HydroSense Soil Water Measurement System Revision: 7/10 C o p y r i g h t © 1 9 9 9 - 2 0 1 0 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 SOIL WATER MEASUREMENT SYSTEM (CD620, CS620) 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 Soil Water Measurement System (CD620, CS620) 1. General Description FIGURE 1-1. The HydroSense system consists of the CS620 sensor (left), the CD620 display (right), and two rods. 1.1 Introduction The components of the HydroSense system are the CS620 sensor, CD620 display, and two rods. Campbell Scientific offers 12-cm long rods (pn 18591) or 20-cm long rods (pn 18592). The sensor, display, and rods are purchased separately.
HydroSense Soil Water Measurement System (CD620, CS620) 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.
HydroSense Soil Water Measurement System (CD620, CS620) Weight 390 g (14 oz) Cable Spiral cable, 200 cm extended. *saturation is typically around 50% volumetric water content 3. Unpacking and Setup NOTE • Remove the protective strip from the display window. • Screw the rods into the threaded inserts of the CS620. Use the openended wrench to tighten the nut on the end of the rods, ensuring that the rods are securely attached.
HydroSense Soil Water Measurement System (CD620, CS620) and hold the MENU button then press the READ button. Release both buttons. Unless the mode is changed again, HydroSense will be in Water Content Measurement Mode when READ is next pressed to wake the unit. • While holding the probes so rods are in free air, press READ. The VWC displayed should be between -3% and 3%. VWC Period MENU SELECT • 0% P12cm 0.77ms In Water Content Measurement Mode, MENU is used to select the rod length.
HydroSense Soil Water Measurement System (CD620, CS620) The two-line display provides the following information 1) The volumetric water content in percent (VWC). See Appendix A for definition of water content. 2) Which probe rod length is selected (see Section 4.4 for rod length selection). 3) The period of the square wave output from the probe in milliseconds. 4.
HydroSense Soil Water Measurement System (CD620, CS620) 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.
HydroSense Soil Water Measurement System (CD620, CS620) 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 Soil Water Measurement System (CD620, CS620) 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 READ ENTER Site Exit MENU SELECT READ ENTER Press Select until desired Site is selected MENU SELECT Cal 100 Site 1 MENU SELECT MENU SELECT Site 2..
HydroSense Soil Water Measurement System (CD620, CS620) 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 Soil Water Measurement System (CD620, CS620) 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.
HydroSense Soil Water Measurement System (CD620, CS620) 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 8.2) or use of different length rods.
HydroSense Soil Water Measurement System (CD620, CS620) 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. The probe rods act as a waveguide and the applied signal travels to the end of the rods and reverses the direction of travel.
HydroSense Soil Water Measurement System (CD620, CS620) 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 Soil Water Measurement System (CD620, CS620) NOTE In December 2009, the rods were redesigned (see Figure 8-2). Rods shipped prior to December 2009 had a disc-shaped collar instead of a nut. The open-ended wrench is not used with the older rod design; pliers are used instead. Because of this, the open-ended wrench began shipping with the CS620 in December 2009. FIGURE 8-2. Newer CS620 rod design (left) and older CS620 rod design (right).
HydroSense Soil Water Measurement System (CD620, CS620) • After screwing the rods into the probe threaded inserts to finger tight, use the open-ended wrench to tighten the nut, ensuring that the rods are securely attached. • Full contact between the nut and probe body is required for proper operation.
HydroSense Soil Water Measurement System (CD620, CS620) 16
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 . g cm −3 13 = 1− = 0.50 ρ solid 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.
Appendix B.
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