WO2021066378A1

WO2021066378A1 - Soil moisture sensor for measuring amount of moisture through refractive index

Info

Publication number: WO2021066378A1
Application number: PCT/KR2020/012812
Authority: WO
Inventors: 김민회; 심은선; 유경민; 이상훈
Original assignee: 한밭대학교 산학협력단
Priority date: 2019-10-01
Filing date: 2020-09-23
Publication date: 2021-04-08
Also published as: KR102233557B1

Abstract

The present invention relates to a soil moisture sensor for measuring the amount of moisture through a refractive index and, more specifically, to a soil moisture sensor, which measures the amount of moisture in soil by using the variance, according to the proportion of water, air, or soil coming in contact with the outer wall surface of a light reflective bar, in the amount of light arriving at a light-receiving unit after being emitted from a light-emitting unit and then reflected or refracted, and thus minimizes the influence of the constituent components and organic content of soil, thereby improving measurement accuracy. To this end, a soil moisture sensor located in soil in order to measure the amount of moisture in the soil, according to the present invention, comprises: a light reflective bar which has a bending part or a curved part and which is formed in a bar shape so that at least a predetermined portion thereof is accommodated in the soil; a light-emitting unit located at one end of the light reflective bar so as to emit light toward the inside of the light reflective bar; a light-receiving unit located at the other end of the light reflective bar so as to detect light, which is emitted from the light-emitting unit so as to be reflected on the inner side of the light reflective bar and arrive at the other end thereof; and a control unit for calculating the moisture content in the soil through the total amount of light emitted from the light-emitting unit and the total amount of light detected by the light-receiving unit.

Description

Soil moisture sensor measuring moisture content through refractive index

The present invention relates to a soil moisture sensor that measures the amount of moisture through a refractive index, and more particularly, light irradiated from the light emitting unit is reflected or refracted according to the ratio of water, air or soil in contact with the outer wall surface of the light reflecting rod to reach the light receiving unit. The present invention relates to a soil moisture sensor that improves measurement accuracy by minimizing the influence of soil constituents and organic matter content by measuring the moisture content in the soil using varying degrees.

In fields such as agriculture, civil engineering, and disaster prevention, there is a need to measure the amount of moisture contained in the soil, and various soil moisture measurement methods have been developed and used.

Soil moisture measurement methods include a Time Domain Reflectometry (TDR) method, a tension meter method, a method using a gypsum block, a method using electrical resistance, and a method using light reflection.

In the TDR measurement method, the electromagnetic wave generated by the waveform generator flows through the transmission line. If the cross section of the transmission line changes while the electromagnetic wave is flowing through the transmission line, the impedance of the point changes and the electromagnetic wave is reflected in that section.

If you know the propagation speed of an electromagnetic wave passing through a transmission line, you can find the length of the transmission line through the reverberation time. Using this principle, the water content of the soil can be obtained by using the property of changing the propagation speed of a wave according to a change in permittivity. However, the TDR measurement method varies depending on the density of the soil.

The tensiometer method measures the metric potential gradient in the soil using a porous cup, a tube filled with water, and a vacuum gauge connected thereto. The tensiometer is a ceramic sensing unit, which is a porous cup capable of permeating both moisture and solute. It consists of a water column to supplement and a pressure gauge that indicates the metric potential in the soil. The tensiometer requires additional supplementation to maintain a certain amount of water, and has disadvantages such as the ceramic sensing unit being easily damaged.

In addition, the measurement method using a gypsum block is a method of measuring moisture until the moisture content of gypsum and soil moisture is equilibrated after mounting it on a flat plate and inserting it into the soil. This may increase the error of the moisture measurement value according to the corrosion of the gypsum caused by moisture in the soil, and there is a trouble of having to frequently replace the gypsum block.

In addition, the method using electrical resistance is a method of measuring the moisture content in the soil by using the change in the electrical resistance value between two points. The method of using electrical resistance does not take into account changes in soil density and temperature, so there is a disadvantage that even if the value of soil moisture changes according to the density of the soil, it cannot be recognized.

In addition, the method using light reflection is a method of detecting the moisture content in the soil by irradiating light from the light source to the soil and collecting and analyzing the reflected light by the light receiving unit.

That is, the method using light reflection as a method of detecting the moisture distribution in the soil through the reflective characteristics of the soil has the following problems.

The light reflected off the soil varies greatly depending on the composition of the soil and the level of organic matter content in addition to the moisture contained in the soil, and the absorption amount varies greatly depending on the wavelength of the light used. This is because soil constituents and organic substances each have their own absorption wavelength.

Therefore, since the measured value may vary due to factors other than the moisture content of the soil, there is a problem that it is not accurate to measure the moisture content of the soil to the degree of reflection of light.

Such a soil moisture measurement method has a problem that the cost is too expensive even if the measurement reliability is low or high, and thus a proposal of a soil moisture sensor having a relatively low cost and high reliability is urgently required.

The present invention has been devised to solve the above problems, and the total amount of light reaching the light receiving unit is changed according to the moisture content of the soil in contact with the outer wall of the light reflecting rod. The purpose of this is to provide a soil moisture sensor that measures the moisture content through a refractive index that minimizes the influence of soil constituents and organic matter content by measuring the moisture content in the soil, thereby improving measurement accuracy.

The present invention has the following features to achieve the above object.

The present invention is a soil moisture sensor located inside the soil for measuring the moisture content in the soil, the soil moisture sensor is formed in a rod shape having a bent portion or a bent portion, and a light reflecting rod for receiving a certain portion or more in the soil, A light-emitting unit positioned at one end of the light reflecting rod to irradiate light inside the light reflecting rod, and a light-emitting unit positioned at the other end of the light reflecting rod and irradiated from the light emitting unit to detect light reflected from the inner side of the light reflecting rod to reach the other end. ; And a control unit for calculating the moisture content in the soil through the total amount of light irradiated from the light emitting unit and the total amount of light sensed from the light receiving unit.

Here, the light reflecting rod is made of a transparent medium having a refractive index (n) of 1.3 or more, and preferably has a'U' shape.

In addition, it is preferable that the light receiving unit is a photodiode.

According to the present invention, as the moisture content in the soil is measured by using the refractive index between the light reflecting rod and the medium in contact with the outer wall surface thereof, there is an effect of minimizing changes in the measured value according to the constituents of the existing soil and the organic matter content.

In addition, there is an effect of solving the problem of increasing the difference in measured values due to factors other than the moisture content of the soil as the absorption amount according to the wavelength of light irradiated according to the composition of the soil or the content of organic matter changes significantly.

1 is a perspective view schematically showing a soil moisture sensor according to an embodiment of the present invention.

2 is a state diagram showing a sensing process of the soil moisture sensor according to an embodiment of the present invention.

3A and 3B are enlarged views of part A of FIG. 2.

4 is a graph measuring a change in water amount and light amount over time of a soil moisture sensor according to an embodiment of the present invention.

5 is a graph showing a relationship between the amount of moisture in the soil through the measured amount of FIG. 4 and the amount of relative light detected by the light receiving unit.

6 is a graph of measuring moisture content and relative light intensity for 30000 minutes with a soil moisture sensor according to an embodiment of the present invention.

7 is a graph showing a relationship between the amount of moisture in the soil through the measured amount of FIG. 6 and the amount of relative light detected by the light receiving unit.

In order to explain the present invention and the operational advantages of the present invention and the object achieved by the implementation of the present invention, the following describes a preferred embodiment of the present invention and looks at with reference thereto.

First, terms used in the present application are only used to describe specific embodiments, and are not intended to limit the present invention, and expressions in the singular may include a plurality of expressions unless clearly differently in context. In addition, in the present application, terms such as "comprise" or "have" are intended to designate the existence of features, numbers, steps, actions, components, parts, or a combination thereof described in the specification, but one or more other It is to be understood that the presence or addition of features, numbers, steps, actions, components, parts, or combinations thereof, does not preclude the possibility of preliminary exclusion.

In describing the present invention, when it is determined that a detailed description of a related known configuration or function may obscure the subject matter of the present invention, a detailed description thereof will be omitted.

1 is a perspective view schematically showing a soil moisture sensor according to an embodiment of the present invention, FIG. 2 is a state diagram showing a sensing process of the soil moisture sensor according to an embodiment of the present invention, and FIG. 3 is FIG. It is an enlarged view of part A of.

Referring to the drawings, the soil moisture sensor 100 according to an embodiment of the present invention has a large bent portion or a bent portion and is formed in a rod shape to accommodate a predetermined portion or more in the soil, and the light reflecting rod 10 The light-emitting unit 20 is positioned at one end of the rod 10 to irradiate light into the light-reflecting rod 10, and the light-emitting unit 20 is located at the other end of the light-reflecting rod 10 and is irradiated from the light-emitting unit 20 to reflect light. The moisture content in the soil is determined through the total amount of light irradiated from the light-receiving unit 30 and the light irradiated from the light-emitting unit 20 and the total amount of light detected from the light-receiving unit 30 to detect light reflected from the inner wall of the rod 10 and reaching the other end. It consists of a control unit 40 that calculates.

Here, the light reflecting rod 10 is a bent or bent rod and is positioned in a state accommodated in the soil, and a light-emitting portion 20 and a light-receiving portion 30 are disposed at one end and the other end, respectively.

Of course, if necessary, the light-emitting unit 20 and the light-receiving unit 30 may be located inside from both ends of the light reflecting rod 10, but it is preferable that the light-emitting unit 20 and the light-receiving unit 30 are located at the end side to provide a sufficient length for light to be reflected. .

The light reflecting rod 10 guides the light irradiated from the light emitting unit 20 to reach the light receiving unit 30, and a'U' shape, an'L' shape, or a curved straight shape is also possible.

1 and 2 are shown in the shape of a'U'-shaped rod according to an embodiment of the present invention. As in one embodiment, when formed as a'U'-shaped light reflecting rod 10, sufficient The curved surface is formed so that when the light irradiated from the light emitting unit 20 reaches the outer wall surface of the light reflecting rod 10, the incident angle is large, so that total reflection can be smoothly performed.

That is, when the light reflection rod 10 is accommodated in the soil, the incident angle and the light reflection rod 10 when the light irradiated from the light emitting unit 20 reaches the outer wall surface of the light reflection rod 10, that is, a boundary point with the outside. ) And the refraction index of the medium in contact with it from the outer wall side, the reflection or refraction of the irradiated light is determined to be reflected or refracted inside the light reflecting rod 10 to pass to the outside.

This can be explained according to Snell's law of refraction. According to Snell's law of refraction, the critical angle (θ _c ) at _{which total reflection occurs is θ c} =sin ^-1 (n ₂ /n ₁ ). When light travels from water (n=1.33) to air, θ _c = 48.8°, and when it travels from crown glass (n=1.52) to air, θ _c = 41.1°. Any light incident at an angle greater than this critical angle is reflected.

Accordingly, the refractive index of the light reflecting rod 10 according to the present invention is composed of a medium of at least 1.3 or more, which is similar to or greater than the refractive index of water, and preferably glass or polymer may be applied.

Accordingly, when the light reflecting rod 10 is formed of crown glass (n=1.52) according to an embodiment of the present invention, when water contacts the outer wall surface, the critical angle (θ _c ) is θ _c =sin ^-1 (1.33 /1.52) = 61°, and when air contacts the outer wall, the critical angle (θ _c ) becomes θ _c =sin ^-1 (1/1.52) = 41.1°.

Accordingly, when water comes in contact, light with an incidence angle less than 61° is refracted outward and passes through, and when air contacts light, light with an incidence angle less than 41.1° is refracted and passed outward. A much larger amount of light will be detected toward the light receiving unit 30.

That is, as shown in FIG. 3, the light irradiated from the light emitting unit 20 is the critical angle (θ) in the case of (a) filled with air (A) in the soil (S) in contact with the light reflecting rod 10 and the outer wall surface. _{As c} ) is lowered, the probability of occurrence of total reflection is increased, and in the case of (b) filled with water (W), the critical angle (θ _c ) is relatively high, so that the probability of occurrence of total reflection is lowered.

In the present invention, the total sensing amount of the light receiving unit 30 according to the soil moisture content outside the light reflecting rod 10, that is, the total amount of light reached by reflection is determined, and accordingly, the control unit 40 The moisture content in the soil is measured by detecting the total amount of light reaching the light receiving unit 30 relative to the total amount of light irradiated from (20).

Previously, light was irradiated into the soil and the moisture content in the soil was measured by analyzing the light reflected and returned by the components in the soil. It varies greatly depending on the composition and the degree of organic matter content, and has a problem in that the amount of absorption varies greatly depending on the wavelength of light to be irradiated. However, the present invention has a problem that the refractive index varies depending on the component medium of the soil in contact with the light reflecting rod (10). Since the change is used, the change of the refractive index changed by the moisture content has a much greater effect than the change of the refractive index by the constituents of the soil and the content of organic substances, so more precise and reliable moisture content measurement is possible.

Of course, there is a slight change in the refractive index depending on the wavelength of the irradiated light, but this also has a very low effect than the change in the refractive index changed by the moisture content.

The light source of the light emitting unit 20 applied to the present invention can be applied as long as it is a light source capable of irradiating light, and the wavelength of light can be any electromagnetic wave series such as visible light, ultraviolet light, infrared light, etc. When considering, it is preferable to be irradiated with visible light.

In addition, the light-receiving unit 30 is provided to sense light reflected from the light-emitting unit 20, and various types of light-receiving elements may be applied, and a photodiode may be applied as a representative example.

Meanwhile, as described above, the controller 40 receives information on the total amount of light reached from the light-receiving unit 30 and compares it with the light irradiation amount of the light-emitting unit 20 to generate moisture content or content rate data in the soil.

This control unit 40 can detect the total amount of light detected by the light receiving unit 30, but configured to detect the light detected by the light receiving unit 30 by wavelength, and through the detection amount by wavelength or the distribution of light by wavelength. A correction process of moisture content or content rate data may be performed.

In this correction process, in addition to the moisture distribution in the soil, a difference in the refractive index of light is generated depending on the composition of the soil and the content of organic matter, and the amount of light detected by the light receiving unit 30 is different, so that the moisture content or content rate data generated by the control unit 40 It is to correct the error of

To this end, when data on the light-receiving characteristics according to the wavelength of light for each soil component and the data on the light-receiving characteristics according to the type or content of organic substances are previously stored, the light-receiving characteristics according to the amount and wavelength of light detected by the light receiving unit 30 are analyzed. This makes it possible to generate more precise moisture content or content rate data.

FIG. 4 is a graph measuring a change in water amount and light amount over time of a soil moisture sensor according to an embodiment of the present invention, and FIG. 5 is a graph showing a relationship between the amount of moisture in the soil and the relative amount of light detected by the light receiving unit through the measured amount of FIG. 4 6 is a graph in which the moisture content and the relative light amount are measured for 30000 minutes by the soil moisture sensor according to an embodiment of the present invention, and FIG. 7 is a graph showing the moisture content in the soil through the measurement amount of FIG. 6 and the relative light amount detected by the light receiving unit. It is a relationship graph.

Referring to the drawings, FIG. 4 is a data measured while the light reflecting rod 10 of the soil moisture sensor according to an embodiment of the present invention is composed of a polymer (polydimethylsiloxane) rod, and water is continuously added. It can be seen that the moisture content increases as the passing time, and accordingly, it can be seen that the relative amount of light detected by the light receiving unit 30 decreases. As illustrated in FIG. 5, it can be seen that the relative amount of light decreases as the amount of moisture increases, and the amount of relative light increases as the amount of moisture decreases.

In addition, FIG. 6 is also a measurement of the amount of moisture and the relative amount of light detected by the light receiving unit 30 for 30000 minutes by configuring the light reflecting rod 10 as a glass rod. As shown in the figure, as the amount of water increases or decreases, the relative amount of light is reversed. It can be seen that the amount of light decreases or increases, and as shown in FIG. 7, the relative amount of light and the amount of water increase as the amount of water increases, and the amount of light increases as the amount of water decreases.

As described above, the present invention has been described with reference to an embodiment shown in the drawings, but this is only exemplary, and those of ordinary skill in the art can recognize that various modifications and other equivalent embodiments are possible therefrom. I will understand.

Therefore, the true technical scope of the present invention should be determined by the technical spirit of the appended claims.

Claims

In the soil moisture sensor located inside the soil to measure the moisture content in the soil,

The soil moisture sensor 100

A light reflecting rod 10 having a bent portion or a bent portion and formed in a rod shape to accommodate a certain portion or more in the soil;

A light-emitting unit 20 positioned at one end of the light-reflecting rod 10 to irradiate light into the light-reflecting rod 10;

A light-receiving unit 30 positioned at the other end of the light-reflecting rod 10 and irradiated from the light-emitting unit 20 to detect light reflected from the inner side of the light-reflecting rod 10 and reaching the other end; And

A control unit 40 for calculating a moisture content in the soil through the total amount of light irradiated from the light emitting unit 20 and the total amount of light sensed by the light receiving unit 30;

Soil moisture sensor for measuring the amount of moisture through the refractive index comprising a.
The method of claim 1,

The light reflecting rod 10 is

Soil moisture sensor for measuring the amount of moisture through the refractive index, characterized in that consisting of a transparent medium having a refractive index (n) of 1.3 or more.
The method of claim 1,

The light reflecting rod 10 is

A soil moisture sensor that measures the amount of moisture through a refractive index, characterized in that it has a'U' shape.
The method of claim 1,

The light receiving unit 30 is

A soil moisture sensor that measures the amount of moisture through a refractive index, characterized in that it is a photodiode.