Data Sheet

Ambient Temperature and
Humidity Measurements
9
9.1 Temperature & RH Measurements and Dew Point, Vapor Pressure,
and Mixing Ratio Calculations
The removable MR13 connects to the top of the MR277 and senses ambient
Temperature and Relative Humidity. Calculations based on these Tempera-
ture and Relative Humidity measurements are also provided. These calcula-
tions are Dew Point Temperature, Vapor Pressure (in units of kilo-Pascals),
and Mixing ratio (in Grains Per Pound).
Dew Point is the temperature at which moisture begins to condense on a
surface.
Vapor Pressure is a measurement of the amount of water vapor in a volume of
air. The reading increases as the amount of water vapor increases.
Mixing ratio is the amount of water vapor in air.
To view these ambient measurement readings and calculations, first select
the IGM™ Custom display mode from the menu (Measurement). Next, select
the desired parameters in the ‘Settings’ menu (Settings/IGM™ Custom mode).
In the IGM™ Custom menu you can press Select
at each of the desired pa-
rameters. Press Return
to exit to the normal operating mode.
The Image modes that can display ambient measurements are: Thermal
MSX®, Thermal, Digital Camera, and Psychrometrics. Use the menu to select
an Image mode (Image mode).
Figure 9.1 Psychrometrics screen example showing Relative Humidity & Temperature meas-
urements measured by the MR13 sensor. The MR277 then calculates Dew Point temperature,
Vapor pressure, and Mixing ratio based on the Temperature and RH measurements
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