KR102224169B1 - Soil moisture sensor and method of operation thereof - Google Patents

Abstract

A soil moisture sensor and a method of operating the same are disclosed. The soil moisture sensor according to an embodiment of the present invention includes a first probe including a pair of first electrodes extending in a first direction to penetrate the soil, and the pair of first electrodes of the first probe. And a first resonant circuit connected via a pair of first ports and to which a first AC signal is applied, a first resonant circuit having the same impedance as the first resonant circuit, and being a reference AC signal and having the same characteristics as the first AC signal. 2 A second resonant circuit to which an AC signal is applied and a first electrical signal formed in the first resonant circuit are received, a second electrical signal formed in the second resonant circuit is received, and a second electrical signal of the first electrical signal is received. And a determination circuit for determining moisture in the soil based on a first resonance frequency and a second resonance frequency of the second electrical signal.

Description

Soil moisture sensor and its operation method {SOIL MOISTURE SENSOR AND METHOD OF OPERATION THEREOF}

The present invention relates to a soil moisture sensor that measures the moisture content of the soil and an operation method thereof, and specifically, a soil moisture sensor that measures the moisture content of the soil by detecting a change in frequency formed in a sensing circuit according to the moisture content in the soil. And it relates to a method of operation.

Existing soil moisture measurement methods include dry basis weight method, tactile method that evaluates soil moisture by the texture of each soil, method of measuring the electrical conductivity of moisture absorbed in the gypsum block capillary pores, and moisture tension in unglazed porous cups. There are a system method, a neutron probe method, and the like.

The method of determining the weight percentage of moisture by the dry basis weight method has been a representative method of moisture measurement for a long time, but the procedure was cumbersome and took a long time, causing discomfort, and the texture method, which evaluates soil moisture by the texture of each soil, was evaluated. It is inefficient because individual variations are large and considerable training is required. The method of measuring the electrical conductivity of moisture absorbed in the gypsum block capillary pores with a relatively simple method has the disadvantage that the pores of the gypsum block are very fine, and when the soil moisture tension is low, almost all pores are saturated, resulting in unsatisfactory results. , The unglazed porous cup moisture tension meter method is also widely adopted for determining the irrigation point, but has a disadvantage in that it does not work in a region where the moisture tension is higher than 1 atmosphere.

The neutron probe method has disadvantages in that it is not widely used in general because the initial calibration procedure is complicated, the transport measurement operation is cumbersome, and the price is very high.

In addition, the TDR (Time Domain Reflectometry) method, which uses the principle that only the dielectric properties of water according to the rotational motion of water molecules are highlighted, has been proposed because the movement of ions in the Giga Herz field is negligibly reduced. TDR analyzes the time difference or voltage difference according to the number of reflected frequencies according to the degree of permittivity according to soil moisture by firing a high energy frequency of gigahertz level to a sensor that uses an uncovered iron rod inserted into the soil as a condenser. This is the way to do it. TDR quantifies soil moisture by simply amplifying the reflected electromagnetic wave transformed into a soil capacitor and reading it with an oscilloscope using the principle that electromagnetic waves are transformed by a condenser, which raises the disadvantage that the necessary equipment is relatively complex and expensive. Has been.

For this reason, there is an urgent need to develop and introduce a low-cost soil moisture measurement device that is simpler, simpler in operation and procedure, and can measure and collect accurate data in a short time.

On the other hand, in Japanese Patent Application Laid-Open No. 2016-217795 "Moisture Sensor and Moisture Measuring Device", an equivalent inductance due to a change in the amount of moisture contained in the soil is achieved by using a moisture sensor having electrodes formed in the shape of comb teeth intersecting each other. A moisture sensor has been disclosed that forms a resonant circuit in which a resonant frequency changes according to the change and calculates a resonant frequency oscillated by the resonant circuit. The prior art is characterized in that it detects by replacing an impedance change with an inductance change using a resonance circuit.

However, even according to the prior art, it is difficult to measure the resonant frequency quickly and precisely because the process of calculating the measured amplitude value by converting the measured amplitude value rather than directly measuring the resonance frequency is complicated. For this reason, when measuring the moisture content of the soil in real time, there is a problem that noise is generated and the measured value is inaccurate.

Japanese Patent Application Publication No. 2016-217795, "Moisture sensor and moisture measuring device", (published on December 22, 2016)

The prior art varies the frequency of the input electrical signal applied to the resonant circuit, scans the magnitude of the output electrical signal formed in the resonant circuit in response to the input electrical signal, and calculates the frequency in the case of having the maximum magnitude as the resonant frequency. Take the composition. For this reason, the prior art has an error as much as the resolution of the variable frequency of the input electrical signal, is an indirect method of calculating the resonant frequency by detecting the size of the electrical signal, and the accuracy is degraded, and the frequency of the input electrical signal must be varied. There is a problem that it takes.

The present invention was derived in order to solve the problems that appear in the prior art, and each circuit having a capacitance formed in a probe for a soil moisture sensor using soil as a medium and a circuit having a reference capacitance. The purpose of the present invention is to provide a soil moisture sensor that can accurately and real-time determine the moisture state of the soil by measuring and comparing the frequency of the high frequency signal in two circuits by oscillating a high frequency signal to quantify the moisture content in the soil. .

In addition, the soil moisture sensor according to the present invention is non-destructive and semi-permanent, provides stability of the device, and does not require a configuration to change the frequency of the input electrical signal, so it can significantly reduce the production cost compared to the conventional soil moisture sensor. It aims to be.

An object of the present invention is to propose a circuit and an operating method capable of effectively detecting a shift in a resonance frequency of the soil moisture sensor. In addition, since the soil moisture sensor according to the present invention does not require a process of varying the frequency of the input electrical signal, it is an object of the present invention to shorten the soil moisture sensing time.

The present invention is a configuration derived to achieve the above object, the soil moisture sensor according to an embodiment of the present invention is a first including a pair of first electrodes extending in a first direction to penetrate into the soil. A probe, a first resonance circuit connected through the pair of first electrodes of the first probe and a pair of first ports and to which a first AC signal is applied, and has the same impedance as the first resonance circuit, A reference AC signal and a second resonant circuit to which a second AC signal having the same characteristics as the first AC signal is applied and a first electric signal formed in the first resonant circuit are received, and formed in the second resonant circuit. And a determination circuit configured to receive a second electrical signal and determine moisture in the soil based on a first resonant frequency of the first electrical signal and a second resonant frequency of the second electrical signal.

The determination circuit is formed in the first resonance circuit based on the capacitance formed between the pair of first electrodes by moisture contained in the soil positioned between the pair of first electrodes. A quantitative change in the first resonant frequency of the first electrical signal is detected, and moisture contained in the soil is determined based on the quantitative change in the detected first resonant frequency.

The determination circuit is between the second resonance frequency and the first resonance frequency, which is a reference resonance frequency of the second electrical signal formed in the second resonance circuit under the influence of the second AC signal applied to the second resonance circuit. A difference is detected, and moisture contained in the soil is determined based on a difference between the second resonance frequency and the first resonance frequency.

If the difference between the second resonant frequency and the first resonant frequency is greater than or equal to a first threshold, the determination circuit determines the presence of moisture contained in the soil by considering that the first resonant frequency has caused a significant change.

The determination circuit includes a multiplier for multiplying the first resonance frequency and the second resonance frequency, a low pass filter connected to an output terminal of the multiplier to remove a high frequency component, and the low pass filter. And a time-to-digital converter connected to the output terminal and digitally counting a frequency of a third frequency component signal corresponding to a difference between the first resonance frequency and the second resonance frequency.

Further comprising a second probe including a pair of second electrodes formed to approach or penetrate the surface layer of the soil, the second resonance circuit and the pair of second electrodes included in the second probe They can be interconnected via a pair of second ports.

The determination circuit is based on a second capacitance formed between the pair of second electrodes, the second resonant frequency of the second electrical signal formed in the second resonant circuit, the quantitative between the first resonant frequency The moisture contained in the soil can be determined based on the difference.

In the method of operating the soil moisture sensor according to an embodiment of the present invention, the first oscillator extends in a first direction to penetrate the soil. Applying a first AC signal via a first resonant circuit connected to one electrode and a pair of first ports, a second oscillator having the same characteristics as the first oscillator, the first resonant circuit Applying a second AC signal, which is a reference AC signal, to a second resonant circuit having the same impedance as, and a determination circuit is formed in the first probe and the first resonant circuit under the influence of the first AC signal. Receiving a signal, the determination circuit receiving a second electrical signal formed in the second resonant circuit under the influence of the second AC signal applied to the second resonant circuit, and the determination circuit 1 determining the moisture contained in the soil between the pair of first electrodes of the first probe based on a first resonant frequency of the electrical signal and a second resonant frequency of the second electrical signal Includes.

The step of determining, by the determination circuit, the moisture contained in the soil is based on the capacitance formed between the pair of first electrodes by the moisture contained in the soil positioned between the pair of first electrodes. Based on the step of detecting a quantitative change in the first resonant frequency of the first electrical signal formed in the first resonant circuit, and based on a quantitative change in the detected first resonant frequency, the moisture contained in the soil It may include the step of determining.

The determination circuit further comprises a step of detecting a difference between the first resonance frequency and the second resonance frequency, and the step of determining, by the determination circuit, moisture contained in the soil, comprises the first resonance frequency and the second resonance frequency. The moisture contained in the soil positioned between the pair of first electrodes of the first probe may be determined based on the difference between the resonance frequencies.

The second oscillator is connected to the second resonant circuit via a pair of second ports, and the second probe includes a pair of second electrodes formed to approach or penetrate the surface layer of the soil. It may further include applying the second AC signal via the second port of the pair.

According to the present invention, a high frequency signal is oscillated in each of a circuit having a capacitance formed in a probe for a soil moisture sensor using soil as a medium and a circuit having a reference capacitance to measure the frequency of the high frequency signal in the two circuits. By comparing and quantifying the moisture content in the soil, it is possible to more accurately and quickly grasp the moisture state of the soil in real time.

In addition, according to the present invention, the soil moisture sensor can be used non-destructively and semi-permanently, and the stability of the soil moisture sensor device can be ensured.

In addition, according to the present invention, when the determination circuit of the soil moisture sensor is manufactured with one chip, the sensor circuit and the reference resonance circuit are arranged close together, and the same type of device is used to reduce process variation. Since the measurement error can be reduced, it is possible to accurately determine the moisture content in the soil in real time.

1 is a view showing a soil moisture sensor according to an embodiment of the present invention.
2 is a view showing a soil moisture sensor according to an embodiment of the present invention.
3 is a diagram for explaining an operating principle of a first probe and a second probe.
4 is a diagram showing a soil moisture sensor according to an embodiment of the present invention.
5 is a flowchart illustrating a method of determining moisture contained in soil according to an exemplary embodiment of the present invention.
6 is a flowchart illustrating a method of sensing moisture contained in soil according to an embodiment of the present invention.

In addition to the above objects, other objects and features of the present invention will become apparent through the description of the embodiments with reference to the accompanying drawings. A preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings. In describing the present invention, if 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. Hereinafter, a soil moisture sensor and a method of operation thereof according to an embodiment of the present invention will be described in detail with reference to FIGS. 1 to 6.

1 is a view showing a soil moisture sensor 100 according to an embodiment of the present invention.

Referring to FIG. 1, a soil moisture sensor 100 according to an embodiment of the present invention includes a first probe 110, a first resonance circuit 140, a first port 141, and a first oscillator 147. ), a second resonant circuit 240, a second oscillator 247, and a determination circuit 250.

The first probe 110 includes a pair of first electrodes 111 and 112 including an electrode 111 and an electrode 112 disposed in parallel to face the electrode 111. The pair of first electrodes 111 and 112 of the first probe 110 may be formed to extend in a direction toward the soil so as to penetrate the soil.

The first resonant circuit 140 is connected via a pair of first electrodes 111 and 112 of the first probe 110 and a pair of ports 141, and is connected to the first probe 110. Apply an alternating current signal. In addition, the first resonant circuit 140 includes a first inductor 145 and a first capacitor 144. The first inductor 145 may take the form of a coil, but may be implemented in the form of a semiconductor pattern having a controllable inductance. Referring to FIG. 1, a first parasitic resistor 146 formed in the first resonant circuit 140 is illustrated. According to an embodiment of the present invention, a resistor R'(not shown) may be additionally disposed for balancing between the first resonant circuit 140 and other circuits to be described later.

The first oscillator 147 applies a first AC signal to the first resonant circuit 140. The first resonant frequency (ω1) of the first electrical signal formed in the first resonant circuit 140 by the application of the first AC signal is the impedance of the first resonant circuit 140 and a pair of the first probe 110 It may be determined based on a capacitance formed by moisture contained in the soil positioned between the first electrodes 111 and 112 of.

In addition, the first oscillator 147 may apply the first AC signal to the pair of first electrodes 111 and 112 of the first probe 110 via the port 141. Synthesis of capacitance formed by moisture contained in the soil in which the applied first AC signal is located between the first resonant circuit 140 and the pair of first electrodes 111 and 112 of the first probe 110 A first electric signal is formed in the first resonant circuit 140 and the first probe 110 by combining the impedance. In this case, the port 141 functions as an interface port between the first resonant circuit 140 and the pair of first electrodes 111 and 112 of the first probe 110.

Meanwhile, the soil moisture sensor 100 of the present invention comprises a first resonance circuit 140, a first oscillator 147, a second resonance circuit 240, a second oscillator 247, and a determination circuit 250. It can be implemented as an integrated circuit (IC) of, in this case, the integrated circuit is a pair of first electrodes 111 and 112 of the first probe 110 through the first port 141 having an interface port function. Can be connected.

In this way, when the determination circuit 250 of the soil moisture sensor is manufactured as a single chip, the sensor circuit and the reference resonance circuit are disposed adjacent to each other and are manufactured using the same type of device. ), it is possible to reduce the measurement error, so it is possible to accurately determine the moisture content in the soil in real time.

The first resonant frequency ω1 of the first electrical signal may be determined based on moisture contained in the soil positioned between the pair of first electrodes 111 and 112 of the first probe 110.

That is, due to a change in capacitance formed by moisture contained in the soil between the pair of first electrodes 111 and 112 of the first probe 110, the impedance of the first resonant circuit 140 and The capacitance formed in the first probe 110 is connected in parallel to change the composite impedance having the arithmetically summed capacitance. The combined impedance and the first AC signal are combined to form a first electric signal having a first resonant frequency ω1 in the first resonant circuit 140. Likewise, a first electric signal having a first resonant frequency ω1 is formed in the first probe 110 including the pair of first electrodes 111 and 112.

The second resonant circuit 240 is designed to have the same impedance as the first resonant circuit 140. In particular, the inductor L and the capacitor C in the second resonance circuit 240 may be designed to have the same values as the first inductor 145 and the first capacitor 144 in the first resonance circuit 140. . In addition, the second resonant circuit 240 may be disposed close to the first resonant circuit 140 to be less affected by process variation during manufacturing.

Meanwhile, although the parasitic resistance component R in the second resonant circuit 240 is shown, the impedances of the first resonant circuit 140 and the second resonant circuit 240 are accurately matched according to an embodiment of the present invention. A resistor R'(not shown) may be additionally included to improve the balancing.

A second AC signal applied by the second oscillator 247 is applied to the second resonant circuit 240. The applied second AC signal is combined with the impedance of the second resonant circuit 240 to form a second electric signal in the second resonant circuit 240. The second AC signal is a reference AC signal, and thus, a second electric signal formed in the second resonant circuit 240 is a reference electric signal. At this time, the second electric signal has a second resonant frequency (ω2) that is a reference resonant frequency.

Since the second resonance circuit 240 is not exposed to the outside, the electrical characteristics of the second resonance circuit 240 are not affected regardless of the presence or absence of moisture contained in the soil. Accordingly, the second electrical signal can maintain the second resonance frequency ω2, which is the reference resonance frequency, regardless of the presence or absence of moisture contained in the soil.

A first electrical signal having a first resonant frequency ω1 formed in the first resonant circuit 140 and a second electrical signal having a second resonant frequency ω2 formed in the second resonant circuit 240 are determined by the determination circuit 250 ). Operations of the second oscillator 247 and the second resonant circuit 240 may also be controlled by a control unit/controller/processor (not shown) included in the determination circuit 250.

The determination circuit 250 receives a first electric signal having a first resonant frequency ω1 formed in the first resonant circuit 140 and a second resonant frequency ω2 formed in the second resonant circuit 240 Receives a second electrical signal having a, and is positioned between the pair of first electrodes 111 and 112 of the first probe 110 based on the first resonant frequency ω1 and the second resonant frequency ω2 The amount of moisture contained in the soil can be determined.

At this time, the determination circuit 250 determines the amount of moisture contained in the soil between the pair of first electrodes 111 and 112 of the first probe 110 through the change value of the first resonance frequency ω1. It can be judged whether it is degree.

The determination circuit 250 is based on the capacitance formed according to the degree of moisture contained in the soil between the pair of first electrodes 111 and 112 of the first probe 110, the first resonance circuit ( 140) detects a quantitative change in the first resonant frequency ω1 of the first electrical signal, and based on the quantitative change in the detected first resonant frequency ω1, the pair of first probes 110 1 The amount of moisture contained in the soil positioned between the electrodes 111 and 112 may be measured.

Specifically, the capacitance can be expressed by the following equation.

Here, C is the capacitance/capacitance, ε is the dielectric constant, S is the area of the opposite electrode, and d is the distance between the electrodes. The dielectric constant ε and the capacitance C are proportional to each other. Also,

(진공의 유전율)

(Vacuum permittivity)

(비유전율)

(Relative dielectric constant)

As a characteristic value, the dielectric constant ε uses the relative dielectric constant εr, which is the ratio of the dielectric constant ε0 of a constant vacuum, as a characteristic value. Since the relative permittivity of air is similar to that of vacuum, and the relative permittivity of water εr is 80, which is relatively much larger than that of air and soil particles, the dielectric constant of soil is strongly influenced by the moisture content of the soil. Since the voids between the soil are also air, it does not significantly affect the change in the relative dielectric constant due to the moisture content. On the other hand, the relative permittivity of vacuum is always 1 regardless of the change in temperature, but the permittivity of water decreases as the temperature increases. Therefore, as the amount of water contained in the soil increases at a constant temperature, the dielectric constant of the soil will increase, and thus the capacitance of the soil will increase.

The resonance frequency f of the circuit for sensing moisture contained in the soil and the reference circuit can be expressed by the following equation.

Here, L is inductance and C is capacitance. The resonant frequency f and the capacitance C are inversely proportional to each other. Therefore, as the capacitance of the soil increases, the resonance frequency f decreases.

In a circuit for sensing moisture contained in soil, coupling to the first probe 110 as the amount of moisture contained in the soil between the pair of first electrodes 111 and 112 of the first probe 110 increases. Since the resulting capacitance increases, the first resonant frequency ω1 of the first electric signal formed by the combined capacitance of the first resonant circuit 140 connected in parallel and added arithmetically will decrease.

The pair of first electrodes 111 and 112 of the first probe 110 measuring the moisture content of the soil is connected only to the first resonance circuit 140 via the first port 141, and the reference resonance circuit It is not connected to the second resonance circuit 240 of. The first resonant frequency ω1 of the first electrical signal may be determined based on moisture contained in soil located between the pair of first electrodes 111 and 112 of the first probe 110. Specifically, impedance and capacitance of the first resonant circuit 140 due to a change in capacitance formed according to the amount of moisture contained in the soil located between the pair of first electrodes 111 and 112 of the first probe 110 The first resonant frequency ω1 of the first electric signal also changes as the combined impedance added arithmetically by being connected in parallel is changed.

On the other hand, unlike the first resonance circuit 140, the second resonance circuit 240 is not connected to the first probe 110 for measuring the moisture content of the soil, so the second resonance frequency (ω2) regardless of the presence or absence of moisture in the soil. Keeps the same. In this case, the second resonant circuit 240 may generate a second electric signal having a second resonant frequency ω2 based on a capacitance using air as a medium.

Therefore, when the frequency difference between the second electrical signal of the second resonant circuit 240 and the first electrical signal of the first resonant circuit 140 is detected, the first resonant frequency ω1 of the first resonant circuit 140 is 2 It is possible to quantitatively analyze whether or not it is shifted at the resonance frequency (ω2), and if it is shifted, the degree of shift.

The reference resonant circuit tracks the change in the first resonant frequency ω1 generated in the first resonant circuit 140, and noise added to the first resonant frequency ω1 measured by the determination circuit 250 ) Can be removed in real time, and the amount of change in the first resonant frequency (ω1) can be accurately measured.

When the first probe 110 is inserted into the soil, the first resonance frequency (ω1) changes due to the influence of the capacitance/capacitance formed between the first electrodes 111 and 112 via the soil. In dry soil, for example, dry sand, or dry wasteland, the change in the first resonance frequency ω1 is not large, and in the case of soil containing moisture, the change in the first resonance frequency ω1 is largely detected.

The determination circuit 250 includes a second resonant frequency (ω2) that is a reference resonant frequency of the second electrical signal formed in the second resonant circuit 240 under the influence of the second AC signal applied to the second resonant circuit 240. The difference between the first resonance frequencies ω1 may be detected, and the amount of moisture contained in the soil may be determined from the first probe 110 based on the difference between the second resonance frequency and the first resonance frequency (ω2-ω1).

On the other hand, when a foreign material such as a conductor enters the soil between the first probes 110, or when the moisture contained in the soil is very large, for example, when it becomes muddy, a pair of the first probes 110 Electrical characteristics between the first electrodes 111 and 112 may greatly deviate from the initially assumed range. In addition, when there is too much moisture contained in the soil, the capacitance/capacitance coupled to the first probe 110 is the initially assumed range even when the water flows out of the soil, or when the soil is immersed in water. Can greatly escape. In this case, according to an embodiment of the present invention, the first resonance frequency (ω1) becomes larger than the second resonance frequency (ω2), so that the difference between the second resonance frequency (ω2) and the first resonance frequency (ω1) is negative. Can be.

In this case, the determination circuit 250 may determine that the sensing is not appropriate and notify the user of an error through a visual or audible means such as a display or a speaker.

Meanwhile, the determination circuit 250 may have a plurality of reference values for the resonance frequency according to the quantitative change of the first resonance frequency ω1. When the moisture content of the soil is not measured, that is, when there is no soil positioned between the pair of first electrodes 111 and 112 of the first probe 110, the first resonance frequency (ω1) and the second resonance If the difference between the frequency ω2 is defined as a first threshold, the determination circuit 250 makes a significant change in the first resonant frequency ω1 when the change value of the first resonant frequency ω1 is greater than or equal to the first threshold value. It can be regarded as caused, and it can be determined that the moisture contained in the soil is present in an amount with a valid meaning.

A capacitor C disposed close to the first resonant circuit 140 and having the same capacitance as the first capacitor 144 so as to have the same impedance, an inductor L having the same inductance as the first inductance 145, and The second resonant circuit 240 having the resistance R having the same resistance value as the first parasitic resistance 146 is applied from the second oscillator 247 having the same frequency or phase as the first oscillator 147. The second electric signal having a second resonant frequency ω2, which is a reference resonant frequency formed from the two AC signals, may have a specific frequency difference value from the first electric signal having the first resonant frequency ω1.

The determination circuit 250 sets this specific frequency difference value as an offset and defines it as a first threshold, so that the difference between the second resonance frequency ω2 and the first resonance frequency ω1 is equal to or greater than the first threshold value. Only in the case, it can be determined that the first resonance frequency ω1 has caused a significant change, and that the amount of moisture contained in the soil is as much as an amount with a valid meaning.

In addition, according to an embodiment of the present invention, the determination circuit 250 determines the change value of the first resonant frequency ω1 as a second threshold value, a third threshold value, and a fourth threshold value according to a multiple of the first threshold value. It can be determined by dividing the level of moisture contained in the soil by defining it as a plurality of reference values such as.

The determination circuit 250 may further include a controller/controller/processor (not shown) for controlling operations of the first oscillator 120 and the first resonant circuit 110 therein. A first AC signal is applied from the first oscillator 120 to the first resonant circuit 110 by a control command from the controller, and the first resonant frequency (ω1) of the first electric signal formed in the first resonant circuit 110 The determination circuit 250 may receive the information about.

Also, the determination circuit 250 may perform a calibration process. When the determination circuit 250 does not measure the soil moisture content, that is, performs a calibration process in a state in which there is no moisture contained in the soil located between the pair of first electrodes 111 and 112 of the first probe 110 can do. At this time, the first resonance circuit 140 or the second resonance circuit 240 may be adjusted so that the difference between the first resonance frequency ω1 and the second resonance frequency ω2 becomes zero through the calibration process.

A first resonance frequency (ω1) and a second resonance frequency (ω1) and a second resonance frequency that are detected in the absence of moisture contained in the soil between the pair of first electrodes 111 and 112 of the first probe 110 through the calibration process. The difference between ω2) may be stored in a separate memory or storage and processed as offset information in the future soil moisture sensing process.

After calibration, adjustment of the difference between the first resonance frequency ω1 and the second resonance frequency ω2 may be performed using a means such as adjusting the value of the variable resistor R′.

2 is a diagram showing a soil moisture sensor 200 according to an embodiment of the present invention. 2, the soil moisture sensor 200 includes a first probe 110, a first resonance circuit 140, a first port 141, a first oscillator 147, a second probe 210, and It includes a 2 resonance circuit 240, a second port 241, a second oscillator 247, and a determination circuit 250.

2, the first resonant circuit 140, the first port 141, the first oscillator 147, the second resonant circuit 240, the second port 241, the second oscillator 247, and the first Since the probe 110 has been sufficiently described from the items shown in FIG. 1, duplicate descriptions will be omitted. The description of the operation of the determination circuit 250 of FIG. 2 and that of the determination circuit 250 of FIG. 1 will be omitted.

Referring to FIG. 2, the second resonant circuit 240 is connected to a pair of second electrodes 211 and 212 of the second probe 210 via a second port 241. The second probe 210 will be described in detail in FIG. 3.

3 is a diagram for explaining the principle of operation of the first probe 110 and the second probe 210. Referring to FIG. 3, the first probe 110 may measure the amount of moisture contained in the soil positioned between the pair of first electrodes 111 and 112 that penetrate deeply into the soil as described above. . The second probe 210 is disposed parallel to the first probe 110 and includes a pair of second electrodes 211 and 212 extending in a direction penetrating the soil.

The second probe 210 is electrically connected to the second resonant circuit 240 and the second oscillator 247, which are reference resonant circuits via the second port 241, which is measured by the first probe 110. It may be used to remove an offset according to the moisture content or temperature of the soil. Therefore, the second probe 210 is made to penetrate only the surface layer of the soil so that there is no significant difference from the temperature in the measurement state and can measure the capacitance value of the soil itself with little moisture contained in the soil. 1 The length may be shorter than that of the probe 110.

The second probe 210 is shorter than the first probe 110 in order to penetrate only the surface layer of the soil or contact the surface layer of the soil, and is adjacent to the first probe 110 and disposed in parallel, so that the first probe In (110), the capacitance value 126 due to moisture contained in the soil can be measured in the deep or inner part of the soil, and in the second probe 210, the electrostatic capacity due to moisture contained in the soil in the surface portion of the soil can be measured. The capacitance value 125 can be measured.

In the deep or inner part of the soil, the evaporation of moisture is small, so that the capacitance value 126 due to the moisture contained in the soil can be measured accurately. However, since the evaporation amount of moisture is large in the surface part of the soil, It is possible to measure the capacitance value 125 for the soil itself (soil excluding moisture) that does not contain moisture.

The determination circuit 250 is, through a calibration process, a capacitance value 126 by moisture contained in the soil substantially in the deep or inner portion of the soil and substantially no moisture contained in the soil in the surface portion of the soil, Considering the capacitance value 125 of the soil itself, it is determined whether the moisture content of the soil located between the pair of first electrodes 111 and 112 of the first probe 110 exists as a significant value. I can.

In this case, the determination circuit 250 is substantially the first resonance frequency (ω1) generated by the capacitance value 126 by the moisture contained in the soil in the deep or inner portion of the soil and substantially in the surface portion of the soil. The amount of moisture in the soil may be sensed based on the difference value of the second resonance frequency ω2 generated by the capacitance value 125 for the soil without moisture contained in the soil as a minimum threshold value.

4 is a diagram showing a soil moisture sensor 300 according to an embodiment of the present invention. The soil moisture sensor 300 according to an embodiment of the present invention includes a first probe 110, a first resonance circuit 140, a first port 141, a first oscillator 147, and a second resonance circuit 240. ), a second port 241, a second oscillator 247, and a decision circuit 350.

4, the first probe 110, the first resonant circuit 140, the first port 141, the second resonant circuit 240, the second port 241, the first oscillator 147, and the second Since the oscillator 247 has been sufficiently described from the items shown in FIGS. 1 to 3, a redundant description will be omitted. The description of the operation of the determination circuit 350 of FIG. 4 and that of the determination circuit 250 of FIGS. 1 and 3 will be omitted.

In FIG. 4, the determination circuit 350 includes a multiplier 352, a low pass filter 354, and a time-to-digital converter 356.

The multiplier 352 multiplies the first resonant frequency ω1 and the second resonant frequency ω2. The low pass filter 354 is connected to the output terminal of the multiplier 352 to remove high frequency components. Accordingly, a low frequency signal of a third frequency component corresponding to a difference between the first resonance frequency ω1 and the second resonance frequency ω2 is generated.

The time-to-digital converter 356 is connected to the output terminal of the low-pass filter 354 to digitally count the frequency of the third frequency component signal. In this case, the time-to-digital converter 356 may output a digitized value proportional to the frequency of the third frequency component signal.

According to an embodiment, the time-to-digital converter 356 may generate a pulse signal having a fourth frequency proportional to the frequency of the third frequency component signal of the third frequency component signal. The fourth frequency may be the same as the frequency of the third frequency component signal, but due to the influence of the transfer function reflected through the multiplier 352 and the low pass filter 354, the fourth frequency is different from the first frequency. It can also have a frequency. The time-to-digital converter 356 may count the number of pulses of the pulse signal having the fourth frequency for a predetermined time period, or may generate a digital count value for the pulse width or period of the pulse signal having the fourth frequency. .

The digitized count value generated by the determination circuit 350, that is, a digitized value proportional to the frequency of the third frequency component signal, is converted into an analog signal proportional to the digitized value again according to the configuration of the soil moisture sensor 300 It may be transmitted to the main processor side of the soil moisture sensor 300. In this case, the voltage, current, frequency, or amplitude of the analog signal may be converted to be proportional to the frequency of the third frequency component signal.

The first threshold value and the second threshold value applied by the determination circuit 250 of the previous embodiment may be applied to a digital count value generated as an output of the time-to-digital converter 356. Depending on the embodiment of the determination circuit 350, a sampler and a comparator for the third frequency component signal may be included. In this case, the sampler and the comparator are set to the second threshold for smooth operation of the determination circuit 350. It can be designed by selecting an operating frequency sufficiently larger than the corresponding frequency component.

The time required for the soil moisture sensor 300 to determine the moisture contained in the soil is on the order of hundreds of milliseconds to several seconds, and the process of determining the soil moisture of the present invention is completely resulted within a few hundred microseconds to several milliseconds Can be detected. As described above, since the soil moisture sensor 300 according to the present invention uses a Time-to-Digital Converter instead of a PLL loop, stable operation of the circuit is possible without a control loop, the cost is lower, and the implementation of the configuration circuit is simple. .

The determination circuit 350 of the present invention may generate a determination result as a separate signal by applying the first threshold value and the second threshold value to the digital count value and transmit it to the main processor of the soil moisture sensor 300.

In the case of the first threshold value, the main processor may detect that the amount of moisture contained in the soil has a significant value, and in the case of the second threshold value, the main processor may determine that there is a greater amount of moisture contained in the soil. In addition, it is possible to determine the level of the amount of moisture contained in the soil according to a plurality of threshold values set as a plurality of set reference values. In an embodiment of the present invention, the second threshold may be greater than the first threshold.

Meanwhile, the determination circuit 250 of the soil moisture sensors 100 and 200 shown in FIGS. 1 to 2 may be designed to operate in the same manner as the determination circuit 350 of the soil moisture sensor 300 shown in FIG. 4. May be. In addition, the soil moisture sensor 100, 200, 300 of the present invention includes a first resonance circuit 140, a first oscillator 147, a second resonance circuit 240, a second oscillator 247, and a determination circuit ( 250 and 350 may be implemented as one integrated circuit (IC). In this case, the integrated circuit includes the first probe 110 through the first port 141 and the second port 241 having an interface port function, respectively. It may be connected to a pair of first electrodes 111 and 112 and a pair of second electrodes 211 and 212 of the second probe 210.

5 is a flowchart illustrating a method of determining moisture contained in soil according to an exemplary embodiment of the present invention. The soil moisture sensing method of the present invention may be implemented by the soil moisture sensor 100 of FIG. 1 or a control unit (not shown) therein.

Referring to FIG. 5, a first AC signal is applied to the pair of first electrodes 111 and 112 of the first probe 110 and the first resonance circuit 140 by the first oscillator 147 ( S510). The operation of the first oscillator 147 or the application of the first AC signal may be controlled by a controller/controller/processor (not shown).

Due to the application of the first AC signal, the determination circuit 250 is formed in the first resonant circuit 140 connected to the first probe 110 and receives a first electrical signal having a first resonant frequency ω1. (S520).

A second AC signal is applied to the second resonance circuit 240 by the second oscillator 247 (S512). The operation of the second oscillator 247 or the application of the second AC signal may be controlled by a controller/controller/processor (not shown).

Due to the application of the second AC signal, the determination circuit 250 is formed in the second resonant circuit 240 and receives a second electric signal having a second resonant frequency ω2 (S522). Steps S512 and S522 may be executed in parallel with steps S510 and S520.

The determination circuit 250 receiving the first electrical signal and the second electrical signal detects a difference between the first resonant frequency ω1 and the second resonant frequency ω2 (S530). Soil in which the determination circuit 250 is located between the pair of first electrodes 111 and 112 of the first probe 110 based on the difference between the first resonant frequency ω1 and the second resonant frequency ω2 It is determined whether the moisture contained in is a significant amount (S540).

If the determination circuit 250 does not determine that the moisture contained in the soil positioned between the pair of first electrodes 111 and 112 of the first probe 110 is a significant amount, the current process is terminated. If necessary, after a certain period of time or when a certain condition is satisfied, step S510 may be repeated again.

If the determination circuit 250 determines that the moisture contained in the soil located between the pair of first electrodes 111 and 112 of the first probe 110 is a significant amount, it is contained in the soil from the first probe 110 The amount of moisture is determined based on the difference between the first resonant frequency ω1 and the second resonant frequency ω2 (S550).

6 is a flowchart illustrating a method of sensing moisture contained in soil according to an embodiment of the present invention. The soil moisture sensing method of the present invention may be implemented by the soil moisture sensors 100, 200, and 300 of FIGS. 1 to 4, or a controller/controller/processor (not shown) therein.

Referring to FIG. 6, a first AC signal is applied to the first probe 110 by the first oscillator 147 via the first resonance circuit 140 (S610). Then, the determination circuit 250 receives a first electrical signal formed in the first resonance circuit 140 connected to the first probe 110 and having a first resonance frequency ω1 (S620).

A second AC signal is applied to the second probe 210 by the second oscillator 247 via the second resonance circuit 240 (S612). Then, the determination circuit 250 receives a second electrical signal formed in the second resonance circuit 240 connected to the second probe 210 and having a second resonance frequency ω2 (S622). Steps S612 and S622 may be executed in parallel with steps S610 and S620.

Then, the determination circuit 250 detects a difference between the first resonant frequency ω1 of the first electrical signal and the second resonant frequency ω2 of the second electrical signal (S630).

The determination circuit 250 is based on the difference between the first resonant frequency ω1 and the second resonant frequency ω2, the soil located between the pair of first electrodes 111 and 112 of the first probe 110 It is determined whether or not the moisture contained in is a significant amount (S640).

If the determination circuit 250 does not determine that the moisture contained in the soil positioned between the pair of first electrodes 111 and 112 of the first probe 110 is a significant amount, the current process is terminated. If necessary, after a certain period of time or when a certain condition is satisfied, step S610 may be repeated again.

If the determination circuit 250 determines that the moisture contained in the soil located between the pair of first electrodes 111 and 112 of the first probe 110 is a significant amount, it is contained in the soil from the first probe 110 The amount of moisture is determined based on the difference between the first resonance frequency ω1 and the second resonance frequency ω2, which is a reference resonance frequency with respect to the surface layer of the soil from the second probe 210 (S650).

A method of operating a circuit according to an embodiment of the present invention may be implemented in the form of program instructions that can be executed through various computer means and recorded in a computer-readable medium. The computer-readable medium may include program instructions, data files, data structures, and the like alone or in combination. The program instructions recorded on the medium may be specially designed and configured for the present invention, or may be known and usable to those skilled in computer software. Examples of computer-readable recording media include magnetic media such as hard disks, floppy disks, and magnetic tapes, optical media such as CD-ROMs and DVDs, and magnetic media such as floptical disks. -A hardware device specially configured to store and execute program instructions such as magneto-optical media, and ROM, RAM, flash memory, and the like. Examples of program instructions include not only machine language codes such as those produced by a compiler, but also high-level language codes that can be executed by a computer using an interpreter or the like. The hardware device described above may be configured to operate as one or more software modules to perform the operation of the present invention, and vice versa.

However, the present invention is not limited or limited by the embodiments. The same reference numerals shown in each drawing indicate the same members. The length, height, size, width, etc. introduced in the embodiments and drawings of the present invention may be exaggerated to aid understanding.

As described above, in the present invention, specific matters such as specific components, etc., and limited embodiments and drawings have been described, but this is provided only to help a more general understanding of the present invention, and the present invention is not limited to the above embodiments. , If a person of ordinary skill in the field to which the present invention belongs, various modifications and variations are possible from these descriptions.

Therefore, the spirit of the present invention is limited to the described embodiments and should not be defined, and all things that have equivalent or equivalent modifications to the claims as well as the claims to be described later will be said to belong to the scope of the spirit of the present invention. .

100, 200, 300: soil moisture sensor 110: first probe
140: first resonant circuit 141: first port
147: first oscillator 210: second probe
240: second resonant circuit 247: second oscillator
250, 350: decision circuit

Claims (11)

A first probe including a pair of first electrodes extending in a first direction to penetrate the soil;
A first resonance circuit connected to the pair of first electrodes of the first probe through a pair of first ports and to which a first AC signal is applied;
A second resonance circuit to which a second AC signal having the same impedance as the first resonance circuit and which is a reference AC signal and having the same characteristics as the first AC signal is applied; And
Receiving a first electrical signal formed in the first resonant circuit, receiving a second electrical signal formed in the second resonant circuit, a first resonant frequency of the first electrical signal and a second electrical signal 2 a determination circuit for determining the moisture of the soil based on the resonance frequency;
Including,
The determination circuit is
Detecting a difference between the second resonant frequency and the first resonant frequency, which is a reference resonant frequency of the second electric signal formed in the second resonant circuit under the influence of the second AC signal applied to the second resonant circuit, ,
The moisture contained in the soil is determined based on the difference between the second resonance frequency and the first resonance frequency, and if the difference between the second resonance frequency and the first resonance frequency is greater than or equal to a first threshold value, the first resonance Judging the presence of moisture contained in the soil, assuming that the frequency caused a significant change,
A soil moisture sensor that determines whether sensing is effective according to a sign of a difference between the second resonance frequency and the first resonance frequency. The method of claim 1,
The determination circuit is
The first electrical signal formed in the first resonant circuit based on capacitance formed between the pair of first electrodes by moisture contained in the soil positioned between the pair of first electrodes A soil moisture sensor that detects a quantitative change in the first resonance frequency of and determines moisture contained in the soil based on the quantitative change in the detected first resonance frequency. delete delete The method of claim 1,
The determination circuit is
A multiplier for multiplying the first resonant frequency and the second resonant frequency;
A low pass filter connected to an output terminal of the multiplier to remove a high frequency component; And
A time-to-digital converter connected to the output terminal of the low-pass filter to digitally count a frequency of a third frequency component signal corresponding to a difference between the first resonance frequency and the second resonance frequency ;
Soil moisture sensor comprising a. The method of claim 1,
A second probe including a pair of second electrodes formed to approach or penetrate the surface layer of the soil;
Including more,
The second resonance circuit is a soil moisture sensor that is interconnected via the pair of second electrodes included in the second probe and a pair of second ports. The method of claim 6,
The determination circuit is based on a second capacitance formed between the pair of second electrodes, the second resonant frequency of the second electrical signal formed in the second resonant circuit, the quantitative between the first resonant frequency A soil moisture sensor that determines the moisture contained in the soil based on the difference. The first oscillator is connected to the pair of first electrodes of a first probe including a pair of first electrodes extending in a first direction so as to penetrate the soil through a pair of first ports. Applying a first AC signal via a first resonance circuit;
Applying, by a second oscillator having the same characteristics as the first oscillator, a second AC signal, which is a reference AC signal, to a second resonant circuit having the same impedance as the first resonant circuit;
Receiving, by a determination circuit, a first electric signal formed in the first probe and the first resonant circuit under the influence of the first AC signal;
Receiving, by the determination circuit, a second electric signal formed in the second resonant circuit under the influence of the second AC signal applied to the second resonant circuit;
Detecting, by the determination circuit, a difference between the first resonant frequency and the second resonant frequency; And
The soil contains the determination circuit located between the pair of first electrodes of the first probe based on a first resonant frequency of the first electrical signal and a second resonant frequency of the second electrical signal Determining moisture;
Including,
The step of determining, by the determination circuit, the moisture contained in the soil
Based on the difference between the first resonance frequency and the second resonance frequency, the moisture contained in the soil positioned between the pair of first electrodes of the first probe is determined, and the second resonance frequency and the second resonance frequency If the difference between the first resonance frequencies is greater than or equal to a first threshold value, it is considered that the first resonance frequency has caused a significant change, and the presence of moisture contained in the soil is determined,
Soil moisture sensing method for determining whether the sensing is effective according to a sign of a difference between the second resonance frequency and the first resonance frequency. The method of claim 8,
The step of determining, by the determination circuit, the moisture contained in the soil
The first electrical signal formed in the first resonant circuit based on capacitance formed between the pair of first electrodes by moisture contained in the soil positioned between the pair of first electrodes Detecting a quantitative change in the first resonant frequency of; And
Determining moisture contained in the soil based on a quantitative change in the detected first resonance frequency;
Soil moisture sensing method comprising a. delete The method of claim 8,
The second oscillator is connected to the second resonant circuit via a pair of second ports, and the second probe includes a pair of second electrodes formed to approach or penetrate the surface layer of the soil. Applying the second AC signal via a pair of second ports;
Soil moisture sensing method further comprising a.

Images