KH20 Krypton Hygrometer
6
5. Datalogger Programming
The KH20 sensor outputs 0 to 5 Vdc analogue signal. These signals can be
measured using the VoltDiff instruction on the CRBasic dataloggers or the Volt
(Diff) (P2) instruction on the traditional Edlog dataloggers.
5.1 KH20 Calibration
Each KH20 is calibrated over a vapour range of approximately 2 to 19 g/m
3
. The
calibration is performed twice under the following two conditions: window clean,
and scaled. The water vapour absorption coefficient for three different vapour
ranges are calculated from the collected calibration data: full range, dry range, and
wet range. Table 2 shows a sample of the KH20 vapour ranges over which three
different water vapour absorption coefficients are calculated. See Appendix A for
more information on KH20 calibration.
Table 2. KH20 Calibration Ranges
Ranges
Vapour Density (g/m
3
)
Full Vapour Range
2 – 19
Dry Vapour Range
2 – 9.5
Wet Vapour Range
8.25 – 19
Before the water vapour absorption coefficient,
k
w
, is entered into the datalogger
program for the KH20, the following decisions must be made:
•
Will the windows be allowed to scale?
•
What vapour range is appropriate for the site?
Once the decision is made, the appropriate
k
w
can be chosen from the calibrations
sheet. The calibration sheet also contains the path length,
x
, for a specific KH20.
Using the water vapour absorption coefficient for either the dry or the wet vapour
range will produce more accurate measurements than using that for the full range.
If the vapour range of the site is unknown, or if the vapour range is on the border
line between the dry and the wet vapour ranges, the full range should be used.
