CN205607894U - Soil moisture measuring soil probe based on time domain transmission - Google Patents

Abstract

The utility model relates to a soil moisture measuring soil probe based on time domain transmission, it includes probe perception board, moisture perception transmission line and shell, probe perception board front end is provided with preceding through -hole, and probe perception board is 3 layers of PCB board, and moisture perception transmission line middle part is passed preceding through -hole, the welding of moisture perception transmission line is in on the signal line on the upper and lower surface of probe perception board, form signal transmission path, the shell is made by hard metal, and the shell package wraps the preceding, left of probe perception board and right three side, and the upper surface and the lower surface of probe perception board expose the perception moisture information that is used for, the metal casing is connected with the ground wire of probe perception board. The utility model discloses simple structure can plug -and -play, insert soil after, probe perception board and moisture perception transmission line are abundant to be contacted with soil, can sensitive ground perception moisture information. Metal casing had both guaranteed the firm of probe with the ground wire of perception board is continuous, had detached the interference to high frequency signal again, had improved the reliability of sensor.

Description

A kind of soil probe of soil moisture measurement based on time-domain transmission

Technical field

This utility model relates to soil moisture measurement technology, particularly relates to the soil probe of a kind of soil moisture measurement based on time-domain transmission.

Background technology

In soil moisture measurement mainstream technology the most both at home and abroad it is: time domain reflectometry (Time Domain Reflectrometry, be called for short TDR) method, standing wave ratio (Standing Wave Ratio, be called for short SWR) method, frequency domain decomposition method (Frequency Domain Decomposition, and time-domain transmission (Time Domain Transmissometry, be called for short TDT) method FD).Soil moisture sensor based on TDR principle is generally to accept and most widely used apparatus measures method in current soil moisture measurement method.Certainty of measurement is high, fast response time, measure wide ranges, typically need not demarcate, easy and simple to handle, field and indoor all can use, and shortcoming maximum for TDR is that circuit is complicated, cost is high, due to the chip lacking high accuracy, quick, integrated level is high, in the realization of hardware circuit, therefore there is difficulty significantly.The Wang Yiming of China Agricultural University in 2009 instructs Wang Kedong to have employed a kind of substitution method (being referred to as P-TDR for the time being): sinusoidal wave by single-frequency substitutes pulse square wave, " rising edge comparing square wave calculates time difference " is substituted by the method for " the most sinusoidal wave phase contrast calculates the transmission time difference of high-frequency signal accurately ", successfully have developed domestic TDR soil water measuring instrument, its precision has reached international most advanced level.The measurement result of frequency domain decomposition method FD method is affected bigger by soil property, and cost is also high more than standing-wave ratio method, and certainty of measurement is not as good as TDR.Standing wave ratio SWR method: advantage is that certainty of measurement is higher, fast response time is insensitive to electromagnetic interference, low cost, can immediately insert use and also can imbed stationary monitoring use for a long time.Shortcoming be precision still not as good as TDR, and affected by soil types relatively big, different soils demarcated, measured value is unstable.

Time-domain transmission (Time Domain Transmissometry, it is called for short TDT) method, although its operation principle is all by measuring the time difference measurements soil dielectric constant that electromagnetic wave is propagated in soil media compared with TDR, but is very different in principle.One frequency electromagnetic waves is different, what TDR selected is high-frequency impulse, containing profuse harmonic wave in signal source, each harmonic wave amplitude and phase place in transmitting procedure all can occur change in various degree to cause wave distortion, determine soil moisture content information by comparing the signal rising edge distortion reflected.And TDT signal source is the sine wave of single-frequency, reflected signal mainly phase place changes, and therefore can both may determine that soil moisture content information by analyzing its phase information.Its TDR probe end unlike two is open circuit, signal does not mate because of terminating impedance and reflects, and the probe of TDT is the loop closed, signal does not reflects, many factors affecting certainty of measurement, degree of stability such as the signal multiple reflections that causes owing to eliminating probe end impedance mismatch theoretically, incidence wave and echo interfere with each other, signal loss, therefore have high accuracy, high reliability, high sensitivity and high stability to the detection of soil moisture information minor variations with extraction.The advantage of TDT is that time measuring circuit is relatively easy, and equipment cost is low, and certainty of measurement and technical performance are suitable with TDR.Shortcoming is the stylus structure that probe cannot make terminal open circuit, middle measurement of must placing into the soil the most in use, and the monitoring that can only fix uses, and relatively big to soil disturbance when imbedding, and destroys the structure of original-state soil.But it still has the highest application and researching value.

Soil probe is used to perception and gathers soil moisture information.In the past in the face of the summary of soil sensor is it is known that zone sensors has TDR during TDT advantage: certainty of measurement is high, fast response time, measures wide ranges, typically need not demarcate, easy and simple to handle etc..But owing to soil probe must be placed into the soil before measuring, it is impossible to meet the needs of plug and play and seriously constrain the extensive application of TDT sensor.As illustrated in fig. 1 and 2, China Agricultural University Feng Lei in 2011 devises 2 sections of TDT soil probes in its thesis for the doctorate.The probe of U-shaped structure, shortcoming is owing to the restriction of structure cannot be inserted directly in soil, and can only fix in placing into the soil monitoring use, and can destroy the structure of undisturbed soil when embedment.The problem that can not be inserted directly into soil surveying to solve U-shaped to pop one's head in, as shown in Figure 3, Feng Lei devises again 1 section of spiral wound formula TDT probe, parallel two-conductor line curl is wrapped on the pole of insulation, the advantage of this probe is to pop one's head in into single bar, is directly inserted in soil measurement, and conductor length is longer, therefore the relative error of measure of time is little.The shortcoming of this probe is, owing to conductor is wound around on the insulating material, therefore the medium around wire is not only soil, also has the impact of insulant, therefore the transmission time is not only relevant with the dielectric constant of soil, the dielectric constant gone out by transmission Time Calculation is the dielectric constant that soil is compound with insulant, and the dielectric constant of soil to be obtained just can must obtain by demarcating.And owing to conductor spacing is longer, therefore loss of signal is relatively big, is also disadvantageous factor to measuring.

Beijing Forestry University Zhao Yan east et al. in JIUYUE, 2015 about " high salinity based on phase-detection is studied with highest organic soil earth moisture transducer ", and blue two kinds of sensors being respectively adopted above-mentioned doctor Feng Lei about " shrub moisture transducer probe designs based on TDT principle and experiment " in May, 2014 Beijing Forestry University king sea.The utility model patent having been applied for " a kind of method using survey duration commercial measurement Soil Water Content " by China Agricultural University stone celebrating orchid et al. in 2014, Application No. CN201410241004.9, and the utility model patent of " a kind of based on the soil moisture tester of regular way when surveying ", Application No. CN201420288686.4, the two patent uses double V-shaped probe.

Utility model content

(1) to solve the technical problem that

When the technical problems to be solved in the utility model is TDT in prior art, zone sensors can not the technical problem of plug and play.

(2) technical scheme

In order to solve above-mentioned technical problem, this utility model provides the soil probe of a kind of soil moisture measurement based on time-domain transmission, and it includes probe sense plate, moisture perception transmission line and shell；Probe sense plate front end is provided with front through hole, probe sense plate is multi-layer PCB board, through described front through hole in the middle part of moisture perception transmission line, the upper and lower two side portions of moisture perception transmission line is laid on the upper and lower lateral surface of described probe sense plate respectively, forms signal transmission passage；Described shell is made up of hard metal, and before shell wraps probe sense plate, the side of three, left and right, the upper and lower surface of probe sense plate is exposed for perception moisture information；Metal shell is connected with the ground wire of probe sense plate.

Further, described probe sense plate includes middle shield, and described middle shield all applies copper in pcb board planar range, and middle shield is connected with the ground wire of pcb board.Middle shield is the metal level arranged in the middle of one or several of multi-layer PCB board.

Further, the edge near described probe sense plate is provided with via, is provided with metal layer in via, and the middle shield of described pcb board is connected with the ground wire at pcb board edge by the metal layer of via.

Further, the upper inferolateral surface of described multi-layer PCB board arranging holding wire, described moisture perception transmission line is copper cash, and described copper cash is fixing on the signal line by welding manner.

Further, described front through hole is plated-through-hole, arranges the coat of metal inside plated-through-hole, and two described holding wires on the upper and lower lateral surface of described probe sense plate are connected by the described coat of metal, and the coat of metal is not connected with the middle shield of pcb board.

Further, described ground wire along before probe sense plate, left and right side along arranging, described metal shell directly with described ground contact.

Further, described case inside is provided with groove, and described probe sense plate is inlaid in described groove pluggablely；Described shell is made of stainless steel.

Further, described probe sense plate is sticker type, and probe sense plate front end is provided with an angle of 90 degrees, and described case nose is provided with the corners corresponding with an angle of 90 degrees.

Further, the described a length of 100-150mm of probe sense plate, a width of 15-24mm, thickness is 2-4mm.

Further, the number of plies of described multi-layer PCB board is at least 3 layers.

Further, described copper wire diameter is 1-1.5mm.

Soil probe accuracy testing of the present utility model

Frequency electromagnetic waves is in the time difference of soil probe:ε is relative dielectric constant, is 1 in atmosphere, is 80 in water.L is probe length 120cm.Time of transmitting in probe is placed on water can extend because dielectric constant becomes big.

In experimentation, insert a probe in the beaker of full scale 500ml and maintain static, gradually add water toward beaker, 50ml for the first time, increases 10ml the most every time, owing to soil probe length in water is gradually increased, the high frequency signal transmission time is also gradually increased, the i.e. phase contrast of high-frequency signal becomes larger, and add water 10ml every time, measuring circuit AD623 the 6th pin output voltage such as table 1.

Table 1

● data process:

Upper branch road exportsOwing to this magnitude of voltage comprises amplitude fading, so calculating its phase value to need first normalized, i.e. magnitude of voltage except in maximum 1054, making magnitude of voltage between-1～1.Then normalization being carried out anticosine computing, when calculated phase values it is noted that its phase continuity, therefore the phasometer formula after π should beWith water content relation curve as shown in Figure 8, upper branch road phase contrast is with water content relation curve as shown in Figure 9 for upper branch voltage.

● measurement result analysis

The process of data above phase place is fitted with water content relation curve, obtains fitting function:

Y=3E-08x⁶-4E-06x⁵+0.0001x⁴-0.0023x³+0.0165x²-0.0455x+1.8981

Wherein, y is phase contrast, and x is water content.This matched curve, using the relation curve as phase contrast from now on Yu water content, carrys out inverting water content value according to measurement voltage during measurement.

Measured value is calculated coefficient R with matched curve

$R=\frac{\underset{i=1}{\overset{n}{\mathrm{\Σ}}}(x_i-\stackrel{\‾}{x})(y_i-\stackrel{\‾}{y})}{\sqrt{\underset{i=1}{\overset{n}{\mathrm{\Σ}}}{(x_i-\stackrel{\‾}{x})}^2}\·\sqrt{\underset{i=1}{\overset{n}{\mathrm{\Σ}}}{(y_i-\stackrel{\‾}{y})}^2}}$

Wherein, n is the measurement number of samples for regression analysis；x_iIt it is the native water content recorded at i-th sampling point；It is the average of all sampling point measured values；y_iIt is by the signal phase difference recorded at i-th sampling point calculated water content predictive value according to regression equation；It is the average of all sampling point predictive values.

$\stackrel{\‾}{x}=\underset{i=1}{\overset{n}{\mathrm{\Σ}}}{x}_i,\stackrel{\‾}{y}=\underset{i=1}{\overset{n}{\mathrm{\Σ}}}{y}_i$

Coefficient R (the most also uses R²Replace) reflect the dependency between regression equation and measurement data, R²Value closer to 1, illustrate that the dependency between regression equation and measurement data is the best.R²Dimensionless, its span is between 0～1.

Root-mean-square error RMSE computing formula is as follows:

$RMSE=\sqrt{\frac{1}{n}\underset{i=1}{\overset{n}{\mathrm{\Σ}}}{(x_i-y_i)}^2}$

By being brought in above-mentioned formula by the test data recorded, it is calculated R=0.9948, RMSE=0.011, illustrates that certainty of measurement has reached expected value.

(3) beneficial effect

Technique scheme of the present utility model has the advantages that this utility model simple in construction, it is possible to plug and play, overcomes the shortcoming that traditional U-shaped transmission line can not i.e. be inserted.And after inserting soil, probe sense plate fully contacts with soil with moisture perception transmission line, it is possible to perception moisture information delicately.Metal shell is connected with the ground wire of sense plate and both ensure that the firm of probe, eliminates again the interference to high-frequency signal, improves the reliability of sensor.

Accompanying drawing explanation

Fig. 1 is a kind of U-shaped TDT soil probe structure schematic diagram in prior art；

Fig. 2 is another kind of U-shaped TDT soil probe structure schematic diagram in prior art；

Fig. 3 is spiral wound formula TDT probe structure schematic diagram in prior art；

Fig. 4 is the structural representation of the probe sense plate of this utility model embodiment；

Fig. 5 is the cut-away view of outer cover of this utility model embodiment；

Fig. 6 is the sectional view of the probe sense plate of this utility model embodiment；

Fig. 7 is probe sense plate and the soil moisture measurement sensor annexation schematic diagram of this utility model embodiment；

Fig. 8 is to detect upper branch voltage and water content relation curve in test in this utility model embodiment；

Fig. 9 is to detect upper branch road phase contrast and water content relation curve in test in this utility model embodiment；

Wherein, 10: probe sense plate；11: front through hole；12: ground wire；11a: the coat of metal；13: via；13a: metal layer；14: installing hole；15: middle shield；16: holding wire；20: moisture perception transmission line；30: shell；31:U type groove.

Detailed description of the invention

With embodiment, embodiment of the present utility model is described in further detail below in conjunction with the accompanying drawings.Following example are used for illustrating this utility model, but can not be used for limiting scope of the present utility model.

In description of the present utility model, it should be noted that except as otherwise noted, " multiple " are meant that two or more；Term " on ", D score, "left", "right", " interior ", " outward ", " front end ", " rear end ", " head ", the orientation of the instruction such as " afterbody " or position relationship be based on orientation shown in the drawings or position relationship, it is for only for ease of description this utility model and simplifies description, rather than instruction or the device of hint indication or element must have specific orientation, with specific azimuth configuration and operation, therefore it is not intended that to restriction of the present utility model.Additionally, term " first ", " second ", " the 3rd " etc. are only used for describing purpose, and it is not intended that indicate or hint relative importance.

In description of the present utility model, in addition it is also necessary to explanation, unless otherwise clearly defined and limited, term " is installed ", " being connected ", " connection " should be interpreted broadly, and connects for example, it may be fixing, it is also possible to be to removably connect, or be integrally connected；Can be to be mechanically connected, it is also possible to be electrical connection；Can be to be joined directly together, it is also possible to be indirectly connected to by intermediary.For the ordinary skill in the art, visual concrete condition understands above-mentioned term concrete meaning in this utility model.

As shown in figs. 4-7, the soil probe of a kind of based on time-domain transmission the soil moisture measurement that the present embodiment provides, it includes probe sense plate 10, moisture perception transmission line 20 and shell 30；Probe sense plate 10 front end is provided with front through hole 11, probe sense plate 10 is 3 layers of pcb board, through front through hole 11 in the middle part of moisture perception transmission line 20, moisture perception transmission line about 20 two side portions is laid in the upper and lower surface of probe sense plate 10 respectively, forms signal transmission passage；Shell 30 is made up of hard metal, and before shell 30 wraps probe sense plate 10, the side of three, left and right, the upper and lower surface of probe sense plate 10 is exposed for perception moisture information；Metal shell 30 is connected with the ground wire 12 of probe sense plate 10.The metal shell 30 function in electric property and holding wire 20 collectively form signal transmission passage.Wherein, 14 is installing hole.

The ground wire 12 of pcb board is connected with the ground wire of soil moisture measurement sensor；And the two ends of moisture perception transmission line 20 are connected with outfan and the input of the high-frequency oscillation signal of soil moisture measurement sensor respectively.

Probe sense plate 10 includes middle shield 15, and middle shield 15 all covers multi-layer PCB board in pcb board planar range, and middle shield 15 is connected with the ground wire 12 of pcb board.

Arranging holding wire 16 on the upper inferolateral surface of probe sense plate 10, holding wire 16 is formed by the copper corrosion that covers of multi-layer PCB board the upper and lower, and moisture perception transmission line 20 is φ 1.5mm copper cash, and copper cash is fixed on holding wire 16 by welding manner.

Front through hole 11 is plated-through-hole, arranges coat of metal 11a, coat of metal 11a and connected by two holding wires 16 on the upper and lower lateral surface of probe sense plate inside plated-through-hole, and coat of metal 11a is not connected with the middle shield 15 of pcb board.Holding wire 16 forms signal transmission line together with moisture perception transmission line 20.

The ground wire 12 of probe sense plate is formed by the copper corrosion that covers of multi-layer PCB board upper strata and/or lower floor, ground wire 12 along before probe sense plate, left and right side along arranging, metal shell 30 directly contacts connection with ground wire 12.Edge near probe sense plate 10 is provided with via 13, is provided with metal layer 13a in via 13, and the middle shield 15 of pcb board is connected with the ground wire 12 at pcb board edge by the metal layer 13a of via.Middle shield 15 interfering with each other between shielding upper and lower two layer signals of pcb board completely.

And shell 30 is made of stainless steel.Being provided with groove 31 inside housing 30, probe sense plate 10 is inlaid in groove 31 pluggablely.Probe sense plate 10 is sticker type, and probe sense plate 10 front end is provided with an angle of 90 degrees, and shell 30 front end is provided with the corners corresponding with an angle of 90 degrees.The a length of 150mm of probe sense plate 10, a width of 24mm, thickness is 3mm.

This utility model compared with prior art, has the advantage that

1. probe end closed loop, eliminates probe end open-circuit impedance and does not mates and many factors affecting certainty of measurement, degree of stability such as the signal multiple reflections, incidence wave and the echo that cause interfere with each other, signal loss, and therefore perception moisture information is more sensitive and accurate.

2. overcome common time-domain transmission TDT soil probe and interfere with each other and can make high-frequency signal wave distortion, amplitude fading the shortcoming affecting certainty of measurement in the case of not taking shielding due to the high-frequency signal of transmitted in both directions.

3. by other instrument soil must be excavated during common time-domain transmission TDT soil probe measurement and measure in being placed into the soil by sensor probe again, this utility model uses the sticker type insertable special construction can be with plug and play, convenient and swift.

4. low cost, can realize.

Embodiment of the present utility model is given for the sake of example and description, and is not exhaustively or this utility model to be limited to disclosed form.Many modifications and variations are apparent from for the ordinary skill in the art.Selecting and describing embodiment is in order to principle of the present utility model and actual application are more preferably described, and makes those of ordinary skill in the art it will be appreciated that this utility model thus design are suitable to the various embodiments with various amendments of special-purpose.

Claims (10)

1. the soil probe of a soil moisture measurement based on time-domain transmission, it is characterised in that It includes probe sense plate, moisture perception transmission line and shell；Probe sense plate front end is arranged Having front through hole, probe sense plate is multi-layer PCB board, through described in the middle part of moisture perception transmission line Front through hole, the upper and lower two side portions of moisture perception transmission line is laid on described probe sense plate respectively On upper and lower lateral surface, form signal transmission passage；Described shell is made up of hard metal, outward Before shell wraps probe sense plate, three, left and right side, the upper surface of probe sense plate and Lower surface exposes for perception moisture information；Metal shell is connected with the ground wire of probe sense plate.

The soil of soil moisture measurement based on time-domain transmission the most according to claim 1 is visited Pin, it is characterised in that described probe sense plate includes middle shield, described middle shield Copper are all applied, in order to isolate the mutual of high-frequency signal between levels in pcb board planar range Interference, middle shield is connected with the ground wire of pcb board.

The soil of soil moisture measurement based on time-domain transmission the most according to claim 2 is visited Pin, it is characterised in that the edge near described probe sense plate is provided with via, conducting Metal layer, the metallization by via of the middle shield of described pcb board it is provided with in hole Layer is connected with the ground wire at pcb board edge.

The soil of soil moisture measurement based on time-domain transmission the most according to claim 2 is visited Pin, it is characterised in that on the upper inferolateral surface of described multi-layer PCB board, holding wire is set, described Moisture perception transmission line is copper cash, and described copper cash is fixing on the signal line by welding manner.

The soil of soil moisture measurement based on time-domain transmission the most according to claim 4 is visited Pin, it is characterised in that described front through hole is plated-through-hole, arranges the coat of metal inside plated-through-hole, The described coat of metal is by two described holding wires on the upper and lower lateral surface of described probe sense plate Connecting, the coat of metal is not connected with the middle shield of pcb board.

The soil of soil moisture measurement based on time-domain transmission the most according to claim 1 is visited Pin, it is characterised in that described ground wire along before probe sense plate, left and right side along arranging, Described metal shell directly with described ground contact.

The soil of soil moisture measurement based on time-domain transmission the most according to claim 1 is visited Pin, it is characterised in that described case inside is provided with groove, and described probe sense plate is pluggable Be inlaid in described groove；Described shell is made of stainless steel.

The soil of soil moisture measurement based on time-domain transmission the most according to claim 1 is visited Pin, it is characterised in that described probe sense plate is sticker type, probe sense plate front end is provided with An angle of 90 degrees, described case nose is provided with the corners corresponding with an angle of 90 degrees.

The soil of soil moisture measurement based on time-domain transmission the most according to claim 1 is visited Pin, it is characterised in that the described a length of 100-150mm of probe sense plate, a width of 15-24mm, Thickness is 2-4mm.

The soil of soil moisture measurement based on time-domain transmission the most according to claim 1 Probe, it is characterised in that the number of plies of described multi-layer PCB board is at least 3 layers.