Campbell CS650 User manual

Revision: 08/2021

Campbell Scientific, Inc.

Table of contents

1. Introduction 1

2. Precautions 1

3. Initial inspection 1

4. QuickStart 2

5. Overview 4

6. Specifications 6

6.1 Electrical specifications 7

6.2 Operational specifications 8

7. Installation 10

7.1 Orientation and placement 10

7.2 Proper insertion 10

7.3 Data logger wiring 11

7.4 Programming 12

8. Operation 13

8.1 A200 and Device Configuration Utility 13

8.1.1 Using the A200 13

8.1.1.1 Driver installation 13

8.1.1.2 RS-232 wiring 13

8.1.1.3 Powering the sensor 14

8.1.1.4 Determining which COM port the A200 has been assigned 14

8.1.2 Device Configuration Utility 14

8.1.2.1 Settings Editor tab 15

8.1.2.2 Send OS tab 18

8.2 SDI-12 measurements 19

8.2.1 M3! and M4! commands 20

8.2.2 Use of multiplexers 22

8.3 Water content reflectometer method for measuring volumetric water content 22

8.3.1 Description of measurement method 22

8.3.2 Topp equation 23

Table of Contents - i

8.3.3 Electrical conductivity 23

8.3.3.1 Soil electrical conductivity 23

8.3.3.2 Temperature correction of soil electrical conductivity 24

8.3.4 Error sources in water content reflectometer measurement 24

8.3.4.1 Sensor-to-sensor variability error 24

8.3.4.2 Insertion error 25

8.3.5 Temperature dependence and correction 25

8.3.5.1 Accurate soil temperature measurement 26

8.4 Water content reflectometer user-calibration 26

8.4.1 Need for soil specific calibration equation 26

8.4.2 User-derived calibration equation 26

8.4.3 Collecting laboratory data for calibration 27

8.4.4 Collecting field data for calibration 29

8.4.5 Calculations 32

9. Maintenance and troubleshooting 32

10. References 34

Appendix A. Importing Short Cut code into CRBasic Editor 35

Appendix B. Example programs 36

B.1 CR1000X with one CS650 sensor 36

B.2 CR1000X with two CS650 sensors on same control port 37

B.3 CR1000X with 12 CS650 sensors on multiplexer 38

Appendix C. Discussion of soil water content 40

Appendix D. SDI-12 sensor support 41

D.1 SDI-12 command basics 41

D.1.1 Acknowledge active command (a!) 42

D.1.2 Send identification command (al!) 42

D.1.3 Start verification command (aV!) 43

D.1.4 Address query command (?!) 43

D.1.5 Change address command (aAb!) 43

D.1.6 Start measurement commands (aM!) 43

D.1.7 Stopping a measurement command 44

D.1.8 Send data command (aD0! … aD9!) 44

D.2 SDI-12 transparent mode 45

D.2.1 Changing an SDI-12 address 45

Table of Contents - ii

D.3 References 47

Table of Contents - iii

1. Introduction

The CS650 and CS655 are multiparameter smart sensors that use innovative techniques to

monitor soil volumetric water content, bulk electrical conductivity, and temperature. They output

an SDI-12 signal that many Campbell Scientific data loggers can measure.

The CS650 has 30cm length rods, whereas the CS655 has 12cm length rods. This manual uses

CS650 to reference model numbers CS650 and CS655. Unless specifically stated otherwise,

information in the manual applies equally to both models.

NOTE:

This manual provides information only for CRBasic data loggers. For retired Edlog data logger

support, see an older manual at www.campbellsci.com/old-manuals .

2. Precautions

lREAD AND UNDERSTAND the Safety section at the back of this manual.

lAlthough the CS650 is rugged, it should be handled as a precision scientific instrument.

lExternal radio frequency (RF) sources can affect the sensor operation. Therefore, the sensor

should be located away from significant sources of RF such as ac power lines and motors.

3. Initial inspection

lUpon receipt of the CS650, inspect the packaging and contents for damage. File damage

claims with the shipping company.

lThe model number and cable length are printed on a label at the connection end of the

cable. Check this information against the shipping documents to ensure the expected

product and cable length were received.

CS650 and CS655 Water Content Reflectometers 1

4. QuickStart

A video that describes data logger programming using Short Cut is available at:

www.campbellsci.com/videos/cr1000x-data logger-getting-started-program-part-3 .Short

Cut is an easy way to program your data logger to measure the sensor and assign data logger

wiring terminals. Short Cut is available as a download on www.campbellsci.com . It is included

in installations of LoggerNet,RTDAQ, and PC400.

The following procedure also describes programming with Short Cut.

1. Open Short Cut and click Create New Program.

2. Double-click the data logger model.

3. In the Available Sensors and Devices box, type CS650. You can also locate the sensor in the

Sensors >Meteorological >Soil Moisture >CS650/CS655 Water Content Reflectometer

folder. The four different options monitor different parameters. For this tutorial, double-

click to select CS650/CS655 Water Content Reflectometer (VWC, EC, T, P, PA, and VR). The

soil temperature defaults to degree C, and the sensor is measured hourly. These are

changed by clicking the Temperature or Measure sensor box and selecting an option. Enter

the correct SDI-12 Address for the CS650 or CS655. After entering the Properties, click on

the Wiring tab to see how the sensor is to be wired to the data logger.

CS650 and CS655 Water Content Reflectometers 2

4. Repeat step three for other sensors you want to measure.

5. In Output Setup, type the scan rate. If you chose to measure the CS650 hourly rather than

every scan, this scan interval must be evenly divisible into an hour. Type a meaningful table

name and type the Data Output Storage Interval.

CS650 and CS655 Water Content Reflectometers 3

6. Select the measurement and its associated output options.

7. Click Finish and save the program. Send the program to the data logger if the data logger

is connected to the computer.

8. If the sensor is connected to the data logger, check the output of the sensor in the data

display in LoggerNet,RTDAQ, or PC400 to make sure it is making reasonable

measurements.

5. Overview

The CS650 measures volumetric water content, electrical conductivity, dielectric permittivity, and

temperature of soils or other porous media. These values are reported through SDI-12

communications.

CS650 and CS655 Water Content Reflectometers 4

FIGURE 5-1. CS650 (left) and CS655 Water Content Reflectometers

Volumetric water content (VWC) is derived from the sensor sensitivity to the dielectric

permittivity of the medium surrounding the sensor stainless-steel rods. The CS650 is configured

as a water content reflectometer, with the two parallel rods forming an open-ended transmission

line. A differential oscillator circuit is connected to the rods, with an oscillator state change

triggered by the return of a reflected signal from one of the rods. The two-way travel time of the

electromagnetic waves that are induced by the oscillator on the rod varies with changing

dielectric permittivity. Water is the main contributor to the bulk dielectric permittivity of the soil

or porous media, so the travel time of the reflected wave increases with increasing water content

and decreases with decreasing water content, hence the name water content reflectometer. The

average travel time of the reflected wave multiplied by a scaling factor of 128 is called the period

average. Period average is reported in microseconds and is considered to be the raw output of a

water content reflectometer.

Electrical conductivity is determined by exciting the rods with a known non-polarizing waveform

and measuring the signal attenuation. Signal attenuation is reported as a dimensionless voltage

ratio, which is the ratio of the excitation voltage to the measured voltage along the sensor rods

when they are excited at a fixed 100kHz frequency. Voltage ratio ranges from 1 in non-

conductive media to about 17 in highly conductive media. Values greater than 17 are highly

unstable and indicate that the soil conditions are outside of the specified operating range of the

sensor.

Temperature is measured with a thermistor in contact with one of the rods.

It is well known that transmission line oscillators used for water content measurements suffer

from unwanted increases in oscillation period as increasing electrical conductivity causes

CS650 and CS655 Water Content Reflectometers 5

transmission line signal attenuation. The CS650 handles this problem by making an electrical

conductivity measurement then correcting the oscillator period accordingly. On-board

processing within the sensor head calculates electrical conductivity from the signal attenuation

measurement and combines the result with the oscillation period measurement to calculate the

dielectric permittivity of the media and finally applies the Topp equation (Topp et al. 1980) to

estimate volumetric water content.

Sensor electronics are encapsulated in the rugged epoxy sensor head.

A five-conductor cable including the drain or shield wire provides power and ground as well as

communications with the CS650. The CS650 is intended to communicate with SDI-12 recorders,

including Campbell Scientific data loggers. Alternatively, use the orange wire to transmit and

receive RS-232. The A200 USB-to-Serial Module allows RS-232 communications between a

computer and the CS650 by means of Campbell Scientific’s Device Configuration Utility software.

Features:

lMeasurement corrected for effects of soil texture and electrical conductivity

lEstimates soil-water content for a wide range of mineral soils

lVersatile sensor—measures dielectric permittivity, bulk electrical conductivity (EC), and soil

temperature

lCompatible with Campbell Scientific CRBasic data loggers: CR6 series, CR3000, CR1000X

series, CR800 series, CR300 series, and CR1000

6. Specifications

Table 6-1 (p. 6) compares the size of the CS650 and CS655 reflectometers.

Table 6-1: Size specifications

CS650 CS655

Rods 300 mm long

3.2 mm diameter

32 mm spacing

120 mm long

3.2 mm diameter

32 mm spacing

Sensor head L 85 mm

W 63 mm

D 18 mm

L 85 mm

W 63 mm

D 18 mm

CS650 and CS655 Water Content Reflectometers 6

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