KH20 Krypton Hygrometer 2/10 C o p y r i g h t © 2 0 1 0 C a m p b e l l S c i e n t i f i c , I n c .
Warranty and Assistance The KH20 KRYPTON HYGROMETER is warranted by CAMPBELL SCIENTIFIC, INC. to be free from defects in materials and workmanship under normal use and service for twelve (12) months from date of shipment unless specified otherwise. Batteries have no warranty. CAMPBELL SCIENTIFIC, INC.'s obligation under this warranty is limited to repairing or replacing (at CAMPBELL SCIENTIFIC, INC.'s option) defective products.
KH20 Table of Contents PDF viewers note: These page numbers refer to the printed version of this document. Use the Adobe Acrobat® bookmarks tab for links to specific sections. 1. General Description.....................................................1 2. Specifications ..............................................................1 2.1 Measurements ...........................................................................................1 2.2 Electrical....................................................
KH20 Table of Contents Tables 1. Datalogger Connections for Differential Measurement ............................. 5 2. KH20 Calibration Ranges .......................................................................... 6 A-1. Linear Regression Results for KH20 ln(mV) vs. Vapor Density ...... A-2 A-2. Final Calibration Values for KH20....................................................
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-H2O), 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.
KH20 Krypton Hygrometer 2.3 Physical Dimensions Sensor Head: 11.5” x 9” x 1.25” (29 cm x 23 cm x 3 cm) Electronics Box: 7.5” x 5” x 2” (19 cm x 13 cm x 5 cm) Rain Shield with Mount: 11.5” x 7” x 2.5” (29 cm x 18 cm x 6.5 cm) Mounting Pipe: 20” (50 cm) Carrying Case: 25” x 15” x 7” (64 cm x 38 cm x 18 cm) Weight Sensor Head: 3.55 lbs (1.61 kg) Electronics Box: 1.4 lbs (6.4 kg) Rain Shield with Mount: 4.75 lbs (2.2 kg) Mounting Pipe with Nu-rail: 1.0 lbs (0.45 kg) Carrying Case: 9.45 lbs (4.
KH20 Krypton Hygrometer 3.2.2 Mounting the KH20 Sensor Mount the KH20 sensor head as follows: 1. Attach the 20 inch long mounting boom to the KH20. 2. Mount a crossarm onto a tripod or tower. 3. Mount the 12 inch long pipe (CSI p/n 18048) to a crossarm via 1” x 3/4” Nu-rail (CSI p/n 1049). 4. Mount the KH20 onto the 12” long pipe using a 3/4” x 3/4” Nu-rail (CSI p/n 1017). Mount the KH20 such that the source tube, the longer of the two tubes, is positioned on top, as shown in Figure 1.
KH20 Krypton Hygrometer 2. Before mounting the rain shield onto a tripod, first mount the electronics box inside the rain shield. Remove the four pan-head screws from the back panel of the rain shield. Align the electronics box, and use the four pan-head screws to secure the electronics box onto the back panel. Make sure the electronics box is pushed all the way up, and the screws are positioned at the bottom of the mounting slot on the electronics box (see Figure 2).
KH20 Krypton Hygrometer 4. Connect the three cables to the bottom of the electronics box around the U-bolt on the rain shield (see Figure 3). If there is not enough room for the connectors around the U-bolt, make sure the electronics box is mounted at a highest possible position (see step 2). FIGURE 3. Attaching cables to the electronics box. 5. Place the front cover back on the rain shield and tighten the two pan-head screws to secure it in place. 6.
KH20 Krypton Hygrometer 5. Datalogger Programming The KH20 sensor outputs 0 to 5 Vdc analog 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 vapor range of approximately 2 to 19 g/m3. The calibration is performed twice under the following two conditions: window clean, and scaled.
KH20 Krypton Hygrometer 5.2 Example 1, CR3000 Program to Measure Water Vapor Fluctuations The following example program measures the KH20 at 10Hz, and stores the average values into a data table called ‘stats’, as well as the raw data into a data table called ‘ts_data’. NOTE The KH20 cannot be used for measuring absolute water vapor concentration. 'CR3000 Series Datalogger 'This datalogger program measures KH20 Krypton Hygrometer.
KH20 Krypton Hygrometer '*** Variables *** Public panel_temp Public batt_volt Public kh(2) Public rho_w Alias kh(1) = kh_mV Alias kh (2) = ln_kh Units panel_temp = deg_C Units batt_volt = volts Units kh_mV = mV Units ln_kh = ln_mV Units rho_w = g/m^3 '*** Data Output Tables *** 'Processed data DataTable (stats,True,-1) DataInterval (0,OUTPUT_INTERVAL,Min,10) Minimum (1,batt_volt,FP2,False,False) Average (1,panel_temp,FP2,False) Average (2,kh(1),IEEE4,False) EndTable 'Raw time-series data.
KH20 Krypton Hygrometer 6. 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.
KH20 Krypton Hygrometer should see an immediate decrease in the voltage reading, and it should go close to zero. No noticeable change in the voltage output, when the optical path is completely blocked, indicates a problem in the detector tube. If the decrease in the voltage reading takes place but the reading remains below 50 mV, when the paper is removed from the optical path, the source tube may be at fault. Obtain an RMA from Campbell Scientific, Inc. and send the unit in for repair. 6.
Appendix A. Calibrating KH20 A.1 Basic Measurement Theory The KH20 uses an empirical relationship between the absorption of the light and the material through which the light travels. This relationship is known as the Beer’s law, the Beer-Lambert law, or the Lambert-Beer law. According to the Beer’s law, the log of the transmissivity is anti-proportional to the product of the absorption coefficient of the material, k, the distance the light travels, x, and the density of the absorbing material, ρ.
Appendix A. Calibrating KH20 8 7.5 KH2O Output (mV) 7 6.5 6 5.5 5 4.5 4 1.74 3.02 4.17 5.44 6.71 7.95 9.2 10.47 11.69 12.9 14.22 15.46 16.78 18.04 19.25 Vapor Density (g/m3) FIGURE A-1. KH20 ln(mV) vs. Vapor Density We can perform the linear regression on the plot above to obtain the slope for the relationship between the ln(mV) and the vapor density. The slope for the graph above will be the coefficient, kwx which we are after. Table A-1 below shows the result of linear regression analysis.
Appendix A. Calibrating KH20 the KH20 calibration certificate contains. The data shown in Table A-2 is from an actual KH20. TABLE A-2. Final Calibration Values for KH20 Vapor Range (g/m3) Slope (xkw) Y Intercept ln (V0) Coefficient (kw) Full Range 1.74 ~ 19.25 -0.205 3087 -0.144 Dry Range 1.74 ~ 9.20 -0.216 3259 -0.151 Wet Range 7.95 ~ 19.25 -0.201 2899 -0.
Appendix A.
Campbell Scientific Companies Campbell Scientific, Inc. (CSI) 815 West 1800 North Logan, Utah 84321 UNITED STATES www.campbellsci.com • info@campbellsci.com Campbell Scientific Africa Pty. Ltd. (CSAf) PO Box 2450 Somerset West 7129 SOUTH AFRICA www.csafrica.co.za • cleroux@csafrica.co.za Campbell Scientific Australia Pty. Ltd. (CSA) PO Box 444 Thuringowa Central QLD 4812 AUSTRALIA www.campbellsci.com.au • info@campbellsci.com.au Campbell Scientific do Brazil Ltda.
