CS655 Bodenfeuchtesensor 12cm

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1. Can the CS650 and the CS655 be repaired?

   Damage to the CS650 or the CS655 electronics or rods cannot be repaired because these components are potted in epoxy. Cable damage, on the other hand, may possibly be repaired. For more information, refer to the Repair and Calibration page.

2. What are the major differences between the CWS655 and the CS655?

   The CWS655 is a wireless sensor with measurement electronics, radio, and power supply all integrated in a single device. The CWS655, however, requires the use of a CWB100 base station radio connected to a datalogger. Only the rods of the CWS655 should be buried in the soil; burying the body of the CWS655 will prevent the sensor from communicating with the CWB100.

   The CS655 is a cabled multiparameter smart sensor that sends data by RS-232 serial or SDI-12 communication through a direct connection to a datalogger. The CS655 is suitable for burial at any depth.

3. Can the CS650 and the CS655 measure water content in compost?

   Campbell Scientific does not recommend using the CS650 or the CS655 to measure water content in compost. A compost pile is a very hostile environment for making dielectric measurements with soil water content sensors. All of the following combine to make it very difficult to determine a calibration function: high temperature, high and varying electrical conductivity, high organic matter content, heterogeneity of the material in the pile, changing particle size, and changing bulk density. The temperature and electrical conductivity values reported by the CS650 or CS655 may give some useful information about processes occurring in the compost pile, but these sensors will not be able to give useful readings for water content.  

4. How can it be determined if soil is out-of-bounds for a CS650 or a CS655?

   If information is available on soil texture, organic matter content, and electrical conductivity (EC) from soil surveys or lab testing of the soil, it should be possible to tell if the soil conditions fall outside the range of operation of the sensor. Without this information, an educated guess can be made based on soil texture, climate, and management:

   • Soil that is coarse textured (such as sand, loamy sand, or sandy loam) works well with a CS650 if the EC is low.
   • If the soil is located in an arid or semiarid region, it may have high EC.
   • If the soil is frequently fertilized or irrigated with water that has higher EC, it may have high EC.
   • If the climate provides enough rain to flush accumulated salts below the root zone, the EC is expected to be low and suitable for a CS650.

   When in doubt about soil texture and electrical conductivity, Campbell Scientific recommends using a CS655 because of the sensor’s wider range of operation in electrically conductive soils, as compared with the CS650.

5. With regard to the CS650 and the CS655, is there a generic calibration equation for organic soil?

   No. The equation used to determine volumetric water content in the firmware for the CS650 and the CS655 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 CS650 or a CS655 in organic 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 the CS650/CS655 manual. A linear or quadratic equation that relates period average to volumetric water content will work well.

6. On the CS650 and the CS655, is it possible to disable the logic that causes NAN values?

   No. It is not possible to disable the logical tests in the firmware. If soil conditions cause frequent NAN values, it may be possible to perform a soil-specific calibration that will provide good results.

   If permittivity is reported but the volumetric water content value is NAN, Campbell Scientific recommends a soil-specific calibration that converts permittivity to water content. This will take advantage of the bulk electrical conductivity correction that occurs in the firmware.

   If both permittivity and volumetric water content have NAN values, it may be possible to perform a calibration that converts period average directly to volumetric water content.

   For details on performing a soil-specific calibration, refer to “The Water Content Reflectometer Method for Measuring Volumetric Water Content” section in the CS650/CS655 manual. After a soil-specific equation is determined, it may be programmed into the data logger program or used in a spreadsheet to calculate the soil water content.

7. How are the CS650 and the CS655 different?

   The CS650 has rods that are 30 cm long, and the CS655 has rods that are 12 cm long. The difference in rod length causes some changes in specifications. For example, the CS650 is slightly more accurate in its permittivity and water content readings, but the CS655 works over a larger range of electrical conductivity. In addition, the CS650 handles a larger measurement volume and provides good accuracy in low EC (electrical conductivity) sand and sandy loam. The CS655 is typically more accurate in soil, works well over a wide range of soil textures and EC, and is easier to install because of its shorter rods.

8. What is the -VS option for the CS650 and the CS655?

   A CS650 or CS655 can be ordered with an SDI-12 address option of -VS. With the -VS option, the SDI-12 address is set at the factory before the sensor is shipped. The last digit of the sensor’s serial number becomes that sensor’s SDI-12 address. Typically, the -VS option is chosen when there are multiple sensors that will communicate with the data logger on the same SDI-12 communications terminal. 

   If the -VS option is not selected when ordering, the CS650 or CS655 will ship with its SDI-12 address set to 0 (the default -DS option). The address can be changed to a non-zero value using the A200 Sensor to PC Interface or by connecting the sensor to an SDI-12 communications terminal and sending the aAb! Command as described in the “SDI-12 Sensor Support” appendix of the CS650/CS655 manual.

9. Is it necessary to purchase a DIN Rail Mounting Kit with a CS650 or a CS655?

   If a system has multiple CS650 or CS655 sensors, it will be necessary to connect many wires to a 12 V supply and many wires to ground. The DIN Rail Mounting Kit is useful for attaching many wires to the same source in a clean and organized way. For more details, see the 5458 DIN Rail Terminal Kit instruction manual. 

   Other methods of connecting several wires together, such as terminal strips or wire nuts, would also work.

10. With the CS650 and the CS655, where is the soil temperature measurement made?

    A thermistor is encased in the epoxy head of the sensor next to one of the stainless-steel rods. This provides an accurate point measurement of temperature at the depth where that portion of the sensor head is in contact with the soil. This is why a horizontal placement is the recommended orientation of the CS650 or CS655. The temperature measurement is not averaged over the length of the sensor rods.