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, 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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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.
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.
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 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.
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.
If a system has multiple CS650 or CS655 sensors, it will be necessary to connect many wires to a 12 V supply and many wires to ground. The DIN-Rail Mounting Kit is useful for attaching many wires to the same source in a clean and organized way. For more details, see the 5458 DIN-Rail Terminal Kit instruction manual.
Other methods of connecting several wires together, such as terminal strips or wire nuts, would also work.
The volumetric water content reading is the average water content over the length of the sensor’s rods.
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.
The electrical conductivity (EC) of sea water is approximately 48 dS/m. The CS655 can measure permittivity in water with EC between 0 and 8 dS/m. EC readings become extremely unstable at conductivities higher than 8 dS/m and are reported as NAN or 9999999. Because EC is part of the permittivity equation, an EC reading of NAN leads to a permittivity reading of NAN as well. Thus, the CS655 cannot provide good readings in sea water.
With regard to sea ice, the electrical conductivity drops significantly when sea water freezes and the permittivity changes from approximately 88 down to approximately 4, as the water changes from a liquid to a solid state. With both EC and permittivity falling to levels that are within the CS655 measurement range, the sensor is expected to give valid readings in sea ice. The sensor is rugged and can withstand the cold temperatures. However, as the ice melts, there will be a point at which the electrical conductivity becomes too high to acquire a valid reading for either permittivity or electrical conductivity.