Campbell CS616 Instruction Manual Download

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Appendix A. Discussion of Soil Water Content

A-2

Summary of Contents for CS616

Page 1: ...CS616 and CS625 Water Content Reflectometers Revision 10 12 C o p y r i g h t 2 0 0 2 2 0 1 2 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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Page 3: ...removing reinstalling and shipping defective products to Campbell Campbell will return such products by surface carrier prepaid within the continental United States of America To all other locations Campbell will return such products best way CIP Port of Entry INCOTERM 2010 prepaid This warranty shall not apply to any products which have been subjected to modification misuse neglect improper servi...

Page 4: ...ng container Campbell Scientific s shipping address is CAMPBELL SCIENTIFIC INC RMA _____ 815 West 1800 North Logan Utah 84321 1784 For all returns the customer must fill out a Statement of Product Cleanliness and Decontamination form and comply with the requirements specified in it The form is available from our web site at www campbellsci com repair A completed form must be either emailed to repa...

Page 5: ...ple 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 C...

Page 6: ...cussion 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 Diff...

Page 7: ...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 iii ...

Page 8: ...Table of Contents iv ...

Page 9: ... 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...

Page 10: ...rmittivity 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 squa...

Page 11: ... 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 max...

Page 12: ...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 o...

Page 13: ...er 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 g...

Page 14: ...ater 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 p...

Page 15: ...l 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 M...

Page 16: ..._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 ...

Page 17: ...ent 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 Exampl...

Page 18: ...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 ...

Page 19: ...nal 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...

Page 20: ...orage 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 ...

Page 21: ...to volumetric water content Sensors are read hourly and average water content and temperature are written to storage every 4 hours CS625 leads CR200 X green Single Ended Channel 1 SE1 black ground for SE1 orange Control Port 1 C1 red SW Battery clear G 109 leads CR200 X black Switched excitation channel 1 EX1 red Single Ended Channel 5 SE5 purple G clear G CR200 X program to read 1 109 temperature...

Page 22: ...struction 138 See Section 6 4 5 1 CS616 Sample Edlog Program 1 for example on using Instruction 138 1 CS616 Water Content Reflectometer P138 1 1 Reps 2 00 SE Channel 3 00 Control Port Code 4 0000 Loc _________ 5 1 0 Mult 6 0 0 Offset 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...

Page 23: ... multiplied by Enter a 1 for probe output period in microseconds A multiplier is often used for calibration or to convert the input location value to different units Offset A constant that is added to the input location value An offset of 0 has no effect on the input location value An offset is often used for calibration or to convert the data to different units With a multiplier of 1 and an offse...

Page 24: ...ut location that will store the period measurement The period output is in microseconds An Input Location is a place in the datalogger s memory where a measurement is temporarily stored until it is used in intermediate storage output or overwritten An input location is reserved for each measurement in the datalogger program Additional locations can be created by the user Mult A factor that the inp...

Page 25: ...ge every 4 hours 4 Measure soil temperature and CS616 output period every 4 hours Correct CS616 output period for temperature and write result to datalogger final storage 5 Hourly measure datalogger battery voltage internal temperature and 48 CS616 probes using AM16 32 multiplexer 6 4 5 1 CS616 Sample Edlog Program 1 Set Flag 1 to read output of one CS616 using CR10X instruction 138 and convert ou...

Page 26: ...C5 4 Do P86 1 21 Set Flag 1 Low 5 End P95 Table 2 Program 02 0 0000 Execution Interval seconds Table 3 Subroutines End Program Input Locations 1 period 1 0 1 2 VWC 1 0 1 6 4 5 2 CS616 Sample Edlog Program 2 Every 5 minutes measure CS616 output period using instruction 27 and convert to volumetric water content Write hourly average to datalogger final storage CS616 CR10X green Single Ended Channel ...

Page 27: ...5 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 Turn Off CS616 probe 1 51 Set Port 1 Low 5 If time is P92 Turn On Data Storage every hour 1 0 Minutes Seconds into a 2 60 Interval same units as above 3 10 Set Output Flag High Flag 0 6 Real Time P77 Store a time stamp 1 1220 Year Day Hour Minute midnight 2400 7 Average P71 Store the...

Page 28: ... for 3 CS616 outputs y 6 7 8 for 3 CS616s enables The red leads are connected to 12Vdc and the blacks and shields are connected to ground 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...

Page 29: ...utput period every four hours Correct CS616 output period for temperature and write result to datalogger final storage 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 ...

Page 30: ...0 Offset The following four instructions correct CS616 period for soil temperature The corrected period is stored as variable NewCS616 5 Polynomial P55 1 1 Reps 2 3 X Loc CS616 3 4 F X Loc TempCS616 4 0 526 C0 5 0 052 C1 6 0 00136 C2 7 0 0 C3 8 0 0 C4 9 0 0 C5 6 Z X Y P35 1 2 X Loc Tref 2 1 Y Loc TSoil 3 5 Z Loc TFactor 7 Z X Y P36 1 5 X Loc TFactor 2 4 Y Loc TempCS616 3 4 Z Loc TempCS616 8 Z X Y ...

Page 31: ... Input Locations 1 TSoil 1 1 1 2 Tref 1 1 1 3 CS616 1 2 1 4 TempCS616 1 2 2 5 TFactor 1 1 1 6 NewCS616 1 1 1 7 WaterCont 1 1 1 6 4 5 5 CS616 Sample Edlog Program 5 Hourly measure datalogger battery voltage internal temperature and 48 CS616 probes The AM16 32 series multiplexer slide switch on the top panel is set to 4X16 Can execute measurement sequence manually by setting Flag 1 high Sensor lead ...

Page 32: ... 2 Loc DL_Temp 3 If time is P92 Every 60 Minutes Start Multiplexer Measurement Loop 1 0 Minutes Seconds into a 2 60 Interval same units as above 3 11 Set Flag 1 High 4 If Flag Port P91 User can start Measurement Loop by setting Flag 1 High 1 11 Do if Flag 1 is High 2 30 Then Do 5 Do P86 Set control port 1 high i e Reset Multiplexer 1 41 Set Port 1 High 6 Beginning of Loop P87 16 loops X 3ea CS616 ...

Page 33: ...lynomial P55 Convert 48ea Period measurements into water content 1 48 Reps 2 3 X Loc Period_1 3 52 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 0 C5 15 If time is P92 Store hourly averages every 4 hours 1 0 Minutes Seconds into a 2 240 Interval same units as above 3 10 Set Output Flag High Flag 0 16 Real Time P77 Data Storage time stamp 1 1220 Year Day Hour Minute midnig...

Page 34: ...e dielectric permittivity of the material surrounding the line As water content increases the propagation velocity decreases because polarization of water molecules takes time The travel time of the applied signal along 2 times the rod length is essentially measured The applied signal travels the length of the probe rods and is reflected from the rod ends traveling back to the probe head A part of...

Page 35: ...ss accuracy by a linear calibration equation The manufacturer supplied quadratic provides accuracy of 2 5 volumetric water content for soil electrical conductivity 0 5 dS m 1 and bulk density 1 55 g cm 3 in a measurement range of 0 VWC to 50 VWC 16 18 20 22 24 26 28 30 32 0 0 1 0 2 0 3 0 4 calibration data linear fit quadratic fit Output period microseconds Volumetric Water Content fractional FIGU...

Page 36: ...etric Water Content fractional FIGURE 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 The compacted soil response shows the effect of compaction and high clay content The signal attenuation caused by compaction or high clay content causes an offset in the respo...

Page 37: ...for linear and quadratic forms Linear quadratic C0 C1 C0 C1 C2 0 4677 0 0283 0 0663 0 0063 0 0007 The linear equation is VWC 0 4677 0 0283 period The quadratic equation is VWC 0 0663 0 0063 period 0 0007 period2 Period is in microseconds The result of both calibration equations is volumetric water content on a fractional basis Multiply by 100 to express in percent volumetric water content FIGURE 7...

Page 38: ...dy 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 0950 0 0211 0 0010 TABLE 7 3 Calibration coefficients for sandy clay loam with bulk density 1 6 g cm 3 and ...

Page 39: ... bulk solution v solid Τ with σbulk being the electrical conductivity of the bulk soil σsolution the soil solution σsolid the solid constituents θv the volumetric water content and Τ a soil specific transmission coefficient intended to account for the tortuosity of the flow path as water content changes See Rhoades et al 1989 for a form of this equation which accounts for mobile and immobile water...

Page 40: ...me soils when bulk density exceeds 1 5 g cm 3 The response to changing water content is still well behaved but the slope will decrease with increasing bulk density 7 5 Error Sources in Water Content Reflectometer Measurement 7 5 1 Probe to Probe Variability Error All manufactured CS616s CS625s are checked in standard media The limits for probe response in the standard media ensure accuracy of 2 vo...

Page 41: ... to give a well behaved response to changes in water content but a soil specific calibration is required See Section 8 Water Content Reflectomer User Calibration for calibration information 7 6 Temperature Dependence and Correction The error in measured volumetric water content caused by the temperature dependence of the CS616 CS625 is shown in FIGURE 7 4 The magnitude of the temperature sensitivi...

Page 42: ...al between the probe rods when a pulse is applied to them If the material between the rods is electrically conductive a path for current flow exists and the applied signal is attenuated Since the parallel rod design in soil is inherently a lossy medium and attenuation is frequency dependent both the amplitude of the reflection and the rise time or bandwidth are affected Instead of a relatively sho...

Page 43: ...16 CS625 period microseconds and Cn the calibration coefficient The standard calibration coefficients are derived from factory laboratory measurements using curve fitting of known volumetric water content to probe output period Linear form θ τ τ v C C 0 1 with θv the volumetric water content m3 m 3 τ the water content reflectometer period microseconds Co the intercept and C1 the slope Two data poi...

Page 44: ...by data taken near the driest and wettest expected water contents The measurement sensitive volume around the probe rods must be completely occupied by the calibration soil Only soil should be in the region within 4 inches of the rod surface The probe rods can be buried in a tray of soil that is dry or nearly dry The soil will be homogeneous around the probe rods if it is poured around the rods wh...

Page 45: ... the soil Equilibration can be verified by frequently observing the CS616 CS625 period output When period is constant equilibration is achieved Collect a set of calibration data values and repeat the water addition procedure again if needed With soil at equilibrium record the CS616 CS625 period value Take subsamples of the soil using containers of known volume This is necessary for measurement of ...

Page 46: ... programmed to measure probe output period 2 Cylindrical sampling devices to determine sample volume for bulk density e g copper tubing of diameter 1 and length about 2 3 Containers and scale to measure soil sample weight 4 Oven to dry samples microwave oven can also be used Data needed for CS616 CS625 calibration are the CS616 CS625 output period microseconds and an independently determined volum...

Page 47: ...ibrium record the CS616 CS625 period value Soil hydraulic properties are spatially variable Obtaining measurements that are representative of the soil on a large scale requires multiple readings and sampling The average of several core samples should be used to calculate volumetric water content Likewise the CS616 CS625 should be inserted at least 3 times into the soil recording the period values ...

Page 48: ... cylinder the volume is volume d h π 2 2 where d is the inside diameter of the cylinder and h is the height of the cylinder During soil sampling it is important that the cores be completely filled with soil but not extend beyond the ends of the cylinder Once soil core samples are obtained place the soil filled cylinder in a small tray of known empty weight This tray will hold the core sample durin...

Page 49: ... 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 Manteghi P J Shouse W J Alves 1989 Soil electrical conductivity and soil salinity New formulations and calibrations Soil Sci Soc Am J 53 433 4...

Page 50: ...CS616 and CS625 Water Content Reflectometers 42 ...

Page 51: ...the dried soil mdry θg water soil wet dry dry m m m m m Volumetric water content θv is the volume of liquid water per volume of soil Volume is the ratio of mass to density ρb which gives θ ρ ρ θ ρ ρ v water soil water water soil soil g soil water volume volume m m The density of water is close to 1 and often ignored Soil bulk density ρbulk is used for ρsoil and is the ratio of soil dry mass to sam...

Page 52: ...Appendix A Discussion of Soil Water Content A 2 ...

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Page 54: ...entific Canada Corp CSC 11564 149th Street NW Edmonton Alberta T5M 1W7 CANADA www campbellsci ca dataloggers campbellsci ca Campbell Scientific Centro Caribe S A CSCC 300 N Cementerio Edificio Breller Santo Domingo Heredia 40305 COSTA RICA www campbellsci cc info campbellsci cc Campbell Scientific Ltd CSL Campbell Park 80 Hathern Road Shepshed Loughborough LE12 9GX UNITED KINGDOM www campbellsci c...

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