The goal was to evaluate the measurement uncertainty and time constant of relative
humidity measurements with a Vaisala HMP155 probe. These probes are used in
the observation network of the Slovenian environmental agency (ARSO) to perform
measurements of temperature and relative humidity. Three instruments were cali-
brated in the calibration laboratory at ARSO. The measurement uncertainty was
evaluated in the range of relative humidity from 20 % to 95 % in the temperature
range between -10 ◦C and 40 ◦C.
Measurements were performed in a humidity generator, and a comparative ca-
libration method was used. The tested instruments deviated from the reference
meter by −0.2 to 11.0 percent. The largest deviations were at the lowest tempe-
rature, while the deviations were significantly smaller at higher temperatures. The
measurement uncertainties ranged from 1.0 to 2.4 percent. At low temperatures,
the uncertainties were higher than the values given in the technical documentation,
while at temperatures above 20 ◦C they were approximately the same as in the do-
cumentation.
Time constant measurements were performed with a sudden change in relative
humidity from 40 to 95 percent and vice versa. The average value of the time
constant was 11.69 seconds, which is less than the value stated in the technical do-
cumentation.
|
