High Accuracy and Precision
Designed for long-term monitoring
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Overview

The CS616 measures the volumetric water content from 0% to saturation. The probe outputs a megahertz oscillation frequency, which is scaled down and easily read by a Campbell Scientific datalogger.

Benefits and Features

  • Compatible with most Campbell Scientific dataloggers
  • High accuracy and high precision
  • Fast response time
  • Designed for long-term unattended water content monitoring
  • Compatible with AM16/32-series multiplexers allowing measurement of multiple sensors
  • Probe rods can be inserted from the surface or buried at any orientation to the surface.

Detailed Description

The CS616 is comprised of two 30-cm-long stainless steel rods connected to the measurement electronics. The circuit board is encapsulated in epoxy, and a shielded four-conductor cable is connected to the circuit board to supply power, enable probe, and monitor the output.

The CS616 measures the volumetric water content of porous media (such as soil) using the time-domain measurement method; a reflectometer (cable tester) such as the TDR100 is not required. This method consists of the CS616 generating an electromagnetic pulse. The elapsed travel time and pulse reflection are then measured and used to calculate soil volumetric water content.

Response Characteristics

The signal propagating along the parallel rods of the CS616 is attenuated by free ions in the soil solution and conductive constituents of the soil mineral fraction. In most applications, the attenuation is not enough to affect the CS616 response to changing water content, and the response is well described by the standard calibration. However, in soil with relatively high soil electrical conductivity levels, compacted soils, or soils with high clay content, the calibration should be adjusted for the specific medium. Guidance for making these adjustments is provided in the operating manual.

Specifications

  • Operational Temperature: 0° to +70°C
  • Probe-to-Probe Variability: ±0.5% VWC in dry soil, ±1.5% VWC in typical saturated soil
  • Accuracy: ±2.5% VWC using standard calibration with bulk electrical conductivity of ≤0.5 dS m-1, bulk density of ≤1.55 g cm-3, and measurement range of 0% VWC to 50% VWC
  • Precision: better than 0.1% VWC
  • Resolution: 0.1% VWC
  • Output: ±0.7 V square wave with frequency dependent on water content
  • Current Drain: 65 mA @ 12 Vdc (when enabled); 45 μA (quiescent typical)
  • Power Supply Voltage: 5 Vdc minimum;
    18 Vdc maximum
  • Enable Voltage: 4 Vdc minimum; 18 Vdc maximum
  • Electromagnetic: CE compliant; meets EN61326 requirements for protection against electrostatic discharge
  • Rod Length: 300 mm (11.8 in)
  • Rod Diameter: 3.2 mm (0.13 in)
  • Rod Spacing: 32 mm (1.3 in)
  • Probe Head Height: 85 mm (3.3 in)
  • Probe Head Width: 63 mm (2.5 in)
  • Probe Head Depth: 18 mm (0.7 in)
  • Weight without cable: 280 g (9.9 oz)
  • Cable Weight: 35 g per m (0.38 oz per ft)

Compatibility

RF Considerations

The RF emissions are below FCC and EU limits as specified in EN61326 if the CS616 is enabled less than 0.6 ms, and measurements are made less frequently than once a second. External RF sources can also affect the CS616 operation. Consequently, the CS616 should be located away from significant sources of RF such as ac power lines and motors.

Installation Tool

The CS650G makes inserting soil-water sensors easier in dense or rocky soils. This tool can be hammered into the soil with force that might damage the sensor if the CS650G were not used. It makes pilot holes into which the rods of the sensors can then be inserted. It replaces both the 14383 and 14384.

Datalogger Considerations

The reflectometer connects directly to one of the datalogger’s single-ended analog inputs. A datalogger control port is typically used to enable the CS616 for the amount of time required to make the measurement. Datalogger instructions convert the probe square-wave output to period which is converted to volumetric water content using a calibration.

Compatible Contemporary Datalogger

CR200(X) Series CR800/CR850 CR1000 CR3000 CR6 CR7X CR9000X

Compatible Retired Dataloggers

CR500 CR510 CR10 CR10X 21X CR23X CR9000 CR5000

Frequently Asked Questions

Number of FAQs related to CS616: 36

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  1. Yes, as long as the datalogger can detect a ±700 mV square wave over a frequency range of 29 to 67 kHz.

  2. Yes. For program examples and guidance on using a multiplexer with one of these reflectometers, see the CS616 and CS625 instruction manual.

  3. The CS616 has a faster period output than the CS615-L, so it does not work with the 21X dataloggers.

  4. The cable for the sensors is rugged and resistant to damage from the sun and typical weather conditions. However, it is susceptible to damage from rodents, machinery, shovels, and so forth. Running the cable through electrical conduit or PVC pipe will help protect it, but this is not an absolute requirement.  In areas where rodent activity is low, direct burial in a trench is usually sufficient. A particularly vulnerable location is where the buried cables exit the ground and enter the enclosure housing the datalogger. At that exit point, take steps to protect the cable from damage.  

  5. The period value is corrected to the temperature at which the water content calibration was performed, and then the water content equation is applied to the corrected period. Temperature correction is soil specific because the effect that temperature has on the period value varies with soil texture and electrical conductivity. A temperature correction equation that was developed for a sandy loam soil with low bulk electrical conductivity is provided in the CS616 and CS625 instruction manual.

  6. No. The output is too fast to be measured on the pulse channel of a 21X or CR7.

  7. If the electrical conductivity within the waste is less than 5 dS/m and there is good contact between the probe rods and the waste, the CS616/CS625 should respond predictably to changes in water content. The heterogeneous nature and changing bulk density of solid waste, however, make calibration difficult.

  8. Campbell Scientific does not recommend splicing sensor cables. Sensors may be ordered with custom cable lengths, and Campbell Scientific recommends purchasing the correct length for the application. If the sensor cable needs to be lengthened, a junction box (if practical) is a more favorable option than a splice.

    Note: A splice will void the sensor warranty, but a junction box does not modify the sensor and therefore does not void the warranty.

  9. Cutting down rods should only be done at the user’s own risk. Doing so will cause the probe to need recalibration. Campbell Scientific does not provide calibrations for shorter rod lengths for the CS616 or the CS625.

    With shorter rods, the probe will work, but there will be some reduction in accuracy because the length of the rod in the soil contributes a smaller proportion to the total transit time. However, probes with shorter rods will work in more saline soils.

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