CN201464387U - Phase detection principle-based soil moisture content tester - Google Patents
Phase detection principle-based soil moisture content tester Download PDFInfo
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- CN201464387U CN201464387U CN2009201104905U CN200920110490U CN201464387U CN 201464387 U CN201464387 U CN 201464387U CN 2009201104905 U CN2009201104905 U CN 2009201104905U CN 200920110490 U CN200920110490 U CN 200920110490U CN 201464387 U CN201464387 U CN 201464387U
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Abstract
The utility model relates to a phase detection principle-based moisture content tester, which comprises a high-frequency sine signal generator, a signal separation circuit, a probe, a circulator, a phase detector and the like, wherein the phase detector is used for receiving a parameter signal transmitted by the signal separation circuit and a reflected signal transmitted by the circulator, and outputting a phase difference direct current voltage signal of the parameter signal and the reflected signal to an analogue-to-digital converter; the analogue-to-digital converter is connected with the phase detector and is used for converting the direct current voltage signal generated by the phase detector into a digital signal and inputting the digital signal to a microprocessor; and the microprocessor is used for controlling the working frequency of the high-frequency sine signal generator, calculating the propagation time of a testing signal on the probe according to the digital signal output by the analogue-to-digital converter, and calculating soil moisture content according to the propagation time by utilizing a known empirical formula. The tester of the utility model not only can be technically implemented, but also is low in production cost and easy to popularize and apply at home.
Description
Technical field
The utility model relates to a kind of device for testing water content of soil, relates in particular to a kind of device for testing water content of soil based on phase detection principle.
Background technology
Promotion and application along with the agricultural water conservation technology, in production and scientific research activity, more and more need in real time, monitor fast and exactly soil moisture, to guarantee the irrigation in good time, an amount of to crops, perhaps following soil water regime is predicted, as the reference frame of regional water transfer, water distribution and formulation irrigation project in conjunction with weather forecast.Though existing certain methods and technology (as: oven drying method of weighing, neutron instrument and tensiometer etc.) also are used for monitoring soil moisture, but research and practice show, time-domain reflectomer (Time Domain Reflectometry, be called for short TDR) advantage of aspect such as tool is real-time, quick and accurate in several mensuration soil moisture technology, use the TDR time-domain reflectomer abroad and also play a significant role at aspects such as monitoring landslide, garbage loading embeading, rivers and reservoir dam safety.
Traditional TDR instrument produces one and has minimum rising edge (＜200ps) step voltage signal, it is propagated along the probe that inserts in the soil with form of electromagnetic wave, and be reflected at the end of probe, can obtain whole TDR waveform by the high-speed sampling oscillograph, on the TDR waveform, adopt the bitangent method to determine the time (as shown in Figure 1) that electromagnetic wave is propagated on probe.The apparent dielectric constant Ka of probe surrounding soil is calculated by following formula:
Wherein c is the speed that electromagnetic wave is propagated in a vacuum, and t is the time of electromagnetic wave along the probe propagation in the insertion soil, and L is the physical length of probe.The specific inductive capacity of free water is 80.36 (20 ℃), and the specific inductive capacity of air is 1, and the specific inductive capacity of soil particle is generally 3～5, so the specific inductive capacity of wet soil depends primarily on soil moisture content.Soil moisture content is provided by following experimental formula:
θ
v＝-5.3×10
-2+2.92×10
-2K
a-5.5×10
-4K
a 2+4.3×10
-6K
a 3 (2)
Required IC chip precision and the specification requirement of quick step signal generator, super high-speed A/D converter and the high-accuracy high-resolution time reference that uses in the external time-domain reflectomer (TDR) is higher, and cost is high.The TDR time-domain reflectomer that China produces and R﹠D institution uses at present is mainly from imports (as: Tectronix 1502C, Trase, MP-917, Trime etc.) such as the U.S., Canada and Germany.About 10,000 dollars of the unit price of TDR time-domain reflectomer, the set of equipments price is several ten thousand dollars, is badly in need of designing a kind of same function that possesses at present, but the substituting product solution that design is more reasonable, cost is cheaper.
The utility model content
(1) technical matters that will solve
The purpose of this utility model is to overcome the deficiencies in the prior art, and a kind of device for testing water content of soil based on phase detection principle (TDR) is provided, and not only can realize technically, and price is significantly less than external product, is easy to apply at home.
(2) technical scheme
At above problem, a kind of device for testing water content of soil based on phase detection principle that the utility model proposes comprises:
The high frequency sinusoidal signal generator is used to produce the high frequency sine voltage signal of single-frequency;
Demultiplexing circuit links to each other with described high frequency sinusoidal signal generator, is used for the high frequency sine voltage signal that described high frequency sinusoidal signal generator produces is separated into reference signal and is used for test signal;
Probe is connected with the test signal output terminal of described demultiplexing circuit by concentric cable, and is used for placing soil to be measured with the reflection measurement signal;
Circulator links to each other with described demultiplexing circuit, is used for the signalling channel as described test signal, and as the signalling channel of the reflected signal of described test signal after probe end is reflected;
Phase detectors are connected with circulator with demultiplexing circuit respectively, are used for the reference signal of received signal separation circuit transmission and the reflected signal that circulator sends, and the phase differential d. c. voltage signal of the two is exported to analog to digital conversion circuit;
Analog to digital conversion circuit is connected with described phase detectors, is used for the d. c. voltage signal that phase detectors produce is transformed into input microprocessor after the digital signal;
Microprocessor, be used to control the frequency of operation of described high frequency sinusoidal signal generator, and calculate the travel-time of test signal on probe, and utilize the known experience formula to calculate soil moisture content according to this travel-time according to the digital signal of analog-digital conversion circuit as described output.
Wherein, described high frequency sinusoidal signal generator comprises the phase-locked loop circuit of being made up of quartz oscillator, phase frequency detector, low-pass filter, voltage controlled oscillator and frequency divider.
Wherein, described tester also comprises a microprocessor peripheral circuit, and this peripheral circuit is made up of the LCD demonstration, keyboard, storer, the USB interface that are connected with microprocessor, is used to provide man machine operation interface and data communication interface.
Wherein, the probe needle body of described probe and probe end are covered with the PVC insulating coating that thickness is 1mm.
Wherein, the probe of described probe and the junction of concentric cable be provided with size moderate make that its characteristic impedance in the probing shell material and concentric cable characteristic impedance equate be connected the copper post.
(3) beneficial effect
A kind of new time domain reflecting soil moisture tester based on phase detection principle (TDR) and soil moisture measurement method that this patent utility model provides, not only can realize technically, and product is cheap, and cost is significantly less than external product, is easy to apply at home.
Description of drawings
Fig. 1 is the synoptic diagram that traditional TDR measures the electromagnetic wave propagation time method;
Fig. 2 is a test signal travel path synoptic diagram of the present utility model;
Fig. 3 is the circuit composition frame chart of the utility model device for testing water content of soil;
Fig. 4 is the composition frame chart of the utility model high frequency sinusoidal signal source circuit;
Fig. 5 is the cut-away view of the parallel three bar type band PVC insulation courses probe of present embodiment;
Fig. 6 is the P-TDR system software workflow diagram on the present embodiment microprocessor.
Embodiment
A kind of device for testing water content of soil based on phase detection principle (TDR) and the method thereof that the utility model proposes are described as follows in conjunction with the accompanying drawings and embodiments. and following embodiment only is used to illustrate the utility model; and be not to restriction of the present utility model; the those of ordinary skill in relevant technologies field; under the situation that does not break away from spirit and scope of the present utility model; can also make various variations and modification; therefore all technical schemes that are equal to also belong to category of the present utility model, and scope of patent protection of the present utility model should be limited by each claim.
Traditional TDR instrument produces one and has minimum rising edge (＜200ps) step voltage signal, it is propagated along the probe that inserts in the soil with form of electromagnetic wave, and be reflected at the end of probe, can obtain whole TDR waveform by the high-speed sampling oscillograph, on the TDR waveform, adopt the bitangent method to determine the time (as shown in Figure 1) that electromagnetic wave is propagated on probe.The apparent dielectric constant Ka of probe surrounding soil is calculated by following formula:
Wherein c is the speed that electromagnetic wave is propagated in a vacuum, and t is the time of electromagnetic wave along the probe propagation in the insertion soil, and L is the physical length of probe.The specific inductive capacity of free water is 80.36 (20 ℃), and the specific inductive capacity of air is 1, and the specific inductive capacity of soil particle is generally 3～5, so the specific inductive capacity of wet soil depends primarily on soil moisture content.Soil moisture content is provided by following experimental formula:
θ
v＝-5.3×10
-2+2.92×10
-2K
a-5.5×10
-4K
a 2+4.3×10
-6K
a 3 (2)
As shown in Figure 2, be the travel path synoptic diagram of test signal, the sine voltage signal of the single-frequency that phaselocked loop produces is propagated along concentric cable and probe with form of electromagnetic wave, and is reflected at the end of probe.Circulator is separated reflected signal, enters phase detectors with incoming signal.Phase detectors are converted to d. c. voltage signal with the phase differential of incoming signal and reflected signal, and AD converter is converted to digital quantity with analog voltage signal and sends into CPU and handle.
One row are sinusoidal wave to arrive same points along two different propagated, and the mistiming of propagating on their phase differential and two paths is directly proportional:
Wherein:
Be phase differential; The mistiming of Δ t for propagating; F is a sine wave freuqency; T is a sine wave period.
As the sine wave of f=500MHz, T=2ns will make the time measurement error less than 50ps, need only be no more than 9 ° by phase measurement error.
The maximin of the specific inductive capacity of soil, water, air mixture is known, and the length of probe can determine according to actual needs, and the probe long with 15cm is example, and maximum duration and shortest time that electromagnetic wave is propagated along probe differ 8ns.This patent utility model use single-frequency sine wave signal as test signal, and adopt the TDR soil moisture measurement method of phase-detection commercial measurement electromagnetic wave propagation time.
As shown in Figure 3, be circuit composition frame chart based on Time Domain Reflectometry (TDR) device for testing water content of soil of phase detection principle.
The sine wave signal that the high_frequency sine wave signal source produces propagates into probe along concentric cable, end at probe produces reflection, reflection wave is propagated along probe and concentric cable, in circulator, be separated, and entering phase measurement and amplitude measurement module respectively with reference signal, the DC voltage that phase detecting module produces is transformed into the digital signal input microprocessor through digital to analog converter.The peripheral circuit of microprocessor is made up of LCD demonstration, keyboard, storer, USB interface.
As shown in Figure 4, it is the composition frame chart of the utility model high frequency sinusoidal signal source circuit, the phase-locked loop circuit that use is made up of quartz oscillator, phase frequency detector, low-pass filter, voltage controlled oscillator and frequency divider is as signal generator, output frequency can be controlled by microprocessor, range of adjustment 300MHz～1GHz, minimal adjustment step-length 0.2MHz.
Time Domain Reflectometry (TDR) soil moisture tester based on phase detection principle is improved on the basis of the parallel three bar types probe that traditional TDR system adopts usually, on three stainless steel probe rods and the head (end) of probe rod all to have covered thickness be the PVC insulating coating of 1mm, the scope that the probe impedance that causes with the variation that reduces because of soil moisture content changes, in addition, insulating coating can also reduce the influence of soil conductivity to phase measurement.Also do meticulous design in the probe and the junction of concentric cable, made the scope at the discontinuous position of impedance dwindle greatly, thereby further improved the precision that soil moisture content is measured.
As shown in Figure 5, be the cut-away view of parallel three bar type band PVC insulation courses probe, the part of detecting of probe is three parallel metal rods, and is long, diameter, and adjacent two interrod spacings are L, d, D/2 has covered the PVC insulation course that thickness is on the every rod.Metal bar extend in the probing shell, use screw that it is connected with concentric cable, middle metal bar links to each other with the inner wire of concentric cable, the metal bar of both sides links to each other with the outer conductor of concentric cable, size by suitable selection probe and concentric cable junction copper post, make its characteristic impedance in PVC medium (being the probing shell material) equate, thereby reduce test signal emission herein, improve measuring accuracy with the concentric cable characteristic impedance.
As shown in Figure 6, for running on the P-TDR system software workflow diagram on the utility model microprocessor, its major function is: the phase differential and the voltage amplitude that obtain incoming signal and reflected signal by analog to digital conversion circuit, the time that the calculating electromagnetic wave signal is propagated on sensor probe and the damping capacity of signal obtain soil volumetric(al) moisture content and conductivity by updating formula; Provide man-machine interface by LCD display module and keyboard, show soil moisture and results of conductivity measurement and working state of system, and various running parameters are set; Measurement result is saved in the FLASH storer so that check and upload to computing machine later on; With the computing machine communication, make further analyzing and processing so that systematic parameter is set and measurement data is uploaded to computing machine by computing machine.
Common output according to phase detectors can only obtain the phase differential between-180～180 °, because for random phase difference
Differ the phase differential in several cycles with it
, the output of phase detectors is identical.In order to solve the uncertain problem of this complete cycle issue, can take following method: make the output frequency of signal source change a less value
Δω supposes being changed to of the phase differential that causes like this
Δθ, promptly signal frequency be ω and ω+
ΔThe phase differential of correspondence is respectively during ω
With
Because other condition does not become, so t in both cases
t, t
rValue be identical, according to formula
Can get:
Because
Δω is very little, so
ΔThe value of θ also very little (between-180～180 °);
Δω can get according to actual needs on the occasion of and negative value, so
Δθ also can be just can be negative.Like this, by right
ΔThe value of ω is carried out suitable selection and just can be guaranteed
With
Identical complete cycle issue is arranged, so
Δθ does not just have the uncertain problem of complete cycle issue (its complete cycle issue is 0).
ΔAfter the value of θ is determined, again according to formula (0-2) by ω and
ΔThe value of ω just can calculate
Accurate size.
Time Domain Reflectometry (TDR) soil moisture tester based on phase detection principle has very high precision in the measurement of signal propagation time, the average error in the time range of 0～12ns between P-TDR measurement result and the calculated value is less than 10ps.
Studies show that based on Time Domain Reflectometry (TDR) soil moisture tester of phase detection principle the measurement of soil moisture content is had very high precision, root-mean-square error is less than 0.02m
3/ m
3, its performance and traditional PDR soil moisture test macro are suitable.
The soil texture has certain influence to Time Domain Reflectometry (TDR) the soil moisture tester measurement result based on phase detection principle, if but the widely different soil of quality is divided three classes, the soil of each type uses a specific calibration formula, can ignore the influence of soil property when then surveying the soil volumetric(al) moisture content.If specific soil is carried out independent demarcation, can reach higher precision based on Time Domain Reflectometry (TDR) soil moisture tester of phase detection principle.
Claims (5)
1. the device for testing water content of soil based on phase detection principle is characterized in that, described tester comprises:
The high frequency sinusoidal signal generator is used to produce the high frequency sine voltage signal of single-frequency;
Demultiplexing circuit links to each other with described high frequency sinusoidal signal generator, is used for the high frequency sine voltage signal that described high frequency sinusoidal signal generator produces is separated into reference signal and is used for test signal;
Probe is connected with the test signal output terminal of described demultiplexing circuit by concentric cable, and is used for placing soil to be measured with the reflection measurement signal;
Circulator links to each other with described demultiplexing circuit, is used for the signalling channel as described test signal, and as the signalling channel of the reflected signal of described test signal after probe end is reflected;
Phase detectors are connected with circulator with demultiplexing circuit respectively, are used for the reference signal of received signal separation circuit transmission and the reflected signal that circulator sends, and the phase differential d. c. voltage signal of the two is exported to analog to digital conversion circuit;
Analog to digital conversion circuit is connected with described phase detectors, is used for the d. c. voltage signal that phase detectors produce is transformed into input microprocessor after the digital signal;
Microprocessor, be used to control the frequency of operation of described high frequency sinusoidal signal generator, and calculate the travel-time of test signal on probe, and utilize the known experience formula to calculate soil moisture content according to this travel-time according to the digital signal of analog-digital conversion circuit as described output.
2. device for testing water content of soil as claimed in claim 1 is characterized in that described high frequency sinusoidal signal generator comprises the phase-locked loop circuit of being made up of quartz oscillator, phase frequency detector, low-pass filter, voltage controlled oscillator and frequency divider.
3. device for testing water content of soil as claimed in claim 1, it is characterized in that, described tester also comprises a microprocessor peripheral circuit, this peripheral circuit is made up of the LCD demonstration, keyboard, storer, the USB interface that are connected with microprocessor, is used to provide man machine operation interface and data communication interface.
4. device for testing water content of soil as claimed in claim 1 is characterized in that, the probe needle body of described probe and probe end are covered with the PVC insulating coating that thickness is 1mm.
5. soil water amount tester as claimed in claim 3, it is characterized in that, the probe of described probe and the junction of concentric cable be provided with size moderate make that its characteristic impedance in the probing shell material and concentric cable characteristic impedance equate be connected the copper post.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN2009201104905U CN201464387U (en) | 2009-08-11 | 2009-08-11 | Phase detection principle-based soil moisture content tester |
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| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN2009201104905U CN201464387U (en) | 2009-08-11 | 2009-08-11 | Phase detection principle-based soil moisture content tester |
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| CN201464387U true CN201464387U (en) | 2010-05-12 |
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN103048364A (en) * | 2012-11-28 | 2013-04-17 | 华南农业大学 | Soil moisture content measuring device and method based on frequency characteristic of RC (Remote Control) network |
| CN105371792A (en) * | 2014-08-25 | 2016-03-02 | 广西南宁西格汇居电子科技有限公司 | Turning axis digital phase distinguishing measurement method |
-
2009
- 2009-08-11 CN CN2009201104905U patent/CN201464387U/en not_active Expired - Lifetime
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN103048364A (en) * | 2012-11-28 | 2013-04-17 | 华南农业大学 | Soil moisture content measuring device and method based on frequency characteristic of RC (Remote Control) network |
| CN105371792A (en) * | 2014-08-25 | 2016-03-02 | 广西南宁西格汇居电子科技有限公司 | Turning axis digital phase distinguishing measurement method |
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|---|---|---|---|
| C14 | Grant of patent or utility model | ||
| GR01 | Patent grant | ||
| AV01 | Patent right actively abandoned |
Granted publication date: 20100512 Effective date of abandoning: 20090811 |