Campbell CS650 User manual

Revision: 08/2021
Copyright © 2011 – 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

Table 6-1: Size specifications
CS650 CS655
Sensor weight 280 g 240 g
Cable weight 35 g m-1 35 g m-1
Ingress protection rating: IP68
6.1 Electrical specifications
Sensor output: SDI-12 Serial RS-232
Warmup 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 or U terminal1
Electromagnetic compatibility: View EU Declaration of Conformity documentation at
www.campbellsci.com/cs650 .
External RF sources can affect CS650 measurements. CS650
circuitry should be located away from radio transmitter aerials
and cables, or measurements discarded during RF
transmissions.
Active current drain (3 ms): 45 mA typical @ 12 VDC (80 mA @ 6 VDC, 35 mA @ 18 VDC)
Quiescent current drain: 135 mA @ 12 VDC
Average current drain: I = 0.09n + [3.5 + 0.024(n-1)]n/s
I = average current in milliamps
n = number of CS650s
s = number of seconds between measurements
(see FIGURE 6-1 (p. 8))
1Campbell Scientific recommends using separate terminals when possible.
CS650 and CS655 Water Content Reflectometers 7

FIGURE 6-1. CS650 and CS655 average current drain
FIGURE 6-1 (p. 8) shows average current drain for different measurement rates and quantities of
CS650 sensors. If the time between measurements is five minutes or longer, average current
drain is approximately 0.15 milliamps per sensor.
6.2 Operational specifications
Table 6-2 (p. 8) provides the operational specifications.
Table 6-2: Relative dielectric permittivity specifications
CS650 CS655
Relative dielectric permittivity
Range 1 to 81
Accuracy†
1 to 40:
40 to 80:
±(2% of reading + 0.6) for
solution electrical conductivity
(EC) ≤3 dS/m
±1.4 for solution EC ≤3 dS/m
±(3% of reading + 0.8) for solution
EC ≤8 dS/m
±2 for solution EC ≤2.8 dS/m
Precision‡ <0.02
CS650 and CS655 Water Content Reflectometers 8

Table 6-2: Relative dielectric permittivity specifications
CS650 CS655
Volumetric water content
Range 0% to 100%
Accuracy† ±1% (with soil specific calibration),
±3% (typical with factory VWC
model) where solution EC
<3dS/m
±1% (with soil specific calibration),
±3% (typical with factory VWC
model) where solution EC
<10dS/m
Precision‡ <0.05%
Electrical conductivity
Range solution EC 0 to 3 dS/m 0 to 8 dS/m
Range bulk EC 0 to 3 dS/m 0 to 8 dS/m
Accuracy† ±(5% of reading + 0.05 dS/m)
Precision‡ 0.5% of bulk electrical conductivity (BEC)
Temperature
Range –50 to 70 °C
Resolution 0.001 °C
Accuracy† ±0.1 °C (for typical soil temperatures
[0 to 40 °C] when sensor body is buried in soil),
±0.5 °C for full temperature range
Precision‡ ±0.02 °C
Sensing volume* 7800 cm33600 cm3
*Sensing volume approximately 7.5 cm radius around each sensor rod and 4.5 cm beyond the end of the rods
†Accuracy specifications are based on laboratory measurements in a series of solutions with dielectric permittivities
ranging from 1 to 81 and solution electrical conductivities ranging from 0 to 3 dS/m.
‡Precision describes the repeatability of a measurement. It is determined for the CS650 by taking repeated
measurements in the same material. The precision of the CS650 is better than 0.05 % volumetric water content and
0.01 dS/m electrical conductivity.
CS650 and CS655 Water Content Reflectometers 9

7. Installation
If you are programming your data logger with Short Cut, skip Data logger wiring (p. 11) and
Programming (p. 12). Short Cut does this work for you. See QuickStart (p. 2) for a Short Cut
tutorial.
7.1 Orientation and placement
The CS650 measures the bulk dielectric permittivity, average volumetric water content, and bulk
EC along the length of the rods, which is 30cm for the CS650 and 12cm for the CS655. The
sensor rods can insert vertically into the soil surface or buried at any orientation to the surface.
Install the sensor horizontal to the surface to detect the passing of wetting fronts or other vertical
water fluxes.
The sensitive volume depends on the surrounding media. In soil, the sensitive volume extends
approximately 7.5cm (3in) from the rods along their length and 4.5cm (1.8in) beyond the end of
the rods. Consequently, if the sensor is buried horizontally closer than 7.5cm from the soil
surface, it includes air above the surface in its measurements and underestimates soil water
content.
The thermistor used to measure temperature is in contact with one of the stainless steel rods at
the base of the epoxy sensor body. Because of the low thermal conductivity of stainless steel, the
thermistor does not measure the average temperature along the rod, but instead provides a
point measurement of the temperature within the epoxy. For a valid soil temperature reading,
the sensor body must be in thermal equilibrium with the soil. Also bury the sensor head in the soil
so that it is insulated from diurnal temperature fluctuations.
7.2 Proper insertion
The method used for sensor installation affects the accuracy of the measurement. Insert the
sensor rods as close to parallel as possible. The sensor is more sensitive to permittivity close to
the rods. Air voids around the rods result in reduced measurement accuracy. Most soils recover
from disturbances caused by installation.
The CS650G Rod Insertion Guide Tool with Pilot Rod helps maintain the proper spacing and
parallel orientation of the rods during sensor insertion. It also helps the insertion of the sensor in
high density or rocky soils.
CS650 and CS655 Water Content Reflectometers 10

FIGURE 7-1. CS650G Rod Insertion Guide Tool with Pilot Rod
7.3 Data logger wiring
Campbell Scientific data loggers typically use SDI-12 to measure the sensor because RS-232
communications require more terminals per CS650 and RS 232 programming is more
complicated than SDI-12 programming.
Table 7-1 (p. 11) shows the SDI-12 wiring for the CS650 water content reflectometer. SDI-12 data is
transmitted to a CRBasic data logger odd numbered control or U terminal. Wiring information for
RS-232 communications is provided in RS-232 wiring (p. 13).
Table 7-1: Wire color, function, and data logger connection for SDI-12
Color Function Data logger connection
Green SDI-12 data C, SDI-12, or
Uconfigured for SDI-121
Red SDI-12 power 12V
Black SDI-12 reference G
Clear Shield G
Orange Not used G
1Uterminals are automatically configured by the measurement instruction.
CS650 and CS655 Water Content Reflectometers 11

NOTE:
The orange wire is only used for RS-232 communications and should be grounded when
using SDI-12.
For the CR6 and CR1000X data loggers, triggering conflicts may occur when a companion
terminal is used for a triggering instruction such as TimerInput(),PulseCount(), or
WaitDigTrig(). For example, if the CS650 is connected to C3 on a CR1000X, C4 cannot be
used in the TimerInput(),PulseCount(), or WaitDigTrig() instructions.
7.4 Programming
Short Cut is the best source for up-to-date programming code for Campbell Scientific data
loggers. If your data acquisition requirements are simple, you can probably create and maintain a
data logger program exclusively with Short Cut. If your data acquisition needs are more complex,
the files that Short Cut creates are a great source for programming code to start a new program
or add to an existing custom program.
NOTE:
Short Cut cannot edit programs after they are imported and edited in CRBasic Editor.
AShort Cut tutorial is available in QuickStart (p. 2). If you wish to import Short Cut code into
CRBasic Editor to create or add to a customized program, follow the procedure in Importing
Short Cut code into CRBasic Editor (p. 35). Programming basics for CRBasic data loggers are
provided in this section. Complete program examples for select CRBasic data loggers can be
found in Example programs (p. 36).
Use the SDI12Recorder() instruction to measure the sensor. This instruction sends a request
to the sensor to make a measurement then retrieves the measurement values from the sensor.
See SDI-12 measurements (p. 19) for more information.
For most CRBasic data loggers, the SDI12Recorder() instruction has the following syntax:
SDI12Recorder(Destination, SDIPort, SDIAddress, “SDICommand”, Multiplier, Offset,
FillNAN, WaitonTimeout)
The Destination parameter must be an array. The required number of values in the array
depends on the command (Table 8-3 (p. 19)).
FillNAN and WaitonTimeout are optional parameters (refer to CRBasic Help for more
information).
CS650 and CS655 Water Content Reflectometers 12

8. Operation
8.1 A200 and Device Configuration Utility
The A200 Sensor-to-Computer Interface allows communications between a CS650 and a
computer to change sensor settings through Device Configuration Utility software.
8.1.1 Using the A200
8.1.1.1 Driver installation
If the A200 has not been previously plugged into your computer and your computer operating
system is not Windows 7, the A200 driver needs to be installed.
NOTE:
Drivers should be installed before plugging the A200 into the computer.
To download the A200 drivers, go to www.campbellsci.com/downloads/a200-sensor-interface-
usb-driver and click Download Now.
8.1.1.2 RS-232 wiring
One end of the A200 has a terminal block while the other end has a type B female USB port. The
terminal block provides 12V,G,Tx, and Rx terminals for connecting the sensor (see FIGURE 8-1 (p.
13) and Table 8-1 (p. 14)).
FIGURE 8-1. A200 Sensor-to-Computer Interface
A data cable that ships with the A200 has a USB type-A male connector for attaching to a
computer USB port, and a type B male connector for attaching to the A200 USB port.
CS650 and CS655 Water Content Reflectometers 13

Table 8-1: CS650 wiring code for RS-232 and A200
Color Function A200 terminal
Orange RxD Rx
Green TxD Tx
Red Power +12 VDC
Black Reference G
Clear Shield G
8.1.1.3 Powering the sensor
The A200 provides power to the sensor when it is connected to a computer USB port. An internal
dc/dc converter boosts the 5VDC supply from the USB connection to a 12VDC output that is
required to power the sensor.
8.1.1.4 Determining which COM port the A200 has been assigned
When the A200 driver is installed, the A200 is assigned a COM port number. This COM port
number is needed when using Device Configuration Utility. Often, the assigned COM port is the
next port number that is free. However, if other devices were previously installed (some of which
may not be plugged in), the A200 may be assigned a higher COM port number.
To check which COM port has been assigned to the A200, monitor the appearance of a new
COM port in the list of COM ports offered in your software package such as LoggerNet before
and after the installation, or look in the Windows Device Manager list under the ports section
(access via the control panel).
8.1.2 Device Configuration Utility
The Device Configuration Utility is available as a download on www.campbellsci.com/downloads .
It is included in installations of LoggerNet,RTDAQ, or PC400.
Connect the CS650 to the A200 as shown in Table 8-1 (p. 14). Connect the computer to the A200
USB port with the supplied USB cable.
Launch Device Configuration Utility and search for CS650 Series from the Device Type list on the
left. Select 9600 from the Baud Rate list.
CS650 and CS655 Water Content Reflectometers 14

Browse for and select the Communications Port used for your device. (see Determining which
COM port the A200 has been assigned (p. 14)).
Select Ok then Connect to begin communications with the CS650.
8.1.2.1 Settings Editor tab
The Settings Editor tab shows settings stored in the CS650 operating system. Settings that may
be modified include User Name,SDI-12 Address, and RS-232 Baud Rate. Attempts to change any
of the other settings results in a “Commit failed. Unrecognized error condition” error message.
Device Configuration Utility polls the CS650 every two seconds while connected and the results
are displayed under Real-Time Measurements (Table 8-2 (p. 18)). This is useful for verifying
sensor performance.
CS650 and CS655 Water Content Reflectometers 15

Default communications settings are 9600 baud, no parity, 1 stop bit, 8 data bits, and no error
checking. After any changes to CS650 settings, select Apply to write the changes to the CS650
operating system. A configuration summary is then shown. The summary may be printed or
saved electronically for future reference.
CS650 and CS655 Water Content Reflectometers 16