Vaisala HMP240 User Manual
Page 52
HMP240
User's Guide
M210300en
50
The basic capacitance of the new sensor may differ considerably from that of
the previous one. Therefore the corresponding humidity reading of the
transmitter may be below 0 %RH at the low or above 100 %RH at the high
calibration point. However, the current/voltage reading of the analogue output
shows only the minimum or maximum value of the selected current/voltage
scale and the output value may not change even though the arrow switches are
pressed several times. If this happens, press the up or down arrow switch
continuously to bring the output back into the selected scale; this may take as
long as half a minute.
6.1.4 Humidity calibration table
Temperature
°C
15
20
25
30
35
°F
59
68
77
86
95
LiCl
%RH
*)
11.3
11.3
11.3
11.3
4...20 mA
5.81
5.81
5.81
5.81
0...20 mA
2.26
2.26
2.26
2.26
0...1 V
0.113
0.113
0.113
0.113
0...5 V
0.565
0.565
0.565
0.565
0...10 V
1.13
1.13
1.13
1.13
NaCl
%RH
75.6
75.5
75.3
75.1
74.9
4...20 mA
16.10
16.08
16.05
16.02
15.98
0...20 mA
15.12
15.10
15.06
15.02
14.98
0...1 V
0.756
0.755
0.753
0.751
0.749
0...5 V
3.780
3.775
3.765
3.755
3.745
0...10 V
7.56
7.55
7.53
7.51
7.49
Table 1
Greenspan's calibration table
*) If the LiCl solution is used or stored at temperatures below +18 °C
(+64 °F), its equilibrium humidity changes permanently.
6.2
Temperature calibration
The temperature channel has been calibrated at the factory and since it is very
stable, calibration should be performed only when there is strong reason to
believe that the adjustments have changed.
Temperature calibration should be done against some accurate temperature
reference. It can be done either by using the press switches inside the housing,
through the serial bus or the menus on the local display. Either a one-point
offset correction or a two-point calibration are possible.
NOTE
If neither channel normally outputs the T reading,
during the calibration channel 2 outputs the T reading
-20...+80
°
C, corresponding to the current/voltage scale
selected for this channel.