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 dataloggers can measure. It has shorter rods than the CS650, for use in problem soils.
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. |
Rods | Not replaceable |
Sensors | Not interchangeable |
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 |
Current Drain |
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Active (3 ms) |
|
Quiescent | 135 µA typical (@ 12 Vdc) |
Electrical Conductivity |
|
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 |
Accuracy |
|
Precision | < 0.02 |
Volumetric Water Content |
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Range | 0 to 100% (with M4 command) |
Water Content Accuracy |
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Precision | < 0.05% |
Soil Temperature |
|
Range | -50° to +70°C |
Resolution | 0.001°C |
Accuracy |
|
Precision | ±0.02°C |
Please note: The following shows notable compatibility information. It is not a comprehensive list of all compatible 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 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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Campbell Scientific strongly discourages shortening the sensor’s rods. The electronics in the sensor head have been optimized to work with the 12 cm long rods. Shortening these rods will change the period average. Consequently, the equations in the firmware will become invalid and give inaccurate readings.
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.
A CS650 or CS655 can be ordered with an SDI-12 address option of -VS. With the -VS option, the SDI-12 address is set at the factory before the sensor is shipped. The last digit of the sensor’s serial number becomes that sensor’s SDI-12 address. Typically, the -VS option is chosen when there are multiple sensors that will communicate with the data logger on the same SDI-12 communications terminal.
If the -VS option is not selected when ordering, the CS650 or CS655 will ship with its SDI-12 address set to 0 (the default -DS option). The address can be changed to a non-zero value using the A200 Sensor to PC Interface or by connecting the sensor to an SDI-12 communications terminal and sending the aAb! Command as described in the “SDI-12 Sensor Support” appendix of the CS650/CS655 manual.
The CS650 and CS655 are warranted by Campbell Scientific to be free from defects in materials and workmanship under normal use and service for 12 months from the date of shipment. For further details, see the “Warranty” section of the CS650/CS655 manual.
The volumetric water content reading is the average water content over the length of the sensor’s rods.
Both the CS650 and the CS655 can detect water as far away as 10 cm in wet sand. That distance decreases as the soil dries down to approximately 4 cm in dry sand. In practice, a depth of 5 cm will give a water content reading that is within the sensor accuracy specification even if a small amount of air near the soil surface is detected and averaged into the reading.
Note: Campbell Scientific does not recommend installing the sensor in a depth shallower than 5 cm.
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.
Some customers have successfully used water content reflectometers, such as the CS650 and the CS655, to measure water content of wet concrete mix to ensure consistency between different batches of concrete. However, after concrete begins the curing process, salts are formed that make the electrical conductivity too high for the CS650 and the CS655 to operate. Thus, these sensors cannot be embedded in wet concrete to measure the water content of the concrete as it cures and dries.
Yes. Keeping the sensor rods parallel during installation is especially difficult in gravel, but it can be done. Gravel has large pore spaces that drain quickly, so the water content readings will likely show rapid changes between saturation and very dry. If small changes of water content at the dry end are of interest, a soil-specific calibration may need to be performed to convert period average directly to volumetric water content.
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.
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