Vaisala HMP230 User 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