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 .
Warranty and Assistance The HYDROSENSE is warranted by CAMPBELL SCIENTIFIC, INC. to be free from defects in materials and workmanship under normal use and service for twelve (12) months from date of shipment unless specified otherwise. Batteries have no warranty. CAMPBELL SCIENTIFIC, INC.'s obligation under this warranty is limited to repairing or replacing (at CAMPBELL SCIENTIFIC, INC.'s option) defective products.
HydroSense Table of Contents PDF viewers note: These page numbers refer to the printed version of this document. Use the Adobe Acrobat® bookmarks tab for links to specific sections. 1. General Description....................................................1 1.1 Introduction...............................................................................................1 1.2 HydroSense Modes ...................................................................................2 2. Specifications ...............
HydroSense Table of Contents A. Definition of Water Content Terms ....................... A-1 A.1 Definition of Water Content Terms..................................................... A-1 B. How Many Soil Water Content Measurements Are Enough .......................................................... B-1 B.1 B.2 B.3 B.4 Introduction to Spatial Variability ....................................................... B-1 An Example ...............................................................................
HydroSense 1. General Description FIGURE 1-1. HydroSense display unit and probe with 12 cm rods. 1.1 Introduction The HydroSense Soil Water Content Measurement System provides a simple and portable means to measure soil water content. Two modes of operation allow the display of volumetric water content in percent or relative water content based on lower and upper reference values chosen by the user.
HydroSense 1.2 HydroSense Modes The Water Content Measurement Mode displays the measurement result as percent volumetric water content and shows the period of the probe output in milliseconds. In the Water Deficit Mode, HydroSense measurements are taken at lower and upper water contents chosen by the user and stored in memory as reference values. The reference values are then applied to subsequent measurements to determine the amount of water that must be added to bring the soil to the upper water content.
HydroSense Weight approx 400 gm Cable Spiral cable, 200cm extended. *saturation is typically around 50% volumetric water content 3. Unpacking and Setup CAUTION • Remove the protective strip from the display window. • Screw the rods into the probe threaded inserts to finger tight, use pliers to apply a small force and give a snug fit. Threads should be clean before rods are screwed into probe. (see Section 8.2).
HydroSense VWC Period MENU SELECT • 0% P12cm 0.77ms In Water Content Measurement Mode, MENU is used to select the rod length. In the Water Deficit Mode, MENU is used to select the site number and to store reference water content values. To save power, HydroSense automatically goes into sleep mode after approximately two minutes of inactivity. Pressing the READ button wakes the unit and makes a measurement. 4. Water Content Measurement Mode 4.
HydroSense 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.
HydroSense 4.5 Measuring Volumetric Water Content To measure volumetric water content fully insert probe rods and press READ. The correct rod length must be selected so the HydroSense display unit applies the correct calibration to convert the probe output to water content. 4.6 Measurements in Special Materials The HydroSense was principally designed for use in agricultural soils, but the technology underlying the instrument supports many potential applications.
HydroSense Relative Water Content Site Currently Selected RWC 33 Deficit mm 34 Deficit 12 cm Probe Site 1 20 Deficit 20 cm Probe FIGURE 5-1. HydroSense display in Water Deficit Mode 5.3 Calibration—Setting the Lower and Upper Reference Levels Lower and upper reference levels must be set to use the HydroSense in the Water Deficit Mode. HydroSense measurements are used to set the reference levels for a particular site.
HydroSense WC Deficit 33 34 Site1 20 Press ENTER to store Cal 0 or Cal 100 readings or to exit the selection routine. MENU SELECT Cal 0 Site Exit READ ENTER MENU SELECT READ ENTER Press Select until desired Site is selected MENU SELECT Cal 100 Site 1 MENU SELECT MENU SELECT Site 2..5 READ ENTER Cal Exit Press Enter to select Site Note: To enter reference values for a site, the site must be selected once to enter a Cal 0 value and again to enter a Cal 100 value. FIGURE 5-2.
HydroSense prompt is displayed. With CAL 0 displayed, the probe rods are inserted and the READ button is pressed. This stores the measured value in HydroSense memory as the lower reference level for the chosen site. After irrigating to the desired upper reference level, the HydroSense is set to CAL 100 and a measurement taken by inserting the probe rods and pressing READ. This value is stored as the upper reference level for the chosen site. HydroSense is now calibrated for the chosen site.
HydroSense 6.1 Probe Rod Insertion Making a measurement with HydroSense is a simple matter of inserting the probe rods and pressing the READ button. However, the accuracy of the measurement can be degraded if the rods are inserted incorrectly. The rods must be completely inserted. If the probe rods are not fully inserted and air instead of soil occupies the space around the rods, a portion of the sensitive volume is not occupied by the medium intended to be measured and error will result.
HydroSense rocky soil, the measured water content can differ by several percent if a large rock occupies part of the sensitive volume of one measurement but not the other. 6.3 Rod Length and Insertion Angle Rods for the HydroSense probe are available in 12 and 20 cm length. There is no significant difference in performance between rod lengths and the choice of length depends on the application. Threaded inserts on the probe body allow easy replacement of damaged rods (see Section 8.
HydroSense making it possible to relate water content to measured dielectric permittivity. Additionally, water and air are the only soil constituents that change with time. The electronics embedded in the probe body generate the high frequency electromagnetic energy necessary to polarize water molecules to the extent needed to measure the dielectric permittivity. The travel time of electromagnetic energy along a waveguide is dependent on the dielectric permittivity.
HydroSense 8. Maintenance 8.1 Replacing Battery FIGURE 8-1. Rear view of the HydroSense display unit with battery cover removed The only user-replaceable components in the HydroSense display unit are the two 1.5 volt AAA batteries used to power the unit. Under normal use, battery life should be well in excess of 1 year. When the batteries require replacement, a small battery symbol will appear on the bottom right hand corner of the display.
HydroSense The friction between the rod collar and the insert surface along with thread friction will generally provide good rod attachment and loosening is unlikely. If rod loosening does occur, a thread coating compound can be used to enhance friction. There are two thread compounds that laboratory testing indicates minimal effect on the HydroSense measurement. A package with Loctite 222MS THREADLOCKER is included with each CS620 probe. There is enough thread coating to treat several rods.
Appendix A. Definition of Water Content Terms A.1 Definition of Water Content Terms Soil water content is expressed on a gravimetric or volumetric basis. 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). θg = m water m wet − m dry = m soil m dry Volumetric water content (θv) is the volume of liquid water per volume of soil.
Appendix A. Definition of Water Content Terms θv = ε = 1− θ g ∗ ρsoil ρ water = 0.267 cm 3 cm − 3 ρbulk 13 . g cm −3 = 1− = 0.50 ρsolid 2.6 g cm − 3 The porosity of 0.50 defines the maximum possible volumetric 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.
Appendix B. How Many Soil Water Content Measurements Are Enough B.1 Introduction to Spatial Variability Soil water content can vary significantly among several locations which are near each other and apparently similar. Water content measurements using the most accurate methods available provide evidence of significant differences in soil structure and texture even when the measurements are limited to an area of only 1 square meter.
Appendix B. How Many Soil Water Content Measurements Are Enough The relationship between confidence interval and probability can be described using the following expressions. µ −k σ n < x<µ+k σ n [1] with µ the actual population mean, σ the actual population standard deviation and n the number of values used to calculate the mean, x . The confidence coefficient, k, is used to specify a probability value. A probability of 90% or 0.
Appendix B. How Many Soil Water Content Measurements Are Enough N is the number of water content measurements and L is the acceptable range as defined by the user. For example, the acceptable water content range might be ±2.5% so L would be 5.0. Equation 4 relies on a good estimate of the population standard deviation.
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