PT103909A - SOIL PROPERTIES MEASUREMENT SYSTEM - Google Patents

Abstract

The present invention relates to a system for measuring various soil properties such as thermal properties, electrical conductivity, water content and water flow. IT IS ESSENTIALLY CHARACTERIZED TO BE COMPOSED OF: A MULTIFUNCTIONAL PROBE WHICH PRINCIPLE OF OPERATION IS BASED ON THE HEAT IMPULSE TO THE AREA OF PLANT ROOTS THAT IS WHICH IS FORMED BY SIX STAINLESS STEEL PIPES WHICH HOLD IN A FIRST TUBE A HEATING ELEMENT AND OTHERS FOUR TEMPERATURE SENSORS; A SET OF INTEGRATED CIRCUITS THAT ALLOWS THE CONTROL, ACQUISITION AND PROCESSING OF THE DATA COLLECTED IN THE REFERENCE PROBE, JOINT OF THE ONE THAT IS FOUND INSERTED IN THE REFERED PROBE; AND A MICROCONTROLLER ALSO INCLUDED IN THE REFERENCE PROBE.

Description

1

DESCRIPTION " SOIL PROPERTIES MEASUREMENT SYSTEM " The present invention relates to a system for measuring various soil properties: thermal properties, electrical conductivity, water content and water flow. It is essentially characterized by all the components necessary for the control, acquisition and processing of data from a multifunctional probe. Once processed, the data is displayed on an LCD (Liquid Crystal Display) or sent over a wireless network. Said components comprise temperature sensors, heating actuator, conditioning circuits and signal processing, wireless communication system, energy production and storage system and management electronics.

TECHNICAL FIELD OF THE INVENTION The present invention consists of a system for measuring the thermal properties, electrical conductivity, water content and water flow of the soil, making it possible to view or send, through a wireless network, the measurements. 2

SUMMARY OF THE INVENTION The present invention consists of a system for measuring the thermal properties, electrical conductivity, water content and soil water flow, enabling the viewing or sending, through a wireless network, of the measurements. It is essentially characterized in that all components necessary for the control, acquisition and processing of data are included in a multifunctional probe. Once processed, the data is displayed on an LCD (Liquid Crystal Display) or sent over a wireless network. Said components comprise temperature sensors, heating actuator, conditioning circuits and signal processing, wireless communication system, energy production and storage system and management electronics.

This new system will allow the application of the multifunction probe, based on the heat impulse, to the zone of the roots of the plants. This possibility will be due to the fact that this invention allows an autonomous operation of the multifunctional probe which is composed of six small metal tubes (figure 1). One of these tubes is a heating element, four of these tubes contain temperature sensors. The autonomous operation of the multifunctional probe will allow its use in the field for, inter alia, irrigation control. This new system will also allow an innovative approach that will change potential monitoring applications in soil ecology and hydrology because its size is relatively small and the system will simultaneously measure multiple soil environmental variables including water, heat and water flow and nutrients.

Soil processes and properties are heterogeneous depending on their values of spatial and temporal interest scales. Due to inherent heterogeneity, soil measurements are dependent on the measured volume. Normally, the hydrologic characterization of the soil requires more than one type of soil measurement. When more than one variable or soil parameter is measured, multiple instruments are used whose values belong to different locations and volumes. Therefore, multifunctional instruments are essential in order to minimize the effects of soil heterogeneity and to make accurate hydrological measurements of soil.

Background of the Invention

In the field of irrigation it is necessary to ensure that the water is properly controlled and supplied to the vegetation. Thus, for the efficient management in the short and long term, the use of reliable soil water content sensors is required. It is also necessary to know, not only the absence or excess of water, but also the content and movement of chemical agents (eg fertilizers) that contribute to water pollution. Nowadays there are a large number of soil water content sensors, based on several techniques that can be grouped as follows: Nuclear Techniques. In this group are located the sensors based on neutron bombardment, Gamma ray attenuation and nuclear magnetic resonance. U.S. Patents 4,926,267 and 5,559,450 are examples of the use of these techniques. This type of sensor, although very fast and precise, requires a minimum distance from the surface, which prevents a small spatial sampling (eg near the roots of the vegetation). Another disadvantage is the high price of this type of equipment that makes its use in agriculture almost impracticable, as well as the fact that it is radioactive, which requires special care in handling. Electromagnetic Techniques. In this group are located the sensors:

Resistive / Conductive. U.S. patent 4,796,654 is an example. This type of sensors consists of measuring the resistive / conductive properties of the wet soils through electrodes inserted in the soil and a means of determining the resistance / conductance between these electrodes. Soil resistance / conductivity is greatly affected by salinity and acidity 5, thus requiring a comparative method to calibrate the sensor for each type of soil. This type of sensors is difficult to install and maintain;

Capacitive. Patents W02007002994, US7170302B2 and US20070145984A1 are one example. It consists of the measurement of the capacity between two electrodes inserted in the soil, because the water content in the soil changes the value of the dielectric constant of the soil. Measurements, if done at a low frequency, are greatly affected by soil conductivity, although it may be indicative of salinity or level of fertilizer present in the soil. At high frequencies the soil impedance is essentially capacitive and derived from the water content in the soil but maintaining, however, a dependence on soil type and temperature.

Reflectometry in the time domain (TDR). US6657443, US5726578 and US4918375 are an example. This method consists of determining the dielectric constant of the medium and involves measuring the propagation of electromagnetic waves. The propagation constants of electromagnetic waves in the soil, such as velocity and attenuation, depend on the water content in the soil. Thus, the dielectric constant of the soil can be determined using a TDR instrument connected to a transmission line placed on the ground constituting a good method for the determination of its water content. This soil water determination is essentially independent of soil texture, temperature and salt content. To date this is the most effective method of measuring soil water content at the roots. Although accurate, this method requires high cost circuits in order to accurately measure the transmission line delay (on the order of GHz).

Microwave. US7135871B1 is an example. It consists of the transmission of a microwave through a conductor inserted in the ground. This signal will suffer a delay in proportion to the dielectric constant of the surrounding soil.

Despite the existence of various methods for measuring soil water content, these are either costly or difficult to maintain. Although the water content in the soil is obtained in the present invention, the electrical conductivity of the soil, the thermal properties of the soil and the flow of water and nutrients in the soil are also obtained at a low cost and with data transmission through a network wireless.

BRIEF DESCRIPTION OF THE DRAWINGS The following description is based on the accompanying drawings which represent a preferred non-limiting embodiment in which: Figure 1 shows a view of a multifunctional probe and the arrangement variants of the tubes; Figures 2 and 3 schematically represent central processing units 7; and Figure 4 is a graph of the temperature response after the application of a 8-second heat pulse in an agar solution.

General Description of the Invention

More specifically, the present invention consists of a system composed of a number of interconnected integrated circuits enabling the control, acquisition and processing of data from a multifunctional probe. The system allows the measurement of thermal properties, electrical conductivity, water content and soil water flow.

Measurement of the thermal properties (C, κ and λ) and the volumetric content of water in the soil (Θ) The measurement of the thermal properties of the soil using the heat impulse method is based on the solution of the heat conduction equation of a source line of infinite heat in a homogeneous and isotropic medium which initially is at a uniform temperature. For a heat impulse with a duration of t0 (s), the solution for the temperature change, ΔΤ (K) at a distance r (m) from the heat source is given by (de Vries, 1952): ΔΓ (γ , γ) b) -ElO]; pâraf > t < > (1) where q 'is the energy supplied per unit length of the heater element and per unit time (W m' 1), C and κ are the volumetric heat capacity (J m ~ 3 K & 1) and the diffusibility thermal (m2 s'1), respectively, and -Ei (x) is the exponential integral function of argument x. The thermal conductivity of the soil, λ (W m'1 K " 1), is obtained through the product of C by κ. For measurements r represents the distance between the heater element and the temperature sensing element. Once determined C through equation (1), the volumetric water content in the soil, Θ (m3 m ~ 3), can be determined from (De Vries, 1963): C = pbcs-Cwê (2) assuming that the value of specific air heat can be ignored and values of specific heat of the solid phase and water are available. In equation (2), r denotes the density of the material (kg m " 3), c is the specific heat (J kg " 1 K " 1), Cw = pwcw and the subscripts' b ',' s' and 'w 'are, respectively, the soil, the solid phase and the water.

Electrical Conductivity (ECb and EC)

After specific calibration, using soil solutions of known concentrations, the electrical conductivity of the medium, ECb, can be related to the electrical conductivity of a soil solution, ECW. Rhoades et al. (1976) proposed an expression to estimate 9 the electrical conductivity of a soil solution from measurements of Θ, • 7-7 · - ο.θ ~ - bB " 7 "(3)

where, ECb (Ω ^ 1), is the electrical conductivity of the medium, ECW (Ω-1), is the electrical conductivity of the soil solution, and, ECS (Ω'1), is the electrical conductivity of the soil surface.

Flow of water (Jv)

By measuring the difference in temperature responses between the upper temperature sensing element (Fig. 1, Tube 5) and lower (Fig. 1, Tube 6) additional information is obtained to estimate the flow density of the water, <; JW. Wang et al. (2002) proposed the following relation: /, * < 4 > where the subscripts 'u' and 'd' indicate, respectively, the upper and lower positions. The System 0 system (Figure 2 and 3) is composed of a central processing unit (microcontroller) where software is run responsible for the entire operation of the system. The central processing unit connects analog to digital signal converters, signal conditioners, digital-to-analog signal converters and a radio frequency data transmission and reception module or a LCD display and serial connection.

DETAILED DESCRIPTION OF THE INVENTION The present invention is composed of three parts: a multifunctional probe whose principle of operation is based on the heat pulse to the root zone of probe plants which is formed by six stainless steel tubes housing in a first tube a heater element and in another four temperature sensors, a set of interconnected integrated circuits that allows the control, acquisition and processing of data collected in said probe, which set is inserted in said probe, and - a microcontroller also included in said probe. The catheter

Said tubes forming the probe are of stainless steel and have an external diameter of α, four of these tubes 1, 2, 3 and 4 of length of b with b / a equal to or greater than 20, while the other two tubes 5 and 6 is half the length, b / 2. For example, the probe may be composed of six stainless steel tubes with 1.27 mm outside diameter and 0.84 mm internal diameter. Four of these tubes (fig. 1, tubes 1, 2, 3 and 4) are 26 mm in length external to the fixture, while the other two (fig. 1, tubes 5 and 6) are half the length, 13 mm. Said tubes may be disposed within the probe through an arrangement in " Square " and in the " Wenner " arrangement. The heater element (FIG. 1, Tube 3) is constructed by introducing a high resistivity fine wire to obtain an energy per unit length of 100 J / m or more. For example, it has a diameter of 79 μm in diameter, and a resistance of 20 μm -1 in order to obtain a resistance of approximately 30 Ω.

Temperature sensor tubes (Fig. 1, Tubes 2, 4, 5 and 6) are constructed by placing a thermistor (0.46 mm diameter, 10 kΩ at 25 ° C and 0.004 ° C measured accuracy at 20 ° C) in the center of the tubes. For the Wenner arrangement (fig.1, 1, 2, 3 and 4) the tubes 1 and 4 are connected for current injection and the voltage difference is read in the tubes 2 and 3. For the Squared arrangement the injection of current is made in tubes 2 and 5, and for reading the voltage difference, pipes 4 and 6 are used. For electrical conductivity, both for the Weener arrangement and for the Square arrangement, the electrodes are the tubes themselves, since they are of metal (stainless steel). 12

All tubes were filled with epoxy glue with high thermal conductivity and excellent electrical insulation. All tubes are fixed to a pre-punched PVC disc, 22 mm in diameter and 8 mm thick. The separation between all tubes is 6 mm. The Electronic System The data acquisition, control and control system consists of several integrated circuits that perform the functions of temperature acquisition, electrical conductivity acquisition, heat impulse control, processing and transmission of radio frequency information (Fig. 2) or displays values / graphics on an LCD (fig 3).

The temperature acquisition is done by connecting the half-bridge thermistors to four sigma-delta (Σ-Δ) analog-to-digital (AD converters) converters. For this purpose, four AD converters can be used, one on each integrated circuit or the four on a single integrated circuit with simultaneous acquisition. The resistance resistance measurement of the thermistors is through the Steinhart-converted Hart equation. The acquisition of electrical conductivity is achieved by the application of an electric current to the external electrodes (Fig. 1, Tubes 1 and 4) in measuring the voltage difference at the internal electrodes (Fig. 1, Tubes 2 and 3). The current is applied through a digital-to-analog converter (DAC) on the microcontroller. The voltage difference measurement is obtained by connecting the internal electrodes to the AD converters of the microcontroller. The electrical conductivity can also be obtained through an integrated circuit for this purpose. Control of the heat impulse is achieved by enabling a DC-DC converter whose output voltage is programmable (between 5 V and 12 V) through a DAC converter of the microcontroller. The emitted energy (amount of accumulated heat, q ') is obtained by measuring the voltage at a precision resistance (1 Q, 0.01% tolerance). The pulse time, t0, is controlled by the microcontroller timer (usually 8 s).

Every process is controlled through a program developed for the microcontroller. The program is responsible for: reading the soil electrical conductivity through equation (3); application of the heat impulse (time, t0, and energy, q ', configurable); reading the resistance value of the thermistors and subsequent conversion to temperature (sampling time and configurable total acquisition time); (1), and the volumetric content of water in the soil (Θ) through equation (2) - see figure 4; calculation of water flow through equation (4); (see Figure 2) or 14 to display values / graphics on an LCD (Figure 3).

Lisbon, March 28, 2008

LUIS SILVA CARVALHO Official Agent of Ptapried * of Industrial RUA VICTOR CORDON, 14 1200 LISBOA

Claims (16)

A system for measuring soil properties, characterized in that it is composed of: - a multifunctional probe whose principle of operation is based on the heat impulse to the zone of the roots of plants probe which is formed by six tubes of stainless steel which houses in a first tube a heating element and in another four temperature sensors, a set of integrated circuits that allows the control, acquisition and processing of data collected in said probe, which set are inserted in said probe, and - a microcontroller also included in said probe. A soil measurement system according to the preceding claim, characterized in that said probe constituent tubes are of stainless steel and have an external diameter of a, four of which are tubes 1, 2, 3 and 4 of length of b with b / a equal to or greater than 20, while the other two tubes 5 and 6 are half the length, b / 2. The soil properties measuring system according to the preceding claims, characterized in that the heater element, pipe 3, is constructed through a high resistivity wire in order to obtain an energy per unit length of 100 J / m. 2 A soil metering system according to the preceding claims, characterized in that the temperature sensor tubes, tubes 2, 4, 5 and 6 are constructed by placing a thermistor in the center of the tubes. A soil property measuring system according to the preceding claims, characterized in that the pipes can be disposed inside the probe through an arrangement in " Square " and in the " Wenner " arrangement. A soil property measuring system according to the preceding claims, characterized in that for the arrangement of " Wenner " the tubes 1 and 4 are connected to the current injection, the voltage difference being read in the tubes 2 and 3, while for the arrangement in " Square " the injection of the stream is made in the tubes 2 and 5 and the reading of the voltage difference is made in the tubes 4 and 6. A soil property measuring system according to the preceding claims, characterized in that the electrical conductivity for the " Wenner " and for the arrangement in " Square " the electrodes are the tubes themselves. The soil properties measuring system according to the previous claims, characterized in that all the pipes are fixed to a pre-drilled PVC disk, filled with epoxy adhesive of high thermal conductivity and very good electrical insulation and separation between all the tubes between 10 mm and 5 mm. A soil measurement system according to the preceding claim, characterized in that the separation between all the pipes is 6 mm. Ground measurement system according to claim 1, characterized in that the data acquisition, control and processing system is carried out by integrated circuits which perform the functions of temperature acquisition, electric conductivity acquisition, impulse control heat, processing and sending information by radio frequency or displays values / graphics on an LCD screen. The soil properties measurement system according to the preceding claim characterized the acquisition of temperature by connecting the half-bridge thermistors to four analog-to-sigma-delta digital signal converters placed on each integrated circuit. A soil measurement system according to claim 11, characterized in that the sigma-delta signal converters are placed in a single integrated circuit with simultaneous acquisition of the temperature. A soil metering system according to claim 10, characterized in that the acquisition of electrical conductivity is achieved by applying an electric current to the external electrodes, tubes 1 and 4 in the measurement of the voltage difference in the internal electrodes, tubes 2 and 3, the current being applied through a digital-to-analog signal converter existing in, and measuring the voltage difference is obtained by connecting the internal electrodes to the analog-digital converters of the microcontroller. A soil measurement system according to claim 13, characterized in that the acquisition of the electrical conductivity can be achieved by means of an integrated circuit suitable for this purpose. A soil measurement system according to claim 10, characterized in that the heat impulse control is achieved by enabling a DC-DC converter whose output voltage is programmable through a digital signal converter to analogue of the microcontroller, the emitted energy being obtained by measuring the voltage at a precision resistor, the pulse time being controlled by a microcontroller timer. 5 A soil property measurement system according to the preceding claims, characterized by the existence of a program designed for the microcontroller responsible for the reading of the electrical conductivity of the soil, application of the heat pulse, reading of the resistance value of the thermistors and subsequent conversion to temperature, calculation of thermal properties, volumetric content of water in the soil, calculation of water flow, radio frequency data transmission when requested or values / graphs. Lisbon, March 28, 2008 LUIS SILVA CARVALHO Agent Agent of Prepriedede kdutriíi RUA VICTOR CORDON, U 1200 LISBOA