Designed for long-term monitoring
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. Refer to the Compatibility section for datalogger compatibility.
Read MoreBenefits 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.
Technical 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.
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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 |
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| 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
Please note: The following shows notable compatibility information. It is not a comprehensive list of all compatible products.
Dataloggers
| Product | Compatible | Note |
|---|---|---|
| CR1000 (retired) | ||
| CR1000X | ||
| CR300 (retired) | ||
| CR3000 | ||
| CR310 | ||
| CR350 | ||
| CR6 | ||
| CR800 (retired) | ||
| CR850 (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.
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Technical Papers
Compliance
FAQs for
Number of FAQs related to CS616: 36
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Each CS616 connects to a single-ended analog input channel, so a maximum of 16 CS616 reflectometers may be connected to the wiring panel of a CR1000. For more than 16, consider using a multiplexer such as the AM16/32B. With a multiplexer, it is possible to read 48 CS616 reflectometers using only three single-ended analog input channels of the CR1000.
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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.
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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.
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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.
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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.
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Yes, as long as the data logger can detect a ±700 mV square wave over a frequency range of 29 to 67 kHz.
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Yes. The dielectric permittivity of water varies with temperature, which will cause the CS616/CS625 period to decrease with increasing temperature and increase with decreasing temperature. In addition, the electrical conductivity of the soil water solution is temperature dependent, causing the CS616/CS625 period to increase with increasing temperature and decrease with decreasing temperature. The net effect of those two opposing forces depends on the soil texture and electrical conductivity. The temperature correction equation in the CS616 and CS625 instruction manual was developed using a sandy loam soil with relatively low electrical conductivity. For soils with finer texture or higher electrical conductivity, Campbell Scientific recommends a soil-specific temperature correction equation.
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No. The output is too fast to be measured on the pulse channel of a 21X or CR7.
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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.
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The CS616/CS625 will survive frozen soil conditions, but the principle behind using bulk soil dielectric permittivity to estimate water content requires that the water be in liquid form. When soil water freezes, its dielectric drops from approximately 80 to 4, making it indistinguishable from soil solids. Consequently, the CS616/CS625 is not able to measure the water content of frozen soil.
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