CN104198537A - Method and device for detecting moisture content and electric conductivity of soil - Google Patents

Abstract

The invention relates to a method and a detection device for detecting soil moisture content and electrical conductivity. The detection method includes: inserting two soil moisture detection electrodes into the soil to be tested; inserting two soil conductivity detection electrodes between the above two soil moisture detection electrodes; applying two different frequencies to the measured soil alternately The sinusoidal excitation signal; obtain the output voltage value of the measured soil under two different frequency sinusoidal excitation signals, calculate the resistance value and capacitance value of the measured soil from the output voltage value, and obtain the value according to the resistance value and capacitance value Soil moisture content: obtain the voltage value and current value between two soil conductivity detection electrodes under a sinusoidal excitation signal of any frequency, and combine the distance parameters between the soil moisture content detection electrode and the soil conductivity detection electrode to obtain Soil conductivity. The invention is suitable for the vehicle-mounted large-area rapid detection of soil moisture content and electrical conductivity, which can greatly improve the detection efficiency and reduce the detection cost.

Description

A method and device for detecting soil moisture content and electrical conductivity

technical field

The invention relates to the technical field of soil moisture content and electrical conductivity detection, in particular to a soil moisture content and electrical conductivity detection method and detection device based on dual-frequency alternating excitation.

Background technique

There are many detection methods of soil moisture content, such as the drying weighing method of collecting soil samples and weighing, which can not only obtain the mass moisture content of the soil, but also obtain the volume moisture content of the soil. It is based on the neutron attenuation method that water has a strong attenuation characteristic for neutron energy. According to the different soil moisture content, the resistance is also different. According to the dielectric constant of water (generally about 80 at normal temperature) and the dielectric constant of soil skeleton (generally between 3 and 5 at normal temperature) and the dielectric constant of air (approximately equal to 1), the soil dielectric constant The characteristic method, that is, the difference in soil moisture content is reflected in the difference in soil dielectric constant. From this, frequency domain decomposition method, time domain reflection method, standing wave rate method, capacitance method and other methods are developed to measure soil dielectric constant. The soil moisture content is deduced from the measured soil dielectric constant. Each of these methods has its advantages and disadvantages and is suitable for different applications. In short, things are always contradictory, simple is not reliable, and reliable is not simple.

Soil conductivity can reflect the parameters of salinity, moisture, organic matter content, available nutrients, soil texture structure and porosity in soil to varying degrees, and is an indispensable and important parameter for studying soil. There are two types of detection methods for soil conductivity: non-contact and contact. The non-contact method is represented by the electromagnetic induction earth conductivity meter (EM38 series) produced by the Canadian company Geonics limited, which can measure without contacting the soil, and has the advantages of fast measurement, high efficiency and low cost. However, subject to the measurement principle of electromagnetic induction, the relative position of the instrument, the environmental electromagnetic field, and even the metal accessories attached to the human body will cause large errors in the detection. The contact detection of soil conductivity is based on the standard current-voltage four-terminal method principle, which overcomes the shortcomings of non-contact electromagnetic induction measurement, but it needs to insert the detection electrode into the soil and make good contact with the soil. Studies have shown that the size of soil electrical conductivity is not only related to soil salinity, but also related to soil moisture content. Therefore, it is very necessary to detect soil moisture while detecting soil electrical conductivity.

Contents of the invention

The invention aims at the deficiencies of the prior art, and provides a soil moisture content and electrical conductivity detection method and detection device based on dual-frequency alternating excitation, so as to realize rapid detection of soil moisture content and electrical conductivity in a large area by a vehicle.

To achieve the above object, the present invention adopts the following technical solutions:

A method for detecting soil moisture content and electrical conductivity, the detection method comprising the following steps:

(1) Insert two soil moisture detection electrodes into the soil to be tested.

(2) Insert two soil conductivity detection electrodes between the above two soil moisture detection electrodes, and make the two soil moisture detection electrodes and the two soil conductivity detection electrodes be located on the same straight line.

(3) Two sinusoidal excitation signals with different frequencies are applied alternately to the measured soil.

(4) Obtain the output voltage values of the measured soil under two sinusoidal excitation signals of different frequencies respectively, by combining the input voltage values and The circuit parameters calculate the resistance value and capacitance value of the measured soil, and obtain the soil moisture content according to the resistance value and capacitance value of the measured soil.

(5) Obtain the voltage and current values between the two soil conductivity detection electrodes under a sinusoidal excitation signal of any frequency, and combine the distance parameters between the soil moisture content detection electrodes and the soil conductivity detection electrodes to obtain the soil conductivity.

The invention also relates to a detection device adopting the detection method of soil moisture content and electrical conductivity. The detection device includes a host computer, a single-chip microcomputer, a dual-frequency sinusoidal excitation signal generation circuit, a soil moisture content detection control circuit, a soil moisture content detection control circuit actuator, a soil moisture detection electrode, a soil moisture detection circuit, and a soil conductivity detection electrode. , Soil conductivity detection circuit and A/D conversion circuit.

Specifically, the host computer is interactively connected with the single-chip microcomputer.

Said single-chip microcomputer, its input and output ends are interactively connected with the water content detection control circuit, its output end is connected with the input end of the dual-frequency sinusoidal excitation signal generating circuit, and its input end is connected with the output end of the A/D conversion circuit.

In the dual-frequency sinusoidal excitation signal generation circuit, its output terminal is connected to the input terminal of the soil moisture content detection electrode through the soil moisture content detection control circuit actuator; the input terminal of the soil moisture content detection control circuit actuator is connected to the soil The output end of the moisture content detection control circuit is connected.

The output terminal of the soil moisture detection electrode is connected to the input terminal of the moisture detection circuit; the output terminal of the soil moisture detection circuit is connected to the input terminal of the A/D conversion circuit.

The soil conductivity detection electrode is connected to the input end of the soil conductivity detection circuit; the output end of the soil conductivity detection circuit is connected to the input end of the A/D conversion circuit.

Further, the soil moisture content detection electrodes and the soil conductivity detection electrodes are arranged in pairs, and the two soil conductivity detection electrodes arranged in pairs are located between the two soil moisture content detection electrodes arranged in pairs.

Furthermore, the dual-frequency sinusoidal excitation signal generating circuit includes a first sinusoidal excitation signal source and a second sinusoidal excitation signal source that are independent of each other, and the frequencies of the first sinusoidal excitation signal source and the second sinusoidal excitation signal source are different.

The beneficial effects of the present invention are:

(1) The present invention uses dual-frequency sinusoidal signals to alternately and repeatedly excite the measured soil, and can obtain the resistance value and capacitance value of the measured soil at the same time. The resistance value of soil reflects the conductivity of soil to a certain extent, which is related to soil salinity, moisture, organic matter content, available nutrients, soil texture structure and porosity. The capacitance value of the soil reflects the volumetric water content of the soil to a certain extent.

(2) The present invention uses the current-voltage four-terminal method to detect the soil electrical conductivity while detecting the moisture content of the soil. Because the soil conductivity under two different frequency sinusoidal excitation signals can be obtained, the difference between the two soil conductivity values can be used to reflect the differences in the types of soluble salts in the soil to varying degrees.

(3) The present invention obtains soil moisture content, soil electrical conductivity and analyzes other soil properties by directly detecting soil resistance, capacitance, and electrical conductivity, and is especially suitable for rapid detection of soil moisture content and electrical conductivity in a large area on a vehicle, which can be greatly improved. Improve detection efficiency and reduce detection cost.

Description of drawings

Fig. 1 is the system block diagram of soil moisture content and electrical conductivity detection device among the present invention;

Fig. 2 is a schematic diagram of the distribution of soil moisture detection electrodes and soil conductivity detection electrodes in the present invention;

Fig. 3 is the schematic diagram of the principle of the method for detecting soil moisture content in the present invention;

Fig. 4 is the schematic diagram of the principle of soil conductivity detection method in the present invention;

Fig. 5 is a simplified implementation system block diagram of the soil moisture content and electrical conductivity detection device in the present invention.

in:

1. Host computer, 2. Single-chip microcomputer, 3. Soil moisture content detection control circuit, 4. Dual-frequency sinusoidal excitation signal generation circuit, 5. Soil moisture content detection control circuit actuator, 6. Soil moisture content detection circuit, 7. Soil Moisture content detection electrode, 8. Soil conductivity detection electrode, 9. Soil conductivity detection circuit, 10. A/D conversion circuit.

Detailed ways

The present invention will be further described below in conjunction with accompanying drawing:

A method for detecting soil moisture content and electrical conductivity, the detection method comprising the following steps:

(1) Insert two soil moisture detection electrodes into the soil to be tested.

(2) Insert two soil conductivity detection electrodes between the above two soil moisture detection electrodes, and make the two soil moisture detection electrodes and the two soil conductivity detection electrodes be located on the same straight line.

(3) Two sinusoidal excitation signals with different frequencies are applied alternately to the measured soil.

(4) Obtain the output voltage values of the measured soil under two sinusoidal excitation signals of different frequencies respectively, by combining the input voltage values and The circuit parameters calculate the resistance value and capacitance value of the measured soil, and obtain the soil moisture content according to the resistance value and capacitance value of the measured soil.

(5) Obtain the voltage and current values between the two soil conductivity detection electrodes under a sinusoidal excitation signal of any frequency, and combine the distance parameters between the soil moisture content detection electrodes and the soil conductivity detection electrodes to obtain the soil conductivity.

Further, the two soil moisture detection electrodes and the two soil conductivity detection electrodes are metal electrodes that can be inserted into the soil. The above four electrodes are distributed in a straight line with equal distances, two soil moisture detection electrodes are on both sides, and two soil conductivity detection electrodes are in the middle. In addition, in the process of soil moisture content and electrical conductivity detection, the above four electrodes should be inserted into the soil at least 10cm above, and make it in contact with the soil.

Further, the specific process of alternately applying two sinusoidal excitation signals of different frequencies to the measured soil is as follows: set the two sinusoidal excitation signals of different frequencies as ui1 and ui2 respectively. First, through multiple experiments, determine the time interval t of alternately applying two sinusoidal excitation signals with different frequencies. Then, according to first t time length ui1, then t time length ui2, or first t time length ui2, then t time length ui1, the sinusoidal excitation signal is cyclically applied to the soil under test until the detection ends.

As shown in FIGS. 1-4 , the present invention also relates to a detection device using the above-mentioned detection method for soil moisture content and electrical conductivity detection method. The detection device includes a host computer 1, a single-chip microcomputer 2, a dual-frequency sinusoidal excitation signal generation circuit 4, a soil moisture content detection control circuit 3, a soil moisture content detection control circuit actuator 5, a soil moisture content detection electrode 7, and a soil moisture content detection circuit. 6. Soil conductivity detection electrode 8 , soil conductivity detection circuit 9 and A/D conversion circuit 10 .

Specifically, the host computer is used to communicate with the single-chip microcomputer, control the single-chip microcomputer to collect and send the detection data of soil moisture content and electrical conductivity, and process, display and store the detection data obtained by the single-chip computer. The single-chip microcomputer is used to control the dual-frequency sinusoidal excitation signal generation circuit and the soil moisture content detection control circuit, and obtain data converted by the A/D conversion circuit from the soil moisture content detection circuit and the soil conductivity detection circuit. The dual-frequency sinusoidal excitation signal is used to generate two different frequency sinusoidal excitation signals, which are applied to the measured soil, the soil moisture content detection circuit and the soil conductivity detection electrode through the soil moisture content detection electrode. The soil moisture content detection circuit is used to obtain output signals under two sinusoidal excitation signals with different frequencies. According to the detection data of the soil moisture content detection circuit, combined with two sinusoidal excitation signals of different frequencies and the parameters of the soil moisture content detection circuit, the resistance and capacitance of the measured soil can be obtained. The soil conductivity detection circuit is used to detect the voltage between two soil conductivity detection electrodes under sinusoidal excitation signals of different frequencies. According to the detection data of the soil conductivity detection circuit, combined with the current value, the two soil moisture detection electrodes, and the distance parameters between the two soil conductivity detection electrodes, the size of the soil conductivity can be calculated.

Further, the host computer 1 and the single-chip microcomputer 2 are interactively connected. Described single-chip microcomputer 2, its input and output end and soil moisture content detection control circuit 3 are interactively connected, and its output end is connected with the input end of dual-frequency sinusoidal excitation signal generation circuit 4, and input end is connected with the output of A/D conversion circuit 10 end connected. The output end of the dual-frequency sinusoidal excitation signal generation circuit 4 is connected to the input end of the soil moisture detection electrode 7 through the soil moisture content detection control circuit actuator 5; the soil moisture content detection control circuit actuator 5 The input end is connected with the output end of the soil moisture content detection control circuit 3 . The output end of the soil moisture detection electrode 7 is connected to the input end of the moisture detection circuit 6 ; the output end of the soil moisture detection circuit 6 is connected to the input end of the A/D conversion circuit 10 . The soil conductivity detection electrode 8 is connected to the input end of the soil conductivity detection circuit 9 ; the output end of the soil conductivity detection circuit 9 is connected to the input end of the A/D conversion circuit 10 .

Further, the soil moisture content detection electrodes 7 and the soil conductivity detection electrodes 8 are arranged in pairs, and the two soil conductivity detection electrodes 8 arranged in pairs are located between the two soil moisture content detection electrodes arranged in pairs. between 7.

Furthermore, the dual-frequency sinusoidal excitation signal generating circuit 4 includes a first sinusoidal excitation signal source u _i1 and a second sinusoidal excitation signal source u _i2 that are independent of each other, and the first sinusoidal excitation signal source u _i1 and the second sinusoidal excitation signal source u i1 The frequencies of the excitation signal sources u _i2 are different.

The soil moisture content detection control circuit 3 is a commonly used power drive circuit, and its function is to amplify the power of the signal output by the single chip microcomputer 2, so that there is enough power to drive the soil moisture content detection control circuit actuator 5, the described The soil moisture content detection control circuit actuator 5 is a commonly used relay.

The soil moisture content detection circuit 6 is a commonly used high-frequency filter circuit, the purpose of which is to filter out interference clutter and improve detection accuracy.

The soil conductivity detection circuit 9 is a commonly used high-frequency filter circuit, the purpose of which is to filter out interference clutter and improve detection accuracy.

Working principle of the present invention is:

As shown in Figures 1 to 2, the upper computer 1 controls the single-chip microcomputer 2 to collect and send the detection data of soil moisture content and electrical conductivity. The host computer 1 receives the detection data from the single chip microcomputer 2 and processes, stores and displays the detection data. The single-chip microcomputer 2 sends a control signal to control the dual-frequency sinusoidal excitation signal generation circuit 4 and the soil moisture content detection control circuit 3 to work. The dual-frequency sinusoidal excitation signal generated by the dual-frequency sinusoidal excitation signal generation circuit 4 is gated by the actuator 5 of the soil moisture content detection control circuit, and then applied to the measured soil through a pair of soil moisture content detection electrodes 7 spaced at a certain distance. Soil moisture content detection circuit 6. The signal obtained by the soil moisture content detection circuit 6 is converted by the A/D conversion circuit 10 and collected by the single chip microcomputer 2 . The dual-frequency sinusoidal excitation signal applied to the soil to be measured by the soil moisture detection electrode 7 generates a corresponding voltage signal on a pair of soil conductivity detection electrodes 8 spaced at a certain distance. The voltage signal is detected by the soil conductivity detection circuit 9 and converted by the A/D conversion circuit 10 and then collected by the single chip microcomputer 2 .

Fig. 3 is a schematic diagram of the principle of the soil moisture content detection method, wherein the amplitude of the first sinusoidal excitation signal source ui1 is Ui1, the angular frequency is ω1, and the internal resistance is r1. The amplitude of the second sinusoidal excitation signal source ui2 is Ui2, the angular frequency is ω2, and the internal resistance is r2. The capacitance of the measured soil is Cx, and the resistance of the measured soil is Rx. R is the load sampling resistor, and U0 is the output voltage on the load sampling resistor R. As shown in FIG. 3 , under the control of the soil moisture content detection control circuit 3 , the actuator 5 of the soil moisture content detection control circuit makes the switch K close to terminal a and disconnect from terminal b. At this time, suppose the output voltage across the resistor R is u _o1 , then

${\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; ol</span>}}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; il</span>}}}{{\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; R</span>}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; r</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}<span\; class="notranslate">\; \&CenterDot;</span>\mathrm{<span\; class="notranslate">\; R</span>}$

but

${\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; \&CenterDot;</span>\mathrm{<span\; class="notranslate">\; R</span>}}{{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; ol</span>}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; R</span>}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; r</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>$

In the formula (1), X ₁ is the reactance of the measured soil under the excitation of the sinusoidal excitation signal u _i1 .

After the time interval t, under the control of the soil moisture content detection control circuit 3, the soil moisture content detection control circuit actuator 5 makes the switch K disconnect from terminal a and close from terminal b. The voltage is u _o2 , then

${\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; o</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}}{{\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; R</span>}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; r</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; \&CenterDot;</span>\mathrm{<span\; class="notranslate">\; R</span>}$

but

${\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>\mathrm{<span\; class="notranslate">\; R</span>}}{{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; o</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; R</span>}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; r</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>$

In formula (2), X ₂ is the reactance of the measured soil under the excitation of sinusoidal excitation signal u _i2 .

also because:

${\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; =</span>\frac{\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; \&CenterDot;</span>{\mathrm{<span\; class="notranslate">\; c</span>}}_{\mathrm{<span\; class="notranslate">\; x</span>}}}}{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; x</span>}}<span\; class="notranslate">\; \&CenterDot;</span>{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>{\mathrm{<span\; class="notranslate">\; c</span>}}_{\mathrm{<span\; class="notranslate">\; x</span>}}}}<span\; class="notranslate">\; .</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; )</span>$

${\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; =</span>\frac{\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; \&CenterDot;</span>{\mathrm{<span\; class="notranslate">\; c</span>}}_{\mathrm{<span\; class="notranslate">\; x</span>}}}}{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; x</span>}}<span\; class="notranslate">\; \&CenterDot;</span>{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; \&CenterDot;</span>{\mathrm{<span\; class="notranslate">\; c</span>}}_{\mathrm{<span\; class="notranslate">\; x</span>}}}}<span\; class="notranslate">\; .</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 4</span>}<span\; class="notranslate">\; )</span>$

From formula (3) and (4) get

${\mathrm{<span\; class="notranslate">\; c</span>}}_{\mathrm{<span\; class="notranslate">\; x</span>}}<span\; class="notranslate">\; =</span>\frac{\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{{\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; -</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{{\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}}{{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}<span\; class="notranslate">\; .</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 5</span>}<span\; class="notranslate">\; )</span>$

${\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; x</span>}}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}{\frac{{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}}{{\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}<span\; class="notranslate">\; -</span>\frac{{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}{{\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}}}<span\; class="notranslate">\; .</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 6</span>}<span\; class="notranslate">\; )</span>$

Substituting equations (1) and (2) into equations (5) and (6) respectively, we get

${\mathrm{<span\; class="notranslate">\; c</span>}}_{\mathrm{<span\; class="notranslate">\; x</span>}}<span\; class="notranslate">\; =</span>\frac{\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\frac{{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}\mathrm{<span\; class="notranslate">\; R</span>}}{{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; 02</span>}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; R</span>}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; r</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; -</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\frac{{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}\mathrm{<span\; class="notranslate">\; R</span>}}{{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; 01</span>}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; R</span>}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; r</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; )</span>}}{{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 7</span>}<span\; class="notranslate">\; )</span>$

${\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; x</span>}}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}{\frac{{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}}{\frac{{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}\mathrm{<span\; class="notranslate">\; R</span>}}{{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; 01</span>}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; R</span>}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; r</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; -</span>\frac{{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}{\frac{{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}\mathrm{<span\; class="notranslate">\; R</span>}}{{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; 02</span>}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; R</span>}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; r</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 8</span>}<span\; class="notranslate">\; )</span>$

The relative permittivity ε _r can be obtained from c _x :

_εr = Cx/k (9)

(9) where k is a constant related to the structural parameters of a pair of soil moisture detection electrodes 6 and the distance between the two electrodes.

The relationship between soil moisture content and relative permittivity _εr can be calculated using the Topp formula:

θ _V (ε _r )＝-5.3+2.92ε _r -0.055ε _r ² +0.00043ε _r ³ (10)

In formula (10), θV(ε _r ) is the soil water content related to the relative permittivity ε _r of the soil, and the unit is (V/V)%.

There is also a quantitative relationship between soil moisture content and soil electrical resistance, which can be expressed as:

${\mathrm{<span\; class="notranslate">\; \&theta;</span>}}_{\mathrm{<span\; class="notranslate">\; V</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; Rac</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; /</span>\sqrt{\mathrm{<span\; class="notranslate">\; Rac</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 11</span>}<span\; class="notranslate">\; )</span>$

In formula (11), θ _V (R _ac ) is the soil moisture content related to the soil resistance R _ac , unit (V/V)%; R _ac is the soil resistance value, k ₁ and k ₂ are the structural parameters related to the detection mechanism , soil type and other constants.

Compatible with soil resistance and capacitance detection data, the comprehensive model of soil moisture content can be obtained as follows:

θ _V ＝αθ _V (ε _r )+βθ _V (R _ac ) (12)

In formula (12), θ _V is soil water content, α and β are constants and α+β=1.

Fig. 4 is a schematic diagram of the principle of the soil electrical conductivity detection method. Among them, P is the soil moisture content detection electrode and is one of the electrodes for soil conductivity detection excitation signal application; Q is the soil moisture content detection electrode and is the second electrode for soil conductivity detection excitation signal application; M is the soil conductivity detection electrode. One; N is the soil conductivity detection electrode two. As shown in FIG. 4, four electrodes P, Q, M, and N are arranged on the same straight line, respectively. Electrode P and electrode Q separated by a certain distance are used as soil moisture detection electrode 7 . The electrode P is connected to one end of the excitation signal source through the actuator 5 of the soil moisture content detection control circuit, the electrode Q is connected to one end of the load sampling resistor R, and the other end of the load sampling resistor R is connected to the other end of the excitation signal source to form a current circuit. The loop current i can be obtained by dividing the voltage _U0 across the load sampling resistor R by the resistor R. The electrode M and the electrode N, which are separated by a certain distance, are located between the electrode P and the electrode Q. The voltage between the electrode M and the electrode N is detected by the soil conductivity detection circuit 9, then the conductivity σ of the measured soil is:

σ＝{[(1/d _PM -1/d _PN )+(1/d _QN -1/d _QM )]/(2π)}×i/V _MN (13)

In formula (13), d _PM is the distance between electrode P and electrode M, d _PN is the distance between electrode P and electrode N, d _QN is the distance between electrode Q and electrode N, and d _QM is the distance between electrode Q The distance to the electrode M, V _MN is the voltage between the electrode M and the electrode N, i is the loop current, and i=Uo/R.

Fig. 5 is a simplified implementation system block diagram of the soil moisture content and electrical conductivity detection device in the present invention. What is different from the foregoing embodiments is that there is no soil moisture content detection control circuit 3 and soil moisture content detection control circuit actuator 5 in this embodiment, and an instruction is directly sent to the dual-frequency sinusoidal excitation signal generation circuit 4 by the single-chip microcomputer 2, so that it Generate a sinusoidal excitation signal ui1 with an angular frequency of ω1, apply it to the soil moisture content detection electrode 7, and at the same time, the single-chip microcomputer 2 collects the detection data from the A/D conversion circuit 10, and marks the data. After the delay time t, the single-chip microcomputer 2 is interrupted Send the previous instruction to the dual-frequency sinusoidal excitation signal generation circuit 4 to generate a sinusoidal excitation signal ui2 with an angular frequency of ω2, which is applied to the soil moisture content detection electrode 7, and the single-chip microcomputer 2 collects data from the A/D conversion circuit 10 of the detection data, and mark the data differently, and then repeat the above process after a delay time t, to obtain continuous real-time detection data of soil moisture content and electrical conductivity.

The above-mentioned embodiments are only descriptions of preferred implementations of the present invention, and are not intended to limit the scope of the present invention. Variations and improvements should fall within the scope of protection defined by the claims of the present invention.

Claims (2)

1. soil moisture content and a conductivity detection method, is characterized in that: this detection method comprises the following steps:

(1) two soil moisture content detecting electrodes are inserted in tested soil;

(2) between above-mentioned two soil moisture content detecting electrodes, insert two soil conductivity detecting electrodes, and two soil moisture content detecting electrodes and two soil conductivity detecting electrodes are located along the same line;

(3) tested soil alternate cycles is applied to the sinusoidal excitation signal of two different frequencies;

(4) obtain respectively the output voltage values of tested soil under the sinusoidal excitation signal of two different frequencies, output voltage values by the tested soil obtaining respectively under the sinusoidal excitation signal of two different frequencies, calculate resistance value and the capacitance of tested soil in conjunction with input voltage value and circuit parameter, and according to the resistance value of tested soil and capacitance, try to achieve soil moisture content;

(5) obtain magnitude of voltage and the current value under the sinusoidal excitation signal of arbitrary frequency between two soil conductivity detecting electrodes, and in conjunction with the distance parameter between soil moisture content detecting electrode and soil conductivity detecting electrode, try to achieve soil conductivity.

2. the pick-up unit of a kind of soil moisture content according to claim 1 and conductivity detection method, is characterized in that: comprise that host computer (1), single-chip microcomputer (2), bifrequency sinusoidal excitation signal circuit for generating (4), soil moisture content detect control circuit (3), soil moisture content detects control circuit topworks (5), soil moisture content detecting electrode (7), soil moisture content testing circuit (6), soil conductivity detecting electrode (8), soil conductivity testing circuit (9) and A/D change-over circuit (10);

Described host computer (1) is connected alternately with single-chip microcomputer (2);

Described single-chip microcomputer (2), its input/output terminal detects control circuit (3) with soil moisture content and is connected alternately, its output terminal is connected with the input end of bifrequency sinusoidal excitation signal circuit for generating (4), and its input end is connected with the output terminal of A/D change-over circuit (10);

Described bifrequency sinusoidal excitation signal circuit for generating (4), its output terminal detects control circuit topworks (5) by soil moisture content and is connected with the input end of soil moisture content detecting electrode (7); The input end that described soil moisture content detects control circuit topworks (5) is connected with the output terminal that soil moisture content detects control circuit (3);

Described soil moisture content detecting electrode (7), its output terminal is connected with the input end of soil moisture content testing circuit (6); Described soil moisture content testing circuit (6), its output terminal is connected with the input end of A/D change-over circuit (10);

Described soil conductivity detecting electrode (8) is connected with the input end of soil conductivity testing circuit (9); Described soil conductivity testing circuit (9), its output terminal is connected with the input end of A/D change-over circuit (10).