1
KH20 Krypton Hygrometer
1. General Description
The KH20 is a krypton hygrometer for measuring water vapour fluctuations in the
air. The name KH20 (KH-twenty) was derived from KH2O (K-H
2
O), and the
sensor has been known with this name since 1985. It is typically used with the
CSAT3 3-D sonic anemometer for measuring latent heat flux (LE), using Eddy
Covariance technique. Please refer to the Open Path Eddy Covariance System
operator’s manual for details on flux measurements using the KH20 sensor.
The KH20 sensor uses a krypton lamp that emits two absorption lines: major line
at 123.58 nm and minor line at 116.49 nm. Both of these lines are absorbed by
water vapour, and a small amount of the minor line is absorbed by oxygen. The
KH20 is not suitable for absolute water vapour concentration measurements due
to its signal offset drift.
The KH20 heads are sealed and will not suffer damage should they get wet. In
addition, the electronics box and the connectors are housed inside a rain shield
(#14113) that protects them from moisture. The KH20 is suitable for long-term
continuous outdoor applications.
The KH20 sensor is comprised of two main parts: the sensor head and the
electronics box. The sensor head comes with cables with 6 ft of lead length that
connect the sensor to the electronics box. It is shipped with a rain shield (#14113)
to protect the electronics box and the connectors from moisture, a 20 inch 3/4 IPS
threaded aluminium pipe (#3874), a 3/4” x 3/4” Nu-Rail (#1017), and a 5/32 inch
Allen wrench (#4697) for mounting. The sensor comes with a signal/power cable
which has 25 ft lead length. If a longer cable is desired, the customer can order a
replacement cable (# KH20CBL-L) and specify the desired lead length after -L.
Discussion on the principles and theory of measurement is included
in Appendix A.
2. Specifications
2.1 Measurements
Calibration Range:
1.7 to 19.5 g/m
3
(nominal)
Frequency Response:
100 Hz
Operating Temperature Range:
-30 to +50°C
2.2 Electrical
Supply Voltage:
10 V to 16 Vdc
Current Consumption:
20 mA max at 12 Vdc
Power Consumption:
0.24 Watts
Output Signal Range:
0 to 5Vdc
NOTE
