clean the sample cell sample chamber
• Replace the sample cell
• Check the tubing and replace if necessary.
• Eliminate the cause
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