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 data loggers can measure.
Note: The cable termination options for this sensor are not suitable for use with an ET107 station. For this type of station, use the CS650-LC sensor instead, which has a suitable cable connector.
Read MoreThe 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 data logger 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. |
Rods | Not replaceable |
Sensors | Not interchangeable |
Sensing Volume | 7800 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 | 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 |
Current Drain |
|
Active (3 ms) |
|
Quiescent | 135 µA typical (@ 12 Vdc) |
Electrical Conductivity |
|
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 |
Accuracy |
|
Precision | < 0.02 |
Volumetric Water Content |
|
Range | 0 to 100% (with M4 command) |
Water Content Accuracy |
|
Precision | < 0.05% |
Soil Temperature |
|
Range | -50° to +70°C |
Resolution | 0.001°C |
Accuracy |
|
Precision | ±0.02°C |
Note: The following shows notable compatibility information. It is not a comprehensive list of all compatible or incompatible products.
Product | Compatible | Note |
---|---|---|
CR1000 (retired) | ||
CR1000X | ||
CR300 | ||
CR3000 (retired) | ||
CR310 | ||
CR350 | ||
CR6 | ||
CR800 (retired) | ||
CR850 (retired) |
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 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 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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Campbell Scientific strongly discourages shortening the sensor’s rods. The electronics in the sensor head have been optimized to work with the 30 cm long rods. Shortening these rods will change the period average. Consequently, the equations in the firmware will become invalid and give inaccurate readings.
CS650 and CS655 sensors are read one at a time using SDI-12 commands. Consequently, they are never active at the same time and do not interfere with each other electrically. When installing the sensors close together, a general guideline is to keep them at least 10 cm apart.
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.
Modifications to the CS650 or CS655, including shortening the cable, will void the warranty. However, shortening the cable will not affect the sensor’s performance. If a decision is made to shorten the cable, care should be taken to avoid damaging the cable jacket and exposing bare wire except at the ends that connect to the data logger or multiplexer terminals.
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 permittivity of saturated sediments in a stream bed is expected to read somewhere between 25 and 42, while the permittivity of water is close to 80. A CS650 or CS655 installed in saturated sediments could be used to monitor sediment erosion. If the permittivity continuously increases beyond the initial saturated reading, this is an indication that sediment around the sensor rods has eroded and been replaced with water. A calibration could be performed that relates permittivity to the depth of the rods still in the sediment.
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.
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.
Damage to the CS650 or the CS655 electronics or rods cannot be repaired because these components are potted in epoxy. Cable damage, on the other hand, may possibly be repaired. For more information, refer to the Repair and Calibration page.
The CS650-series sensors have several logical tests built into their firmware to ensure that the sensors do not report a number that is known to be erroneous. Erroneous readings are either outside the sensor’s operational limits or outside of published accuracy specifications.
A reported value of NAN or 9999999 does not necessarily mean that there is a problem with the sensor hardware. The conditions outlined below can lead to a value of NAN or 9999999 for permittivity and volumetric water content.
SDI-12 communications issue
If all of the following are true, there is likely an issue with the SDI-12 communications between the sensor and the data logger: the sensor is being polled with an M1! SDI-12 command, the permittivity value reported is NAN, and subsequent values are all zeroes or never change. Possible causes include the following:
Calculated permittivity is less than 0 or greater than 88
The equation used to convert period average and electrical conductivity values to permittivity is a three-dimensional surface with two independent variables and eleven coefficients, plus an offset. Some rare combinations of period and electrical conductivity result in a permittivity calculation that is less than air (1) or greater than water at 0°C (88). These rare combinations are not expected when the sensor is in soil.
Bulk electrical conductivity (EC) is greater than 1.14 dS/m
When bulk electrical conductivity is greater than 1.14 dS/m, the solution EC is greater than 3 dS/m, which is the upper limit for accurate readings with the CS650. When this occurs, the soil is considered out-of-bounds and will report a value of NAN or 9999999 for both permittivity and volumetric water content.
Calculated permittivity is less than 80% of the permittivity limit
A permittivity limit based on the bulk electrical conductivity (EC) reading is used to determine whether the bulk EC at saturation exceeds the sensor’s operational limit. That permittivity limit is calculated and compared to the permittivity reading. If the measured permittivity is more than 20% beyond the permittivity limit, both permittivity and volumetric water content are reported as NAN or 9999999. This is the most common cause of NAN values with the CS650-series sensors, and it occurs because of the soil properties and not because of a sensor malfunction.
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