Θ+ θ, Prh p, Pp p ppm – Vaisala PTU300 User Manual
Page 207
Appendix B _______________________________________________________ Calculation Formulas
VAISALA _______________________________________________________________________ 205
∑
−
=
Θ
+
Θ
=
3
1
4
ln
ln
i
i
i
ws
b
b
P
(6)
where:
bi = coefficients
b-1 = -0.58002206 * 104
b0 = 0.13914993 * 101
b1 = -0.48640239 * 10-1
b2 = 0.41764768 * 10-4
b3 = -0.14452093 * 10-7
b4 = 6.5459673
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:
T
d
=
dewpoint temperature (°C)
P
w
=
water vapor pressure (hPa)
P
ws
=
water vapor 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)