Vaisala HUMICAP HM44, User Manual, Page: 37 / 52

Chapter 8 ________________________________________________________________ Calibration
VAISALA __________________________________________________________________________ 35
CHAPTER 8
CALIBRATION
Calibration interval
The HMP44 probes are calibrated at the factory. A new probe should be calibrated first time 6
months from implementation, after that annually. In case the adjustment is needed, contact
Vaisala SSD Service or local Vaisala representative (see Chapter 9, Maintenance).
Calibration coefficients
During calibration, the HMI41 calculates new adjustment coefficients for the probe and the
previously set coefficients are no longer valid. It is recommended to check the new
coefficients and write them down. The coefficients can be checked by pressing ENTER for
about 5 seconds continuously and the offset correction is displayed; press ENTER once more
and the gain correction is displayed.
Calibration mode
The calibration can be performed with Vaisala HMK15 calibrator and saturated salt solutions.
Check the reference values from the calibration table below:
Temperature °C 15 20 25 30 35
LiCl %RH *) 11.3 11.3 11.3 11.3
NaCl %RH 75.6 75.5 75.3 75.1 74.9
K
2
SO
4
%RH 97.9 97.6 97.3 97.0 96.7
Greenspan’s calibration table
*) Do not use or store the LiCl solution in temperatures below +18°C as its humidity
equilibrium may change permanently
Calibration procedure is included in the HMI41 setup mode. Note that the calibration is done
for currently selected probe.
Enter the setup mode, refer to Enter the setup menu on page 9.