237 CAMPBELL | Alldatasheet
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5] SCIENTIFIC \\/ WHEN MEASUREMENTS MATTER Overview The 237 measures leaf wetness by determining the electrical resistance on the surface of the sensor (a wet surface is less resistant). It is primarily used to determine the percentage of time that a leaf surface is wet, versus the time it is dry. Benefits and Features & e Leaf Wetness Sensor Sensitive yet Durable Compatible with most Campbell Scientific dataloggers Note 1: The 237 is designed for short duration ac excitation; dc excitation or continuous ac excitation may damage the sensing grid. Note 2: Users of the 237F should contact Campbell Scientific for a copy of the manual. ) Sensor is shipped unpainted so customer can choose appropriate surface finish that best fits their application ) Imitates characteristics of a leaf Technical Description The 237 consists of a circuit board with interlacing gold- plated fingers. Condensation on the sensor lowers the resistance between the fingers, which is measured by the datalogger. Droplets must touch two fingers simultaneously to change the sensor resistance. For this reason, the 237 is typically coated with flat latex paint, which spreads water droplets. The colour and type of paint affect sensor performance. Campbell Scientific supplies the sensor unpainted allowing customers to determine the appropriate paint to apply to the sensor's surface. The appropriate pigmentation should closely emulate the properties of a typical leaf. Calibration The resistance of the sensor at the wet/dry transition point should be determined. A sharp change in resistance occurs in the wet-dry transition on the uncoated sensor; normally the transition is between 50 and 200 kohms. Coated sensors have a poorly defined transition which normally occurs from 20 kohms to above 1,000 kohms. For best results, the leaf wetness sensor should be field calibrated since the transition point will vary for different areas and vegetation. For comprehensive details, visit: www.campbellsci.eu/237
(uncoated sensor) Normally 20 to 1000 kohm (coated sensor) 0°to 100°C -40° to +150°C Sensor may crack when temperature drops below -40°C. Painting Hole Spacing Hole Diameter Dimensions Weight Sensor is shipped unpainted so customer can choose appropriate surface finish to best match the application. 6.73cm (2651n.) 0.54cm (0213in) 76x7.1x0.64cm (30x275x 0.251in) 91 g (3 0z) with 305 m (10 ft) cable For comprehensive details, visit: www.campbellsci.eu/237 CAMPBELL 80 Hathern Road, Shepshed, LE12 9GX UK | +(0)1509 828888 | sale@campbellsci.couk | www.campbellsci.eu SCIENTIFIC AUSTRALIA | BRAZIL | CANADA | CHINA | COSTA RICA | FRANCE | GERMANY | INDIA | SOUTH AFRICA | SPAIN | THAILAND | UK | USA ©2021 Campbell Scientific, Ltd. | 01/20/2021