CN105842261B - A kind of soil moisture measurement sensor and implementation method based on time-domain transmission - Google Patents
A kind of soil moisture measurement sensor and implementation method based on time-domain transmission Download PDFInfo
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- CN105842261B CN105842261B CN201610230213.2A CN201610230213A CN105842261B CN 105842261 B CN105842261 B CN 105842261B CN 201610230213 A CN201610230213 A CN 201610230213A CN 105842261 B CN105842261 B CN 105842261B
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- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
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Abstract
The invention discloses a kind of soil moisture measurement sensor and implementation method based on time-domain transmission, sensor includes: signal source, moisture perceptron, phase-shifter and soil probe；Signal source is for generating three road high_frequency sine wave signals, third road high-frequency signal gives soil probe for perceiving soil moisture information, is sent after probe returns to moisture perceptron and revolves signal more than obtaining phase difference relevant with Soil moisture to the progress phase bit comparison of first via high-frequency signal.In order to eliminate interference caused by signal amplitude decaying, measurement sensor increases the quadrature branch of 90 degree of phase difference, that is the second road high-frequency signal obtains phase difference dextrorotation signal as orthogonal reference signal and soil probe return path signal phase bit comparison after 90 degree of phase shifts of phase-shifter, and two-way phase signal is sent to processing display measured value in single-chip microcontroller.Measurement accuracy of the present invention is high, measured value is stable, is easily achieved and at low cost, and performance is but reached advanced world standards, and is with a wide range of applications.
Description
Technical field
The present invention relates to electronic technology fields, and in particular to a kind of soil moisture measurement sensor based on time-domain transmission and
Implementation method.
Background technique
Soil moisture measurement mainstream technology is both at home and abroad at present: Time Domain Reflectometry (Time Domain Reflectrometry,
Abbreviation TDR) method, standing wave ratio (Standing Wave Ratio, abbreviation SWR) method, frequency domain decomposition (Frequency Domain
Decomposition, abbreviation FD) method and time-domain transmission (Time Domain Transmissometry, abbreviation TDT) method.
Soil moisture sensor based on TDR principle be in current soil moisture measurement method generally receive and it is most widely used
Apparatus measures method.Measurement accuracy is high, and fast response time, measurement range is wide, does not need generally to demarcate, easy to operate, field
It all can be used with indoor, TDR measurement result is influenced very little by Soil salinity, in measurement high organic content soil, high clay, mine
When the especially high or especially low soil of object content soil, bulk density, need to demarcate.TDR is maximum the disadvantage is that circuit is complicated, cost
Height exists significantly difficult due to lacking high-precision, chip quick, integrated level is high in the realization of hardware circuit.
FD method is also a kind of measurement method of dielectric method, is using vector voltage measuring technique, since the dielectric of soil is normal
Number ε is the complex function of frequency, and imaginary part is related with the conductivity of soil, and real part is related with soil moisture content.The measurement of FD method
As a result influenced by soil property bigger, cost is also high more than standing-wave ratio method, and the too late TDR of measurement accuracy.
The advantages of SWR method is that measurement accuracy is higher, and fast response time is insensitive to electromagnetic interference, at low cost, can be inserted immediately
Enter to use and can also be embedded to stationary monitoring use for a long time.The disadvantage is that precision is still not as good as TDR, and is affected by soil types, to not
It is demarcated with soil, measured value is unstable.
Although TDT method working principle is all the time difference propagated in soil media by measuring electromagnetic wave compared with TDR
Soil dielectric constant is measured, but is very different in principle.One frequency electromagnetic waves are different, and what TDR was selected is high-frequency impulse,
Contain profuse harmonic wave in signal source, each harmonic wave amplitude and phase in transmission process can all occur different degrees of variation and
Lead to wave distortion, distorts by comparing reflected signal rising edge to determine soil moisture content information.And TDT signal source
It is the sine wave of single-frequency, does not cause to reflect by probe open-end, is extracted by the circuit of signal integrity
Include the Soil moisture in phase change, therefore can determine that soil moisture content is believed by analyzing its phase information both
Breath.TDR probe end unlike secondly is open circuit, and signal is because terminating impedance mismatch reflects, and the probe of TDT is
Closed circuit, signal do not reflect, repeatedly anti-due to theoretically eliminating signal caused by probe end impedance mismatch
It penetrates, many influence measurement accuracy, the factor of stability such as incidence wave and back wave interfere with each other, signal loss, therefore to soil
The detection and extraction of earth moisture information minor change have high-precision, high reliability, high sensitivity and high stability.TDT's
Advantage is that time measuring circuit can not depend on chip inlet and may be implemented yet, and equipment cost is low, measurement accuracy and technical performance
It is suitable with TDR.The disadvantage is that probe can not be made into the stylus structure of terminal open circuit, it is necessary to which middle measurement of placing into the soil can only fix
Monitoring use, and be embedded to when it is larger to soil disturbance, destroy the structure of original-state soil, also can not pass through and probe connection electricity
Road directly measures soil moisture.
Summary of the invention
It is at low cost since can not to meet measuring circuit simultaneously easy to accomplish for domestic existing soil moisture measurement method, it surveys
The problem of accuracy of measurement is high, measured value stabilization and plug and play, the present invention proposes a kind of soil moisture measurement based on time-domain transmission
Sensor and implementation method.
In a first aspect, the present invention proposes a kind of soil moisture measurement sensor based on time-domain transmission, comprising: high-frequency signal
Source, moisture perceptron, phase-shifter and soil probe；
The signal source for generate three road high-frequency signals and respectively with the moisture perceptron, the phase-shifter and described
Soil probe is separately connected, and first via high-frequency signal is sent to the moisture perceptron as same phase reference signal, the second tunnel
High-frequency signal is sent to the phase-shifter, and third road high-frequency signal is sent to the soil probe；
The phase-shifter is connect with the moisture perceptron, for carrying out at 90 degree of phase shifts to second road high-frequency signal
Reason is sent to the moisture perceptron as orthogonal reference signal；
The soil probe is connect with the moisture perceptron, for receiving third road high-frequency signal, and described in warp
Moisture perceptual signal line transmission on soil probe platelet to perceive soil moisture information, then soil probe is returned
The soil moisture perceptual signal send to the moisture perceptron；
What the moisture perceptron was used to return the same phase reference signal, the orthogonal reference signal and the probe
Soil moisture perceptual signal comprising soil moisture information carries out phase comparative analysis, obtains the phase relevant to Soil moisture
Potentiometer signal.
Preferably, the signal source includes high frequency oscillator and buffer amplifier；
The high frequency oscillator is connect by coupled capacitor with the buffer amplifier, for generating the height of three road 200MHz
Frequency sine-wave；
The buffer amplifier is connect with the multiplier, the phase-shifter and the soil probe simultaneously, for exporting
The high_frequency sine wave signal of the three roads 200MHz, and first via high-frequency signal is exported as the same phase reference signal to described
Multiplier, second road high-frequency signal to the phase-shifter and third road high-frequency signal are to the soil probe.
Preferably, the moisture perceptron includes multiplier, low-pass filter；
The multiplier connects with the signal source, the phase-shifter, the soil probe and the low-pass filter simultaneously
It connects, is carried out for the high-frequency signal comprising moisture information to the received same phase reference signal and soil probe passback
It is multiplied, while being multiplied to the received orthogonal reference signal with the soil probe return path signal, using described low
Bandpass filter；The remaining rotation signal and sinusoidal signal of the phase difference comprising moisture information are respectively obtained,
Preferably, further includes: variable gain instrument amplifier；
The variable gain instrument amplifier is used to increase the relevant phase signal of the received soil water content
Benefit amplifies processing.
Second aspect, the present invention also propose a kind of soil moisture measurement implementation method based on time-domain transmission, comprising:
Frequency electromagnetic waves upload sowing time in soil probe transmission line, due to having wrapped up soil media (soil around transmission line
Permittivity ε, between the dielectric constant of water and air), spread speed is slack-off, equivalent to increase one compared in air
A time delay, i.e. frequency electromagnetic waves are propagated in the soil increases a phase difference.The phase difference is the function of soil moisture content.This
Invention extracts the phase difference in frequency electromagnetic waves, the i.e. method of coherent demodulation using the method for phase demodulating.In order to guarantee precision,
It is demodulated using two-way, i.e. in-phase component, the quadrature component of two-way difference demodulation phase difference, then two-way result is made comparisons to exclude
Interference caused by amplitude fading to phase difference.
Signal source generates the identical high-frequency signal of three tunnel amplitude and phase, and the same phase reference signal of the first via is sent to
Moisture perceptron, the second road high-frequency signal are sent to phase-shifter, and third road high-frequency signal is sent to soil probe；
The phase-shifter carries out 90 degree of phase-shift processings to second road high-frequency signal, obtains orthogonal reference signal, and will
The orthogonal reference signal is sent to the moisture perceptron；
The soil probe receives third road high-frequency signal, passes through the moisture perceptual signal route on probe platelet
It is defeated, to acquire soil moisture information and send the soil moisture perceptual signal of soil probe passback back to the moisture sense
Know device；
The moisture perceptron, which perceives the same phase reference signal, the orthogonal reference signal and the soil moisture, to be believed
After number being handled, the phase signal value comprising soil moisture information is obtained.
Preferably, the signal source is made of three groups of LC high-frequency oscillating circuits with buffer amplifier respectively, per height all the way
Frequency oscillator circuit is to be capacitively coupled to buffering by the sine wave of the pure 200MHz of collector LC resonance circuit output frequency
Amplifier, buffer amplifier are made of voltage follower；
First high-frequency signal of signal source, which is used as, is sent to moisture perceptron, the second road high-frequency signal hair with phase reference signal
It send to phase-shifter, third road high-frequency signal is sent to soil probe.
Preferably, the moisture perceptron is to the same phase reference signal, the orthogonal reference signal and the soil water
After dividing perceptual signal to be handled, the phase signal value of soil moisture information is obtained, further comprises:
The multiplier of the moisture perceptron is to the received same phase reference signal and the soil moisture perceptual signal
It is multiplied, while being multiplied to the received orthogonal reference signal with the soil moisture perceptual signal, and pass through respectively
Wave filter filters out high fdrequency component and obtains the cosine component and sinusoidal component of phase difference；
The cosine component and sinusoidal component of the phase difference are sent to the single-chip microcontroller in the digital display circuit of sensor respectively
In go operation, obtain soil water content value.
Preferably, the cosine component of the phase difference and sinusoidal component are sent to respectively in the digital display circuit of sensor
Operation is gone in single-chip microcontroller, after obtaining soil water content value, further includes:
Variable gain instrument amplifier amplifies processing to the received phase signal comprising soil moisture information.
As shown from the above technical solution, the present invention generates three road high-frequency oscillation signals by signal source, wherein signal all the way
By soil probe return after perceived soil moisture information, in addition two-way respectively as coherent demodulation same phase reference signal and
Orthogonal reference signal further obtains the moisture content of soil to be measured to signal processing by moisture perceptron, and circuit uses state
Interior general-purpose device can be realized, at low cost, and measurement accuracy is high, while measured value is stablized, and performance reaches the first water inlet of external TDR
It is flat, but price is significantly less than same kind of products at abroad price, so that domestic soil moisture measurement sensor eliminates the reliance on import, simultaneously
Circuit can select on domestic market general-purpose device to realize, convenient for wideling popularize.
Detailed description of the invention
In order to more clearly explain the embodiment of the invention or the technical proposal in the existing technology, to embodiment or will show below
There is attached drawing needed in technical description to be briefly described, it should be apparent that, the accompanying drawings in the following description is only this
Some embodiments of invention for those of ordinary skill in the art without creative efforts, can be with
Other attached drawings are obtained according to these figures.
Fig. 1 be the structure of a kind of soil moisture measurement sensor based on time-domain transmission that one embodiment of the invention provides and
Signal flow diagram；
Fig. 2 is the structure for another soil moisture measurement sensor based on time-domain transmission that one embodiment of the invention provides
And signal flow diagram；
Fig. 3 is a kind of schematic diagram for soil moisture measurement method based on time-domain transmission that one embodiment of the invention provides；
Fig. 4 is a kind of circuit diagram for soil moisture measurement method based on time-domain transmission that one embodiment of the invention provides；
Fig. 5 is the upper branch voltage and water content relationship for a kind of moisture aware circuit that an embodiment of the present invention provides
Curve graph；
Fig. 6 is that a kind of upper branch phase difference for moisture aware circuit that an embodiment of the present invention provides and water content close
It is curve graph；
Fig. 7 is a kind of process for soil moisture measurement implementation method based on time-domain transmission that one embodiment of the invention provides
Schematic diagram.
Specific embodiment
With reference to the accompanying drawing, the specific embodiment of invention is further described.Following embodiment is only used for more clear
Illustrate to Chu technical solution of the present invention, and not intended to limit the protection scope of the present invention.
Fig. 1 shows the structure and letter of a kind of soil moisture measurement sensor based on time-domain transmission provided in this embodiment
Number flow graph, structure includes: signal source 41, moisture perceptron 42, phase-shifter 43 and soil probe 44；
The signal source 41 for generate three road high-frequency signals and respectively with the moisture perceptron 42, the phase-shifter 43
It is separately connected with the soil probe 44, is sent to the moisture perceptron for first via high-frequency signal as same phase reference signal
42, the second road high-frequency signal is sent to the phase-shifter 43, and third road high-frequency signal is sent to the soil probe 44；
The phase-shifter 43 is connect with the moisture perceptron 42, for carrying out 90 degree of phases to second road high-frequency signal
It moves processing and is used as orthogonal reference signal, and the orthogonal reference signal is sent to the moisture perceptron 42；
The soil probe 44 is connect with the moisture perceptron 42, for receiving third road high-frequency signal, and is passed through
Moisture perceptual signal line transmission on the soil probe platelet to perceive soil moisture information, then is sent to the moisture sense
Know device 42；
The moisture perceptron 42 is used for three road signal gatherings, with the soil moisture from the passback of soil probe back
Perceptual signal carries out phase comparative analysis with the same phase reference signal, the orthogonal reference signal respectively, so that extraction includes
The phase signal value of soil moisture information.
The present embodiment generates three road high-frequency oscillation signals by signal source, wherein all the way as directly defeated with phase reference signal
Enter to moisture perceptron, second road signal is by phase-shifter 90 degree of phase-shift processings of progress as orthogonal reference signal, third road letter
Number by soil probe perceive soil moisture information return to moisture perceptron, further by moisture perceptron to signal processing
The moisture content of soil to be measured is obtained, circuit can be realized using domestic general-purpose device, and at low cost, measurement accuracy is high, survey simultaneously
Magnitude is stablized, and performance reaches the advanced level of international similar product, but price is significantly less than same kind of products at abroad price, so that state
Interior soil moisture measurement sensor eliminates the reliance on import, while circuit can select on domestic market general-purpose device to realize, just
In wideling popularize.
As the optinal plan of the present embodiment, as shown in Fig. 2, wherein signal source 51 (being not drawn into Fig. 2), moisture perceptron
52 (being not drawn into Fig. 2), phase-shifter 53 and soil probe 54 are same as the previously described embodiments, and this embodiment is not repeated.
The signal source 51 includes high frequency oscillator 511 and buffer amplifier 512；
The high frequency oscillator 511 and the buffer amplifier 512 connect, for generating the high frequency sinusoidal of three road 200MHz
Wave；
The buffer amplifier 512 connects with the multiplier 521, the phase-shifter 53 and the soil probe 54 simultaneously
It connects, for exporting the high_frequency sine wave signal of the three roads 200MHz, and exports the same phase reference signal to the multiplier
521, second road high-frequency signal to the phase-shifter 53 and third road high-frequency signal to the soil probe 54.
Signal source will generate three road 200MHz high-frequency signals simultaneously and be supplied respectively to moisture perceptron as the same of phase demodulating
Phase reference signal, orthogonal reference signal and probe input signal, tri- road semaphore request amplitude of Qie Dui is identical, phase stringent synchronization.
It is also required that the pure single, waveform of signal frequency cannot distort, output amplitude reaches 2V or so.In order to meet conditions above letter
Number source is made of LC high frequency oscillator and buffer amplifier two-stage.
The moisture perceptron 52 includes multiplier 521 and low-pass filter 522；
The multiplier 521 simultaneously with the signal source 51, the phase-shifter 53, the soil probe 54 and the low pass
Filter 522 connects, and for being multiplied to the received same phase reference signal with the soil moisture perceptual signal, passes through
Obtained after the low-pass filter 522 comprising soil moisture information phase difference cosine signal, while to it is received it is described just
It hands over reference signal to be multiplied with the soil moisture perceptual signal, is obtained after the low-pass filter comprising soil moisture
The sinusoidal signal of the phase difference of information；
Multiplication processing is carried out to signal by multiplier, signal is filtered by low-pass filter to obtain soil to be measured
Moisture value, circuit is easy to accomplish, at low cost, and measurement accuracy is high, while measured value is stablized, convenient for wideling popularize.
Further, further includes: variable gain instrument amplifier 55；
The variable gain instrument amplifier 55 is connect for received described comprising soil with the low-pass filter 522
The signal of earth moisture value amplifies processing.
By amplifying processing to the signal comprising Soil moisture, subsequent processing and display can be convenient for.
It is further preferred that further include: display 56；
The display 56 shows Soil moisture for receiving the amplified signal comprising Soil moisture.
Soil moisture is shown by display, it can be convenient for for intuitively obtaining Soil moisture.
It is right below in order to further explain the soil moisture measurement sensor provided in this embodiment based on time-domain transmission
Soil moisture measurement principle is described:
The foundation of soil moisture measurement is the dielectric constant of speed and probe surrounding soil that electromagnetic wave is propagated along probe
Square root is inversely proportional, therefore the dielectric constant of soil can be measured according to the speed of Electromagnetic Wave Propagation.Topp according to this survey by method
Gas-solid-liquid mixture permittivity ε in soil was obtained, and then has found different type using Numerical regression analysis method
Empirical equation between the water content and dielectric constant of soil:
W=-5.3 × 10-2+2.92*10-2ε-5.5×10-4ε2+4.3×10-6ε3 (1)
Wherein W is soil volumetric water content, and ε is soil apparent dielectric constant.Due to the medium around probe be soil and
The mixture of water, (air medium dielectric constant microwave medium is 1 to dielectric constant, close to 80) in water, if soil between air and water
It is completely dried, then ε will be 2 to 4, if the 25% of soil volume is water, ε nearly 11~12.To agriculture soil
For earth, the volumetric(al) moisture content for depending mainly on the size of soil of ε.The schematic diagram of soil moisture measurement method as shown in figure 3, by
Signal source generates a high_frequency sine wave signalWherein A is the amplitude of high-frequency signal, ωcFor angle
Frequency,For first phase, three parameters are constant, for simplicity it can also be assumed that initial phaseFrom soil probe
The input of the end A, probe are inserted into soil to be measured, and probe end is not open circuit, and frequency electromagnetic waves are defeated to the end probe B along probe circuit
Out.Assuming that probe physical length is L, then the path length of frequency electromagnetic waves within the probe is 2L, and transmission time is Δ t.Therefore,
Electromagnetic wave increases a phase delay in the phase ratio A point of B pointAmplitude fading is B, at this time the high-frequency signal of B point are as follows:
The propagation time of frequency electromagnetic waves within the probe are as follows:
Wherein v is the speed that electromagnetic wave is propagated in the soil, and c is the speed (3 × 10 that electromagnetic wave is propagated in a vacuum8m/
S), ε is the apparent dielectric constant of soil mixture.
Know that the dielectric constant of soil is related with water content by Topp formula, thereforeIt can be expressed as the letter of water content
Number, i.e.,Formula (2) is brought into obtain:
It can be seen that in the high-frequency signal of B point by formula (5) due to including soil moisture information in phase.Referring to communication skill
The phase-modulation of art, formula (5) can be seen that high-frequency signal uA(t) moisture information has been loaded into high frequency after the probe in soil
In the phase of signal, therefore by extracting the available soil moisture information of phase difference.
Using the method for difference phase demodulation, i.e. uB(t) carrier wave of same frequency (is exactly that signal source generates herein
High-frequency signal uA(t) it is multiplied:
It is obtained by low-pass filter:
Wherein, k is amplitude attenuation factor, is constant to determining water content k, therefore passes through measurement low-pass filter output
Just it can find outIt is direct current signal, to obtain moisture value.
Wherein, in Fig. 2 signal not only have a phase difference after the multiplier of moisture perceptron and low-pass filter and
And amplitude also has decaying, decay factor is k, although constant, but if to calculate phase differenceIt must be it is to be understood that decay factor
k.Therefore actual circuit needs to increase measuring circuit all the way in design and is 90 degree of phase shift.Signal source is for soil moisture sense
Know that device provides three tunnel high frequency electromagnetic wave signals, for extracting soil moisture information.The height of a 200MHz is mainly generated by crystal oscillator
Frequency oscillator signal is divided into three tunnels, generates the pure sine wave of a frequency by the frequency-selective network of a 200MHz respectively, all the way
Soil probe is given, 90 degree of phase shifts will be passed through all the way by addition having in two-way.
The corresponding circuit diagram of the present embodiment is as shown in figure 4, signal source will generate three road 200MHz high-frequency signals difference simultaneously
Supply same phase reference signal, orthogonal reference signal and probe input signal of the moisture perceptron as phase demodulating, tri- tunnel Qie Dui
Semaphore request amplitude is identical, phase stringent synchronization.It is also required that the pure single, waveform of signal frequency cannot distort, export width
Degree reaches 2V or so.It is formed to meet conditions above signal source circuit by LC oscillating circuit and buffer amplifier circuit two-stage.The
Level-one transistor T1 is the high frequency oscillator of 200MHz, and collector loop is made of LC resonance circuit L1, C4, C5 as negative
It carries to guarantee that output signal frequency is tuned at 200MHz, starting of oscillation signal is that have source crystal oscillator to generate process by 200MHz.First order vibration
It swinging the coupled capacitor of output and is output to second level buffer amplifier, T2 is follower, to keep 200MHz frequency purer, transmitting
Pole also uses the circuit LC frequency-selective network.R15, R16 are biasing resistor, and output is coupled by C9 and exported.
The present embodiment is realized by the multiple hardwares circuit to TDT soil moisture measurement method, and has carried out a large amount of research and development
The verifying of comparative experiments progress scheme.I.e. measurement uses phase-modulation, demodulation method in the communication technology: frequency electromagnetic waves are in soil
During earth probe transmission, soil moisture information has been arrived in the phase of high-frequency signal by aqueous soil coated by dielectric, can be seen
At phase modulation process, therefore from the moisture information that can include in complete extraction phase using phase demodulating method.This survey
Amount method is with other method differences in summary: other methods are to find out the relationship of soil water content and probe impedance, are visited
Needle impedance is usually complex impedance, therefore ignores imaginary impedance in actual measurement in order to which physics can be realized, result causes to extract
Moisture value can lost part information.The present embodiment extracts moisture information using phase demodulating, demodulates the phase information come
Whole moisture informations are contained, therefore precision is high.Measurement hardware circuit, letter are designed according to phase demodulation circuit in hardware realization
Number source uses three tunnel two-stage transistor amplifiers, and multiple frequency-selecting tuning ensure that three road output-consistences are good, frequency is pure
It is single；Moisture perceptron overcomes single channel phase bit comparison high frequency signal amplitude fading in TDT method using the bit comparison of two-way phase
Phase change can not be determined together by tangling with phase delay；Hardware circuit is realized using domestic general-purpose device, is substantially reduced
Research and development costs, and it is easily achieved achievements conversion and product promotion.
It is pure that soil moisture measurement sensor provided in this embodiment based on time-domain transmission can generate three tunnel frequencies simultaneously
Net high_frequency sine wave signal single, the amplitude-phase distortion factor is small, and three tunnel signal amplitudes, phase equalization are very good；Water
Divide perceptron that can detect the decaying of the high frequency signal amplitude after soil probe and phase delay simultaneously；High performance high frequency is hard
Part circuit uses domestic common discrete component, and circuit may be implemented and very useful, and cost is relatively low, does not depend on import
Component, easy to manufacture, application easy to spread；It must be by other tools when common time-domain transmission TDT soil probe measurement
Soil is excavated and is measured again in sensor probe is placed into the soil, the present embodiment and the special sticker type for aiming at its design
Insertable soil probe matches can be with plug and play, convenient and efficient, and can effectively shield two-way frequency electromagnetic waves
Interfere with each other, eliminate probe end impedance mismatch caused by signal multiple reflections, incidence wave and back wave interfere with each other,
Numerous influence measurement accuracy, the factor of stability such as signal loss, thus to soil moisture information minor change detection with
Extracting has high-precision, highly sensitive and high stability.It ensure that height using multiple measures on high frequency hardware circuit simultaneously
It is the stabilization of frequency signal, reliable.
In order to measure the measurement accuracy of the soil moisture measurement sensor provided in this embodiment based on time-domain transmission, below
By being verified:
Time difference of the frequency electromagnetic waves in soil probe:ε is relative dielectric constant, in air
It is 1, is 80 in water.L is probe length 120cm.It can prolong because dielectric constant becomes larger when probe is placed on transmission time in water
It is long.
Experimentation:
It inserts a probe into the beaker of full scale 500ml and fixed, gradually adds water toward beaker, first time 50ml,
Increase 10ml every time later, since length of the probe in water gradually increases, the high frequency signal transmission time is also gradually increased, i.e., high
The phase difference of frequency signal becomes larger, and adds water 10ml every time, the 6th pin output voltage of amplifier AD623 in measuring circuit is such as
Table 1.
The 6th pin output voltage of 1 amplifier AD623 of table
Data processing:
Upper branch output voltage values=kcosSince this voltage value includes amplitude fading, so calculating its phase
Value needs normalized first, i.e. voltage value is removed in maximum value 1054, makes voltage value between -1~1.Then to normalization
Anticosine operation is carried out, in calculated phase values it is noted that its phase continuity, therefore the phasometer formula after π should be
2π-arccos
Data processed result is as it can be seen in figures 5 and 6, be respectively upper branch voltage and water content graph of relation and upper branch phase
Potential difference and water content graph of relation.
Measurement result analysis:
It data processing phase and water content relation curve will be fitted above, and obtain fitting function:
Y=3E-08x6-4E-06x5+0.0001x4-0.0023x3+0.0165x2-0.0455x+1.8981
Wherein, y is phase difference, and x is water content.The matched curve is bent by the relationship as phase difference from now on and water content
Line, according to measurement voltage come inverting water content value when measurement.
Measured value and matched curve are calculated
Coefficient R:
Wherein, n is the measurement number of samples for regression analysis；xiIt is the native water content measured in i-th of sampling point；X is institute
There is being averaged for sampling point measured value；yiIt is the water being calculated according to regression equation by the signal phase difference measured in i-th of sampling point
Content prediction value；Y is being averaged for all sampling point predicted values.
Coefficient R (also uses R sometimes2Instead of) reflect correlation between regression equation and measurement data, R2Value get over
Close to 1, illustrate that the correlation between regression equation and measurement data is better.R2Dimensionless, value range is between 0~1.
Root-mean-square error RMSE:
R2=0.9948, RMSE=0.011 are calculated to obtain, illustrates that measurement accuracy has reached desired value.
Fig. 7 shows a kind of soil moisture measurement implementation method based on time-domain transmission of one embodiment of the invention offer
Flow diagram, comprising:
S101, signal source generate the identical high-frequency signal of three tunnel amplitude and phase, and by the same phase reference signal of the first via
It is sent to moisture perceptron, the second road high-frequency signal is sent to phase-shifter, and third road high-frequency signal is sent to soil probe；
S102, the phase-shifter carry out 90 degree of phase-shift processings as orthogonal reference signal to second road high-frequency signal,
And the orthogonal reference signal is sent to the moisture perceptron；
S103, the soil probe receive third road high-frequency signal, through the moisture perceptual signal line on probe platelet
Road transmission, to acquire soil moisture information and send the soil moisture perceptual signal of soil probe passback back to the water
Divide perceptron, includes soil moisture information in the soil moisture perceptual signal；
S104, the moisture perceptron are to the same phase reference signal, the orthogonal reference signal and the soil moisture
After perceptual signal is handled, the phase signal value comprising soil moisture information is obtained.
As the optinal plan of the present embodiment, step S104 further comprises:
S1041, the moisture perceptron multiplier to the received same phase reference signal and the soil moisture sense
Know that signal is multiplied, while being multiplied to the received orthogonal reference signal with the soil moisture perceptual signal, and
High fdrequency component, which is filtered out, through wave filter respectively obtains the cosine component and sinusoidal component of phase difference；
S1042, the cosine component of the phase difference and sinusoidal component are sent to respectively in the digital display circuit of sensor
Operation is gone in single-chip microcontroller, obtains the sinusoidal signal of the phase difference of soil moisture information.
Specifically,
The signal source is made of three groups of LC high-frequency oscillating circuits with buffer amplifier respectively, per higher-order of oscillation electricity all the way
Road is to be capacitively coupled to buffer amplifier by the sine wave of the pure 200MHz of collector LC resonance circuit output frequency,
Buffer amplifier is made of voltage follower；
The high-frequency signal that the set of circuits of signal source generates, which is used as, is sent to moisture perceptron with phase reference signal, and second
Road high-frequency signal is sent to phase-shifter, and third road high-frequency signal is sent to soil probe.
Further, further includes:
S105, variable gain instrument amplifier amplify place to the received phase signal comprising soil moisture information
Reason.
Further, further includes:
S106, display receive the amplified signal comprising Soil moisture, and show Soil moisture.
Soil moisture measurement method described in the present embodiment based on time-domain transmission can be used for executing the sensor reality
Example is applied, principle is similar with technical effect, and details are not described herein again.
In specification of the invention, numerous specific details are set forth.It is to be appreciated, however, that example of the invention can be
Without being practiced in the case where these details.In some instances, well-known methods, structures and techniques have not been shown in detail,
So as not to obscure the understanding of this specification.
Claims (8)
1. a kind of soil moisture measurement sensor based on time-domain transmission characterized by comprising signal source, moisture perceptron,
Phase-shifter and soil probe；
The signal source for generates identical three tunnel amplitudes, high-frequency signal of phase stringent synchronization and respectively with moisture perception
Device, the phase-shifter and the soil probe are separately connected, and are sent to institute for first via high-frequency signal as same phase reference signal
Moisture perceptron is stated, the second road high-frequency signal is sent to the phase-shifter, and third road high-frequency signal is sent to the soil probe；
The phase-shifter is connect with the moisture perceptron, is made for carrying out 90 degree of phase-shift processings to second road high-frequency signal
For orthogonal reference signal, and the orthogonal reference signal is sent to the moisture perceptron；
The soil probe is connect with the moisture perceptron, for receiving third road high-frequency signal and visiting through the soil
Moisture perceptual signal line transmission on needle platelet, to perceive soil moisture information, then will be described in the passback back of soil probe
Soil moisture perceptual signal is sent to the moisture perceptron；
The moisture perceptron is used for three road signal gatherings, perceives letter with from the soil moisture of soil probe passback back
Phase comparative analysis is carried out with the same phase reference signal, the orthogonal reference signal number respectively, so that extracting includes the soil water
Divide the phase signal value of information.
2. sensor according to claim 1, which is characterized in that the signal source includes high frequency oscillator and Hyblid Buffer Amplifier
Device；
The high frequency oscillator is connect by coupled capacitor with the buffer amplifier, for generating the high frequency of three road 200MHz just
String wave；
The buffer amplifier is connect with multiplier, the phase-shifter and the soil probe simultaneously, for exporting three tunnel
The high_frequency sine wave signal of 200MHz, and export first via high-frequency signal as the same phase reference signal to the multiplier,
Second road high-frequency signal is to the phase-shifter and third road high-frequency signal to the soil probe.
3. sensor according to claim 2, which is characterized in that the moisture perceptron includes multiplier and low-pass filtering
Device；
Moisture perceptron extracts the phase difference in high-frequency signal comprising soil moisture information using the method for differential coherent demodulation；
The multiplier is separately connected with the signal source, the phase-shifter, the soil probe and the low-pass filter, is used
In being multiplied to the received same phase reference signal with the soil moisture perceptual signal, after the low-pass filter
It filters out high fdrequency component and obtains the cosine signal of the phase difference comprising soil moisture information, while the received orthogonal reference is believed
It number is multiplied with the soil moisture perceptual signal, filters out high fdrequency component after the low-pass filter and obtain soil moisture
The sinusoidal signal of the phase difference of information.
4. sensor according to claim 3, which is characterized in that further include: variable gain instrument amplifier；
The variable gain instrument amplifier is connect with the low-pass filter, for carrying out at power amplification to received signal
Reason.
5. a kind of implementation method based on the described in any item soil moisture measurement sensors of claim 1-4, which is characterized in that
Include:
Signal source generates the identical high-frequency signal of three tunnel amplitude and phase, and using first via high-frequency signal as same phase reference signal
It is sent to moisture perceptron, the second road high-frequency signal is sent to phase-shifter, and third road high-frequency signal is sent to soil probe；
The phase-shifter to second road high-frequency signal carry out 90 degree of phase-shift processings as orthogonal reference signal, and by it is described just
Reference signal is handed over to be sent to the moisture perceptron；
The soil probe receives third road high-frequency signal, through the moisture perceptual signal line transmission on probe platelet, with
Perception soil moisture information simultaneously send the soil moisture perceptual signal of soil probe passback back to the moisture perceptron；
The moisture perceptron to the same phase reference signal, the orthogonal reference signal and the soil moisture perceptual signal into
After row processing, the phase signal value comprising soil moisture information is obtained.
6. according to the method described in claim 5, it is characterized in that, the signal source respectively by three groups of LC high-frequency oscillating circuits with
Buffer amplifier is constituted, and is the 200MHz pure by collector LC resonance circuit output frequency per high-frequency oscillating circuits all the way
Sine wave, is capacitively coupled to buffer amplifier, and buffer amplifier is designed as voltage follower；
First high-frequency signal of signal source, which is used as, is sent to moisture perceptron with phase reference signal, and the second road high-frequency signal is sent to
Phase-shifter, third road high-frequency signal are sent to soil probe.
7. according to the method described in claim 6, it is characterized in that, the moisture perceptron is to the same phase reference signal, institute
It states orthogonal reference signal and after the soil moisture perceptual signal handled, obtains the phase difference comprising soil moisture information and believe
Number value, further comprise:
Multiplier is multiplied to the received same phase reference signal with the soil moisture perceptual signal, while to received
The orthogonal reference signal is multiplied with the soil moisture perceptual signal, and filters out high fdrequency component through wave filter respectively and obtain
To the cosine component and sinusoidal component of phase difference；
The cosine component and sinusoidal component of the phase difference are sent to respectively in the single-chip microcontroller in the digital display circuit of sensor
Operation obtains the sinusoidal signal of the phase difference of soil moisture information.
8. the method according to the description of claim 7 is characterized in that the cosine component and sinusoidal component of the phase difference are sent respectively
The operation into the single-chip microcontroller in the digital display circuit of sensor, obtain the phase difference of soil moisture information sinusoidal signal it
Afterwards, further includes:
Variable gain instrument amplifier amplifies processing to the received phase signal comprising soil moisture information.
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| CN108776170B (en) * | 2018-08-15 | 2023-07-14 | 郭丽 | High-precision moisture measuring instrument based on TDR and phase detection technology |
| CN109342515A (en) * | 2018-11-29 | 2019-02-15 | 中国水利水电第七工程局有限公司 | Concrete mix moisture percentage measuring device and its measurement method based on TDT with phase bit comparison |
| CN111521650B (en) * | 2020-03-13 | 2022-11-04 | 山东航向电子科技有限公司 | Phase extraction method of direct signal and reflected signal in soil humidity measurement |
| CN113125516B (en) * | 2021-04-01 | 2023-04-14 | 青岛盛瀚色谱技术有限公司 | Wide-range constant-temperature bipolar pulse conductance detector |
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Effective date of registration: 20191211 Address after: Room 32010, No. 3, Shuangqing Road, Haidian District, Beijing 100083 Patentee after: IDS New Tech Co., Ltd Address before: 100193 Beijing Old Summer Palace West Road, Haidian District, No. 2 Patentee before: China Agricultural University |