Dewpoint temperature, Dew/frostpoint temperature – Vaisala HMT120 User Manual
Page 80
User's Guide _______________________________________________________________________
78 ___________________________________________________________________ M211244EN-B
Dewpoint Temperature
The dewpoint temperature (Td) of a moist air sample is the temperature
to which the sample must be cooled to reach saturation with respect to
liquid water.
Dewpoint temperature is calculated using:
1
log
−
=
A
P
m
T
T
w
n
d
[ ]
C
(1)
P
w
is the water vapor pressure (see the equation below). The parameters
A, m, and T
n
depend on temperature according to the following table:
T
A
m
Tn
… 0 °C
6.119866
7.926104
250.4138
0 ... 50 °C
6.1078
7.5000
237.30
50 ... 100 °C
5.9987
7.3313
229.10
100 ... 150 °C
5.8493
7.2756
225.00
150 ... °C
6.2301
7.3033
230.00
Dew/frostpoint Temperature
Dew/frostpoint temperature uses frostpoint calculation when the
dewpoint is below 0 °C. Frostpoint is the temperature at which the air is
saturated with respect to water vapor over an ice surface.
1
log
0
0
−
=
→
<
=
→
≥
A
P
m
T
T
T
T
T
T
w
n
df
d
d
df
d
[ ]
C
(2)
P
w
is the water vapor pressure (see the equation below). The parameters
A, m, and T
n
depend on temperature according to the following table:
Td
A
m
Tn
… 0 °C
6.1134
9.7911
273.47