CN111398373A - Double-frequency-excited soil moisture detector and testing method thereof - Google Patents
Double-frequency-excited soil moisture detector and testing method thereof Download PDFInfo
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- CN111398373A CN111398373A CN202010357632.9A CN202010357632A CN111398373A CN 111398373 A CN111398373 A CN 111398373A CN 202010357632 A CN202010357632 A CN 202010357632A CN 111398373 A CN111398373 A CN 111398373A
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Abstract
The invention relates to a double-frequency excited soil moisture detector and a test method thereof, wherein the double-frequency excited soil moisture detector comprises a shell, a touch screen, a battery, a power switch, a probe and a circuit board unit, the touch screen and the power switch are installed at the top of the shell, the circuit board unit and the battery are installed inside the shell, the probe is installed at the lower part of the shell, a positive plate and a negative plate are arranged in the probe, the positive plate and the negative plate are electrically connected with the circuit board unit, the touch screen, the battery and the power switch are also electrically connected with the circuit board unit, and the circuit board unit comprises a voltage stabilizing source unit, a single chip microcomputer, a square wave signal source unit, a frequency selecting analog switch, a. The capacitance type probe is not easy to wear, the circuit is simple, the capacitance value of the probe can be effectively measured, the conductivity resistance of the detector is improved, and the whole detector is portable in design and convenient to use in practice.
Description
Technical Field
The invention relates to the field of soil moisture detection, in particular to a dual-frequency excitation soil moisture detector and a test method thereof.
Background
The capacitance method is the most widely applied technology at present, and the capacitance method is mostly a resonance method, namely a frequency domain reflection method (FDR) and a vector voltage technology to decompose the soil dielectric constant method from the capacitance detection technology point of view, and the commercial products comprise an SM300 sensor in British, GS3, 10HS, EC-5, HydraProbe II sensors in America, M L x and PR2 sensors in British, although the capacitance sensors have commercial products, the capacitance sensors have some defects, the precision is not high, and the soil conductivity is easy to influence, and researches on ECH2O EC-5, SM200 and ThetaProbe M L x indicate that calibration model parameters of the sensors are related to soil texture and conductivity.
At present, a method for improving the conductivity resistance of a sensor is to measure the conductivity of soil simultaneously and realize the measurement according to a conductivity compensation model established by experiments. For example, the low-frequency capacitance soil moisture detection method with conductivity compensation property in patent CN109444227A and the soil-less culture substrate moisture content and conductivity detection sensor in patent CN202421116U are essentially direct current or low-frequency soil conductivity detection and high-frequency soil moisture detection. The other is to increase the excitation frequency of the excitation signal. Research shows that the signal frequency must be more than 500MHz to obtain a soil moisture signal without influence of conductivity. The frequency of the existing capacitance detection technology can reach 100MHz, the frequency is further improved, a higher signal-to-noise ratio is ensured, the technical difficulty is high, and the cost is high. On the other hand, based on the principle of the dielectric polarization process of the conductive substance, in an equivalent lumped parameter model, the ion migration polarization behavior cannot be eliminated by simply increasing the frequency.
This patent designs a capacitance detection technique for this reason based on resistance-capacitance series connection step response principle, proposes to calculate the soil relative permittivity who is used for converting soil moisture content from dual-frenquency response signal, and then measures soil moisture. The double-frequency excitation capacitance type soil moisture detector with better conductivity resistance is provided.
Disclosure of Invention
The invention aims to provide a dual-frequency excitation soil moisture detector and a testing method thereof, and solves the problem that the soil moisture detector is low in testing precision due to poor conductivity resistance of a soil moisture sensor.
In order to achieve the purpose, the invention provides the technical scheme that: including casing, touch-sensitive screen, battery, switch, probe and circuit board unit, touch-sensitive screen and switch are installed to the top on the casing, casing internally mounted has circuit board unit and battery, the probe is installed to the casing lower part, be provided with positive plate and negative plate in the probe, positive plate and negative plate and circuit board unit electricity are connected, touch-sensitive screen, battery and switch also are connected with circuit board unit electricity, circuit board unit includes steady voltage source unit, singlechip, square wave signal source unit, frequency-selecting analog switch, precision resistor R, crest detection unit and temperature sensor.
Furthermore, the probe and the circuit board unit are of an integrated structure and are composed of a printed circuit board, the printed circuit board of the probe is of a 3-layer plate structure, and the middle layer is provided with a probe positive plate and a probe negative plate.
Furthermore, the voltage stabilizing source unit converts the power supply of the battery into the working voltage of the single chip microcomputer and the square wave signal source unit to provide a stable power supply for the single chip microcomputer and the square wave signal source unit, and the voltage stabilizing source unit adopts an AMS1117-3.3V chip.
Further, the single chip microcomputer is provided with a power-on reset module, a crystal oscillator module and an AD module, and the single chip microcomputer adopts an STC15W408AD chip.
Furthermore, the frequency-selecting analog switch receives a control signal of the single chip microcomputer, and then controls the square wave signal source unit to generate square wave signals with different frequencies, and the square wave signal source unit can generate square wave signals with two frequencies.
Furthermore, one end of the precision resistor R is electrically connected with the output end of the square wave signal source unit, and the other end of the precision resistor R is electrically connected with the positive plate of the probe.
Further, the negative plate of the probe is electrically connected with the negative electrode of the power supply.
Further, the wave crest detection unit comprises a detection diode D, a capacitor and a resistor, wherein the capacitor and the resistor are connected in parallel, one end of the capacitor and the resistor after being connected in parallel is electrically connected with a power supply negative electrode, the other end of the capacitor and a cathode of the detection diode D are electrically connected, an anode of the detection diode D is electrically connected with the positive electrode plate, and the detection diode D adopts a BAT15-03W diode.
Further, the temperature sensor adopts an integrated digital temperature sensor chip with a model of TMP 275.
A test method of a dual-frequency excitation soil moisture detector comprises the following steps:
1) setting up a test principle, adopting a first-order RC series circuit steady-state response principle, and under the excitation of square waves, after the charge and the discharge of a capacitor are stabilized, the relation of wave crest and wave trough voltage of the voltage at the end of the capacitor is as follows
UT＝U0+(Us-U0)(1-e-T/RC) (1)
In the formula of UTPeak voltage value on capacitor, U0The value of the voltage at the trough of the capacitor, Us-square wave high level voltage value, T-square wave period, capacitance C comprising stray capacitance ac and capacitance Cx due to soil moisture change, wherein Cx is proportional to the equivalent relative permittivity of the soil as Cx ═ g (2)
In the formula, g is a proportionality coefficient
Formula (1) can be arranged as
UT＝Us+(Us-U0)e-T/(R(ΔC+g))(3)；
2) Establishing a test model, and calibrating the corresponding output signal U under square wave excitation of f1 and f2 frequencies in a known relative dielectric constant solution respectively1，U2Mathematical model of and relation
＝f(U1)|f1 (4)
＝f(U2)|f2 (5)
The formula (4) and the formula (5) are preferably exponential models of the formula (6).
y＝a+b·e(c/(x+d))(6)；
3) Collecting a test signal, controlling a frequency-selecting analog switch by a singlechip to further control a square wave signal source unit to generate two square wave signals with frequencies f1 and f2, and collecting peak voltages of the two square wave signals with frequencies f1 and f 2;
4) processing the test signal, performing signal processing on the two peak voltages to calculate the soil moisture content, wherein the processing of the test signal comprises the following three steps:
the method comprises the following steps: output signal U under excitation of f1 and f2 frequency square wavesf1、Uf2Respectively calculating the corresponding relative dielectric constants according to the calibration model formula (3) and the calibration model formula (4)f1、f2. Apparently as conductive medium soil, calculated according to the formulas (3) and (4)f1、f2The value contains ion migration polarization information, and a large error can occur when the value is directly used for converting the water content of the soil;
step two: selecting a proper soil dielectric constant formula and a proper test frequency F model, preferably a formula (7) model, referring to the change characteristic of the soil dielectric constant with frequency and the mathematical characteristic of an exponential function in the literature, wherein a, b, c and d are undetermined parameters, c is F1, d is F2, and then (F1,f1)、(f2，f1) A and b can be obtained, and when d is 4 times larger than F-c, the formula (7) has a mathematical property that (F) tends to be a stable value, and a is expressed aseffRelative dielectric constant of soil for conversion of water content of soil
Step three: calculating with reference to Topp model equation (8)effThe corresponding volume water content theta of the soil,
in the formula, theta is the volume water content of the soil;
5) and displaying the measurement result, wherein the result in the step 4) is displayed through the touch screen (2).
The invention has the beneficial effects that: the capacitance type probe has good insulation property and is not easy to wear, the circuit of the given peak detection technology is simple, the capacitance value of the probe can be effectively measured, the conductivity resistance of the instrument can be improved based on the processing of a double-frequency excitation response signal, and the whole tester is portable in design and convenient to use in practice.
Drawings
FIG. 1 is a schematic three-dimensional structure of one embodiment of the present invention;
FIG. 2 is a schematic diagram of the operation of the present invention;
FIG. 3 is a block diagram of the circuit board unit circuit structure of the present invention;
fig. 4 is a schematic circuit diagram of a circuit board unit according to an embodiment of the present invention.
Detailed Description
Example 1
As shown in fig. 1-4, the touch screen type temperature measurement device comprises a shell 1, a touch screen 2, a battery 3, a power switch 4, a probe 5 and a circuit board unit 6, wherein the touch screen 2 and the power switch 4 are installed at the top of the shell 1, the circuit board unit 6 and the battery 3 are installed inside the shell 1, the probe 5 is installed at the lower portion of the shell 1, a positive plate 7 and a negative plate 8 are arranged in the probe 5, the positive plate 7 and the negative plate 8 are electrically connected with the circuit board unit 6, the touch screen 2, the battery 3 and the power switch 4 are also electrically connected with the circuit board unit 6, and the circuit board unit 6 comprises a voltage stabilizing source unit 11, a single chip microcomputer 12, a square wave signal source unit 13, a frequency selecting analog switch 14, a precision resistor R35.
The probe 5 and the circuit board unit 6 are of an integrated structure and are composed of printed circuit boards, the printed circuit board of the probe 5 is of a 3-layer plate structure, and the middle layer is provided with a probe positive plate and a probe negative plate.
The voltage stabilizing source unit 11 converts the power supply of the battery 3 into the working voltage of the single chip microcomputer 12 and the square wave signal source unit 13, and provides a stable power supply for the single chip microcomputer 12 and the square wave signal source unit 13, and the voltage stabilizing source unit 11 adopts an AMS1117-3.3V chip.
The single chip microcomputer 12 is a single chip microcomputer with a power-on reset module, a crystal oscillator module and an AD module, and the single chip microcomputer 12 adopts a STC15W408AD chip.
The frequency-selecting analog switch 14 receives a control signal from the single-chip microcomputer 12, and then controls the square-wave signal source unit 13 to generate square-wave signals with different frequencies, and the square-wave signal source unit 13 can generate square-wave signals with two frequencies.
One end of the precision resistor R15 is electrically connected with the output end of the square wave signal source unit 13, and the other end is electrically connected with the positive plate 7 of the probe 5.
The negative plate 8 of the probe 5 is electrically connected with the negative pole of the power supply.
As shown in fig. 4, the peak detecting unit 16 includes a detector diode D, a capacitor and a resistor, the capacitor and the resistor are connected in parallel, one end of the capacitor and the resistor after being connected in parallel is electrically connected to a negative electrode of a power supply, the other end of the capacitor is electrically connected to a negative electrode of the detector diode D, an anode of the detector diode D is electrically connected to the positive electrode plate 7, the detector diode D is a BAT15-03W diode, the capacitor is C6, and the resistor is R5.
The temperature sensor 17 adopts an integrated digital temperature sensor chip with the model of TMP 275.
A test method of a dual-frequency excitation soil moisture detector comprises the following steps:
1) setting up a test principle, adopting a first-order RC series circuit steady-state response principle, and under the excitation of square waves, after the charge and the discharge of a capacitor are stabilized, the relation of wave crest and wave trough voltage of the voltage at the end of the capacitor is as follows
UT＝U0+(Us-U0)(1-e-T/RC) (1)
In the formula of UTPeak voltage value on capacitor, U0The value of the voltage at the trough of the capacitor, Us-square wave high level voltage value, T-square wave period, capacitance C comprising stray capacitance ac and capacitance Cx due to soil moisture change, wherein Cx is proportional to the equivalent relative permittivity of the soil as Cx ═ g (2)
In the formula, g is a proportionality coefficient
Formula (1) can be arranged as
UT＝Us+(Us-U0)e-T/(R(ΔC+g))(3)；
2) Establishing a test model, and calibrating the corresponding output signal U under square wave excitation of f1 and f2 frequencies in a known relative dielectric constant solution respectively1，U2Mathematical model of and relation
＝f(U1)|f1 (4)
＝f(U2)|f2 (5)
The formula (4) and the formula (5) are preferably exponential models of the formula (6).
y＝a+b·e(c/(x+d))(6)；
The known relative dielectric constant solutions are preferably shown in Table 1.
TABLE 1
3) Collecting a test signal, controlling a frequency-selecting analog switch 14 by a singlechip 12 so as to control a square wave signal source unit 13 to generate two square wave signals with frequencies f1 and f2, and collecting peak voltages of the two square wave signals with frequencies f1 and f 2;
4) processing the test signal, performing signal processing on the two peak voltages to calculate the soil moisture content, wherein the processing of the test signal comprises the following three steps:
the method comprises the following steps: output signal U under excitation of f1 and f2 frequency square wavesf1、Uf2Respectively calculating the corresponding relative dielectric constants according to the calibration model formula (3) and the calibration model formula (4)f1、f2. Apparently as conductive soil media, calculated according to equations (3) and (4)f1、f2The value contains ion migration polarization information, and a large error can occur when the value is directly used for converting the water content of the soil;
step two: selecting a proper soil dielectric constant formula and a proper test frequency F model, preferably a formula (7) model, referring to the change characteristic of the soil dielectric constant with frequency and the mathematical characteristic of an exponential function in the literature, wherein a, b, c and d are undetermined parameters, c is F1, d is F2, and then (F1,f1)、(f2，f1) A and B are obtained,b, equation (7) has the mathematical property that (F) tends to stabilize the value a when F-c is greater than 4 times d, and a is noted aseffRelative dielectric constant of soil for conversion of water content of soil
Step three: calculating with reference to Topp model equation (8)effThe corresponding volume water content theta of the soil,
in the formula, theta is the volume water content of the soil;
5) and displaying the measurement result, wherein the result in the step 4) is displayed through the touch screen (2).
According to the double-frequency excitation soil moisture detector and the test method thereof, the capacitance type probe is good in insulation performance and not prone to abrasion, the given peak detection technology circuit is simple, the capacitance value of the probe can be effectively measured, the conductivity resistance of the detector can be improved based on the processing of double-frequency excitation response signals, and the whole tester is portable in design and convenient to use in practice.
It should be understood that the above examples are only for clarity of illustration and are not intended to limit the embodiments. Other variations and modifications will be apparent to persons skilled in the art in light of the above description. And are neither required nor exhaustive of all embodiments. And obvious variations or modifications therefrom are within the scope of the invention.
Claims (10)
1. The utility model provides a soil moisture detector of dual-frenquency excitation which characterized in that: including casing (1), touch-sensitive screen (2), battery (3), switch (4), probe (5) and circuit board unit (6), touch-sensitive screen (2) and switch (4) are installed to casing (1) top, casing (1) internally mounted has circuit board unit (6) and battery (3), probe (5) are installed to casing (1) lower part, be provided with positive plate (7) and negative plate (8) in probe (5), positive plate (7) and negative plate (8) are connected with circuit board unit (6) electricity, touch-sensitive screen (2), battery (3) and switch (4) also are connected with circuit board unit (6) electricity, circuit board unit (6) are including steady voltage source unit (11), singlechip (12), square wave signal source unit (13), frequency selection analog switch (14), precision resistance R (15), A peak detection unit (16) and a temperature sensor (17).
2. The dual frequency excitation soil moisture detector of claim 1, wherein: the probe (5) and the circuit board unit (6) are of an integrated structure and are composed of printed circuit boards, the printed circuit board of the probe (5) is of a 3-layer plate structure, and a probe positive plate (7) and a probe negative plate (8) are arranged in the middle layer.
3. The dual frequency excitation soil moisture detector of claim 1, wherein: the voltage stabilizing source unit (11) converts a power supply of the battery (3) into working voltages of the single chip microcomputer (12) and the square wave signal source unit (13) to provide a stable power supply for the single chip microcomputer (12) and the square wave signal source unit (13), and the voltage stabilizing source unit (11) adopts an AMS1117-3.3V chip.
4. The dual frequency excitation soil moisture detector of claim 1, wherein: the single chip microcomputer (12) is provided with a power-on reset module, a crystal oscillator module and an AD module, and the single chip microcomputer (12) adopts a chip with the model STC15W408 AD.
5. The dual frequency excitation soil moisture detector of claim 1, wherein: the frequency-selecting analog switch (14) receives a control signal of the singlechip (12) to further control the square wave signal source unit (13) to generate square wave signals with different frequencies, and the square wave signal source unit (13) can generate square wave signals with two frequencies.
6. The dual frequency excitation soil moisture detector of claim 1, wherein: one end of the precision resistor R (15) is electrically connected with the output end of the square wave signal source unit (13), and the other end of the precision resistor R is electrically connected with the positive plate (7) of the probe (5).
7. The dual frequency excitation soil moisture detector of claim 1, wherein: and the negative plate (8) of the probe (5) is electrically connected with the negative electrode of the power supply.
8. The dual frequency excitation soil moisture detector of claim 1, wherein: the wave crest detection unit (16) comprises a detection diode D, a capacitor and a resistor, wherein the capacitor and the resistor are connected in parallel, one end of the parallel connection is electrically connected with a power supply cathode, the other end of the parallel connection is electrically connected with a detection diode D cathode, a detection diode D anode is electrically connected with the positive plate (7), and the detection diode D adopts a BAT15-03W diode.
9. The dual frequency excitation soil moisture detector of claim 1, wherein: the temperature sensor (17) adopts an integrated digital temperature sensor chip with the model of TMP 275.
10. The test method of the dual-frequency-excitation soil moisture detector as claimed in claim 1, characterized by comprising the following steps:
1) setting up a test principle, adopting a first-order RC series circuit steady-state response principle, and under the excitation of square waves, after the charge and the discharge of a capacitor are stabilized, the relation of wave crest and wave trough voltage of the voltage at the end of the capacitor is as follows
UT＝U0+(Us-U0)(1-e-T/RC) (1)
In the formula of UTPeak voltage value on capacitor, U0The value of the voltage at the trough of the capacitor, Us-square wave high level voltage value, T-square wave period, capacitance C comprising stray capacitance Δ C and capacitance Cx due to soil moisture change, wherein Cx is proportional to the equivalent relative permittivity of the soil
Cx＝g (2)
In the formula, g is a proportionality coefficient
Formula (1) can be arranged as
UT＝Us+(Us-U0)e-T/(R(ΔC+g))(3)；
2) Establishing a test model, and calibrating the corresponding output signal U under square wave excitation of f1 and f2 frequencies in a known relative dielectric constant solution respectively1，U2Mathematical model of and relation
＝f(U1)|f1 (4)
＝f(U2)|f2 (5)
The formula (4) and the formula (5) are preferably exponential models of the formula (6).
y＝a+b·e(c/(x+d))(6)；
3) The method comprises the steps that test signals are collected, the single chip microcomputer (12) controls a frequency-selecting analog switch (14) to further control a square wave signal source unit (13) to generate two square wave signals with frequencies f1 and f2, and peak voltages of the two square wave signals with frequencies f1 and f2 are collected;
4) processing the test signal, performing signal processing on the two peak voltages to calculate the soil moisture content, wherein the processing of the test signal comprises the following three steps:
the method comprises the following steps: output signal U under excitation of f1 and f2 frequency square wavesf1、Uf2Respectively calculating the corresponding relative dielectric constants according to the calibration model formula (3) and the calibration model formula (4)f1、f2. Apparently as conductive soil media, calculated according to equations (3) and (4)f1、f2The value contains ion migration polarization information, and a large error can occur when the value is directly used for converting the water content of the soil;
step two: selecting a proper soil dielectric constant formula and a proper test frequency F model, preferably a formula (7) model, referring to the change characteristic of the soil dielectric constant with frequency and the mathematical characteristic of an exponential function in the literature, wherein a, b, c and d are undetermined parameters, c is F1, d is F2, and then (F1,f1)、(f2，f1) A and b can be obtained, and when d is 4 times larger than F-c, the formula (7) has a mathematical property that (F) tends to be a stable value, and a is expressed aseffIs used forRelative dielectric constant of soil for converting water content of soil
Step three: calculating with reference to Topp model equation (8)effThe corresponding volume water content theta of the soil,
in the formula, theta is the volume water content of the soil;
5) and displaying the measurement result, wherein the result in the step 4) is displayed through the touch screen (2).
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| CN115639408A (en) * | 2022-12-23 | 2023-01-24 | 中大智能科技股份有限公司 | High-precision soil conductivity self-adaptive monitoring system |
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| CN115639408A (en) * | 2022-12-23 | 2023-01-24 | 中大智能科技股份有限公司 | High-precision soil conductivity self-adaptive monitoring system |
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