Hygrometry Part 2
Electrical Humidity Sensors
When the wick is wet, the resistance between wires is low and higher current flow causes wires to warm.
At this equilibrium, the dew point (water) is a function of the LiCl dew point.
Semiconductors
Some reported errors in Humicap sensors are due to:
Capacitive sensors have a slightly non-linear transfer function.
Carbon Hygrometer (Hygrister)(resistance type)
Piezoelectric Hygrometer
4. Measurement of the Physical Properties of Air.
Infrared Type of Gas Analyzer
The difference in intensity of IR radiation received by a receiver on other side of chamber is a measure of the amount of moisture in the air.
LI-Cor LI-6262 Differential IR Gas Analyzer
The filter allows 2.59 mm radiation to pass for the detection of water vapor.
Li-Cor Schematic
Output voltage of detector is the difference between the voltage from sample cell and reference cell by:
UV Gas Type Analyzer
Lyman-Alpha Humidiometer
Microwave Hygrometer
5. Condensation or Solidification of water.
Light beam reflected off mirrored surface to a photodetector.
When the temperature of the mirror is the same as the dew point of the air, moisture begins to condense on the mirror.
When dew forms, the vapor pressure over the liquid dew is in equilibrium with the vapor pressure of the air.
6. Chemical Reaction of Reagent and Water
ASOS Dew Point Sensor
PPT Slide
Takes measurement once every 30 seconds.
End
Email: alcorn@ariel.met.tamu.edu
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