Fh i k, Fhg i kj – Vaisala HMP260 User Manual
Page 114
HMP260 SERIES
HMP260-U017en-1.5
Appendix 6: Calculation formulas
1
CALCULATION
The HMP260 series transmitters measure relative humidity and temperature. From these
values dewpoint, mixing ratio and absolute humidity are calculated using the following
equations
dewpoint:
T
T
m
P
RH
A
d
n
ws
=
⋅
⋅
F
H
I
K
−
log
100
1
(1)
mixing ratio:
x
RH
P
p
RH P
ws
ws
=
⋅
⋅
⋅ −
⋅
621 98
100
.
b
g
(2)
absolute humidity: a
RH
P
t
ws
=
⋅
⋅
⋅ +
216 68
100
273 2
.
.
a
f
(3)
where
T
d
=
dewpoint temperature (°C)
P
ws
=
partial pressure of saturated water vapour (mbar)
RH
=
relative humidity (%)
x
=
mixing ratio (g/kg)
p
=
atmospheric pressure (mbar)
a
=
absolute humidity (g/m
3
)
t
=
temperature (°C)
The partial pressure of water P
ws
is calculated using equation
P
A
ws
m t
t T
n
=
⋅
⋅
+
F
HG
I
KJ
10
.
(4)
The parameters A, m, and T
n
depend on temperature according to the following table
t
A
m
T
n
-40 ... 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