CN204679442U - The soil moisture content sensor that differential signal intertexture controls - Google Patents

The soil moisture content sensor that differential signal intertexture controls Download PDF

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Publication number
CN204679442U
CN204679442U CN201520310787.1U CN201520310787U CN204679442U CN 204679442 U CN204679442 U CN 204679442U CN 201520310787 U CN201520310787 U CN 201520310787U CN 204679442 U CN204679442 U CN 204679442U
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China
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moisture content
soil moisture
signal
difference
soil
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CN201520310787.1U
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傅文渊
凌朝东
李国刚
刘一平
林薇
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Huaqiao University
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Huaqiao University
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Abstract

The utility model provides the soil moisture content sensor that a kind of differential signal intertexture controls, and comprising: difference Interleaving control circuit, waveform generator, MCU, power-switching circuit and electrode module; Described difference Interleaving control circuit produces the anti-phase modulation signal of two-way, and feeds back in MCU by electrode output signal change difference; Power-switching circuit provides the different electrical power needed for sensing system, ensures system worked well; Waveform generator produces the excitation input signal V required for difference Interleaving control circuit in1and V in2; Soil moisture content change causes electrode module to polarize, and by trigger flip-flop, the soil moisture content of change is converted into cyclophysis signal, utilizes the cycle of MCU characteristic signals measuring period, and then obtain soil moisture content.This sensor signal total harmonic distortion is less, and output signal linearity performance significantly improves, and reduces the impact of the spuious material of soil on output signal simultaneously.

Description

The soil moisture content sensor that differential signal intertexture controls
Technical field
The utility model relates to a kind of soil moisture content sensor.
Background technology
Along with automatic electronic and sensor technology development, soil moisture content detects the important indicator becoming and weigh industrial or agricultural automaticity.Research soil moisture detection can automatic Prediction and judge plant law of needing the water, improves agriculture automatic electronic process and instructs and save agricultural irrigation water.Traditional soil moisture content measuring method has mass method, NEUTRON METHOD, gamma-rays method, electric-resistivity method, capacitance method, time domain reflectometry, nuclear magnetic resonance method etc.Wherein, mass method principle is simple, and precision is high, has become the measuring method of demarcation.But its measurement has nonreversibility, cannot repeated test.Nuclear magnetic resonance method, NEUTRON METHOD and gamma-rays method adopt radioactive measuring principle, limit its application.Traditional electric-resistivity method is simple to operate, real-time, but measuring accuracy is lower.Time domain reflectometry due to theoretical property and practicality all very strong, and there is advantages such as not destroying sample, fast and easily operation, be use more, development a kind of method measuring soil moisture content faster in recent years, but the method test is comparatively complicated, cost is higher.It is measure soil dielectric constant that capacitance method measures soil moisture content essence.But must contact soil because soil moisture content sensor electrode exports, therefore the non-linear factor of soil can make useful signal distortion, by electrode coupling to sensor internal, causes sensor circuit performance to reduce.Have no the harmonics restraint of pertinent literature report research based on moisture sensor electrode output signal at present.
Based on this, herein in conjunction with electric-resistivity method and capacitance method, propose a kind of method measuring soil moisture content, and devise the soil moisture content sensor controlled based on differential signal intertexture on this basis.Base counter design difference Interleaving control circuit when utilizing integrated.This circuit comprises two Novel bistable triggers, is exported by trigger and is loaded into sensor electrode.When the water-cut variation of soil by electrode-feedback to trigger flip-flop, the difference in change according to feedback loop output signal calculates soil moisture content.Meanwhile, in order to suppress the harmonic distortion of electrode-feedback signal, devise double-width grinding both-end output difference form-separating, and founding mathematical models is to associated circuit components optimal design and simulating, verifying.Finally, sensor hardware structure is built according to the mathematical model set up.The result of actual measurement shows, this sensor has good performance.
Utility model content
Technical problem underlying to be solved in the utility model is to provide a kind of soil moisture content sensor, and signal total harmonic distortion is less, and output signal linearity performance significantly improves, and reduces the impact of the spuious material of soil on output signal simultaneously.
In order to solve above-mentioned technical scheme, the utility model provides the soil moisture content sensor that a kind of differential signal intertexture controls, and comprising: difference Interleaving control circuit, waveform generator, MCU, power-switching circuit and electrode module;
Described difference Interleaving control circuit produces the anti-phase modulation signal of two-way, and feeds back in MCU by electrode output signal change difference; Power-switching circuit provides the different electrical power needed for sensing system, ensures system worked well; Waveform generator produces the excitation input signal V required for difference Interleaving control circuit in1and V in2; Soil moisture content change causes electrode module to polarize, and by trigger flip-flop, the soil moisture content of change is converted into cyclophysis signal, utilizes the cycle of MCU characteristic signals measuring period, and then obtain soil moisture content.
In a preferred embodiment: described difference Interleaving control circuit comprises integrated form timer U 1and U 2; Described U 1and U 2thr end and tri hold respectively with described input signal V in1and V in2connect; Described U 1and U 2con end with gnd end between connect filter capacitor C respectively 2and C 4; Described U 1and U 2rst end with vcc hold be connected after respectively by dropping resistor network and tuning capacitance C 1and C 3access gnd end after connecting; Described U 1and U 2dis end be connected with soil to be detected; Described U 1and U 2out end be connected with described electrode module.
In a preferred embodiment: described input signal V in1and V in2amplitude equal, phase 180 °.
In a preferred embodiment: electrode module is made up of two panels 8mm x 120mm metal; Two panels metal electrode spacing is 12mm; Every plate electrode is according to the copper-base being uniformly distributed etching 1mm.
In a preferred embodiment: described dropping resistor network is first dropping resistor network resistor R1, the R3 be connected in series; And second dropping resistor network R2, the R4 be connected in series.
Compared to prior art, the technical solution of the utility model possesses following beneficial effect:
The utility model, in conjunction with electric-resistivity method and capacitance method, proposes a kind of method measuring soil moisture content, and devises the soil moisture content sensor controlled based on differential signal intertexture on this basis.Base counter design difference Interleaving control circuit when utilizing integrated.This circuit comprises two Novel bistable triggers, is exported by trigger and is loaded into sensor electrode.When the water-cut variation of soil by electrode-feedback to trigger flip-flop, the difference in change according to feedback loop output signal calculates soil moisture content.Meanwhile, in order to suppress the harmonic distortion of electrode-feedback signal, devise double-width grinding both-end output difference form-separating, and founding mathematical models is to associated circuit components optimal design and simulating, verifying.Finally, sensor hardware structure is built according to the mathematical model set up.The result of actual measurement shows, this sensor has good performance.
Accompanying drawing explanation
Fig. 1 is the system architecture diagram of soil moisture content sensor in the utility model preferred embodiment;
Fig. 2 is difference Interleaving control circuit figure in the utility model preferred embodiment;
Fig. 3 is the sectional view of electrode module in the utility model preferred embodiment;
Equivalent circuit diagram when Fig. 4 is difference Interleaving control circuit charging in the utility model preferred embodiment;
Equivalent circuit diagram when Fig. 5 is difference Interleaving control circuit electric discharge in the utility model preferred embodiment;
Fig. 6 is the spectrogram of traditional sensors output signal;
Fig. 7 is soil moisture content sensor output signal spectrum figure in the utility model preferred embodiment;
Fig. 8 is sensor output voltage and soil moisture content variation relation figure in the utility model preferred embodiment;
Fig. 9 is frequency input signal when being 1kHz cinnamon soil, moisture soil and soil moisture content variation relation figure;
Figure 10 is frequency input signal when being 10kHz cinnamon soil, moisture soil and soil moisture content variation relation figure;
Embodiment
Hereafter in conjunction with the accompanying drawings and embodiments the utility model is described further.
Present embodiments provided the soil moisture content sensor that a kind of differential signal intertexture controls, mainly comprise difference Interleaving control circuit, waveform generator, MCU, power-switching circuit and electrode module, concrete framework as shown in Figure 1.Difference Interleaving control circuit produces the anti-phase modulation signal of two-way, and electrode output signal change difference is fed back in MCU.Power-switching circuit provides the different electrical power needed for sensing system, ensures system worked well.Waveform generator produces the excitation input signal required for difference Interleaving control circuit.
Soil moisture content change causes electrode polarization in difference Interleaving control circuit, by trigger flip-flop, the soil moisture content of change is converted into cyclophysis, utilizes the MCU measuring-signal cycle, and then obtain soil moisture content.
Due to the specific inductive capacity of specific inductive capacity medium such as such as mineral particle in soil of soil moisture, and specific inductive capacity is followed the increase of soil moisture content and increases.Therefore, soil moisture content sensor only needs exploring electrode impedance variation, can detect the change numerical value of soil moisture content.Result of study shows, signal source frequency, soil moisture content, soil types and the dielectric property of soil mineral content to soil have an impact, wherein with signal source frequency having the greatest impact to dielectric property.Signal distortion is the important indicator of gauge signal frequency characteristic.Non-linear the cause harmonic component of signal due to circuit component in transmitting procedure produces, and is coupled to output by internal circuit, causes original signal distortion, affects signal transmission quality.The important indicator of gauge signal degree of distortion is total harmonic distortion, and it characterizes the number percent of all additional harmonic distortion sums.Difference Interleaving control circuit in this paper effectively can increase the Spurious Free Dynamic Range of signal, reduces signal distortion, reduces total harmonic distortion, improves signal transmission quality.
Fig. 2 is difference Interleaving control circuit structural drawing, base timer when wherein U1 and U2 is integrated.The model that the present embodiment is selected is 555 timers of En Zhi Pu semiconductor company research and development, and it is the integrated device circuit that a kind of analog-and digital-function combines, and inside comprises basic RS filpflop, voltage comparator, power output stage and impact damper etc.Because time this, base timer is analog-and digital-hybrid circuit, the voltage range therefore worked is large, output can with CMOS, TTL, LVDOS and analog level compatible.Two input signals are respectively Vin1 and Vin2, and output signal is respectively Vout1 and Vout2.The thr end of described U1 with U2 is connected with described input signal Vin1 and Vin2 respectively with tri end; Filter capacitor C2 and C4 is connected respectively between the con end of described U1 and U2 and gnd end; Rst end and the vcc of described U1 with U2 access gnd after being connected with tuning capacitance C1 and C3 respectively by dropping resistor network after holding and being connected and hold, simultaneously as the frequency control unit of base timer time integrated.The dis end of described U1 with U2 is connected with soil to be detected; The out end of described U1 with U2 is connected with described electrode module.
It is equal that input end produces amplitude by waveform generator, the Differential Input V of phase 180 degree in1and V in2.Intrinsic noise and interference can be offset, the even item harmonic wave factor of Spurious Free Dynamic Range of simultaneously eliminating the effects of the act.Signal input has a strong impact on the dielectric property of A, B 2.Adopt differential signal can suppress the even item harmonic wave of input signal as input, improve the linearity of signal.When soil moisture content changes, A, B two end signal change according to the larger linearity, avoid the impact of the factor such as soil mineral impurity, and then the measuring accuracy of base timer when improving integrated.
Electrode module sectional view as shown in Figure 3, is made up of two panels 8mm x 120mm metal.Two panels metal electrode spacing is 12mm.Every plate electrode, according to the copper-base being uniformly distributed etching 1mm, increases the ability of detection polarization effect, effectively reduces the line of electric force edge effect of plate condenser, improves measuring accuracy.
The principle of work of above-mentioned difference Interleaving control circuit is as follows: as input end signal V in1and V in2phase 180 degree, therefore V in1and V in2inverse state is presented, i.e. V at the level numerical value of synchronization in1during for high level, V in2for low level, and V in1during for low level, V in2for high level.Obtained, as input signal V by the principle of base timer time integrated in2voltage amplitude is less than 1/3V ddtime, internal trigger exports as high level, and therefore out port exports as high level.If input signal amplitude continues to increase, if V in2voltage amplitude is greater than 2/3V ddtime, internal trigger is in puts number state, exports as low level.Now input voltage continues to increase, and circuit maintains this state and do not change.When input voltage amplitude is at interval 1/3V dd~ 2/3V ddtime, output voltage maintains input voltage amplitude 1/3V ddtime state.
As input signal V in2voltage amplitude is less than 1/3V ddtime, difference Interleaving control circuit is equivalent to D end open circuit, electric capacity C 1two ends electromotive force increases, and circuit is to C 1charging, simultaneously electric capacity C 4pass through impedance Z xand R m1to release electric charge.Equivalent electrical circuit as shown in Figure 4.As input signal V in2voltage amplitude is greater than 2/3V ddtime, difference Interleaving control circuit is equivalent to A end open circuit, electric capacity C 4two ends electromotive force increases, and power supply is to C 4charging.Meanwhile, time integrated, the D of base timer holds conducting, electric capacity C 1pass through impedance Z xand R m2to release electric charge.Equivalent electrical circuit as shown in Figure 5.
The equivalent circuit theory of difference Interleaving control circuit as shown in Figure 4, wherein Z xfor the equiva lent impedance of soil moisture detection, R m1and R m2base timer equivalent internal resistance when being respectively integrated.In charged state, electric capacity C 4the initial value u (0 of upper voltage -) being not equal to zero, then the Laplace transform result of this capacitance voltage equivalence is u (s)=I (s)/(sC 4)+u (0 -)/s, I (s) is the electric current by this electric capacity.During charged state, C 4both end voltage constantly raises, C 1both end voltage passes through Z xand R m1electric discharge, voltage reduces.During discharge condition, C 1both end voltage constantly raises, C 4both end voltage passes through Z xand R m2electric discharge.Charged state C might as well be established 4both end voltage is u 0(s), electric capacity C 1the initial value of upper voltage is u ' (0 -), A and B point voltage is respectively u 0A(s) and u 0B(s).Discharge condition C 4both end voltage is u 1s (), A and B point voltage is respectively u 1A(s) and u 1B(s).
Therefore, C is set 1=C 4, R 3=R 4, R 1=R 2, then soil moisture impedance Z xoutput signal cycle T with difference Interleaving control circuit and meet relational expression,
T = C 1 2 ( R 1 + R 3 ) 2 ( Z x + R 3 ) 2 Z x ( R 1 + R 3 ) + R 1 ( 4 R 1 - 3 R 3 ) · ( V dd - 2 arctan ( 2 ( Z x ( R 1 + R 3 ) + R 1 ( 4 R 1 - 3 R 3 ) ) C 1 ( R 1 + R 3 ) ( Z x + R 3 ) ) ) - - - ( 1 )
When soil moisture changes, sensor electrode detection soil impedance Z xchange, cause the signal period T of difference Interleaving control circuit that respective change occurs.Measure T by MCU controller, soil moisture content change numerical value can be obtained.
In order to verify above-mentioned analysis conclusion, electronic design automation software Mults im is adopted to carry out analog simulation.The condition of emulation setting is C 1=C 4=0.005 μ F, R 3=R 4=4k Ω, R 1=R 2=4k Ω, input signal amplitude is respectively 12V and 12V, and phase place is respectively 0 degree and 180 degree, and signal frequency is 1kHz.
Fig. 5 to be traditional sensors output signal spectrum figure, Fig. 6 be difference that the present embodiment proposes interweaves Soil Moisture Sensor output signal spectrum figure controlled.Spectrum results is obtained by Fourier analysis, and the signal harmonic exponent number of Multsim analog simulation is 15.As can be seen from the figure, when fundamental frequency is 1kHz, when adopting classical single-end circuit structure, the second harmonic voltage amplitude is 0.429V, and three order harmonics voltage amplitudes are 0.852V, and its total harmonic distortion (THD) is 45.05%.When adopting difference Interleaving control circuit structure in this paper, the voltage amplitude of the second harmonic is 0.016V, and three order harmonicses are 1.12V, and its total harmonic distortion is 31.14%.From theorem 2, difference Interleaving control circuit structure in this paper is due at A, B port differential signal each other, and therefore even item harmonic wave will be offset greatly, although three order harmonicses slightly increase, but the total harmonic distortion of circuit system still has larger improvement, its THD decreases 13.91%.
For without loss of generality, the cinnamon soil of In Fujian Province and moisture soil is selected to test.Soil moisture content sensor exports as voltage signal, and this voltage swing is by impacts such as soil moisture content, Dielectric Constant of NaCl Soil characteristic, input signal source and electrode characteristics.Utilize the sensor output voltage of theory calculate to design, physical relationship is such as formula shown in (17).The method of demarcating is selected to carry out the relation of verificating sensor output voltage and soil moisture content, and the corresponding relation of soil impedance and soil moisture content.Test concrete steps are as follows:
1. test Low Soil Temperature is heated to 110 degrees Celsius of oven dry, the duration is 12 hours;
2. will test soil cooling, place closed container 24 hours;
3. adopt the soil of mass method configuration certain ratio, its soil moisture content is respectively 5%, 10%, 15%, 20%, 25%, 27%, 30%, 35%, 38% and 41%;
4. sensor electrode is inserted test soil, electrode needs to submerge in soil, record output voltage;
5., through calculating, obtain the soil impedance of varying input signal frequency and the pass of soil moisture content.Illustrated by Fig. 7, sensor output voltage increases with soil moisture content and presents non-linear change of successively decreasing.
When soil moisture content is 15% ~ 30%, sensor output voltage linear change.Standardization and theory calculate numerical value in this paper are coincide better between 9% ~ 30% in soil moisture content, and error rate is no more than 5%.And cause error rate between water cut 35% ~ 45% comparatively large due to Dielectric Constant of NaCl Soil characteristic, reach 10%.
Fig. 9 and Figure 10 is respectively frequency input signal when being 1kHz and 10kHz, cinnamon soil, moisture soil and soil moisture content variation relation figure.Test result shows, no matter be cinnamon soil or moisture soil, soil impedance reduces with the increase of soil moisture content.Standardization and theory calculate numerical value in this paper have the good goodness of fit on cinnamon soil and moisture soil water cut.Frequency input signal is respectively 1kHz and 10kHz, and when soil moisture content is between 5% ~ 45%, soil impedance test error is no more than 2%.As can be seen here, the Soil Moisture Sensor that difference intertexture in this paper controls is a kind of method of fast speed real-time measurement soil moisture content.
The present embodiment, in conjunction with electric-resistivity method and capacitance method, devises a kind of soil moisture content sensor controlled based on difference interleave circuit.The factor of analyzing influence soil dielectric constant, establishes the mathematical model of difference Interleaving control circuit.Obtain the signal total harmonic distortion comparatively traditional structure minimizing 13.91% of sensor output according to the model set up, output signal linearity performance significantly improves, and reduces the impact of the spuious material of soil on output signal simultaneously.Measured by MCU controller and change by soil impedance the signal period caused, obtain soil moisture content change numerical value.For cinnamon soil and moisture soil, the performance of the soil moisture content sensor adopting the test of 1kHz and 10kHz signal frequency to control based on difference interleave circuit respectively.Test result shows, sensor output voltage increases with soil moisture content and presents non-linear change of successively decreasing, and water cut is that the error between 9% ~ 45% is no more than 10%.Meanwhile, when soil moisture content is between 5% ~ 45%, soil impedance test error is no more than 2%.
Above-described embodiment is only used for further illustrating a kind of soil moisture content sensor of the present utility model; but the utility model is not limited to embodiment; every above embodiment is done according to technical spirit of the present utility model any simple modification, equivalent variations and modification, all fall in the protection domain of technical solutions of the utility model.

Claims (5)

1. a soil moisture content sensor for differential signal intertexture control, is characterized in that comprising: difference Interleaving control circuit, waveform generator, MCU, power-switching circuit and electrode module;
Described difference Interleaving control circuit produces the anti-phase modulation signal of two-way, and feeds back in MCU by electrode output signal change difference; Power-switching circuit provides the different electrical power needed for sensing system, ensures system worked well; Waveform generator produces the excitation input signal V required for difference Interleaving control circuit in1and V in2; Soil moisture content change causes electrode module to polarize, and by trigger flip-flop, the soil moisture content of change is converted into cyclophysis signal, utilizes the cycle of MCU characteristic signals measuring period, and then obtain soil moisture content.
2. the soil moisture content sensor of a kind of differential signal intertexture according to claim 1 control, is characterized in that: described difference Interleaving control circuit comprises integrated form timer U 1and U 2; Described U 1and U 2thr end and tri hold respectively with described input signal V in1and V in2connect; Described U 1and U 2con end with gnd end between connect filter capacitor C respectively 2and C 4; Described U 1and U 2rst end with vcc hold be connected after respectively by dropping resistor network and tuning capacitance C 1and C 3access gnd end after connecting; Described U 1and U 2dis end be connected with soil to be detected; Described U 1and U 2out end be connected with described electrode module.
3. the soil moisture content sensor of a kind of differential signal intertexture according to claim 2 control, is characterized in that: described input signal V in1and V in2amplitude equal, phase 180 °.
4. the soil moisture content sensor of a kind of differential signal intertexture according to claim 2 control, described in is characterized in that: electrode module is made up of two panels 8mm x 120mm metal; Two panels metal electrode spacing is 12mm; Every plate electrode is according to the copper-base being uniformly distributed etching 1mm.
5. the soil moisture content sensor of a kind of differential signal intertexture according to claim 2 control, is characterized in that: described dropping resistor network is first dropping resistor network resistor R1, the R3 be connected in series; And second dropping resistor network R2, the R4 be connected in series.
CN201520310787.1U 2015-05-14 2015-05-14 The soil moisture content sensor that differential signal intertexture controls Expired - Fee Related CN204679442U (en)

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN104914136A (en) * 2015-05-14 2015-09-16 华侨大学 Differential signal interweaving control soil water content sensor

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN104914136A (en) * 2015-05-14 2015-09-16 华侨大学 Differential signal interweaving control soil water content sensor

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