CS616 30 cm Water Content Reflectometer
High Accuracy and Precision
Designed for long-term monitoring
weather applications water applications energy applications gas flux and turbulence applications infrastructure applications soil applications

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.

Read More

Benefits and Features

  • Compatible with most Campbell Scientific data loggers
  • 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.

Images

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

Measurements Made Volumetric water content (VWC) of porous media (such as soil)
Measurement Range 0% to saturation
Water Content Accuracy ±2.5% VWC (using standard calibration with bulk EC of ≤ 0.5 dS m-1, bulk density of ≤ 1.55 g cm-3, and measurement range of 0% to 50% VWC)
Required Equipment Measurement system
Soil Suitability Long rods and lower frequency are well-suited for soft soil with low electrical conductivity (< 2 dS/m).
Rods Not replaceable
Sensors Not interchangeable
Operating Temperature Range 0° to +70°C
Probe-to-Probe Variability ±0.5% VWC in dry soil, ±1.5% VWC in typical saturated soil
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 Spacing 32 mm (1.3 in.)
Rod Diameter 3.2 mm (0.13 in.)
Rod Length 300 mm (11.8 in.)
Probe Head Dimensions 85 x 63 x 18 mm (3.3 x 2.5 x 0.7 in.)
Cable Weight 35 g per m (0.38 oz per ft)
Weight 280 g (9.9 oz) without cable

Compatibility

Note: The following shows notable compatibility information. It is not a comprehensive list of all compatible or incompatible products.

Dataloggers

Product Compatible Note
21X (retired)
CR10 (retired)
CR1000 (retired)
CR1000X
CR10X (retired)
CR200X (retired)
CR206X (retired)
CR211X (retired)
CR216X (retired)
CR23X (retired)
CR295X (retired)
CR300
CR3000
CR310
CR500 (retired)
CR5000 (retired)
CR510 (retired)
CR6
CR800
CR850
CR9000 (retired)
CR9000X (retired)

Additional Compatibility Information

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 was not used. It makes pilot holes into which the rods of the sensors can then be inserted. It replaces both the 14383 and 14384.

Data Logger Considerations

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


Frequently Asked Questions

Number of FAQs related to CS616: 36

Expand AllCollapse All

  1. Yes. The rugged design of the CS616/CS625 protects the probe electronics from water under these conditions. Many CS616/CS625 reflectometers have been working reliably in very wet conditions for more than ten years.

  2. The sensitive volume of the CS616/CS625 varies with water content. A general guideline is that the sensitive volume is within approximately a 32 mm radius from each rod.

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

  4. If a soil-specific calibration is performed, the CS616/CS625 may be used in soil with a maximum bulk electrical conductivity of 5 dS/m.

  5. Some customers have tried to use the CS616 or CS625 to measure the moisture content within a tree, but the calibration proved to be problematic. Campbell Scientific cannot provide any specific guidance for this application.

  6. 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 data logger. At that exit point, take steps to protect the cable from damage.  

  7. 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.

  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. If the new site has soil with a different soil type, a soil-specific calibration may be needed. For soil that is sandy or sandy loam with low bulk electrical conductivity, the calibration equation in the CS616 and CS625 instruction manual works well. 

Case Studies

South Korea: Damage from Freezing Roads
Korea Expressway Corporation (KEC) was established in 1969 to construct and manage expressways throughout South......read more
Delaware: Environmental Observing System
The Delaware Environmental Observing System (DEOS) is a real-time system dedicated to monitoring environmental conditions......read more
West Texas Mesonet
The West Texas Mesonet (WTM) project was initiated by Texas Tech University in 1999 to......read more