CWS655900 MHz Wireless Soil-Water Probe

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1. 使用CWS655，在哪里进行电导率测量？

   大量的电导率（EC）测量是沿传感器杆进行的，它是在土壤前12厘米上的EC平均读数。

2. Can the CWS655 be repaired?

   Damage to the CWS655 electronics or rods cannot be repaired because these components are potted in epoxy. A faulty or damaged sensor needs to be replaced. For more information,refer to theRepair and Calibrationpage.

3. 使用CWS655，在哪里进行水含量测量？

   The volumetric water content reading is the average water content over the length of the sensor’s rods.

4. 关于CWS655，有机土壤有通用的校准方程吗？

   不. The equation used to determine volumetric water content in the firmware for the CWS655 is the Topp et al. (1980) equation, which works for a wide range of mineral soils but not for organic soils. In organic soils, the standard equations in the firmware will overestimate water content.

   When using a CWS655 in organic soil, it is best to perform a soil-specific calibration.有关执行土壤特异性校准的详细信息，refer to “The Water Content Reflectometer Method for Measuring Volumetric Water Content” section in theCS650/CS655手册. A linear or quadratic equation that relates period average to volumetric water content will work well.

5. With regard to the CWS655, is there a generic calibration equation for artificial soil?

   The equation used to determine volumetric water content in the firmware for the CWS655 is the Topp et al. (1980) equation, which works for a wide range of mineral soils but not necessarily for artificial soils that typically have high organic matter content and high clay content. In this type of soil, the standard equations in the firmware will overestimate water content.

   When using a CWS655 in artificial soil, it is best to perform a soil-specific calibration. For details on performing a soil-specific calibration,refer to “The Water Content Reflectometer Method for Measuring Volumetric Water Content” section in theCS650/CS655手册. A linear or quadratic equation that relates period average to volumetric water content will work well.

6. 如何校正CWS655读数的温度？

   There is not an easy way to correct CWS655 readings for temperature. The CWS655 temperature sensor is located inside the sensor’s epoxy head next to one of the sensor rods. The stainless-steel rods are not thermally conductive, causing the reported soil temperature reading to be the temperature of the sensor head near the soil surface. Because the sensor is installed vertically with the sensor head above ground, the soil temperature reading is not representative of the temperature over the length of the 12 cm rods, but the reading is closer to the temperature of the soil surface. Performing a temperature correction requires a separate temperature sensor to be buried at approximately 6 cm deep and combines that data with the values reported by the CWS655.

7. Can the CWS655 be calibrated by incremental insertion into saturated soil?

   不. The abrupt permittivity change at the interface of air and saturated soil causes a different period average response than would occur with the more gradual permittivity change found when the sensor rods are completely inserted in the soil.

   For example, if a CWS655 was inserted halfway into a saturated soil with a volumetric water content of 0.4, the probe would provide a different period average and permittivity reading than if the probe was fully inserted into the same soil when it had a volumetric water content of 0.2.

8. Does the CWS655 correct readings for temperature changes?

   否。温度传感器位于传感器杆之一旁边的传感器的环氧头部内部。不锈钢杆不是热导电的，因此报道的土壤温度读数实际上是在土壤表面附近的传感器头的温度。

   因为传感器是在接地上方的传感器头垂直安装的，所以土壤温度读数不能代表12 cm杆的长度，但读数更接近土壤表面的温度。由于温度读数不能代表水含量测量的土壤的整个厚度，因此没有尝试纠正温度变化的水含量读数。

9. Can the CWS655 measure water content in greenhouse pots?

   Yes, but the pots would have to be large. The CWS655 can detect water as far away as 10 cm (4 in.) from the rods. If the pot has a diameter smaller than 20 cm (8 in.), the CS655 could potentially detect the air around the pot, which would underestimate the water content. In addition, potting soil is typically high in organic matter and clay, causing the probably need for a soil-specific calibration.

10. How was the general calibration performed for the CWS655?

    Period average and electrical conductivity readings were taken with several CWS655 probes in solutions of varying permittivity and varying electrical conductivity at constant temperature. Coefficients were determined for a best fit of the data. The equation is of the form

    K_a(σ,τ) = C₀*σ³*τ²+ c₁*σ²*τ²+ c₂*σ*τ²+ c₃*τ²+ c₄*σ³*τ + C₅*σ²*τ + C₆*σ*τ + C₇*τ + C₈*σ³+ c₉*σ²+ c₁₀*σ + C₁₁

    where K_ais apparent dielectric permittivity, σ is bulk electrical conductivity (dS/m), τ is period average (μS), and C₁到c₁₁are constants.