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Resumen
La sonda 237 mide la humectación en hoja determinando la resistencia eléctrica de la superficie del sensor (mayor humectación implica menor valor de resistencia). Este sensor se utiliza principalmente para determinar el porcentaje de tiempo que la superficie de la hoja está humeda y seca.
El modelo flexible 237F permite adaptarlo a superficies curvas.
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.
Leer másVentajas y características
- El sensor se entrega sin pintar de forma que el usuario escoja la finalización de la superficie y que mejor se adapte a sus necesidades
- Imita características de una hoja
Imágenes
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Descripción detallada
El 237 consiste en una placa de circuito impreso que en una de sus capas tiene chapado un entralazado dorado. La presencia de condensación hace que la resistencia disminuya, la cual es medida por el datalogger.
Las gotas de agua deben tocar dos de las lineas simultáneamente para cambiar la resistencia del sensor. Por esta razón, al 237 se le aplica habitualmente una capa de pintura latex, que esparce las gotas de agua. El color y el tipo de pintura afectan al rendimiento del sensor. Campbell Scientific suministra el sensor sin pintar, de manera que el usuario puede aplicar la que considere conveniente. La pigmentación debería emular lo mejor posible las propiedades de la hoja.
Calibración
Debe determinarse el punto de transición de húmedo-seco. Si el sensor no se pinta, existe un cambio brusco en la transición húmedo-seco; normalmente la transición se produce entre los 50 y 200 kohms. Los sensores pintados no tienen bien definida la transición, la cual se produce desde 20 kohms a por encima de 1,000 kohms. Para obtener buenas medidas, lo mejor es calibrar el sensor en campo, dado que el punto de transición variará según el área y vegetación.
Especificaciones
| Resistance at Wet/Dry Transition |
|
| Operating Temperature Range | 0° to 100°C |
| Short-Term Survivability Temperature Range |
-40° to +150°C Sensor may crack when temperature drops below -40°C. |
| Painting | Sensor is shipped unpainted so customer can choose appropriate surface finish to best match the application. |
| Hole Spacing | 6.73 cm (2.65 in.) |
| Hole Diameter | 0.54 cm (0.213 in.) |
| Dimensions | 7.6 x 7.1 x 0.64 cm (3.0 x 2.75 x 0.25 in.) |
| Weight | 91 g (3 oz) with 3.05 m (10 ft) cable |
Compatibilidad
Nota: lo siguiente muestra información de compatibilidad notable. No es una lista de todos los productos compatibles.
Dataloggers
| Producto | Compatible | Nota |
|---|---|---|
| CR1000 (retired) | ||
| CR1000X | ||
| CR300 | ||
| CR3000 (retired) | ||
| CR310 | ||
| CR350 | ||
| CR6 | ||
| CR800 (retired) | ||
| CR850 (retired) |
Información de compatibilidad adicional
Data Logger Considerations
The 237 requires one single-ended analog input and one switched excitation channel for measurement.
Documentos
Folletos producto
Manuales
Preguntas frecuentes
Número de FAQs relacionadas con 237: 13
Expandir todoDesplegar todo
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Approximately 0.9 mm.
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Variable, but always negligible. The theoretical maximum for each measurement is 5000 mV at 5 µA for less than 3 ms.
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Paint only with a flat latex paint. Usually, a high-quality, white, flat latex paint is used with a tiny amount of pigment.
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The mounting method used depends on the application. In plant canopies, consider mounting the 237-L so that it receives the least amount of solar radiation at noon. This means tipping the sensor, electrodes up, so that its sensing surface is parallel to the plane of the ecliptic. Tipping the sensor also minimizes the chance of water puddling on its surface.
On non-living surfaces, such as a man-made structure, consider mounting the 237-L flat against a flat surface on the shady side. This will cause the 237-L’s thermal characteristics to be more similar to those of the surface being studied.
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Yes. The thermal characteristics of the 237-L are probably different from those of any surrounding objects, including leaves. Consequently, the 237-L will dry at a rate different from surrounding objects, including leaves.
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No. The sensor signal can only be interpreted as either wet or dry.
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The 237-L is not designed to be used as a conductivity sensor. To our knowledge, a few people have tried this but have been unsuccessful.
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Only in the most basic sense. The signal output from the 237-L can only be interpreted as an indication of the presence of a conductive material bridging the two electrodes on its surface. If the circuit is open (infinite resistance or zero conductance), there is no conductive material. If the circuit is closed, there is conductive material.
The primary use of the 237-L is to indicate the presence of free water on the surface of surrounding objects. The thermal characteristics of the 237-L are probably different from those of any surrounding objects, including leaves. Consequently, the 237-L will dry at a rate different from surrounding objects, including leaves. Data from the 237-L are only interchangeable from measurement site to measurement site if the following are true:
- Each 237-L is prepared and maintained in the same way.
- Each 237-L is mounted in nearly identical environments.
Plant disease researchers found that if a 237-L sensor was placed in a plant canopy at a consistent position, with a consistent coating of a spreading material on its surface (that is, paint), they could estimate when free water was in the plant canopy. From this discovery, they were able to formulate disease emergence models. The resulting models tolerate significant deviation in moisture-presence data. Even so, use of a different spreading material, or difference in sensor positioning, may invalidate the data.
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Both leaf wetness sensors are compatible with all Campbell Scientific data loggers. However, the 237-L is often used in large legacy networks that rely on the 237-L for data continuity. The 237-L does require painting and field calibration, whereas the LWS does not.
Casos de aplicación
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