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
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.
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.
|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).|
|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|
|Output||±0.7 V square wave (with frequency dependent on water content)|
|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|
Note: The following shows notable compatibility information. It is not a comprehensive list of all compatible or incompatible products.
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.
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.
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.
Number of FAQs related to CS616: 36
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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.
Yes, as long as the data logger can detect a ±700 mV square wave over a frequency range of 29 to 67 kHz.
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.
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.
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.
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.
The CS616/CS625 can measure volumetric water content over the entire range from completely dry to saturation. A soil-specific calibration will improve accuracy, especially in very dry soil.
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.
The CS616 and CS625 are water-content reflectometers with measurement electronics built into the probe head. The electronics generate a signal, which is sent directly to the data logger. The CS610-L, and other three-rod probes sold by Campbell Scientific, are TDR probes that have no electronic components and serve as wave guides for a time-domain reflectometer such as the TDR100.
No. Although the CS616/CS625 could be calibrated to convert its period reading to the dielectric permittivity of snow, there is not an easy way to relate the permittivity to liquid water content. This is because the density of snow changes over time and the amount of liquid water that can be held in the solid matrix is relatively small. Additionally, the sensor emits infrared radiation that melts snow away from its rods, similar to the way snow melts around the base of a tree.
The CS616 and CS625 are not appropriate sensors for this application because of the lack of good contact between the rods and the snow, as well as the dynamic nature of the solid matrix.