Vaisala HMP46 User Manual
Page 13
HMI41 AND PROBES
M210316EN-A
Operating Manual
9
The calibration procedure is as follows (see also the calibrator manual):
•
Leave the calibrator and the probe at the calibration site for at least 30
minutes before starting the calibration in order to let the probe
temperature stabilize to the room temperature. Unscrew the plastic
grid (HMP41 and HMP45) or the sintered filter (HMP46) of the
probe.
•
Insert the probe into a measurement hole of the LiCl salt chamber in
the humidity calibrator.
•
Wait until the humidity reading stabilizes (approx. 30 minutes).
Check the temperature and read the closest humidity value in the
calibration table. Adjust the dry end reading with the potentiometer D
(dry) in the probe body to correspond to the value given in the
calibration table; use a suitable trimming screw wrench (see Figure
5.1.1).
•
Insert the thermometer into the 13.5 mm hole of the NaCl salt
chamber and the probe into another hole of the NaCl chamber.
NOTE
When calibrating probes that are being used for long
term measurements (over 1 hour) in high humidities
(90 - 100 %RH), use the K2SO4 salt as the high end
reference.
•
Wait until the humidity reading stabilizes. Read the salt chamber
temperature from the thermometer and then the closest humidity value
from the calibration table. Adjust the wet end reading with the
potentiometer W (wet) to correspond to the value given in the
calibration table.
Table 5.1 Greenspan’s calibration table
°
C
LiCl
NaCl
K2SO4
0
*
75.5
98.8
5
*
75.7
98.5
10
*
75.7
98.2
15
*
75.6
97.9
20
11.3
75.5
97.6
25
11.3
75.3
97.3
30
11.3
75.1
97.0
35
11.3
74.9
96.7
40
11.2
74.7
96.4
45
11.2
74.5
96.1
50
11.1
74.4
95.8
*
If the LiCl solution is used or stored in temperatures below +18
°
C, its equilibrium
humidity changes permanently