KH20 Krypton Hygrometer
7
6.4 Data Logger Programming
The KH20 sensor outputs 0 to 5 VDC analog signal. These signals can be
measured using the VoltDiff instruction on the CRBasic data loggers.
Programming basics for CRBasic data loggers are in the following sections.
Complete program examples for select CRBasic data loggers can be found in
(p. B-1)
6.4.1 KH20 Calibration
Each KH20 is calibrated over a vapor 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 vapor absorption coefficient for three different
vapor ranges are calculated from the collected calibration data: full range, dry
range, and wet range. TABLE
shows a sample of the KH20 vapor ranges
over which three different water vapor absorption coefficients are calculated.
, for more information on KH20
calibration.
TABLE 6-2. KH20 Calibration Ranges
Ranges
Vapor Density (g/m
3
)
Full Vapor Range
2 – 19
Dry Vapor Range
2 – 9.5
Wet Vapor Range
8.25 – 19
Before the water vapor absorption coefficient,
k
w
, is entered into the data
logger program for the KH20, the following decisions must be made:
•
Will the windows be allowed to scale?
•
What vapor 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 vapor absorption coefficient for either the dry
or the wet vapor range will produce more accurate measurements than using
that for the full range. If the vapor range of the site is unknown, or if the vapor
range is on the border line between the dry and the wet vapor ranges, the full
range should be used.
7. Maintenance and Calibration
The KH20 sensor is designed for continuous field application and requires little
maintenance. The tube ends for the KH20 have been sealed with silicone
elastomer using an injection-mold method. Therefore, the tubes are protected
from water damage, and the KH20 continues to make measurements under
rainy or wet conditions. If the water tends to pool up on the tube window and
blocks the signal, turn the sensor head at an angle so as to shed the water off
the tube window. The rain shield protects the electronics box and the
connectors from moisture.
