Chapter 4. Using Special Features
68 Model PM880 Portable Hygrometer User’s Manual
4.9.1 Response Time Procedure
To effectively utilize CER, the following procedure should be followed:
1. Connect the moisture probe cable to the moisture probe.
2. Turn on the PM880 Hygrometer and activate CER per the instructions
in the previous section.
3. Expose the moisture probe to the ambient air for approximately ten (10)
minutes. This is the minimum amount of time needed for the sensing
element to reach the equilibrium required for CER to operate properly.
Note: The PM880 should display a dewpoint temperature reading in the
range of 0°C to +14°C, depending on the local ambient conditions.
If the dewpoint temperature exceeds +20°C, relocate the moisture
probe to a drier environment to reduce the dewpoint temperature.
Before using CER, it is necessary to purge the pressure regulator, sample
tubing, and sample cell to remove trapped water molecules from the various
surfaces.
Note: The moisture probe should not be installed in the sample cell during
this purge cycle. A blank probe mount can be used as a plug for the
sample cell.
4. Attach the sample gas line to a pressure regulator (set regulate to 0 psig)
and sample cell with appropriate tubing (stainless steel is
recommended), and allow the gas flow to purge the system.
5. After purging, remove the blank probe mount from the sample cell and
install the moisture probe.
Note: Do not disconnect the moisture probe cable from the moisture probe.
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