Campbell CS616 User manual

CS616 and CS625
Water Content Reflectometers
Revision: 10/12
Copyright © 2002-2012
Campbell Scientific, Inc.

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Table of Contents
PDF viewers: These page numbers refer to the printed version of this document. Use the
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1. Introduction.................................................................1
2. Cautionary Statements...............................................1
3. Initial Inspection .........................................................1
4. Overview......................................................................1
5. Sensors Specifications ..............................................2
5.1 Dimensions...........................................................................................3
5.2 Weight..................................................................................................3
5.3 Electrical Specifications.......................................................................3
5.4 Operational Details...............................................................................4
6. Installation...................................................................4
6.1 Orientation ...........................................................................................4
6.2 Potential Problems with Improper Insertion.........................................4
6.3 Wiring ..................................................................................................5
6.4 Datalogger Instructions and Programming...........................................6
6.4.1 Measuring the CS616 Using CRBasic ..........................................6
6.4.1.1 CS616 Sample CRBasic Program 1 ...................................7
6.4.1.2 CS616 Sample CRBasic Program 2 ...................................9
6.4.2 Measuring CS625 Output Using CR200(X) PeriodAvg
Instruction................................................................................11
6.4.3 Sample Programs for CS625.......................................................12
6.4.3.1 CS625 Sample Program 1 ................................................12
6.4.3.2 CS625 Sample Program 2 ................................................13
6.4.4 Measuring CS616 Using Edlog...................................................14
6.4.4.1 Using Edlog Instruction 138.............................................14
6.4.4.2 Using Edlog Instruction 27 (Period Averaging)...............15
6.4.5 Sample Edlog Programs for CS616 ............................................17
6.4.5.1 CS616 Sample Edlog Program 1......................................17
6.4.5.2 CS616 Sample Edlog Program 2......................................18
6.4.5.3 CS616 Sample Edlog Program 3......................................20
6.4.5.4 CS616 Sample Edlog Program 4......................................21
6.4.5.5 CS616 Sample Edlog Program 5......................................23
7. The Water Content Reflectometer Method for
Measuring Volumetric Water Content ..................26
7.1 Description of Measurement Method.................................................26
7.2 Response Curves ................................................................................26
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Table of Contents
7.3 Calibration Equations ........................................................................ 29
7.4 Operating Range................................................................................ 31
7.4.1 Soil Electrical Conductivity ....................................................... 31
7.4.2 Soil Organic Matter, Clay Content and Soil Bulk Density......... 32
7.5 Error Sources in Water Content Reflectometer Measurement .......... 32
7.5.1 Probe-to-Probe Variability Error................................................ 32
7.5.2 Insertion Error ............................................................................ 32
7.5.3 Signal Attenuation Error ............................................................ 32
7.6 Temperature Dependence and Correction ......................................... 33
8. Water Content Reflectometer User-Calibration......34
8.1 Signal Attenuation in Conductive Soils and Need for Site-
Specific Calibration ....................................................................... 34
8.2 The User-Derived Calibration Equation............................................ 35
8.3 Collecting Laboratory Data for Calibration....................................... 35
8.4 Collecting Field Data for Calibration ................................................ 38
8.5 Calculations....................................................................................... 40
9. Maintenance ..............................................................41
10. References.................................................................41
Appendix
A. Discussion of Soil Water Content .........................A-1
Figures
6-1. CS616 Water Content Reflectometer .................................................. 5
6-2. CS625 Water Content Reflectometer .................................................. 6
7-1. CS616 and CS625 linear and quadratic calibrations derived from
loam soil......................................................................................... 27
7-2. CS616 and CS625 response for low EC loam with bulk density
1.4 g cm-3, a low EC sandy clay loam with bulk density
1.6 g cm-3, and a high EC sandy clay loam with bulk density
1.6 g cm-3....................................................................................... 28
7-3. Difference in % volumetric water content between linear and
quadratic forms of calibrations ...................................................... 30
7-4. Percent volumetric water content error corrected for by
temperature correction equation..................................................... 34
Tables
6-1. CS616/625 wiring code. ...................................................................... 5
6-2. CS625 Sample Programs................................................................... 12
6-3. CS616 Sample Edlog Programs ........................................................ 17
7-1. Standard calibration coefficients for linear and quadratic forms....... 29
7-2. Calibration coefficients for sandy clay loam with bulk density
1.6 g cm-3 and electrical conductivity at saturation 0.4 dS m-1
for both linear and quadratic forms................................................ 30
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Table of Contents
7-3. Calibration coefficients for sandy clay loam with bulk density
1.6 g cm-3 and electrical conductivity at saturation 0.75
dS m-1 for both linear and quadratic forms. ....................................30
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Table of Contents
iv

CS616 and CS625 Water Content
Reflectometers
1. Introduction
The CS616 Water Content Reflectometer is an improved version of the CS615
Water Content Reflectometer. The CS625 is a modified CS616 for use with
the Campbell Scientific CR200(X) series dataloggers. The difference between
the CS616 and the CS625 is the output voltage level.
Both water content reflectometers are designed to measure volumetric water
content of soils or other porous media. The water content information is
derived from the probe sensitivity to the dielectric constant of the medium
surrounding the probe rods.
Before installing the CS616 or CS625, please study
•Section 2, Cautionary Statements
•Section 3, Initial Inspection
2. Cautionary Statements
•Although the CS616/CS625 is rugged, it should be handled as precision
scientific instrument.
•External RF sources can affect CS616/CS625 measurements.
Consequently, the CS616/CS625 circuitry should be located away from
significant sources of RF such as ac power lines and motors.
•CS616/CS625 probes enabled simultaneously and within approximately 9
inches of each other can cause erratic measurements. If probes must be
close to each other, configure the enable lines to the datalogger control
ports so that the probes are not enabled simultaneously.
3. Initial Inspection
•Upon receipt of the CS616/CS625, inspect the packaging and contents for
damage. File damage claims with the shipping company.
•The 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 are received.
4. Overview
The CS616 output is a square wave output and can be connected to our CR800,
CR850, CR1000, CR3000, CR5000, CR510, CR10X, and CR23X dataloggers.
A special CS616 datalogger instruction is used to measure the probe output
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CS616 and CS625 Water Content Reflectometers
period which is converted to volumetric water content using calibration
equations. Datalogger instructions for period averaging can also be used.
The CS625 output is a square wave output and can be connected to Campbell
Scientific CR200(X) series dataloggers. A CRBasic program using Period
Averaging is used to measure the probe output period and convert to
volumetric water content using calibration equations.
The water content reflectometer consists of two stainless steel rods connected
to a printed circuit board. A shielded four-conductor cable is connected to the
circuit board to supply power, enable the probe, and monitor the pulse output.
The circuit board is encapsulated in epoxy.
High-speed electronic components on the circuit board are configured as a
bistable multivibrator. The output of the multivibrator is connected to the
probe rods which act as a wave guide. The travel time of the signal on the
probe rods depends on the dielectric permittivity of the material surrounding
the rods and the dielectric permittivity depends on the water content.
Therefore, the oscillation frequency of the multivibrator is dependent on the
water content of the media being measured. Digital circuitry scales the
multivibrator output to an appropriate frequency for measurement with a
datalogger. The water content reflectometer output is essentially a square
wave. The probe output period ranges from about 14 microseconds with rods
in air to about 42 microseconds with the rods completely immersed in typical
tap water. A calibration equation converts period to volumetric water content.
The CS616/CS625's cable can terminate in:
•Pigtails that connect directly to a Campbell Scientific datalogger
(option –PT).
•Connector that attaches to a prewired enclosure (option –PW). Refer
to www.campbellsci.com/prewired-enclosures for more information.
5. Sensors Specifications
Features:
•High accuracy and high precision
•Fast response time
•Designed for long-term unattended water content monitoring
•Probe rods can be inserted from the surface or buried at any
orientation to the surface
CS616 Compatibility
Dataloggers: CR800 series
CR1000
CR3000
CR5000
CR510
CR10X
CR23X
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CS616 and CS625 Water Content Reflectometers
CS625 Compatibility
Dataloggers: CR200X series
CR200 series
Probe-to-Probe Variability: ±0.5% VWC in dry soil, ±1.5% VWC in
typical saturated soil
Resolution: better than 0.1% volumetric water content
Water Content Accuracy: ±2.5% VWC using standard calibration with
bulk electrical conductivity ≤0.5 deciSiemen
meter-1 (dS m-1) and bulk density ≤1.55 g cm-3
in measurement range 0% VWC to 50% VWC
Precision: better than 0.1% volumetric water content
5.1 Dimensions
Rods: 300 mm (11.8 in) long, 3.2 mm (0.13 in)
diameter, 32 mm (1.3 in) spacing
Probe Head: 85 x 63 x 18 mm (3.3 x 2.5 x 0.7 in)
5.2 Weight
Probe (without cable): 280 g (9.9 oz)
Cable: 35 g m-1 (0.38 oz per ft)
5.3 Electrical Specifications
Output
CS616: ±0.7 volt square wave with frequency
dependent on water content
CS625: 0 to 3.3 volt square wave with frequency
dependent on water content
Power: 65 mA @ 12 Vdc when enabled, 45 μA
quiescent
Power Supply Requirements: 5 Vdc minimum, 18 Vdc maximum
Enable Voltage: 4 Vdc minimum, 18 Vdc maximum
Maximum Cable Length: 305 m (1000 ft)
Electromagnetic
Compatibility: The CS616/CS625 is Πcompliant with
performance criteria available upon request.
RF emissions are below EN55022 limits if the
CS616/CS625 is enabled less than 0.6 ms and
measurements are made at a 1 Hz (1 per
second) or slower frequency. The
CS616/CS625 meets EN61326 requirements
for protection against electrostatic discharge
and surge.
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CS616 and CS625 Water Content Reflectometers
5.4 Operational Details
The accuracy specification for the volumetric water content measurement
using the CS616/CS625 probes is based on laboratory measurements in a
variety of soils and over the water content range air dry to saturated. The soils
were typically sandy loam and coarser. Silt and clay were present in some of
the soils used to characterize accuracy.
Resolution is the minimum change in the dielectric permittivity that can reliably
be detected by the water content reflectometer. The CS616 or CS625 is typically
used to measure soil volumetric water content.
Precision describes the repeatability of a measurement. It is determined for the
CS616 and CS625 by taking repeated measurements in the same material. The
precision of the CS616/CS625 is better than 0.1 % volumetric water content.
Soil Properties
The water content reflectometer operation can be affected when the signal
applied to the probe rods is attenuated. The probe will provide a well-behaved
response to changing water content, even in attenuating soils or other media,
but the response may be different than described by the standard calibration.
Consequently, a unique calibration is required. Change in probe response can
occur when soil bulk electrical conductivity is greater than 0.5 dS m-1. The
major contributor to soil electrical conductivity is the presence of free ions in
solution from dissolution of soil salts. Soil organic matter and some clays can
also attenuate the signal.
6. Installation
6.1 Orientation
The probe rods can be inserted vertically into the soil surface or buried at any
orientation to the surface. A probe inserted vertically into a soil surface will
give an indication of the water content in the upper 30 cm of soil. The probe
can be installed horizontal to the surface to detect the passing of wetting fronts
or other vertical water fluxes. A probe installed at an angle of 30 degrees with
the surface will give an indication of the water content of the upper 15 cm of
soil.
6.2 Potential Problems with Improper Insertion
The method used for probe installation can affect the accuracy of the
measurement. The probe rods should be kept as close to parallel as possible
when installed to maintain the design wave guide geometry. The sensitivity of
this measurement is greater in the regions closest to the rod surface than at
distances away from the surface. Probes inserted in a manner which generates
air voids around the rods will reduce the measurement accuracy. In most soils,
the soil structure will recover from the disturbance during probe insertion.
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CS616 and CS625 Water Content Reflectometers
In some applications, installation can be improved by using the CS650G
insertion guide tool. The CS650G is inserted into the soil and then removed.
This makes proper installation of the water content reflectometer easier in
dense or rocky soils.
6.3 Wiring
TABLE 6-1. CS616/625 wiring code.
color function datalogger connection
red +12 V +12 V
green output SE analog channel
orange enable control port
black signal ground G
clear shield (power ground) G
Both the black ground wire and the clear shield wire must be
connected to datalogger ground.
NOTE
power Red
output gnd Black
output Green
enable Orange
drain/power gnd Clear
FIGURE 6-1. CS616 Water Content Reflectometer
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CS616 and CS625 Water Content Reflectometers
power Red
gnd Black
output Green
enable Orange
drain/gnd Clear
FIGURE 6-2. CS625 Water Content Reflectometer
6.4 Datalogger Instructions and Programming
This section is for users who write their own programs. A
datalogger program can be generated using Short Cut software.
You do not need to read this section if using Short Cut.
NOTE
The output of the CS616 is a square wave with amplitude of ±0.7 Vdc and a
frequency that is dependent on the dielectric constant of the material
surrounding the probe rods. The CRBasic instruction CS616() is used by the
CR800, CR850, CR1000, CR3000, and CR5000 dataloggers to measure the
CS616 output period. Edlog Instruction 138 is specifically designed for the
CR510, CR10X, and CR23X to measure the output period of the CS616. The
period value is used in the calibration for water content. The period in air is
approximately 14.7 microseconds, and the period in saturated soil with porosity
0.4 is approximately 31 microseconds. Edlog Instruction 27, Period Average,
can also be used to measure CS616 output period.
The output of the CS625 is a square wave with amplitude of 0 to 3.3 Vdc and a
frequency that is dependent on the dielectric constant of the material
surrounding the probe rods. The CRBasic instruction PeriodAvg() is used by
the CR200(X) series dataloggers to measure the CS625 output period. The
period value is used in the calibration for water content. The period in air is
approximately 14.7 microseconds, and the period in saturated soil with porosity
0.4 is approximately 31 microseconds.
6.4.1 Measuring the CS616 Using CRBasic
The CRBasic instruction CS616() is used by the CR800, CR850, CR1000
CR3000, and CR5000 dataloggers to measure the CS616 output period (in
microseconds). The CS616() instruction is used to enable and measure a
CS616 Water Content Reflectometer.
CS616(Dest, Reps, SEChan, Port, MeasPerPort, Mult, Offset)
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CS616 and CS625 Water Content Reflectometers
Dest: The Dest parameter is the variable or variable array in which to store the
results of the measurement. Dest must be dimensioned to at least the number of
Reps.
Reps:The Reps parameter is the number of measurements that should be made
using this instruction. If Reps is greater than 1, Dest must be an array
dimensioned to the size of Reps.
SEChan:The SEChan parameter is the number of the single-ended channel on
which to make the first measurement. If the Reps parameter is greater than 1,
the additional measurements will be made on sequential channels.
Port: The Port parameter is the control port that will be used to enable the
CS616 sensor.
Code Description
1 Control Port 1
2 Control Port 2
3 Control Port 3
4 Control Port 4
5 Control Port 5
6 Control Port 6
7 Control Port 7
8 Control Port 8
MeasPerPort:The MeasPerPort parameter is the number of control ports to be
used to control the CS616 sensor(s). If Reps is set to 4, MeasPerPort = 4 will
result in the same port being used for all measurements. MeasPerPort = 1 will
result in four sequential ports being used for the measurements. MeasPerPort =
2 will result in one port being used for the first two measurements, and the next
port being used for the next two measurements.
Mult, Offset:The Mult and Offset parameters are each a constant, variable,
array, or expression by which to scale the results of the measurement.
6.4.1.1 CS616 Sample CRBasic Program 1
The following CR1000 program uses the CS616() instruction to measure eight
CS616 probes connected to the CR1000 datalogger. Although this example is
for the CR1000, other CRBasic dataloggers are programmed similarly.
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CS616 and CS625 Water Content Reflectometers
Wiring for CRBasic
Program Example 1
CS616 CR1000
CS616#1_Green 5H
CS616#2_Green 5L
CS616#3_Green 6H
CS616#4_Green 6L
#1,2,3,4_Orange C7
#1,2,3,4_Blk & Clear GND
#1,2,3,4_Red 12 V
CS616#5_Green 7H
CS616#6_Green 7L
CS616#7_Green 8H
CS616#8_Green 8L
#5,6,7,8_Orange C8
#5,6,7,8_Blk & Clear GND
#5,6,7,8_Red 12 V
Note: All CS616 “12V_Red”
wires connected to CR1000 12 V
terminal (user supplied common
tie post may be required).
CR1000 Program Example 1
'Declare Public and Dim Variables
Public batt_volt
Public Panel_temp
Public Period (8)
Public VWC (8)
Public Flag (1)
Dim I
'Declare Constants
'CS616 Default Calibration Constants
const a0= -0.0663
const a1= -0.0063
const a2= 0.0007
'Flag logic constants
const high = true
const low = false
'Define Data Tables
DataTable (Dat30min,1,-1)
DataInterval (0,30,Min,10)
Minimum (1,batt_volt,IEEE4,0,False)
Average (1,Panel_temp,IEEE4,0)
Sample (8,Period(),FP2)
Sample (8,VWC(),FP2)
EndTable
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CS616 and CS625 Water Content Reflectometers
'Main Program
BeginProg
Scan (5,Sec,0,0) 'scan instructions every 5 sec
Battery (Batt_volt)
PanelTemp (Panel_temp,250)
'
'Set flag 1 High every 30 min (Note: User can manually set flag 1 high/low)
If IfTime (0,30,min) Then flag (1) = high '+++++++++++++++++++++++++++
If Flag (1) = high Then
'measure 8ea CS616 probes on CR1000
CS616 (Period(1),4,9,7,4,1.0,0) 'measure 4ea CS616 probes, enable w/ C7
CS616 (Period(5),4,13,8,4,1.0,0) 'measure 4ea CS616 probes, enable w/ C8
'
For I=1 to 8 'convert CS616 period to Volumetric Water Content
VWC(I)=a0 + al*Period(I) + a2*Period(I)^2
Next
'
flag(1)= low 'set Flag 1 = Low
'
EndIf '+++++++++++++++++++++++++++++++
'
CallTable Dat30min 'Call Output Tables
NextScan
EndProg
6.4.1.2 CS616 Sample CRBasic Program 2
The following CR1000 program uses the AM16/32-series multiplexer to
measure 48 CS616 probes connected in the 4x16 configuration. The program
also measures datalogger battery voltage and temperature.
Wiring for CRBasic Program Example 2
CR1000 AM16/32-series (4x16) CS616*
Control/Common Sensor
Terminals
C4 RES Odd H CS616#1_Green
C5 CLK Odd L CS616#2_Green
12 V 12 V Gnd #1,2,3_Blk & Clear
Gnd Gnd Even H CS616#3_Green
1H COM Odd H Even L #1,2,3_Orange
1L COM Odd L
Gnd Gnd
2H COM Even H
C6 COM Even L
*Three sensors to each set of AM16/32 terminals.
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CS616 and CS625 Water Content Reflectometers
CR1000 Program Example 2
'Declare Public and Dim Variables
Public batt_volt
Public Panel_temp
Public Period (48)
Public VWC (48)
Public Flag (1)
Dim I
'Declare Constants
'CS616 Default Calibration Constants
const a0= -0.0663
const a1= -0.0063
const a2= 0.0007
'Flag logic constants
const high = true
const low = false
'Define Data Tables
DataTable (Dat30min,1,-1)
DataInterval (0,30,Min,10)
Minimum (1,batt_volt,FP2,0,False)
Average (1,Panel_temp,FP2,0)
Sample (48,Period(),FP2)
Sample (48,VWC(),FP2)
EndTable
'Main Program
BeginProg
Scan (5,Sec,0,0) 'scan instructions every 5 sec
Battery (Batt_volt)
PanelTemp (Panel_temp,250)
'
'Set flag 1 High every 30 min (Note: User can manually set flag 1 high/low)
If IfTime (0,30,min) Then flag (1) = high '+++++++++++++++++++++++++++
If Flag (1) = high Then
'measure 48ea CS616 probes on AM16/32 in (4x16) mode
PortSet (4,1) 'Set Mux Reset line High
'
I=1 'Set sub scan loop counter
SubScan (0,mSec,16)
PulsePort (5,10000) 'Clock Mux
CS616 (Period(I),3,1,6,3,1.0,0) 'Measure 3ea CS616 probes
I=I+3
NextSubScan
'
For I=1 to 48 'convert CS616 period to Volumetric Water Content
VWC(I)=a0 + al*Period(I) + a2*Period(I)^2
Next
'
PortSet (4,0) 'Set Mux Reset line Low
flag (1) = low
'
EndIf '+++++++++++++++++++++++++++++++
'
CallTable Dat30min 'Call Output Tables
NextScan
EndProg
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CS616 and CS625 Water Content Reflectometers
6.4.2 Measuring CS625 Output Using CR200(X) PeriodAvg Instruction
The PeriodAvg() instruction is used to measure the period (in microseconds)
or the frequency (in kHz) of a signal on a single-ended channel. This
instruction can be used to measure the CS625 Water Content Reflectometer.
PeriodAvg(Dest, SEChan, Option, Cycles, Timeout, Port, Mult, Offset)
Dest: The Dest parameter is a variable in which to store the results of the
measurement.
SEChan: The SEChan argument is the number of the single-ended channel on
which to make the measurement. Valid options are analog channels 1 through
4. The green wire is connected to this channel number.
Option: The Option parameter specifies whether to output the frequency or the
period of the signal.
Code Description
0 Period of the signal is returned (msec)
1 Frequency of the signal is returned (Hz)
Code 0 is typically used with the CS625 with a multiplier (see below) of 1.
Cycles: The Cycles parameter specifies the number of cycles to average each
scan.
Timeout:The Timeout parameter is the maximum time duration, in
milliseconds, that the datalogger will wait for the number of Cycles to be
measured for the average calculation. An overrange value will be stored if the
Timeout period is exceeded. A value of 1 is recommended if 10 is used for
cycles parameter.
Port: The Port parameter is the control port or analog channel that will be used
to switch power to the CS625 Water Content Reflectometer. Valid options are:
Code Description
0 None
C1 Control Port 1
C2 Control Port 2
3 Analog Channel 3
4 Analog Channel 4
5 Analog Channel 5
P_SW Analog Channel 6/P_SW
Mult, Offset: The Mult and Offset parameters are each a constant, variable,
array, or expression by which to scale the results of the raw measurement. A
multiplier value of 1 is recommended.
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CS616 and CS625 Water Content Reflectometers
6.4.3 Sample Programs for CS625
TABLE 6-2. CS625 Sample Programs
Sample
Program
Number
Program Description
1 Measure volumetric water content with 4 CS625 hourly. Store
average hourly readings to final storage every 4 hours.
2 Measure temperature with 109 probe and use the 109
temperature to correct the period for 1 CS625. Use standard
calibration equation to convert temperature-corrected period to
volumetric water content. Sensors are read hourly and average
water content and temperature are written to storage every 4
hours.
6.4.3.1 CS625 Sample Program 1
Hourly measure temperature with 109 probe and volumetric water content with
4 CS625. Store average hourly readings to final storage every 4 hours.
CS625
leads
CR200(X)
greens Single-Ended Channel 1 thru 4
(SE1-4)
blacks associated grounds for SE1-4
oranges Control Port 1 (C1)
reds SW Battery
clears G
'CR200(X) program to read 4 CS625s
'Standard calibration is used to convert CS625 output
'period to volumetric water content.
'Sensors are read hourly and average water content are written to storage every 4 hours.
'Declare Variables
Public period(4),vwc(4)
Dim i
'Declare Constants
Const a0=-0.0663
Const a1=-0.0063
Const a2=0.0007
'Define Data Tables
DataTable (ofile,1,10)
DataInterval (0,4,hr)
Average (4,vwc,0)
EndTable
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