CS655 12 cm Soil Water Content Reflectometer

Expand AllCollapse All

1. How was the general calibration performed for the CS650 and the CS655?

   Period average and electrical conductivity readings were taken with several sensors 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_a is apparent dielectric permittivity, σ is bulk electrical conductivity (dS/m), τ is period average (μS), and C₁ to C₁₁ are constants.

2. 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.

3. Do the CS650 and the CS655 have surge protection?

   Yes. There is surge protection built into the sensor electronics. The sensor survives a surge of 2 kV at 42 ohm line-to-ground on digital I/O and 2 kV at 12 ohm line-to-ground on power. It also survives a surge of 2 kV at 2 ohm line-to-ground on the rods.

   If additional surge protection is required, consider using the SVP100 Surge Voltage Protector DIN Rail with Mounting Hardware. 

4. 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.

5. 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.

6. What is the warranty for the CS650 and the CS655?

   The CS650 and CS655 are warranted by Campbell Scientific to be free from defects in materials and workmanship under normal use and service for 12 months from the date of shipment. For further details, see the “Warranty” section of the CS650/CS655 manual.

7. With the CS650 and the CS655, where is the water content measurement made?

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

8. 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.

9. With the CS650 and the CS655, where is the electrical conductivity measurement made?

   The bulk electrical conductivity (EC) measurement is made along the sensor rods, and it is an average reading of EC over that distance at whatever depth the rods are placed.

10. Can the CS655 rods be shortened?

    Campbell Scientific strongly discourages shortening the sensor’s rods. The electronics in the sensor head have been optimized to work with the 12 cm long rods. Shortening these rods will change the period average. Consequently, the equations in the firmware will become invalid and give inaccurate readings.