CS650 30 cm Soil Moisture and Temperature Sensor
Innovative
More accurate in soils with high bulk electrical conductivity
weather applications water applications energy applications gas flux and turbulence applications infrastructure applications soil applications

Overview

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.

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Benefits and Features

  • More accurate water content measurements in soils with bulk EC up to 3 dS m-1 without performing a soil-specific calibration
  • Larger sample volume reduces error
  • Measurement corrected for effects of soil texture and electrical conductivity
  • Estimates soil-water content for a wide range of mineral soils
  • Versatile sensor—measures dielectric permittivity, bulk electrical conductivity (EC), and soil temperature

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Detailed Description

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 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.

 

Specifications

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)
  • 45 mA typical (@ 12 Vdc)
  • 80 mA (@ 6 Vdc)
  • 35 mA (@ 18 Vdc)
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
  • ±(2% of reading + 0.6) from 1 to 40 for solution EC ≤ 3 dS/m
  • ±1.4 (from 40 to 81 for solution EC ≤1 dS/m)
Precision < 0.02

Volumetric Water Content

Range 0 to 100% (with M4 command)
Water Content Accuracy
  • ±1% (with soil-specific calibration)
  • ±3% (typical with factory VWC model) where solution EC < 3 dS/m
Precision < 0.05%

Soil Temperature

Range -50° to +70°C
Resolution 0.001°C
Accuracy
  • ±0.1°C (for typical soil temperatures [0 to 40°C] when probe body is buried in soil)
  • ±0.5°C (for full temperature range)
Precision ±0.02°C

Compatibility

Note: The following shows notable compatibility information. It is not a comprehensive list of all compatible or incompatible products.

Data Loggers

Product Compatible Note
CR1000 (retired)
CR1000X
CR300
CR3000 (retired)
CR310
CR350
CR6
CR800 (retired)
CR850 (retired)

Additional Compatibility Information

RF Considerations

External RF Sources

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.

Interprobe Interference

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.

Installation Tool

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.

Downloads

CS650 / CS655 Firmware v.2 (429 KB) 12-02-2015

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.

View Update History

Frequently Asked Questions

Number of FAQs related to CS650: 54

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  1. 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.

  2. 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.

  3. 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.

  4. 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.

  5. 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.

  6. Campbell Scientific does not recommend using the CS650 or the CS655 to measure water content in compost. A compost pile is a very hostile environment for making dielectric measurements with soil water content sensors. All of the following combine to make it very difficult to determine a calibration function: high temperature, high and varying electrical conductivity, high organic matter content, heterogeneity of the material in the pile, changing particle size, and changing bulk density. The temperature and electrical conductivity values reported by the CS650 or CS655 may give some useful information about processes occurring in the compost pile, but these sensors will not be able to give useful readings for water content.  

  7. 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. 

  8. 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.  

  9. 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.

  10. No. It is not possible to disable the logical tests in the firmware. If soil conditions cause frequent NAN values, it may be possible to perform a soil-specific calibration that will provide good results.

    If permittivity is reported but the volumetric water content value is NAN, Campbell Scientific recommends a soil-specific calibration that converts permittivity to water content. This will take advantage of the bulk electrical conductivity correction that occurs in the firmware.

    If both permittivity and volumetric water content have NAN values, it may be possible to perform a calibration that converts period average directly to volumetric water content.

    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. After a soil-specific equation is determined, it may be programmed into the data logger program or used in a spreadsheet to calculate the soil water content.

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