LWS-L Dielectric Leaf Wetness Sensor Revision: 3/09 C o p y r i g h t © 2 0 0 8 - 2 0 0 9 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 LWS-L DIELECTRIC LEAF WETNESS SENSOR 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.
LWS-L 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 3. Installation....................................................................2 4. Wiring............................................................................3 5.
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LWS-L Dielectric Leaf Wetness Sensor 1. General Description Direct measurement of leaf wetness is problematic. Secure long-term attachment of a sensor to a representative living leaf is difficult. Leaf position, sun exposure, and health are in constant flux. To avoid these problems, leaf wetness “sensors” have been developed to estimate by inference the wetness of nearby leaves. The LWS-L estimates leaf surface wetness by measuring the dielectric constant of the sensor’s upper surface.
LWS-L Dielectric Leaf Wetness Sensor mounting holes circuitry sensing area FIGURE 1. LWS-L Dielectric Leaf Wetness Sensor 3. Installation The LWS-L is designed to be mounted on a small diameter rod. Deployment in a plant canopy or on a weather station mast is typical. Two holes in the sensor body are available for mounting with zip ties or 4-40 bolts. FIGURE 2.
LWS-L Dielectric Leaf Wetness Sensor 4. Wiring CR800/850 CR5000 CR3000 CR1000 CR500/510 CR10/10X 21X CR7 CR23X CR200 Color Description White Excitation Switched Excitation Switched Excitation Switched Excitation Switched Excitation Red Analog Out SingleEnded Channel SingleEnded Channel SingleEnded Channel SingleEnded Channel Bare Analog Ground AG 5. Measurement The LWS-L requires excitation voltage between 2.5 and 5 VDC.
LWS-L Dielectric Leaf Wetness Sensor FIGURE 3. Typical LWS-L Response Duration of leaf wetness can be determined either by post processing of data, or by programming the datalogger to accumulate time of wetness based on the Boolean threshold. Accumulation of dust and debris, such as avian fecal matter, will change the Boolean threshold.
LWS-L Dielectric Leaf Wetness Sensor 7.2 Leaf Mimicry The LWS-L is designed to approximate the thermodynamic properties of most leaves. If the specific heat of a typical leaf is estimated at 3750 J kg-1 K-1, density estimated at 0.95 g/cm3, and thickness estimated at 0.4 mm, then the heat capacity of the leaf is ≈1425 J m-2 K-1. This heat capacity is closely approximated by the thin (0.65mm) fiberglass construction of the LWS-L, which has a heat capacity of 1480 J m-2 K-1.
LWS-L Dielectric Leaf Wetness Sensor 8.2 CR1000 Datalogger Program Color Description CR1000 White Excitation EX1 or VX1 Red Analog Out SE1 Bare Analog Ground Public LWS_mV BeginProg Scan(60,Sec, 3, 0) ‘BRHalf(Dest,Reps,Range,SeChan,ExChan,MeasPEx,ExmV,RevEx,Settling,Integ,Mult,Offset) BRHalf(LWS_mV, 1, mV2500, 1, VX1, 1, 2500, False, 10000, _60Hz, 2500, 0) NextScan EndProg 9.
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.
