Appendix A. Measurement Considerations
Model PM880 Portable Hygrometer User’s Manual 177
A.2 Moisture/Temperature Probe Considerations (cont.)
The probe will measure the water vapor pressure in its immediate vicinity;
therefore, readings will be influenced by its proximity to the system walls,
materials of construction, and other environmental factors.The sensor can
be operated under vacuum or pressure, flowing or static conditions.
Observe the following environmental precautions.
a. Temperature Range
The standard probe is operable from –110°C to +70°C (–166°F to 158°F).
b. Moisture Condensation
Be sure the temperature is at least 10°C higher than the dew/frost point
temperature. If this condition is not maintained, moisture condensation
could occur on the sensor or in the sample system, which will cause reading
errors. If this happens, dry out the probe following the procedures outlined
in Application of the Hygrometer.
c. Static or Dynamic Use
The sensor performs equally well in still air or where considerable flow
occurs. Its small size makes it ideal for measuring moisture conditions
within completely sealed containers or dry boxes. It will also perform well
under gas flow conditions as high as 10,000 cm/sec and liquid flow
conditions to 10 cm/sec. Refer to Application of the Hygrometer, for
maximum flow rates in gases and liquids.
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