Vaisala DMT340 - Manual (Page 181)

Appendix A _______________________________________________________ Calculation Formulas
VAISALA _______________________________________________________________________ 179
The water vapor pressure is calculated using:
100
ws
w
P
RH P
⋅ =
(7)
Parts per million by volume is calculated using:
( )
w
w
v
P p
P
ppm
−
⋅ = 6
10
(8)
Symbols:
Td = dewpoint temperature (°C)
Pw = water vapour pressure (hPa)
Pws = water vapour saturation pressure (Pa)
RH = relative humidity (%)
x = mixing ratio (g/kg)
p = atmospheric pressure (hPa)
a = absolute humidity (g/m3)
T = temperature (K)
h = enthalpy (kJ/kg)