Campbell Scientific KH20 Krypton Hygrometer - Manual (Page 5)

KH20 Krypton Hygrometer
1. General Description
The KH20 is a krypton hygrometer for measuring water vapor 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 vapor, and a small amount of the minor line is absorbed by
oxygen. The KH20 is not suitable for absolute water vapor 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
(CSI p/n 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
(CSI p/n 14113) to protect the electronics box and the connectors from
moisture, a 20 inch 3/4 IPS threaded aluminium pipe (CSI p/s 3874), a 3/4” x
3/4” Nu-Rail (CSI p/n 1017), and a 5/32 inch Allen wrench (CSI p/n 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
(p/n KH20CBL-L) and specify the desired lead length after -L.
Discussion on the principles and theory of measurement is
included in Appendix A. NOTE
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
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