The CS655 is a multiparameter smart sensor that uses innovative techniques to monitor soil volumetric-water content, bulk electrical conductivity, and temperature. It outputs an SDI-12 signal that many of our data loggers can measure. It has shorter rods than the CS650, for use in problem soils.
Note: The cable termination options for this sensor are not suitable for use with an ET107 station. For this type of station, use the CS655-LC sensor instead, which has a suitable cable connector.Read More
The CS655 consists of two 12-cm-long stainless steel rods connected to a printed circuit board. The circuit board is encapsulated in epoxy and a shielded cable is attached to the circuit board for data logger connection.
The CS655 measures propagation time, signal attenuation, and temperature. Dielectric permittivity, volumetric water content, and bulk electrical conductivity are then derived from these raw values.
Measured signal attenuation is used to correct for the loss effect on reflection detection and thus propagation time measurement. This loss-effect correction allows accurate water content measurements in soils with bulk EC ≤8 dS m-1 without performing a soil-specific calibration.
Soil bulk electrical conductivity is also calculated from the attenuation measurement. A thermistor in thermal contact with a probe rod near the epoxy surface measures temperature. Horizontal installation of the sensor provides accurate soil temperature measurement at the same depth as the water content. Temperature measurement in other orientations will be that of the region near the rod entrance into the epoxy body.
|Measurements Made||Soil electrical conductivity (EC), relative dielectric permittivity, volumetric water content (VWC), soil temperature|
|Required Equipment||Measurement system|
|Soil Suitability||Short rods are easy to install in hard soil. Suitable for soils with higher electrical conductivity.|
|Sensing Volume||3600 cm3 (~7.5 cm radius around each probe rod and 4.5 cm beyond the end of the rods)|
|Electromagnetic||CE compliant (Meets EN61326 requirements for protection against electrostatic discharge and surge.)|
|Operating Temperature Range||-50° to +70°C|
|Sensor Output||SDI-12; serial RS-232|
|Warm-up Time||3 s|
|Measurement Time||3 ms to measure; 600 ms to complete SDI-12 command|
|Power Supply Requirements||6 to 18 Vdc (Must be able to supply 45 mA @ 12 Vdc.)|
|Maximum Cable Length||610 m (2000 ft) combined length for up to 25 sensors connected to the same data logger control port|
|Rod Spacing||32 mm (1.3 in.)|
|Ingress Protection Rating||IP68|
|Rod Diameter||3.2 mm (0.13 in.)|
|Rod Length||120 mm (4.7 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)|
|Probe Weight||240 g (8.5 oz) without cable|
|Active (3 ms)||
|Quiescent||135 µA typical (@ 12 Vdc)|
|Range for Solution EC||0 to 8 dS/m|
|Range for Bulk EC||0 to 8 dS/m|
|Accuracy||±(5% of reading + 0.05 dS/m)|
|Precision||0.5% of BEC|
Relative Dielectric Permittivity
|Range||1 to 81|
Volumetric Water Content
|Range||0 to 100% (with M4 command)|
|Water Content Accuracy||
|Range||-50° to +70°C|
Note: The following shows notable compatibility information. It is not a comprehensive list of all compatible or incompatible products.
External RF sources can affect the probe’s operation. Therefore, the probe should be located away from significant sources of RF such as ac power lines and motors.
Multiple CS655 probes can be installed within 4 inches of each other when using the standard data logger SDI-12 “M” command. The SDI-12 “M” command allows only one probe to be enabled at a time.
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.
Current CS650 and CS655 firmware.
Note: The Device Configuration Utility and A200 Sensor-to-PC Interface are required to upload the included firmware to the sensor.
Number of FAQs related to CS655: 55
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Mine tailings are highly corrosive and have high electrical conductivity. Some customers have successfully used water content reflectometers, such as the CS650 or the CS655, to measure water content in mine tailings by coating the sensor rods with heat-shrink tubing. This affects the sensor output, and a soil-specific calibration must be performed. Care must be taken during installation to avoid damaging the heat-shrink tubing and exposing the sensor’s rods. In addition, covering the sensor’s rods invalidates the bulk electrical conductivity reading. Unless the temperature reading provided by the CS650 or the CS655 is necessary, a better option may be to use a CS616 with coated rods.
No. The principle that makes these sensors work is that liquid water has a dielectric permittivity of close to 80, while soil solid particles have a dielectric permittivity of approximately 3 to 6. Gasoline and other hydrocarbons have dielectric permittivities in the same range as soil particles, which essentially make them invisible to the CS650 and the CS655.
Because the reported volumetric water content reading is an average taken along the entire length of the rods, the sensor should be fully inserted into the soil. Otherwise, the reading will be the average of both the air and the soil, which will lead to an underestimation of water content. If the sensor rods are too long to go all the way into the soil, Campbell Scientific recommends inserting the rods at an angle until they are fully covered by soil.
Running the cable through electrical conduit or PVC pipe will protect the cable from rodents. A trench 30 to 60 cm deep will protect it from most other human or animal activity. Some customers have found that extra cable can be coiled and left inside a box, such as an irrigation valve box or something similar. When using a box, seal any holes that are large enough for rodents to enter. When cables are exposed on the ground surface, some customers have found that wrapping the cables in the metal screening used for screen doors discourages animals from chewing on them.
Yes, but the pots would have to be large. The CS650 and CS655 can detect water as far away as 10 cm (4 in.) from the rods. If the pot has a diameter smaller than 20 cm (8 in.), the sensor could potentially detect the air around the pot, which would underestimate the water content. In addition, potting soil is typically high in organic matter and clay, causing the probable need for a soil-specific calibration.
Period average and electrical conductivity readings were taken with several sensors in solutions of varying permittivity and varying electrical conductivity at constant temperature. Coefficients were determined for a best fit of the data. The equation is of the form
Ka(σ,τ) = C0*σ3*τ2 + C1*σ2*τ2 + C2*σ*τ2 + C3*τ2 + C4*σ3*τ + C5*σ2*τ + C6*σ*τ + C7*τ + C8*σ3 + C9*σ2 + C10*σ + C11
where Ka is apparent dielectric permittivity, σ is bulk electrical conductivity (dS/m), τ is period average (μS), and C1 to C11 are constants.
The CS650/CS655 manual gives a temperature correction that works in coarse sand, but it should be used cautiously with other soil types. If a temperature correction is required, it is best to determine a soil-specific temperature correction.
When correcting for temperature, the following effects contribute to the sensor output:
The interaction of these effects may be complicated. For example, with increasing temperature, two things happen at the same time: the falling permittivity of water is decreasing the period average, and the increasing EC is increasing the period average. The net result as to whether the period average goes up or down depends on how conductive the soil is and the contributions of the other temperature effects.
The CWS655 is a wireless sensor with measurement electronics, radio, and power supply all integrated in a single device. The CWS655, however, requires the use of a CWB100 base station radio connected to a data logger. Only the rods of the CWS655 should be buried in the soil; burying the body of the CWS655 will prevent the sensor from communicating with the CWB100.
The CS655 is a cabled multiparameter smart sensor that sends data by RS-232 serial or SDI-12 communication through a direct connection to a data logger. The CS655 is suitable for burial at any depth.
In soil that is sandy, sandy loam, or loamy sand with low electrical conductivity, the CS650 is a suitable option because it has slightly better accuracy specifications than the CS655 and a larger measurement volume.