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Campbell Hydrosense, Instruction Manual

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Campbell Hydrosense Instruction Manual Download Page 9

HydroSense

5

4.3  Description of Water Content Measurement Mode

The 

Water Content Measurement Mode 

applies calibration coefficients to

the output of the probe to give volumetric water content in percent.  The
calibration coefficients reside in the operating system and were determined by
the manufacturer.  The calibration was derived from laboratory measurements
in typical agronomic soils.  See Section 6.2 for discussion of HydroSense use in
high salinity, high clay or other atypical materials.

4.4  Selecting Probe Rod Length

VWC           22%           P12cm
Period             0.93ms

MENU

SELECT

Probe
Exit

MENU

SELECT

Probe
12cm

MENU

SELECT

Probe
20cm

MENU

SELECT

READ

ENTER

FIGURE 4-1.  Selecting probe rod length

Summary of Contents for Hydrosense

Page 1: ...INSTRUCTION MANUAL Hydrosense Revision 2 01 C o p y r i g h t c 1 9 9 9 2 0 0 1 C a m p b e l l S c i e n t i f i c I n c ...

Page 2: ...rranties expressed or implied including warranties of merchantability or fitness for a particular purpose CAMPBELL SCIENTIFIC INC is not liable for special indirect incidental or consequential damages Products may not be returned without prior authorization The following contact information is for US and International customers residing in countries served by Campbell Scientific Inc directly Affil...

Page 3: ...asuring Volumetric Water Content 6 4 6 Measurements in Special Materials 6 5 Water Deficit Mode 6 5 1 Description of Water Deficit Mode 6 5 2 Display Information 6 5 3 Calibration Setting the Lower and Upper Reference Levels 7 5 4 A Water Deficit Mode Example 8 6 Proper Measurement Technique and Method Limitations 9 6 1 Probe Rod Insertion 10 6 2 Soil Factors Which Can Affect the Measurement Clay ...

Page 4: ......

Page 5: ...es chosen by the user The relative water content is complemented by deficit values showing how much water is required to bring water content to the upper reference value The combined probe and display weight is approximately 600 gm 1 3 lb Two alkaline AAA batteries in the handheld display provide enough power for several thousand readings A measurement is made by fully inserting the probe rods int...

Page 6: ...ions 4 and 5 for detailed operating information 2 Specifications HydroSense Display Unit Measurement Volumetric Water Content Resolution 1 0 Environmental Splash resistant Display 16 character 2 line LCD Keypad Two button membrane keypad Power 2 x AAA 1 5V DC alkaline batteries Current Consumption Sleep 50µA Idle 1 5mA Measurement 70mA Battery Life Approximately 12 months Dimensions 120 w x 73 d x...

Page 7: ...asurement 3 and in combination with the MENU button to select options READ ENTER Press the READ button and check that HydroSense is in Water Content Measurement Mode The display should be similar to the following graphic but may have different numerical values VWC 0 P12cm Period 0 77ms An NC after VWC indicates the probe is not properly connected If it is necessary to change operating modes the Hy...

Page 8: ...eriod of the probe output in milliseconds The HydroSense operating system applies standard calibrations to convert the probe response to volumetric water content The calibrations were derived from laboratory measurements in typical agronomic soils Section 6 2 discusses the soil factors which can affect probe response such that standard calibrations do not work well 4 2 Display Information VWC 22 P...

Page 9: ...in the operating system and were determined by the manufacturer The calibration was derived from laboratory measurements in typical agronomic soils See Section 6 2 for discussion of HydroSense use in high salinity high clay or other atypical materials 4 4 Selecting Probe Rod Length VWC 22 P12cm Period 0 93ms MENU SELECT Probe Exit MENU SELECT Probe 12cm MENU SELECT Probe 20cm MENU SELECT READ ENTE...

Page 10: ...curve fitting methods to relate the independently measured water contents to the probe output periods 5 Water Deficit Mode 5 1 Description of Water Deficit Mode To use the Water Deficit Mode a lower reference level and an upper reference level must be chosen and a HydroSense reading taken at each level and stored in memory see Section 5 4 for calibration Measurements taken after reference levels a...

Page 11: ...ter which must be added to bring the soil water content to the upper reference level The water deficit calculation applies to a soil depth equal to the probe rod length i e 12 or 20 cm Knowledge of the particular soil allows extrapolation for other depths For example if the soil profile is known to be homogeneous in the surface 30 cm a water deficit calculation of 15 mm using 20 cm rods can be mul...

Page 12: ... rod length must be used for measurement as was used during calibration of the reference levels 5 4 A Water Deficit Mode Example Consider an application where the HydroSense is used to help make irrigation decisions for a crop It is known that unacceptable plant stress occurs at water contents less than 15 and excessive water drains from the plant root zone when water content is greater than 30 Th...

Page 13: ...ter deficit FIGURE 5 3 Relative water content and deficit for example application Figure 5 3 presents the relationship between relative water content and water deficit for the chosen reference levels A measurement taken at this site when water content is 20 would give a relative water content RWC value of approximately 33 and a water deficit value of 20 mm Adding 20 mm of water would bring the wat...

Page 14: ...ending of the rods near the thread is more likely than if the rods are properly tightened Please see maintenance Section 8 2 6 2 Soil Factors Which Can Affect the Measurement Clay Soil Electrical Conductivity Organic Matter and Rocks HydroSense is very sensitive to changes in dielectric permittivity and the probe has water content measurement resolution better than 0 1 While the HydroSense is pred...

Page 15: ...he difference in actual water content in proximal locations which are apparently similar The water contents in two locations which are only tens of centimeters apart can differ by several percent The scale of the measurement using a device such as the HydroSense must be considered in relation to the scale of the field or plot being monitored The sensitive volume of the HydroSense measurement cover...

Page 16: ...roSense is in the sleep mode The HydroSense automatically goes into sleep mode if either of the buttons are not pressed for about 2 minutes Pressing only the READ button starts HydroSense in the last mode selected The Water Content Measurement Mode applies calibration coefficients to the output of the probe to give volumetric water content in percent The calibration coefficients reside in the oper...

Page 17: ...D polarizing washers It is important that batteries are not reversed during replacement as damage to the unit can occur Do not remove the red polarizing washers Replace the cover plate and silver screws Calibration settings will NOT be lost when batteries are replaced 8 2 Rod Installation Replacement Threaded inserts in the probe epoxy body allow user replacement of the 12 and 20 cm rods Using rod...

Page 18: ... well is Vibra Tite by ND Industries This compound has a higher viscosity than most thread coatings and a narrow strip is painted on the threads The applied compound must cure aerobically before the rods are threaded into the probe inserts The cured compound is a resilient plastic which is reusable several times It is important that the rod threads are not completely coated because this can affect...

Page 19: ... ρ v water soil water water soil soil g soil water volume volume m m Soil bulk density ρbulk is used for ρsoil and is the ratio of soil dry mass to sample volume The density of water ρwater is close to 1 and is often ignored Another useful property soil porosity ε is related to soil bulk density as shown by the following expression ε ρ ρ 1 bulk solid The term ρsolid is the density of the soil soli...

Page 20: ...umetric water content The measured θv value of 0 267 indicates the pore space is just over half full of water If the sample is from a 20 cm depth profile there are 5 3 cm of water in the profile Water content indicates how much water is present in the soil It can be used to estimate the amount of stored water in a profile or how much irrigation is required to reach a desired soil wetness ...

Page 21: ...rements are needed to provide a specific level of confidence that the area of interest has been adequately characterized This section of the appendix will demonstrate this statistical approach B 2 An Example As an example the results of 12 volumetric water content measurements taken within a 2 meter radius on a well established and level lawn are presented The measurements were not taken with a Hy...

Page 22: ...ere known there would be no reason to measure them Assuming a normal distribution correcting for the fact that the actual population standard deviation σ must be estimated from measurements and applying the theory of the Student s t distribution equation 2 becomes x t s n x t s n µ 3 with s the estimate of σ based on the measurements and t the value obtained from a table of Student s t values Usin...

Page 23: ...ablish an estimate of the standard deviation by taking several water content measurements then use that standard deviation estimate and the associated t value in 4 The range is specified by the user and the calculated N value defines the number of measurements The same s and t values are used but the number of measurements can be determined for several different ranges N t s L 4 4 2 201 174 5 0 2 ...

Page 24: ...Appendix B How Many Soil Water Content Measurements Are Enough B 4 This is a blank page ...

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Page 26: ...This is a blank page ...

Page 27: ... campbellsci com br suporte campbellsci com br Campbell Scientific Canada Corp CSC 11564 149th Street NW Edmonton Alberta T5M 1W7 CANADA www campbellsci ca dataloggers campbellsci ca Campbell Scientific Ltd CSL Campbell Park 80 Hathern Road Shepshed Loughborough LE12 9GX UNITED KINGDOM www campbellsci co uk sales campbellsci co uk Campbell Scientific Ltd France Miniparc du Verger Bat H 1 rue de Te...

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