The CS650 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 dataloggers can measure.
The CS650 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 cable is attached to the circuit board for datalogger connection.
The CS650 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 ≤3 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||Long rods with large sensing volume (> 6 L) are suitable for soils with low to moderate electrical conductivity.|
|Sensing Volume||7800 cm3 (~7.5 cm radius around each probe rod and 4.5 cm beyond the end of the rods)|
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||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)|
|Probe Weight||280 g (9.9 oz) without cable|
|Active (3 ms)||
|Quiescent||135 µA typical (@ 12 Vdc)|
|Range for Solution EC||0 to 3 dS/m|
|Range for Bulk EC||0 to 3 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|
Please note: The following shows notable compatibility information. It is not a comprehensive list of all compatible 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 CS650 sensors can be installed within 4 inches of each other when using the standard datalogger 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 were 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 CS650: 54
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Three of the values returned by the M3! command are never changed to NAN by logical tests. If non-zero readings for soil temperature, period average, and voltage ratio are displayed, the sensor is working.
A simple test in air and water will also show whether the CS650 or CS655 is functioning. When performing this test, look at the permittivity value and not the water content value. In air, the sensor will read a permittivity value of 1. In room-temperature water, the value should be close to 80. The water container should have a diameter of at least 20 cm (8 in.) and a depth of 33 cm (13 in.). A smaller container will result in a lower permittivity value because the sensor will be measuring some of the air outside the container as well as the water. Tap water is acceptable for this test.
The dielectric of water at room temperature is close to 80. The firmware for both the CS650 and the CS655 is programmed to change volumetric water content to NAN or 9999999 when the permittivity measurements are greater than 42. When testing in water, look at the permittivity reading rather than the water content reading. If a test is being done for functionality, pull the sensor about halfway out of the water to see both permittivity and volumetric water content readings.
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. When liquid water freezes, its dielectric permittivity drops to 3.8, essentially making it look like soil particles to the sensor. A CS650 or CS655 installed in soil that freezes would show a rapid decline in its volumetric water content reading with corresponding temperature readings that are below 0°C. As the soil freezes down below the measurement range of the sensor, the water content values would stop changing and remain steady for as long as the soil remains frozen.
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.
The CS650 and the CS655 are not ideal sensors for measuring water level. However, these sensors do respond to the abrupt change in permittivity at the air/water interface. A calibration could be performed to relate the period average or permittivity reading to the distance along the sensor rods where the air/water interface is located. From that, the water level can be determined. The permittivity of water is temperature dependent, so a temperature correction would be needed to acquire accurate results.
No. The abrupt permittivity change at the interface of air and saturated soil causes a different period average response than would occur with the more gradual permittivity change found when the sensor rods are completely inserted in the soil.
For example, if a CS650 or a CS655 was inserted halfway into a saturated soil with a volumetric water content of 0.4, the sensor would provide a different period average and permittivity reading than if the probe was fully inserted into the same soil when it had a volumetric water content of 0.2.
If information is available on soil texture, organic matter content, and electrical conductivity (EC) from soil surveys or lab testing of the soil, it should be possible to tell if the soil conditions fall outside the range of operation of the sensor. Without this information, an educated guess can be made based on soil texture, climate, and management:
When in doubt about soil texture and electrical conductivity, Campbell Scientific recommends using a CS655 because of the sensor’s wider range of operation in electrically conductive soils, as compared with the CS650.
No. The equation used to determine volumetric water content in the firmware for the CS650 and the CS655 is the Topp et al. (1980) equation, which works for a wide range of mineral soils but not for organic soils. In organic soils, the standard equations in the firmware will overestimate water content.
When using a CS650 or a CS655 in organic soil, it is best to perform a soil-specific calibration. For details on performing a soil-specific calibration, refer to “The Water Content Reflectometer Method for Measuring Volumetric Water Content” section in the CS650/CS655 manual. A linear or quadratic equation that relates period average to volumetric water content will work well.
No. The equation used to determine volumetric water content in the firmware for the CS650 and the CS655 is the Topp et al. (1980) equation, which works for a wide range of mineral soils but not necessarily for artificial soils that typically have high organic matter content and high clay content. In this type of soil, the standard equations in the firmware will overestimate water content.
When using a CS650 or a CS655 in artificial soil, it is best to perform a soil-specific calibration. For details on performing a soil-specific calibration, refer to “The Water Content Reflectometer Method for Measuring Volumetric Water Content” section in the CS650/CS655 manual. A linear or quadratic equation that relates period average to volumetric water content will work well.
No. The temperature sensor is located inside the sensor’s epoxy head next to one of the sensor rods. The stainless-steel rods are not thermally conductive, so the reported soil temperature reading is actually the temperature of the sensor head. If the CS650 or the CS655 is installed horizontally, which is the preferred method, then the sensor head will be at the same temperature as the soil, and the soil temperature value will be accurate. However, if the sensor is installed vertically, and/or with the sensor head above ground, the soil temperature reading will be less accurate. Because the sensor orientation is not known, no temperature correction was written into the firmware.