Vaisala HMP230 Manuel d'utilisateur télécharger pdf (Page 139)

HMP230 SERIES

M210225en-B Appendix 6: Calculation formulas

133

CALCULATION FORMULAS

The HMP230 series transmitters measure relative humidity and temperature.

From these values dewpoint, mixing ratio, absolute humidity and enthalpy in

normal pressure are calculated using the following equations

dewpoint: T

⋅

−

log

100

(1)

mixing ratio:

()

xRH

pRHP

=⋅⋅

⋅− ⋅

621 98

100

. (2)

absolute humidity:

()

aRH

=⋅⋅

⋅+

216 68

100 273 2

(3)

enthalpy:

xxTh ⋅+⋅+⋅= 5.2)00189.001.1( (4)

where

= dewpoint temperature (°C)

= partial pressure of saturated water vapour (mbar)

RH = relative humidity (%)

x = mixing ratio (g/kg)

p = atmospheric pressure (mbar)

a = absolute humidity (g/m

)

T = temperature (°C)

h=enthalpy (kJ/kg)

The partial pressure of water

is calculated using equation:

−=Θ

TCT

(5)

where:

T = temperature in K

= coefficients

= 0.4931358

= -0.46094296 * 10

-2

= 0.13746454 * 10

-4

= -0.12743214 * 10

-7

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Vaisala HMP230 Manuel d'utilisateur Page 139

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