Title of Invention

A GRANULAR MATARI9X SOIL MOISWTURE SENSOR TO MEASURE MOISTURE CONTENT OF A SOILMASS.

Abstract

This invention relates to a granular matrix soil moisture sensor to measure moisture content of a soil mass comprising a PVC pipe (1) with perforated wire mesh cover (7) at both ends and two rectangular electrodes (2) spaced from each other are provided inside said PVC pipe (1), a PVC support (3) for said electrode (2) is provided between the PVC pipe (1) and the electrodes (2), a pair of nylon cloths (4) and gypsum wafers (5) are placed at both ends of the PVC pipe (1), said two rectangular electrodes (2) and the two gypsum wafers (5) encloses a non dissolvable electrically conductive porous body granular matrix (6), wherein the sensor electrical impedance between the two electrodes (2) corresponding to the moisture content of the soil surrounding matrix (6) embedded in the soil varies and the said varied impedances are measured.

Full Text

-2- FIELD OF THE INVENTION This invention relates to a granular matrix soil moisture sensor to measure moisture content of a soil mass. BACKGROUND OF THE INVENTION The knowledge of soil water is important in soil moisture modeling for point and line source emission devices, irrigation scheduling of crops, estimation of losses to the ground water under varied soil condition, estimation of soil water fluxes in the wide range of environment studies including acidification, pollution and nutrient uptake. There are various techniques for measuring soil water content such as Neutron attenuation. Time domain refectometry (TDR), Frequency Domain Reflectometry (FDR), Velocity differentiation domain (VDD), Optical Methods, Heat dissipation, (Soil) Moisture Suction) Tensionmeters, Pressure plate (Resistance Measurement Gypsum blocks, Granular matrix sensors (GMS), Gravimetric method. -3- Though the method of neutron attenuation is accurate it requires skill in handling and operating the instrument and if left unattended there is danger of ratioactive radiation. It cannot be used to measure the soil moisture content at depth less than 15 cm. TDR, VDD and FDR techniques use very high frequency current and complicated circuitry and they are expensive. Tensionmeters have very limited working range. Gypsum blocks dissolve in the water and thus their calibration curve gets affected over time. All prior invention are based on either measuring resistance or voltage across the granular matrix. The present invention is based on measuring impedance which includes the resistive part along with the capacitive part. The developed granular soil moisture sensor can be effectively used for: 1. To schedule irrigation for crops. 2. To estimate soil water flux at different depth 3. To model soil moisture movement under point and line source device. 4. To estimate ground water pollution and soil nitrification. OBJECTS OF THE INVENTION An object of this invention is to propose a granular matrix soil moisture sensor to sense soil moisture. Another object of this invention is to propose a granular matrix soil moisture sensor to sense soil moisture which is not affected by acid / saline soil and water quality as gypsum wafer neutralizes the effect of acid / saline and water quality. -4- Yet another object of this invention is to propose a granular matrix soil moisture sensor to son moisture ana wnerein tne eiectroaes ao not get corroded. A further object of this invention is to propose a granular matrix soil moisture sensor to sense soil moisture which can be interfaced with a microprocessor or computer for automated irrigation system. Further objects and advantages of the invention will be more apparent from the ensuing description. The nature of the invention, its objective and further advantages residing in the same will be apparent form the following description made with reference to the nonlimiting exemplary embodiments of the invention represented in the accompanying drawings: Figure 1 shows the longitudinal sectional view of the soil moisture sensor. Figure 2 shows isometric sectional view of soil moisture at A-A of Figure 1. Figure 3 shows the effect of moisture content of granular matrix on impedance at 100 kHz frequency for different area of electrodes at electrode spacing of 3 cm. Figure 4 shows the effect of moisture content of granular matrix on impedance at 100 kHz for different electrode spacing at area of electrode as 3 cm2. Figure 5 illustrates the effect of moisture content on impedance for different frequencies at electrode spacing of 5 cm with 3 cm2 area. -5- According to this invention there is provided a granular matrix soil moisture sensor to measure moisture content of a soil mass comprising a PVC pipe with perforated wire mesh cover at both ends and two rectangular electrodes spaced from each other are. provided inside said PVC pipe, a PVC support for said electrode is provided between the PVC pipe and the electrodes, a pair of nylon cloths and gypsum wafers are placed at both ends of the PVC pipe, said two rectangular electrodes and the two gypsum wafers encloses a non dissolvable electrically conductive porous body granular matrix, wherein the sensor electrical impedance between the two electrodes corresponding to the moisture content of the soil surrounding matrix embedded in the soil varies and the said varied impedances are measured. DETAILED PECRIPTION The Granular matrix soil moisture sensor assembly consists of PVC pipe (1) enclosing granular matrix (porous material) (6) lying between two rectangular steel electrodes (2) placed parallel to each other. PVC block (3) along the pipe (1) wall support the two steel electrodes (2). Gypsum wafers (5) placed on both sides of the pipe (1) opening enclose the granular matrix (6) and electrodes (2). Two perforated wire meshes (7) are fitted on open ends of the pipe (1). A thin piece of nylon doth between the gypsum wafer (5) and steel wire mesh (7) act as a packing material. -6- The electrical impedance between two electrodes (2) varies with the moisture content of the granular matrix (6) which is in equilibrium with the surrounding soil media. The dependence of electrical impedance of a granular matrix (6) on the amount of water forms the basis of this development. The soil moisture sensor containing a non dissolvable electrically conductive porous body granular matrix (6) of weathered sedimentary rock placed between stainless steel electrodes (2) inside and gypsum wafer (5) outside, when embedded in the soil, the moisture content of granular matrix (6) (porous body) comes in equilibrium with the soil moisture. To apply the voltages across the electrodes the corresponding impedance will change with the voltage, as a function of frequencies. When the soil moisture sensor unit is buried in the soil, it becomes almost part of the soil mass and responds to changes in soil moisture content. Based on rigorous experiments conducted, relationships were established between impedance at a given frequency of applied voltage and soil moisture content measured by the granular matrix sensor for different area and spacing of electrodes. A general expression for determining soil moisture content was established between different electrode parameters and impedance, which is given below Where, Go, = moisture content of granular matrix (dry weight basis, %) Z = impedance (kohm) / = frequency of applied voltage (kHz) A = area of electrode (cm2) L = spacing between electrodes (cm) -7- The geometrical parameters viz area of electrode, distance between the electrodes, thickness of the electrodes used in the sensor are optimized according to the experimental observations and relationship formed thereof. The developed sensor is tested for its moisture content in terms of impedance (resistance + capacitance) which is related with the frequency and magnitude of the applied voltage, as enumerated in the plotted graphs in Figures 3, 4 and 5. -8- Ranqe of Parameters Voltage applied in the electrode Frequency of applied voltage Area of electrode Spacing of electrode Size of granular matrix Bulk density of granular matrix 5 Volts (0 -1 Mega Hz) 50 Hz - 1 MHz 1 cm2 -10 cm2 1 cm - 5 cm 150 micron - 355 micron 0.8 gm / cm2 -1.8 gm / cm2 Typical specification of Granular Matrix Type Soil Moisture Sensor o The area of the Electrode = 2.5 sq. cm o Distance of separation of electrode = 1.5 cm o Size of granular matrix = sand of size greater than 250 micron and smaller than 355 micron is used as granular matrix. o Size of Gypsum Wafer = Gypsum wafer of thickness 3 mm and radium 2 cm o Range of Moisture content by weight of granular matrix 10% (at saturation) to 3% (at dry stage) o Frequency of current for sensing soil moisture is 5 kHz. o The invention described hereinabove is in relation to the non-limiting embodiments and as defined by the accompanying claims. -9- WECLAIM: 1. A granular matrix soil moisture sensor to measure moisture content of a soil mass comprising a PVC pipe (1) with perforated wire mesh cover (7) at both ends and two rectangular electrodes (2) spaced from each other are provided inside said PVC pipe (1), a PVC support (3) for said electrode (2) is provided between the PVC pipe (1) and the electrodes (2), a pair of nylon clothes (4) and gypsum wafers (5) are placed at both ends of the PVC pipe (1), said two rectangular electrodes (2) and the two gypsum wafers (5) encloses a non dissolvable electrically conductive porous body granular matrix (6), wherein the sensor electrical impedance between the two electrodes (2) corresponding to the moisture content of the soil surrounding matrix (6) embedded in the soil varies and the said varied impedances are measured according to mathematical relation Where, effi = moisture content of granular matrix (dry weight basis, %) Z = impedance (kohm) / = frequency of applied voltage (kHz) A = area of electrode (cm2) L = spacing between electrodes (cm)., -10- 2. The granular matrix soil moisture sensor as claimed in claim 1, wherein the electrodes (2) are made of stainless steel. 3. The granular matrix soil moisture sensor as claimed in claims 1 and 2, wherein the area of the electrode is between 1 cm2 to 10 cm2 and a spacing of the electrodes 1 cm to 5 cm. 4. The granular matrix soil moisture sensor as claimed in claim i, wherein the granular matrix consist;; of weathered sedimentary rock having particle size between 150 to 355 micron and a bulk density of 0.8 gm / cm2 to 1.8 gm / cm2. 5. The granular matrix soil moisture sensor as claimed in claim 1, wherein the gypsum wafers (5) has a thickness of 3 mm and radius of 2 cm. 6. The granular matrix soil moisture sensor as claimed in claim 5, wherein the moisture content of granular matrix (6) varies between 0 % at dry stage and 39 % saturation. -11- 7. The granular matrix soil moisture sensor as claimed in claim 1, wherein for sensing soil moisture the frequency of current used is 5 KHz and frequency of applied voltage is 50 Hz to 1 MHz. 8. A granular matrix soil moisture sensor as herein described and illustrated with the accompanying drawings. This invention relates to a granular matrix soil moisture sensor to measure moisture content of a soil mass comprising a PVC pipe (1) with perforated wire mesh cover (7) at both ends and two rectangular electrodes (2) spaced from each other are provided inside said PVC pipe (1), a PVC support (3) for said electrode (2) is provided between the PVC pipe (1) and the electrodes (2), a pair of nylon cloths (4) and gypsum wafers (5) are placed at both ends of the PVC pipe (1), said two rectangular electrodes (2) and the two gypsum wafers (5) encloses a non dissolvable electrically conductive porous body granular matrix (6), wherein the sensor electrical impedance between the two electrodes (2) corresponding to the moisture content of the soil surrounding matrix (6) embedded in the soil varies and the said varied impedances are measured.

Documents:

00705-cal-2000-abstract.pdf

00705-cal-2000-claims.pdf

00705-cal-2000-correspondence.pdf

00705-cal-2000-description(complete).pdf

00705-cal-2000-description(provisional).pdf

00705-cal-2000-drawings.pdf

00705-cal-2000-form-1.pdf

00705-cal-2000-form-13.pdf

00705-cal-2000-form-18.pdf

00705-cal-2000-form-2.pdf

00705-cal-2000-form-3.pdf

00705-cal-2000-form-5.pdf

00705-cal-2000-g.p.a.pdf

00705-cal-2000-latters patent.pdf

705-CAL-2000-FORM 15.pdf