Vaisala hmt120 - Absolute Humidity Calculation; Enthalpy Calculation; Accuracies of Calculated Variables; Accuracy of Dewpoint Temperature °C

A.7 Absolute Humidity Calculation
Absolute humidity (a) is defined as the mass of water vapour in a certain volume. If ideal gas
behaviour is assumed, the absolute humidity can be calculated using the following formula:
 =  


 + 273.15
/
3
where
C 216.679 gK/J
A.8 Enthalpy Calculation
Enthalpy (h) can be calculated from the mixing ratio (x) using the following formula:
ℎ =   1.01 + 0.00189   + 2.5   /
A.9
Accuracies of Calculated Variables
Accuracies of the calculated variables depend on the calibration accuracy of the humidity and
temperature sensors; here the accuracies are given for ± 2 %RH and ± 0.2 °C.
A.9.1 Accuracy of Dewpoint Temperature °C
Table 49 Accuracy of Dewpoint Temperature °C
Temp
Relative Humidity (%RH)
10 20 30 40 50 60 70 80 90 100
-40 °C 1.86 1.03 0.76 0.63 0.55 0.50 0.46 0.43 — —
-20 °C 2.18 1.19 0.88 0.72 0.62 0.56 0.51 0.48 — —
0 °C 2.51 1.37 1.00 0.81 0.70 0.63 0.57 0.53 0.50 0.48
20 °C 2.87 1.56 1.13 0.92 0.79 0.70 0.64 0.59 0.55 0.53
40 °C 3.24 1.76 1.27 1.03 0.88 0.78 0.71 0.65 0.61 0.58
60 °C 3.60 1.96 1.42 1.14 0.97 0.86 0.78 0.72 0.67 0.64
80 °C 4.01 2.18 1.58 1.27 1.08 0.95 0.86 0.79 0.74 0.70
100 °C 4.42 2.41 1.74 1.40 1.19 1.05 0.95 0.87 0.81 0.76
120 °C 4.86 2.66 1.92 1.54 1.31 1.16 1.04 0.96 0.89 0.84
140 °C 5.31 2.91 2.10 1.69 1.44 1.26 1.14 1.05 0.97 0.91
HMT120 User Guide M211244EN-C
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