Vaisala HMT120 - Manual (Page 79)

Appendix A _______________________________________________________ Calculation Formulas
VAISALA ________________________________________________________________________ 77
APPENDIX A
CALCULATION FORMULAS
This appendix contains the formulas used for the calculated output
quantities.
HMT120 transmitter receives relative humidity and temperature from the
HMP110 probe. From these values dewpoint, frostpoint, absolute
humidity, mixing ratio, enthalpy, wet bulb temperature, saturation vapor
pressure and vapor pressure in normal pressure are calculated using the
following equations.
Symbols:
T
d
= Dewpoint temperature (°C)
P
w
= Water vapor pressure (hPa)
P
ws
= Saturation vapor pressure (hPa)
RH = Relative humidity (%)
x = Mixing ratio (g/kg)
p = Atmospheric pressure (hPa)
a = Absolute humidity (g/m3)
T = Temperature (°C)
h
Tw
Tdf
=
=
=
Enthalpy (kJ/kg)
Wet bulb temperature (°C)
Dew/frostpoint temperature (°C)