Patent Description:
It is very important to manage a moisture content in soil while plants are grown. When a moisture content around roots is high, roots absorb water well so as to perform transpiration well. However, when a moisture content is excessive, respiration of roots becomes difficult due to the lack of air around roots and it is difficult to increase microorganisms in soil around roots so that the lack of nutrients supplied to plants is caused. Accordingly, it is necessary to measure a moisture content in soil and to adjust the moisture content to maintain an adequate moisture content. Also, even when plants are watered, it is necessary to check a precise moisture content in soil so as to supply enough water necessary in a growth and development state of plants.

Due to the above reason, a method of measuring a moisture content in soil has been used in the field of growing plants and there are a tensiometer method and a time domain reflectometry (TDR) method as representative examples.

The tensiometer method uses a force of soil to attract water. When a porous plaster cup is filled with water and buried, the water moves into the soil through the porous cup. Here, when the water and a water content in the soil are in equilibrium, the water content is obtained by measuring a negative pressure of pores of the soil using a suction gauge or a mercury liquid manometer.

In the TDR method, probes configured to emit and receive a high-frequency signal are laid at a distance and a water content is measured using a dielectric constant of soil which is extracted from a time in which the emitted high-frequency signal is reflected and returns.

The tensiometer method has disadvantages such as a complicated sensor structure, a high price, and a small measurement range. Also, the TDR method measures a water content between end points of two probes according to a measurement principle and has a disadvantage of being limited to local area measurement. To overcome this, sensors may be installed at several points. However, a problem that a measurement region of each sensor is also limited to a local part still remains. Also, when a plurality of sensors are installed, it is impossible to avoid an increase in a total cost.

Document <CIT> discloses a system for controlling irrigation comprising a plurality of soil moisture probes for capacitively measuring a moisture content in soil, the probes comprising: a conductive wire structure which can be inserted into the soil, having insulatively-coated first and second conductive wires parallel to each other and extending adjacently; a measurement circuit; a ground conductive material; and a moisture content calculation unit.

The present invention is directed to providing a moisture content measurement device for measuring a moisture content in soil, which has a simple structure, is priced low, and is capable of measuring a moisture content in soil over a larger area than a desired area.

One aspect of the present invention not encompassed by the wording of the claims provides a moisture content measurement device for measuring a moisture content in soil. The moisture content measurement device includes a conductive wire structure which is insertable into soil, includes insulatively-coated first and second conductive wires parallel to each other and extending adjacently, and has a certain structure, a capacitance measurement circuit configured to measure capacitance between the first and second conductive wires using alternating current (AC) power, and a moisture content calculation unit configured to calculate the moisture content in soil using the measured capacitance.

The moisture content calculation unit may calculate the moisture content in soil using a relationship in which the moisture content in soil is in proportion to the measured capacitance.

The conductive wire structure may further include a ground conductive wire parallel and extending adjacently to the first and second conductive wires and connected to a ground. Here, the moisture content calculation unit may calculate the moisture content in soil using a relationship in which the measured capacitance is reduced according to an increase of the moisture content in soil.

The moisture content calculation unit may calculate the moisture content in soil on the basis of first and second capacitance values previously measured using the capacitance measurement circuit corresponding to known first and second moisture contents.

The conductive wire structure may have a zigzag shape or a coil structure.

One aspect of the present invention provides a moisture content measurement device for measuring a moisture content in soil.

The moisture content measurement device includes a conductive wire structure which is insertable into soil, includes insulatively-coated first and second conductive wires parallel to each other and extending adjacently and a ground conductive wire parallel and extending adjacently to the first and second conductive wires and connected to a ground, and has a certain structure, a leakage current measurement circuit configured to apply AC power to the first and second conductive wires and to measure a leakage current leaking through the ground conductive wire, and a moisture content calculation unit configured to calculate the moisture content in soil using the measured leakage current.

The moisture content calculation unit calculates the moisture content in soil using a relationship in which the moisture content in soil is in proportion to the measured leakage current.

The moisture content calculation unit may calculate the moisture content in soil on the basis of first and second leakage current values previously measured using the leakage current measurement circuit corresponding to known first and second moisture contents.

According to the present invention, there are effects such as a simple structure, a low cost, and a larger area than a desired area, in which moisture content in soil is measured.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the drawings. Hereinafter, throughout the description and the attached drawings, substantially like elements will be referred to as like reference numerals and a repetitive description thereof will be omitted. Also, in a description of the embodiments of the present invention, a detailed description of well-known functions or components of the related art will be omitted when it is deemed to obscure understanding of the embodiments of the present invention.

<FIG> illustrates components of a device for measuring a moisture content in soil according to a first embodiment useful for understanding the invention.

The device according to the embodiment may include a conductive wire structure <NUM>, a capacitance measurement circuit <NUM>, and a moisture content calculation unit <NUM>.

The conductive wire structure <NUM> is configured to be inserted into soil to measure a moisture content therein and includes insulatively-coated first and second conductive wires <NUM> and <NUM> disposed to be parallel to each other and to adjacently extend.

Since a dielectric is present between the first and second conductive wires <NUM> and <NUM> due to the insulative coating, the conductive wire structure <NUM> may be a sort of capacitor with the first and second conductive wires <NUM> and <NUM> as both electrodes thereof. Capacitance of the conductive wire structure <NUM>, that is, capacitance between the first and second conductive wires <NUM> and <NUM> has a certain value according to a structure (size, shape, or the like) of the conductive wire structure <NUM>.

When the conductive wire structure <NUM> comes into contact with moisture, the moisture is present between and near the first and second conductive wires <NUM> and <NUM> so that dielectric permittivity of the dielectric between the first and second conductive wires <NUM> and <NUM> varies. Here, as moisture in contact increases, the dielectric permittivity further increases. Since capacitance is in proportion to dielectric permittivity, as moisture m contact increases, the capacitance of the conductive wire structure <NUM> increases.

In the embodiment of the present invention, using this principle, a moisture content in soil is measured by inserting the conductive wire structure <NUM> into the soil and measuring the capacitance of the conductive wire structure <NUM>. That is, according to the moisture content in soil, an amount of moisture, which comes into contact with the conductive wire structure <NUM> inserted into the soil, varies according to the moisture content in soil. Here, as the moisture content increases, the capacitance of the conductive wire structure <NUM> increases. Using this relationship, the moisture content in soil may be measured by measuring the capacitance of the conductive wire structure <NUM>. The applicant can see that a moisture content and capacitance are in proportion to each other as a result of performing a test of measuring the capacitance of the conductive w1re structure <NUM> while varying a moisture content in a soil sample. <FIG> is a graph illustrating a relationship between a moisture content in soil and capacitance.

The structure of the conductive wire structure <NUM> may be formed freely according to an area (extent, depth, and the like) to measure a moisture content in soil thereof. As one of simplest example, the conductive wire structure <NUM> may be formed to have a linear structure, may be formed to have a zigzag shape over the area to be measured, or may be formed to have a coil shape. As a length of the conductive wire structure <NUM> increases, a contact area with moisture increases so that accuracy and reliability may further increase.

As an example of the structure of the conductive wire structure <NUM>, <FIG> illustrates a structure in which the conductive wire structure <NUM> extends lengthwise in a zigzag shape over a certain extent and a certain depth to be measured. As another example of the structure of the conductive wire structure <NUM>, <FIG> illustrates a cylindrical coil structure.

Referring back to <FIG>, the capacitance measurement circuit <NUM> measures capacitance of the conductive wire structure <NUM>, that is, capacitance between the first and second conductive wires <NUM> and <NUM> using an alternating current (AC) power source.

In the embodiment, although a circuit using an automatic balancing bridge is exemplified as an example of the capacitance measurement circuit <NUM>, capacitance measurement may be performed using a variety of other measurement methods, for example, a bridge method, a resonance method, a voltage/current (I-V) method, and the like.

The capacitance measurement circuit <NUM> may include an AC power source <NUM>, a first voltmeter <NUM>, a resistor R, an operational amplifier <NUM>, and a second voltmeter <NUM>. The AC power source <NUM> is connected between one end of the first conductive wire <NUM> and a ground to supply an AC voltage, and the other end of the first conductive wire <NUM> is opened. The first voltmeter <NUM> is connected between the one end of the first conductive wire <NUM> and the ground and measures a voltage V<NUM> of the first conductive wire <NUM>. One end of the second conductive wire <NUM> is opened, and one end of the resistor R is connected to the other end of the second conductive wire <NUM>. An inverting terminal of the operational amplifier <NUM> is connected to the one end of the resistor R, a non-inverting terminal thereof is connected to the ground, and an output terminal is connected to the other end of the resistor R. The second voltmeter <NUM> is connected between the output terminal of the operational amplifier <NUM> and the ground and measures a voltage V<NUM> of the output terminal of the operational amplifier <NUM>.

Impedance Z between the first and second conductive wires <NUM> and <NUM> may be measured using the voltage V<NUM> of the first voltmeter <NUM>, the voltage V<NUM> of the second voltmeter <NUM>, and the resistor R according to the following equation.

When the impedance Z is known, it is possible to know the capacitance between the first and second conductive wires <NUM> and <NUM>.

The moisture content calculation unit <NUM> calculates a moisture content in soil, into which the conductive wire structure <NUM> is inserted, using capacitance measured using the capacitance measurement circuit <NUM>. The moisture content calculation unit <NUM> may calculate the moisture content in soil using the above-described principle in which a moisture content in soil is in proportion to capacitance.

To allow the moisture content in soil to be calculated using a proportional relationship between the moisture content and the capacitance, first and second capacitance values previously measured using the capacitance measurement circuit <NUM> may be stored, corresponding to first and second known moisture contents, in the moisture content calculation unit <NUM>. Referring to <FIG>, when a first moisture content Wi, a capacitance value C<NUM> corresponding thereto, a second moisture content W<NUM>, and a capacitance value C<NUM> corresponding thereto are known, a moisture content corresponding to a random measured capacitance value may be calculated using a proportional relationship.

When the conductive wire structure <NUM> is exposed in the air, a moisture content may be zero %. When the conductive wire structure <NUM> is submerged in the water, a moisture content may be <NUM>%. Accordingly, when respective capacitance values measured in an air-exposed state and a water-submerged state of the conductive wire structure <NUM> having a certain structure are stored and capacitance is measured while the conductive wire structure <NUM>, which maintains the structure, is inserted into soil, a moisture content in soil may be calculated using a measured capacitance value on the basis of the capacitance value corresponding to the moisture content of zero% and the capacitance value corresponding to the moisture content <NUM>%.

<FIG> illustrates components of a device for measuring a moisture content in soil according to a second embodiment useful for understanding the invention.

The device according to the embodiment may include a conductive wire structure <NUM>', the capacitance measurement circuit <NUM>, and a moisture content calculation unit <NUM>'.

In the device shown in <FIG>, when a conductive path is formed in soil to be measured due to a certain cause so that the soil is connected to a ground, a current leakage phenomenon occurs through moisture in the soil. Here, an amount of a leakage current is in proportion to a moisture content in soil and capacitance measured by the capacitance measurement circuit <NUM> is not real capacitance of the conductive wire structure <NUM> and is shown as a false measured value caused by the leakage current. The capacitance measured by the capacitance measurement circuit <NUM> is not a real capacitance value of capacitance between the first and second conductive wires <NUM> and <NUM>. However, as the moisture content increases, the leakage current increases so that the capacitance is measured as a reduced value.

In the embodiment, to cause the phenomenon, a conductive path is artificially formed in soil near the first and second conductive wires <NUM> and <NUM> and is connected to the ground. Here, the conductive wire structure <NUM>' is formed by adding a ground conductive wire <NUM>, which extends adjacently and is parallel to the first and second conductive wires <NUM> and <NUM> and is connected to the ground, to the conductive wire structure <NUM> of <FIG>. Then, moisture, which come into contact with the first and second conductive wires <NUM> and <NUM>, also comes into contact with the ground conductive wire <NUM> so that a leakage current flows through the ground conductive wire <NUM>. The ground conductive wire <NUM> may not be coated or may be coated with enamel or the like which has a relatively low resistance against AC so as to be conducted with soil and moisture in soil. Accordingly, when AC power is applied to the first and second conductive wires <NUM> and <NUM>, a leakage current occurs through the ground conductive wire <NUM>. As a moisture content increases, the leakage current increases and a measured capacitance value is reduced.

As a result of an experiment of measuring capacitance of the conductive wire structure <NUM>' using the capacitance measurement circuit <NUM> while varying a moisture content in a soil sample, the applicant may check that a measured capacitance value is linearly reduced as the moisture content increases. <FIG> is a graph illustrating a relationship between a moisture content in soil and a measured capacitance value.

The moisture content calculation unit <NUM>' calculates a moisture content in soil, into which the conductive wire structure <NUM>' is inserted, using capacitance measured using the capacitance measurement circuit <NUM>. On the contrary to the moisture content calculation unit <NUM>, the moisture content calculation unit <NUM>' may calculate a moisture content in soil using a relationship in which the measured capacitance value is linearly reduced as the moisture content in soil increases.

To allow the moisture content in soil to be calculated using the relationship between the moisture content and the measured capacitance value, first and second capacitance values previously measured using the capacitance measurement circuit <NUM> may be stored, corresponding to first and second known moisture contents, in the moisture content calculation unit <NUM>'. Referring to <FIG>, when a first moisture content W<NUM>', a capacitance value C<NUM>' corresponding thereto, a second moisture content W<NUM>', and a capacitance value C<NUM>' corresponding thereto are known, a moisture content corresponding to a random measured capacitance value may be calculated using the relationship between the moisture content and the measured capacitance value.

When the conductive wire structure <NUM>' is exposed in the air, a moisture content may be zero%. When the conductive wire structure <NUM>' is submerged in the water, a moisture content may be <NUM>%. Accordingly, when respective capacitance values measured in an air-exposed state and a water-submerged state of the conductive wire structure <NUM>' having a certain structure are stored and capacitance is measured while the conductive wire structure <NUM>', which maintains the structure, is inserted into soil, a moisture content in soil may be calculated using a measured capacitance value on the basis of the measured capacitance value corresponding to the moisture content of zero% and the measured capacitance value corresponding to the moisture content <NUM>%.

Like the conductive wire structure <NUM> of <FIG>, the conductive wire structure <NUM>' of <FIG> may also be formed to have a variety of structures such as a linear shape, a zigzag shape, a coil shape, and the like. <FIG> illustrates an example in which the conductive wire structure <NUM>' has a cylindrical coil structure.

<FIG> illustrates components of a device for measuring a moisture content in soil according to a third embodiment of the present invention.

The device according to the embodiment may include the conductive wire structure <NUM>', a leakage current measurement circuit <NUM>, and a moisture content calculation unit <NUM>".

As described above with respect to the second embodiment, when AC power is applied to the first and second conductive wires <NUM> and <NUM>, a leakage current occurs through the ground conductive wire <NUM> and the leakage current increases in proportion to an increase of a moisture content. In the embodiment, this is used so that a moisture content in soil is measured by measuring a leakage current flowing through the ground conductive wire <NUM>.

The leakage current measurement circuit <NUM> applies AC power to the first and second wires <NUM> and <NUM> of the conductive wire structure <NUM>' and measures a leakage current leaking through the ground conductive wire <NUM>.

The leakage current measurement circuit <NUM> includes an AC power source <NUM>, a first ammeter <NUM>, a second ammeter <NUM>, and a resistor R. The AC power source <NUM> is connected between one end of the first ammeter <NUM> and the ground and supplies an AC voltage. The first ammeter <NUM> has the other end connected to one end of the first conductive wire <NUM> and measures a current IA1 supplied to the first conductive wire <NUM>. The second ammeter <NUM> has one end connected to the other end of the second conductive wire <NUM> and the resistor R is connected between the other end of the second ammeter <NUM> and the ground so that the second ammeter <NUM> measures a current IA2 output through the second conductive wire <NUM>.

A level of a leakage current Ileak, which flows through the ground conductive wire <NUM>, is measured using a difference between the current IA1 of the first ammeter <NUM> and the current IA2 of the second ammeter <NUM> according to the following equation.

<FIG> is a graph illustrating a relationship between a moisture content in soil and a leakage current flowing through the ground conductive wire <NUM>. As shown in the drawing, a moisture content and a leakage current are in proportion to each other.

The moisture content calculation unit <NUM>" calculates a moisture content in soil, into which the conductive wire structure <NUM>' is inserted, using a leakage current measured using the leakage current measurement circuit <NUM>. The moisture content calculation unit <NUM>" may calculate the moisture content in soil using a principle in which a moisture content in soil is in proportion to a leakage current.

To allow the moisture content in soil to be calculated using a proportional relationship between the moisture content and the leakage current, first and second leakage current values previously measured using the leakage current measurement circuit <NUM> may be stored, corresponding to first and second known moisture contents, in the moisture content calculation unit <NUM>' '. Referring to <FIG>, when a first moisture content W<NUM>", a leakage current value Ileak,<NUM> corresponding thereto, a second moisture content W<NUM>", and a leakage current value Ileak,<NUM> corresponding thereto are known, a moisture content corresponding to a random measured leakage current value may be calculated using the proportional relationship.

When the conductive wire structure <NUM>' is exposed in the air, a moisture content may be zero%. When the conductive wire structure <NUM>' is submerged in the water, a moisture content may be <NUM>%. Accordingly, when respective leakage current values measured in an air-exposed state and a water-submerged state of the conductive wire structure <NUM>' having a certain structure are stored and a leakage current is measured while the conductive wire structure <NUM>', which maintains the structure, is inserted into soil, a moisture content in soil may be calculated using a measured leakage current value on the basis of the measured leakage current value corresponding to the moisture content of zero% and the measured leakage current value corresponding to the moisture content <NUM>%.

According to the embodiments of the present invention, since the conductive wire structure <NUM> or <NUM>' to be inserted into soil includes two or three conductive wires, the conductive wire structure <NUM> or <NUM>' may be formed with a desired size and shape so as to measure a moisture content in soil in a variety of areas as necessary as well as a small area.

When the conductive wire structure <NUM> or <NUM>' is formed to have a coil structure as shown in <FIG> or <FIG>, a surface area which comes into contact with soil is increased in a small area. Also, a length or diameter of a coil is decreased to perform measurement in a local area and is increased to perform measurement in a wide area. The size of the coil may vary according to a size of an area to be measured. Also, a distribution of moisture content may be checked by inserting the conductive wire structures <NUM> or <NUM>' in several parts of soil, and a distribution of moisture content according to a depth may be checked by inserting the conductive wire structures <NUM> or <NUM>' at several depths.

When the conductive wire structure <NUM> or <NUM>' is formed to have a coil structure, a particular porous medium is inserted into a coil, and then a sealed structure in which only a central inlet is exposed and other parts are blocked from the outside is formed and buried in soil, moisture in soil flows into the porous medium in the coil due to a capillary phenomenon so as to be in equilibrium with whole moisture of soil. Accordingly, a sensor capable of measuring a moisture content in soil regardless of a type of a medium to be measured (rock wool, cocopeat, ferrite, soil, or the like) may be formed.

The embodiments of the present invention may be shown as functional block components and a variety of processing operations. The functional blocks may be implemented through a variety of numbers of hardware and/or software components which implement particular functions. For example, an embodiment may employ integrated circuit components such as a memory, processor, logic, look-up table, and the like which are capable of performing a variety functions under the control of one or more microprocessors or other control devices. Like the components of the present invention being executable using software programs or software elements, the embodiment may include a data structure, processes, routines, or a variety of algorithms which are implemented through a combination of other programming components and may be implemented as programming and scripting languages such as C, C++, Java, an assembler, and the like. Functional aspects may be implemented as an algorithm executed by one or more processors. Also, the embodiment may employ conventional arts for electronic environment settings, signal processing, data processing, and/or the like. The terms such as "mechanism," "element," "means," and "component" may be widely used and are not limited to mechanical and physical components. The terms may include the meaning of a series of routines of software in connection with a processor and the like.

Particular executions described in the embodiment are merely examples, and the scope of the embodiment is not limited to any methods. For a concise specification, a description of conventional electronic components, control systems, software, and other functional aspects of the systems will be omitted. Also, connection of lines or connection members between components shown in the drawings are exemplarily shown as functional connection and/or physical or circuit connections and may be a variety of replaceable or additional functional connections, physical connection, or circuit connections in a real apparatus. Also, unless stated in detail such as "essential," "significant," and the like, a component may not be essential for applying of the present invention.

Claim 1:
A moisture content measurement device for measuring a moisture content in soil, comprising:
a conductive wire structure (<NUM>') which is insertable into soil, comprises insulatively-coated first and second conductive wires (<NUM>, <NUM>) parallel to each other and extending adjacently and a ground wire (<NUM>) parallel and extending adjacently to the first and second conductive wires and connected to a ground, and has a certain structure formed to have a size and a shape which is varied according to a size of an area to be measured;
a leakage current measurement circuit (<NUM>) configured to apply AC power to the first and second conductive wires and to measure a leakage current leaking through the ground wire; and
a moisture content calculation unit (<NUM>") configured to calculate the moisture content in soil using the measured leakage current,
wherein the leakage current measurement circuit (<NUM>) comprise an AC power source (<NUM>), a first ammeter (<NUM>), a second ammeter (<NUM>), and a resistor (R),
wherein the AC power source is connected between one end of the first ammeter and the ground and supplies an AC voltage, the first ammeter (<NUM>) has the other end connected to the first conductive wire (<NUM>) and measures a current IA1 supplied to the first conductive wire (<NUM>), the second ammeter (<NUM>) has one end connected to the second conductive wire (<NUM>), and the resistor (R) is connected between the other end of the second ammeter (<NUM>) and the ground (<NUM>) so that the second ammeter measures a current IA2 output through the second conductive wire,
wherein a leakage current Ileak, which flows through the ground wire (<NUM>), is measured by the difference between the current IA1 of the first ammeter (<NUM>) and the current IA2 of the second ammeter (<NUM>).