Vaisala HM40 - Manual (Page 12)

11
Parameters Explained
The table below describes the parameters measured by
the HM40. All of the parameters are measured or
calculated when the meter is on, independent of what is
currently displayed.
Parameter Symbol Unit(s) Description
Relative
humidity RH % Ratio of the partial pressure of
water vapor in the air to the
saturation vapor pressure of air
at the current temperature.
Dewpoint Td °C
°F
Temperature at which the water
vapor in the air will condense into
water at the current pressure.
When the dewpoint is below 0
°C, the meter outputs frostpoint
instead of dewpoint.
Wet bulb
temperature Tw °C
°F
The minimum temperature that
can be reached by evaporative
cooling in the current conditions.
Absolute
humidity a g/m
3
gr/ft
3
Quantity of water in a cubic
meter (or cubic foot) of air.
Mixing ratio x g/kg
gr/lb Ratio of water vapor mass per
kilogram (or pound) of dry air.
Enthalpy h kJ/kg
btu/lb
Sum of the internal energy of a
thermodynamic system.
Temperature T °C
°F
Temperature in Celsius or
Fahrenheit scale.