INSTRUCTION MANUAL CS616 and CS625 Water Content Reflectometers Revision: 2/14 C o p y r i g h t © 2 0 0 2 - 2 0 1 4 C a m p b e l l S c i e n t i f i c , I n c .
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Table of Contents PDF viewers: These page numbers refer to the printed version of this document. Use the PDF reader bookmarks tab for links to specific sections. 1. Introduction ................................................................. 1 2. Cautionary Statements ............................................... 1 3. Initial Inspection ......................................................... 1 4. Overview ...................................................................... 1 5. Specifications .....
Table of Contents 7.4 Operating Range ................................................................................ 29 7.4.1 Soil Electrical Conductivity ....................................................... 29 7.4.2 Soil Organic Matter, Clay Content and Soil Bulk Density ......... 29 7.5 Error Sources in Water Content Reflectometer Measurement .......... 30 7.5.1 Probe-to-Probe Variability Error ................................................ 30 7.5.2 Insertion Error ................................
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.
CS616 and CS625 Water Content Reflectometers 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.
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 5.1 5.2 5.3 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.
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.
CS616 and CS625 Water Content Reflectometers 6.3 Wiring TABLE 6-1. CS616/625 wiring code. NOTE 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. power Red output gnd Black output Green enable Orange drain/power gnd Clear FIGURE 6-1.
CS616 and CS625 Water Content Reflectometers 6.4 Datalogger Instructions and Programming NOTE 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. 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.
CS616 and CS625 Water Content Reflectometers Code 1 2 3 4 5 6 7 8 Description Control Port 1 Control Port 2 Control Port 3 Control Port 4 Control Port 5 Control Port 6 Control Port 7 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.
CS616 and CS625 Water Content Reflectometers 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.
CS616 and CS625 Water Content Reflectometers 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.
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 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 Mu
CS616 and CS625 Water Content Reflectometers 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.
CS616 and CS625 Water Content Reflectometers '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.
CS616 and CS625 Water Content Reflectometers 'CR200(X) program to read 1 109 temperature probe and 1 CS625. 'Use temperature to correct CS625 period. 'Standard calibration is used to convert CS625 output 'period to volumetric water content. 'Sensors are read hourly and average water content and 'temperature are written to storage every 4 hours. 'Declare Variables Public Tsoil Public uncorrected,corrected Public vwc 'Declare Constants 'Water content calibration constants Const a0=-0.0663 Const a1=-0.
CS616 and CS625 Water Content Reflectometers SE Chan: Enter the single-ended analog channel where the sensor’s green wire is connected. When Reps is greater than 1, this entry is the channel for the first CS616. Port: Enter an integer to specify the control port that will be used to enable the CS616 sensor. For the CR510, only C1 can be used to enable a CS616. Code Control Port Option X X specifies the first control port that will be used.
CS616 and CS625 Water Content Reflectometers Reps: Enter the number of CS616s that will be measured with the instruction. The sensors must be wired in consecutive channels. Each measurement uses the same multiplier and offset. Range Option: Enter 2-digit integer to choose output as period in microseconds and range. Suggested value for CS616 is 04. Code x1 x2 x3 x4 Max. Freq.
CS616 and CS625 Water Content Reflectometers 6.4.5 Sample Edlog Programs for CS616 TABLE 6-3. CS616 Sample Edlog Programs Sample Program Number Program Description 1 Set Flag 1 to read output of one CS616 using CR10X instruction 138 and convert output period to volumetric water content 2 Every 5 minutes, measure CS616 output period using instruction 27 and convert to volumetric water content. Write hourly average to datalogger final storage. 3 Read datalogger battery voltage and 3 CS616s hourly.
CS616 and CS625 Water Content Reflectometers 3: Polynomial (P55) 1: 1 Reps 2: 1 X Loc [ period 3: 2 F(X) Loc [ VWC 4: -0.0663 C0 5: -0.0063 C1 6: 0.0007 C2 7: 0.0 C3 8: 0.0 C4 9: 0.0 C5 4: Do (P86) 1: 21 5: ] ] Set Flag 1 Low End (P95) *Table 2 Program 02: 0.0000 Execution Interval (seconds) *Table 3 Subroutines End Program -Input Locations1 period 1 0 1 2 VWC 1 0 1 6.4.5.
CS616 and CS625 Water Content Reflectometers 3: Polynomial (P55) 1: 1 Reps 2: 1 X Loc [ period 3: 2 F(X) Loc [ vwc 4: -0.0663 C0 5: -0.0063 C1 6: 0.0007 C2 7: 0.0 C3 8: 0.0 C4 9: 0.0 C5 4: Do (P86) 1: 51 5: If 1: 2: 3: ] ] ;Turn Off CS616 probe Set Port 1 Low time is (P92) ;Turn On Data Storage every hour 0 Minutes (Seconds --) into a 60 Interval (same units as above) 10 Set Output Flag High (Flag 0) 6: Real Time (P77) ;Store a time stamp.
CS616 and CS625 Water Content Reflectometers ;{CR10X} ; *Table 1 Program 01: 3600 Execution Interval (seconds) 1: Batt Voltage (P10) 1: 7 Loc [ batt ] 2: CS616 Water Content Reflectometer (P138) 1: 3 Reps 2: 1 SE Channel 3: 6 C6 is first of sequential Control Ports used 4: 1 Loc [ period_1 ] 5: 1.0 Mult 6: 0.0 Offset 3: Polynomial (P55) 1: 3 Reps 2: 1 X Loc [ period_1 3: 4 F(X) Loc [ vwc_1 4: -0.0663 C0 5: -0.0063 C1 6: 0.0007 C2 7: 0.0 C3 8: 0.0 C4 9: 0.
CS616 and CS625 Water Content Reflectometers Sensor lead CR10X CS616 green Single-Ended Channel 2 (SE2) CS616 orange Control Port 4 (C4) 107 red Single-Ended Channel 1 (SE1) 107 black Excitation 1 (E1) 107 purple Analog Ground (AG) 107 clear Ground (G) The CS616 red leads are connected to 12 Vdc and the blacks and shields are connected to ground.
CS616 and CS625 Water Content Reflectometers 7: Z=X*Y (P36) 1: 5 2: 4 3: 4 X Loc [ TFactor ] Y Loc [ TempCS616 ] Z Loc [ TempCS616 ] 8: Z=X+Y (P33) 1: 3 2: 4 3: 6 X Loc [ CS616 ] Y Loc [ TempCS616 ] Z Loc [ NewCS616 ] 9: Polynomial (P55) ;Convert corrected probe period to water content. 1: 1 Reps 2: 6 X Loc [ NewCS616 ] 3: 7 F(X) Loc [ WaterCont ] 4: -0.0663 C0 5: -0.0063 C1 6: 0.0007 C2 7: 0.0 C3 8: 0.0 C4 9: 0.
CS616 and CS625 Water Content Reflectometers Sensor lead AM16/32 CS616-1 green 1H CS616-2 green 1L CS616-3 green 2H CS616-1,2,3 orange 2L CS616-4 green 3H CS616-5 green 3L CS616-6 green 4H CS616-4,5,6 orange 4L ...
CS616 and CS625 Water Content Reflectometers 7: Step Loop Index (P90) 1: 3 Step 8: Do (P86) 1: 72 Pulse Port 2 ;Increment input locations by 3/loop pass ;Pulse control port 2 (i.e. Multiplier Clock) 9: CS616 Water Content Reflectometer (P138) ;Measure Period on 3ea CS616 1: 3 Reps 2: 1 SE Channel 3: 13 All reps use C3 4: 3 -- Loc [ Period_1 ] 5: 1.0 Mult 6: 0.0 Offset ;Note: Input "Loc" must be indexed "--" in a loop! How? Use the "F4" Key.
CS616 and CS625 Water Content Reflectometers 53 VWC_2 . . 99 VWC_48 7. 9 1 1 17 1 1 The Water Content Reflectometer Method for Measuring Volumetric Water Content 7.1 Description of Measurement Method The water content reflectometer method for measuring soil water content is an indirect measurement that is sensitive to the dielectric permittivity of the material surrounding the probe rods.
Volumetric Water Content (fractional) CS616 and CS625 Water Content Reflectometers 0.4 0.3 0.2 0.1 0 16 18 20 calibration data linear fit quadratic fit 22 24 26 Output period (microseconds) 28 30 32 FIGURE 7-1.
CS616 and CS625 Water Content Reflectometers Volumetric Water Content (fractional) FIGURE 7-2 compares the CS616/CS625 response in the FIGURE 7-1 loam soil to a higher density sandy clay loam for two different electrical conductivities. The bulk density for both sandy clay loam soils is 1.6 g cm-3. The electrical conductivity at saturation for the sandy clay loam labeled compacted soil is 0.4 dS m-1. The compacted soil, high EC had an electrical conductivity at saturation of 0.75 dS m-1. 0.3 0.2 0.
CS616 and CS625 Water Content Reflectometers 7.3 Calibration Equations TABLE 7-1 lists the calibration coefficients derived in the Campbell Scientific soils laboratory. Both linear and quadratic forms are presented. The choice of linear or quadratic forms depends on the expected range of water content and accuracy requirements. These coefficients should provide accurate volumetric water content in mineral soils with bulk electrical conductivity less than 0.5 dS m-1, bulk density less than 1.
CS616 and CS625 Water Content Reflectometers FIGURE 7-3. Difference in % volumetric water content between linear and quadratic forms of calibrations The linear and quadratic coefficients for the sandy clay loam data in FIGURE 7-3 follow and can be used in similar soils. TABLE 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. Linear Quadratic C0 C1 C0 C1 C2 –0.6200 0.0329 0.
CS616 and CS625 Water Content Reflectometers 7.4 Operating Range 7.4.1 Soil Electrical Conductivity The quality of soil water measurements which apply electromagnetic fields to wave guides is affected by soil electrical conductivity. The propagation of electromagnetic fields in the configuration of the CS616/CS625 is predominantly affected by changing dielectric constant due to changing water content, but it is also affected by electrical conductivity.
CS616 and CS625 Water Content Reflectometers The electromagnetic energy introduced by the probe acts to re-orientate or polarize the water molecules. If other forces are acting on the polar water molecules, the force exerted by the applied signal will be less likely to polarize the molecules. This has the net effect of ‘hiding’ some of the water from the probe. Additionally, some clays sorb water interstitially and thus inhibit polarization by the applied field.
CS616 and CS625 Water Content Reflectometers if there are free ions in soil solution, polar solid constituents such as organic matter or some clay, or conductive mineral constituents. The general calibration equation for the CS616/CS625 will provide good results with attenuation equivalent to about 0.5 dS m-1 bulk electrical conductivity. Between 0.5 dS m-1 and 5 dS m-1, the CS616/CS625 will continue to give a well-behaved response to changes in water content but a soil specific calibration is required.
CS616 and CS625 Water Content Reflectometers Water Content Error with Temperature 8 Water Content Error (%VWC) 6 4 2 0 2 4 10 15 20 Water Content = 30% Water Content = 12% 25 Soil Temperature (C) 30 35 40 FIGURE 7-4. Percent volumetric water content error corrected for by temperature correction equation 8. Water Content Reflectometer User-Calibration 8.
CS616 and CS625 Water Content Reflectometers Some clays are very polar and/or conductive and will also attenuate the applied signal. Additionally, if the clayey soil is compacted, increased bulk density, the conductivity is increased and the response is affected.
CS616 and CS625 Water Content Reflectometers 8.3 Collecting Laboratory Data for Calibration Water content reflectometer data needed for CS616/CS625 calibration are the CS616/CS625 output period (microseconds) and an independently determined volumetric water content.
CS616 and CS625 Water Content Reflectometers The typically used method for packing a container of soil to uniform bulk density is to roughly separate the soil into three or more equal portions and add one portion to the container with compaction. Evenly place the first loose soil layer in the bottom of the container. Compact by tamping the surface to a level in the container that is correct for the target bulk density. Repeat for the remaining layers.
CS616 and CS625 Water Content Reflectometers Method D4643-93 requires heating in microwave for 3 minutes, cooling in desiccator then weighing and repeating this process until weigh is constant. Gravimetric water content is calculated after the container weight is accounted for. θg = m wet − m dry m dry For the bulk density ρ bulk = m dry volume cylinder the dry weigh of the sample is divided by the sample tube volume.
CS616 and CS625 Water Content Reflectometers with θv , the volumetric water content (m3 m-3); τ, the CS616/CS625 period (microseconds); Co , the intercept; and C1 , the slope. The calibration coefficients are derived from a curve fit of known water content and CS616/CS625 period. The number of data sets needed to derive a calibration depends on whether the linear or quadratic form is being used and the accuracy requirement.
CS616 and CS625 Water Content Reflectometers Gravimetric water content is calculated after the container weight is accounted for. θg = m wet − m dry m dry For the bulk density, ρ bulk = m dry volume cylinder the dry weight of the sample is divided by the sample tube volume.
CS616 and CS625 Water Content Reflectometers To obtain soil bulk density, use ρ bulk = m dry volume cylinder Volumetric water content is calculated using θ v = θ g * ρ bulk . 9. Maintenance The CS616/CS625 does not require periodic maintenance. 10. References Rhoades, J.D., P.A.C. Raats, and R.J. Prather. 1976. Effects of liquid-phase electrical conductivity, water content and surface conductivity on bulk soil electrical conductivity. Soil Sci. Soc. Am. J., 40: 651-653. Rhoades, J.D., N.A.
CS616 and CS625 Water Content Reflectometers 40
Appendix A. Discussion of Soil Water Content The water content reflectometer measures volumetric water content. Soil water content is expressed on a gravimetric and a volumetric basis. To obtain the independently determined volumetric water content, gravimetric water content must first be measured. Gravimetric water content (θg) is the mass of water per mass of dry soil. It is measured by weighing a soil sample (mwet), drying the sample to remove the water, then weighing the dried soil (mdry).
Appendix A.
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