Overview

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.

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Benefits and Features

  • 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 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 datalogger 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.

Specifications

General

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.)
Operational Temperature -10° 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 10 sensors connected to the same datalogger control port
Rod Spacing 32 mm (1.3 in.)
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

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 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
  • ±(3% of reading + 0.8) from 1 to 40 for solution electrical conductivity ≤ 8 dS/m
  • ±2 (from 40 to 81 for solution electrical conductivity ≤ 2.8 dS/m)
Precision < 0.02

Volumetric Water Content

-NOTE- Using Topp Equation (m3/m3)
Range 5% to 50%
Accuracy ±3% VWC (typical in mineral soils that have solution electrical conductivity ≤ 10 dS/m)
Precision < 0.05%

Soil Temperature

Range -10° to +70°C
Accuracy ±0.5°C (for probe body buried in soil)
Precision ±0.02°C

Compatibility

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 CS655 probes 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.

Installation Tools

14384 Pilot Tool

The 14384 Pilot Tool has rods with similar diameters and the same spacing as the probe. The tool can be driven into the soil using force levels that might damage the probe. After removing the 14384, the probe is inserted into the established holes.

14383 Installation Tool

The 14383 Installation Tool can be used to help maintain the proper spacing and parallel orientation of rods during insertion. Use of the 14383 may reduce measurement errors by minimizing soil disturbance.

Datalogger Considerations

Compatible Contemporary Dataloggers

CR200(X) Series CR800/CR850 CR1000 CR3000 CR9000X

Compatible Retired Dataloggers

CR500 CR510 CR10 CR10X 21X CR23X CR9000 CR5000 CR7X

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 CS655: 55

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  1. 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.

  2. 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. 

  3. Mine tailings are highly corrosive and have high electrical conductivity. Some customers have successfully used water content reflectometers, such as the CS650 or the CS655, to measure water content in mine tailings by coating the sensor rods with heat-shrink tubing. This affects the sensor output, and a soil-specific calibration must be performed. Care must be taken during installation to avoid damaging the heat-shrink tubing and exposing the sensor’s rods.  In addition, covering the sensor’s rods invalidates the bulk electrical conductivity reading. Unless the temperature reading provided by the CS650 or the CS655 is necessary, a better option may be to use a CS616 with coated rods.

  4. The bulk electrical conductivity (EC) measurement is made along the sensor rods, and it is an average reading of EC over that distance at whatever depth the rods are placed.

  5. 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.

  6. Yes, but the pots would have to be large. The CS650 and CS655 can detect water as far away as 10 cm (4 in.) from the rods. If the pot has a diameter smaller than 20 cm (8 in.), the sensor could potentially detect the air around the pot, which would underestimate the water content. In addition, potting soil is typically high in organic matter and clay, causing the probable need for a soil-specific calibration. 

  7. 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.  

  8. 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.

  9. A thermistor is encased in the epoxy head of the sensor next to one of the stainless-steel rods. This provides an accurate point measurement of temperature at the depth where that portion of the sensor head is in contact with the soil. This is why a horizontal placement is the recommended orientation of the CS650 or CS655. The temperature measurement is not averaged over the length of the sensor rods.

  10. 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 datalogger or multiplexer terminals.