Vaisala HMP230 - Manual (Page 140)

HMP230 SERIES
Appendix 6: Calculation formulas
M210225en-B
134
The vapour pressure (in Pascals) is calculated using equation:
å
− =
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 parameters A, m, and T
n
depend on temperature according to the follow-
ing table:
t A m T
n
0 ... 50 °C 6.1078 7.5000 237.3
50 ... 100 °C 5.9987 7.3313 229.1
100 ... 150 °C 5.8493 7.2756 225.0
150 ... 180 °C 6.2301 7.3033 230.0
When T
d
< 0 and the transmitter is set to dewpoint calculation mode (FROST
OFF), the parameters are as follows:
A = 6.119866 m = 7.926104 Tn = 250.4138
When T
d
< 0 and the transmitter is set to frostpoint calculation mode (FROST
ON), the parameters are as follows:
A = 6.1134 m = 9.7911 Tn = 273.47