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CS625 Water Content Reflectometer for CR200(X)-Series and CR300-Series
Services Available
Repair Yes
Calibration No
Free Support Yes

Overview

The CS625 measures the volumetric water content from 0% to saturation. It is similar to our CS616 but is designed specifically for CR200(X) and CR300-series dataloggers. This reflectometer has a 0 to 3.3 V square wave frequency output that our CR300-series and CR200(X)-series dataloggers can measure.

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Benefits and Features

  • High accuracy and high precision
  • Fast response time
  • Designed for long-term unattended water content monitoring
  • Probe rods can be inserted from the surface or buried at any orientation to the surface.

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Detailed Description

The CS625 consists of two 30-cm-long stainless steel rods connected to a printed circuit board. 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 CS625 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 CS625 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 CS625 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 CS625 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 of porous media (such as soil)
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 0.1% VWC
Resolution 0.1% VWC
Output 0 to 3.3 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.

Data Loggers

Product Compatible Note
CR1000 (retired)
CR200X (retired)
CR206X (retired)
CR211X (retired)
CR216X (retired)
CR295X (retired)
CR300 (retired)
CR3000
CR310 (retired)
CR5000 (retired)
CR800
CR850
CR9000X (retired)

Additional Compatibility Information

RF Considerations

The RF emissions are below FCC and EU limits as specified in EN61326 if the CS625 is enabled less than 0.6 ms, and measurements are made less frequently than once a second. External RF sources can also affect the CS625 operation. Consequently, the CS625 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.

Data Logger Considerations

Each CS625 requires a single-ended input channel. A control port is used to enable one or more probes.

Note: A maximum of four CS625 probes can be measured by one CR200(X) datalogger. Valid channel options are analog channels 1 through 4.


Frequently Asked Questions

Number of FAQs related to CS625: 34

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  1. Yes, as long as the data logger can detect a 0 to 3300 mV square wave over a frequency range of 29 to 67 kHz.

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

  3. Yes. The PeriodAvg() CRBasic instruction may be used to measure the CS625 on a CR1000, CR800-series, or CR3000 datalogger. To make this work, it is important that the Threshold parameter be set to 1650 mV as shown in the following example:

        PortSet (1 ,1 ) ‘Enable CS625 by setting C1 high (orange wire to C1)

        PeriodAvg (PA_uS,1,mV250,1,1650,0,100,10,1.0,0) ‘Read Period on SE1 (green wire to SE1)

        PortSet (1 ,0) ‘Disable CS625 by setting C1 low

  4. Yes, but the CS616/CS625 will need a soil-specific calibration. The high organic matter content of peat will likely cause the CS616/CS625 period to be out of bounds for use with the CS616() CRBasic instruction and P138 Edlog instruction. In that situation, the CRBasic PeriodAvg() instructionor the Edlog P27 Period Average instruction may be used as described in the CS616 and CS625 instruction manual.

  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. Fine roots do not significantly affect the CS616/CS625 reading.

  7. 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.

  8. As long as the period value in the saturated soil is less than 42 ms, “NAN” will not be displayed.  Conditions that can cause the period value to be too high include high electrical conductivity, high clay content, and high organic matter content. Under those conditions, it may be possible to get good results by using the PeriodAvg() or P27 instruction with a soil-specific calibration equation.

  9. 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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