CN211741150U - Conduit type ring structure sensor - Google Patents
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Abstract
A conduit type annular structure sensor belongs to the field of soil measurement. The attached three-needle type ring needle body of its pipe outer wall, place impedance converter in the pipe, the straight needle body of the interior installation center ring needle body of impedance converter, straight needle body is connected with coaxial cable one side, three-needle ring needle body is non-closed annular, a non-blind end and the straight needle body of center ring needle body are connected, the both sides that the side ring needle body is located center ring needle body, three non-closed ring needle body is parallel to each other, a non-blind end of side ring needle body is equipped with the right angle and bends, impedance converter inserts in the pipe lateral wall through-hole, and with attached in the right angle bending end connection of the side ring needle body of pipe outer wall fixed. Use the utility model discloses measure soil moisture, have the on-the-spot simple installation, less to the disturbance of original state soil layer to and can measure a plurality of different degree of depth soil layers simultaneously, and can satisfy the requirement of carrying out the multilayer monitoring to deeper soil layer.
Description
Technical Field
The utility model belongs to a soil measuring field, in particular to pipe formula annular structure sensor reaches.
Background
The Time Domain Reflectometry (TDR) was generated in the thirty years of the last century and was originally used to detect and locate damaged locations of communication cables. With the discovery that the TDR technology can measure the volume water content of soil in the seventies of the last century, the technology is widely applied to the field of agriculture. Since the eighties, the technology is also applied to the field of geotechnical engineering, is applied to the aspects of measuring the water content and the dry density of soil bodies, monitoring the stability of landslides, measuring the underground water level and the electric conductivity, monitoring the pollution of the soil bodies, controlling the quality of chemically reinforced soil and the like, and has attracted extensive attention due to the characteristics of convenience, safety, economy, digitization, easiness in remote control communication and the like.
Fellener-Feldegg [1969] studied the following formula for the transmission of electromagnetic waves in a medium:
where v is the propagation velocity of the electromagnetic wave in the medium, c is the speed of light, k' and k "are the real and imaginary parts, respectively, of the relative permittivity of the medium, and tan ═ k" + (σ "+,)DC/ω0) K is the loss factor. TOPP [1980 ] C]It is pointed out that the soil is basically a homodromous linear homogeneous medium which satisfies: k "< k' and σ when the frequency of the electromagnetic wave is sufficiently highDC/ω0k′＜＜1。
Thus, at this time:
k′≈(c/v)2(2)
TOPP definition of Ka＝(c/v)2To characterize the dielectric constant, it can be seen that an electromagnetic wave of sufficiently high frequency satisfies when propagating in soil:
k′≈Ka＝(c/v)2(3)
at normal temperature, the soil is a three-phase substance formed from air (gas state), soil body granules (solid state) and liquid water, the real parts of relative dielectric constants of air and soil body granules are respectively 1 and 3-4, and the liquid water is up to 75-85 according to different temp., so that the real part of dielectric constant of soil is mainly determined by its water content. Scholars in different fields give different empirical fitting formulas of the characterization dielectric constant and the volume water content of the soil according to different application requirements over the years, and the theoretical basis for measuring the water content of the soil by applying the time domain reflection method principle is laid through the work.
When an electromagnetic pulse excitation signal is transmitted along a transmission line, the impedance of the transmission line is changed due to the interruption, damage or discontinuity of surrounding substances, the impedance change can cause the transmission signal to generate a reflection at the discontinuous point, and the position of the discontinuous point can be accurately judged by precisely measuring the travel time difference of an incident wave and a reflected wave of an electromagnetic wave.
Fig. 1 shows a typical TDR soil moisture measuring system, in which a high-frequency electromagnetic wave signal generated by a TDR apparatus is input to a sensor (probe) inserted into soil through a coaxial cable, and due to a first reflection point generated by a change in impedance, the electromagnetic wave signal continues to travel along the sensor (probe) and reaches the end of the probe with a length L to generate a second reflection, and the reflected wave signal is transmitted back to the TDR apparatus along the sensor, if it is assumed that the time of transmission and reflection of the electromagnetic wave along the sensor is Δ t, there are:
it follows that the key to measuring soil moisture by Time Domain Reflectometry (TDR) is the accurate measurement of the transit time of an electromagnetic wave along a probe.
The TDR sensor applied to the field of soil detection at present is mostly of a pin type structure, and is substantially a simulation of a coaxial cable, wherein a central pin body is connected with an inner conductive copper core of the coaxial cable, and the outside of the central pin body is connected with an outer conductive shielding layer of the coaxial cable, as shown in figure 2.
Structurally, the TDR sensor is divided into a coaxial type and a multi-pin type, and its horizontal section is as shown in fig. 3:
because the coaxial sensor blocks the moisture exchange between the outside of the cylinder and the soil in the cylinder, and simultaneously, in order to avoid the disturbance to the undisturbed soil caused by the insertion and extraction in the soil, a multi-pin sensor (probe) simulating a coaxial cable structure is adopted, and more three-pin structures are mainly used in practical application.
Although the contact pin type probe can well realize the measurement of the TDR soil moisture, in practical application, the measurement of the volume moisture content of soil layers at different depths under the earth surface is more required; for example: the moisture content measurement requires the measurement of the moisture content of three layers of 10cm, 20cm and 40cm under the earth's surface, while the monitoring in soil and water conservation requires the moisture content of five layers of 20cm, 40cm, 60cm, 80cm and 100cm under the earth's surface, and even the meteorological monitoring requires the measurement of the moisture content of eight layers up to 100cm under the earth's surface. In practical measurement, the embedding of the pin probe requires digging a large volume of working pit and then inserting the probe in the longitudinal section parallel to the ground surface according to the depth of practical measurement, which has the following disadvantages:
1) the labor intensity of digging the operation pit is high;
2) the disturbance damage to the field soil body is large;
3) for fixed monitoring items, the cultivation is influenced and the fixed monitoring items are easily damaged by cultivation machines when being buried in farmlands for a long time;
4) when the probe is inserted, hidden obstacles (such as plant rhizomes, stones and the like) are encountered, so that the probe needle body is forked or damaged, and the accuracy of measurement is directly influenced.
The utility model provides a adopt soil moisture measuring transducer of pipe formula structure better overcomes above defect, it is according to the different degree of depth arrangement electrodes that required survey on the pipe, can monitor different levels of soil layer moisture content simultaneously after inserting soil. However, at present, the conduit type sensor is only suitable for a Frequency Domain (FDR) principle method, and is an instrument for measuring soil moisture through the change of the capacitance value of the measured soil, and the instrument is extremely sensitive to the change of the conductivity of the soil. Therefore, formula calibration is often required to be performed according to fixed point timing of the embedding place, so that the actual measurement effect is poor; the time domain reflection method measures soil moisture by measuring the propagation time of electromagnetic waves along the probe, and has high design requirements on the sensor (probe) due to the TDR technical principle.
In summary, the development of a catheter-type sensor (probe) suitable for the time domain reflectometry principle is of great significance.
SUMMERY OF THE UTILITY MODEL
An object of the utility model is to overcome foretell defect, provide a ducted annular structure soil moisture measurement sensor, it is an annular structure's intubate formula probe, has the on-the-spot simple installation, less to the disturbance of original state soil layer to and can carry out the soil moisture content simultaneously to a plurality of different degree of depth soil layers simultaneously and measure, and can satisfy the requirement of carrying out multilayer soil moisture content monitoring to deeper soil layer.
The utility model aims at realizing through the following technical scheme: a ducted annular structure sensor, characterized by: it comprises a catheter and more than one group of probes;
the probe consists of an impedance converter, a straight needle body, an annular needle body and a coaxial cable;
the impedance converter is tubular and is arranged in the catheter, a straight needle body is arranged in the impedance converter along the axial direction of the impedance converter, and one end of the coaxial cable is connected with the straight needle body;
the annular needle body comprises a central annular needle body and side annular needle bodies which are positioned on two sides of the central annular needle body and are arranged in parallel with the central annular needle body, the side annular needle bodies are all in a non-closed annular shape and are attached to the outer wall of the catheter, and one non-closed end of the central annular needle body is connected with the straight needle body; the non-closed end of each side annular needle body is provided with a right-angle bend which is vertical to the annular plane of the annular needle body;
the side wall of the catheter is provided with a through hole, and the impedance converter is inserted into the through hole and is fixedly connected with the right-angle bent end of the side needle body attached to the outer wall of the catheter.
The impedance converter is a T-shaped sleeve and consists of a tubular component and a T-shaped pipe cap, the pipe cap end of the T-shaped pipe cap is fixedly inserted with the tubular component, the sleeve is inserted in the tubular component, and the straight needle body is inserted in the sleeve.
The front end of the straight needle body is provided with an insertion hole, and one end of a coaxial cable is inserted into the insertion hole and connected with the straight needle body.
The tail end of the tube wall of the impedance converter is provided with a notch, and one non-closed end of the central annular needle body is aligned with the notch at the tail end of the tube wall of the impedance converter and is connected with the rear end of the straight needle body.
The conduit and the sleeve are made of high-molecular low-dielectric-constant materials.
The straight needle body, the central annular needle body, the side annular needle bodies, the tubular member and the T-shaped pipe cap are all made of metal materials.
The utility model has the advantages and beneficial effects that:
1) when the parameters such as burying of the sensor for measuring the soil moisture content of the ducted annular structure, monitoring of the soil moisture content of the measured soil and the like are carried out on site, a large operation pit does not need to be dug, and only a cylindrical surface is drilled, so that the labor intensity of work of burying the sensor on site and the like is greatly reduced;
2) the area of a cylindrical operation surface drilled by the soil drill is small, the field soil body is hardly disturbed and damaged, and the measured parameters such as soil moisture content are objective and persuasive;
3) for fixed monitoring items of parameters such as soil, the sensor needs to be buried in a farmland for a long time, and because the pipe type annular structure soil moisture measuring sensor is buried, the operation area is small, and the sensor cannot damage and influence the growth of seeds when mechanically cultivating the spring-ploughed seeds;
4) because the optimal design structure of pipe formula loop configuration soil moisture measurement sensor self, when inserting soil, meet hidden barrier (such as plant rhizome, stone etc.), can not have the condition that causes the branching of needle body or damage, guaranteed soil moisture content isoparametric measurement's stability and accuracy.
In summary, the following steps: a soil moisture measuring sensor adapted to a time domain reflection principle (TDR) and adopting a ducted structure realizes an accurate moisture value of a measured soil by accurately measuring a time of an electromagnetic wave propagating along a probe, which has a great advantage in an actual soil moisture measurement.
Drawings
FIG. 1 is a schematic diagram of a TDR soil moisture measurement system.
Fig. 2 is a schematic diagram of a simulation of a sensor (probe) versus a coaxial cable.
FIG. 3 is a horizontal cross-sectional view of a TDR pin sensor.
Fig. 4 is a schematic structural view of the catheter of the present invention.
Fig. 5 is a schematic structural diagram of the impedance converter of the present invention.
Fig. 6 is a top view of the central ring-shaped needle body of the present invention.
Fig. 7 is a schematic view of the structure of the side ring-shaped needle body of the present invention.
Fig. 8 is a schematic view of the assembly structure of the present invention.
Fig. 9 is a schematic structural diagram of an embodiment of the present invention.
FIG. 10 is a catheter-based annular sensor fit to the comparative data trace.
Wherein:
the device comprises a catheter 1, an impedance converter 2, a tubular component 3, a pipe cap 4, a coaxial cable 5, a cannula 6, a straight needle body 7, a BNC connector 8, a through hole 9, a central annular needle body 10, a side annular needle body 11, a U-shaped notch 12 and a right-angle bend 13.
Detailed Description
In order to make the principle of the present invention clearer, it is necessary to briefly introduce a TDR soil moisture measuring instrument based on the time domain reflection principle used in cooperation with the TDR soil moisture measuring instrument. The TDR soil moisture measuring instrument applicant has obtained a national utility model patent in 2016, patent No.: 201510381857.7.
the device comprises a central processing unit, a signal receiving and transmitting system and a signal processing unit, wherein the central processing unit controls the signal receiving and transmitting system to transmit signals with a plurality of frequencies; the signal transceiving system is used for receiving signals; the digital signal processor is used for acquiring signals; and according to the time of the electromagnetic wave reflected by the digital signal to and fro propagating on the probe, calculating the volume water content of the soil according to a preset calibration formula representing the relation between the dielectric constant and the water content of the soil.
The utility model discloses take the soil moisture content of horizontal plane 10cm, 20cm and 40cm below the surface of the earth as the example of synchronous monitoring.
A conduit type annular structure sensor is characterized in that a conduit 1 with the outer wall diameter of 10cm and the inner wall diameter of 8cm is made of polytetrafluoroethylene made of high-molecular low-dielectric constant materials, an impedance converter 2 is arranged in the conduit 1, the impedance converter 2 is a T-shaped sleeve made of stainless steel and consists of a tubular component 3, a T-shaped pipe cap 4 and a sleeve 6, and the pipe cap end of the T-shaped pipe cap 4 is fixedly connected with the tubular component 3 in an inserted mode; for convenience of description, one end of the T-shaped pipe cap 4 of the impedance converter 2 is referred to as a thin end, and one end of the tubular member 3 is referred to as a thick end; the tubular member 3 has an outer diameter D0Inner diameter of d0Length of L0A U-shaped notch is arranged at the tail end of the tube wall at the thick end of the coaxial cable, a sleeve 6 which is made of polytetrafluoroethylene with high polymer and low dielectric constant and has the same outer diameter as the tubular member 3 is inserted in the tubular member 3, the coaxial cable 5 penetrates into the T-shaped tube cap 4, the outer surface of the end of the penetrated coaxial cable 5 is stripped by 10mm to reach an inner conductor, and a stainless steel columnar straight needle body 7 has the length L0Diameter d0A jack with the diameter the same as that of the inner conductor of the coaxial cable 5 and the length of 10mm is drilled in the center of the straight needle body 7, the inner conductor of the coaxial cable 5 is inserted into the center jack of the straight needle body 7, and the inner conductor of the coaxial cable 5 and the straight needle body 7 are fixed through cold pressing; the straight needle body 7 is inserted into the sleeve 6, the outer insulating layer of the coaxial cable 5 surrounded by the thin end of the T-shaped pipe cap 4 is peeled off, so that the outer conductor of the coaxial cable 5 is tightly connected with the T-shaped pipe cap 4, and the other end of the coaxial cable 5 is connected with a BNC connector 8; according to measurementThe soil moisture content of the ground surface 10cm, 20cm and 40cm horizontal plane is synchronously monitored, and three diameters and the 3 outer diameter D of the tubular component of the impedance converter are drilled on the side wall of the conduit 1 from top to bottom0The distance between the first through hole and the second through hole is 10cm, the distance between the second through hole and the third through hole is 20cm, the tubular component 3 of the impedance converter 2 is tightly inserted into the through holes 9, and the periphery is sealed by resin glue, so that moisture is prevented from permeating along the gaps of the through holes 9; closely attaching three layers of stainless steel three-needle type annular needle bodies to the wall of the catheter 1 from top to bottom, wherein the distance between the 1 st layer of annular needle body and the 2 nd layer of annular needle body is 10cm, the distance between the 2 nd layer of annular needle body and the 3 rd layer of annular needle body is 20cm, the annular needle bodies comprise a central annular needle body 10 and side annular needle bodies 11 which are positioned at two sides of the central annular needle body 10 and are arranged in parallel with the central annular needle body 10, the annular needle bodies are all in a non-closed annular shape, in order to avoid air infiltration between the annular needle bodies and the wall of the catheter 1, grooves can be arranged on the wall of the catheter, and the annular needle bodies are horizontally arranged in the grooves; one non-closed end of the central annular needle body 10 is respectively aligned with a U-shaped notch 12 at the tail end of the thick-end tube wall of the tubular member 3 in the through hole 9, so that the central annular needle body 10 is prevented from being connected with the impedance converter 2 to avoid short circuit and is respectively welded and fixed with the straight needle body 7 in the sleeve 6; one non-closed end of the side annular needle body 11 is provided with a right-angle bend 13, and the right-angle bend 13 is perpendicular to the annular plane of the annular needle body, is also tightly attached to the tube wall of the catheter 1, and is respectively welded and fixed with the tubular member 3.
Establishment of a suitable formula for the catheter-type annular structure sensor:
the theoretical basis for the time domain reflectometry for measuring soil moisture lies in the so-called travel equation (3), where v is the propagation velocity of electromagnetic waves along the probe needle inserted into the soil being measured. However, due to the influence of the structure of the catheter-type annular structure sensor, the outer side of the needle body is the soil to be measured, and the inner side is the polymer low-dielectric constant material for manufacturing the catheter. Therefore, the characteristic dielectric constant of the mixed medium consisting of the soil and the material for manufacturing the conduit is obtained by calculation according to the formula (3). According to the dielectric constant model of the dual dielectric material given by japanese scholars h.miyamoto and j.chikushi et al in 2006,can obtain the measured dielectric constant value t, the actual dielectric constant s of the soil and the dielectric constant of the material for manufacturing the conduitdThe relationship between:
omega is more than or equal to 0 and less than or equal to 1, and alpha is more than 0, which are parameters determined by the dielectric constant of the material used for manufacturing the catheter and the geometric structure of the designed sensor and can be obtained by comparing the measurement results of the pin-type probe TDR of the measurement samples with different dielectric constants and adopting nonlinear regression fitting.
The parameters m and alpha in the fitting formula (6) and the dielectric constant of the material of the conduitdIn order to ensure the consistency of the shaped product, the polytetrafluoroethylene with stable dielectric property is adopted to manufacture the conduit, and the dielectric constant of the polytetrafluoroethylene isd＝2.55。
Experimental data for fitting a formula are acquired through two parts of experimental collection, the high dielectric constant part is obtained by adding glycerol with different proportions to water, and a catheter type sensor and a contact pin type sensor are respectively measured and compared; the part with low water content is manufactured into earth columns according to different water contents by adopting clay, the measurement result of the conduit sensor is compared with the average value of the multipoint synchronous measurement result of the contact pin type sensor for fitting, and is compared with the volume water content obtained by soil sampling and drying measurement of a plurality of groups of artificial cutting rings (figure 10).
The fitting results are shown in table 1, where the DGB probes are the ducted annular structure sensors of the present application, and α is 3.772 and ω is 0.106:
attached table 1
Substituting the fitting result into a formula (6), and calculating to obtain a characteristic dielectric constant fitting formula of the conduit type annular structure sensor:
the laboratory measurement results of the moisture soil and sand soil ratio measurement of each target water content by adopting a formula (7) are respectively shown in attached tables 2 and 3, and the DGB probe in the attached tables is the conduit type annular structure sensor of the application:
attached table 2
Attached table 3
The measurement results of field comparison and measurement of the chaoyang hydrology station, the cypress and longevity hydrology station, the Chuzhou hydrology experiment base in Anhui province and the like in Liaoning province are shown in the attached table 4 by adopting a formula (7), and a DGB probe in the attached table is the conduit type annular structure sensor of the application:
attached table 4
The method adopts the conduit type annular structure sensor to measure the moisture of the field soil such as the Korea hydrology station, the Bai shou hydrology station, the Anhui Chuzhou hydrology experiment base and the like in Liaoning province, takes synchronous monitoring of soil moisture content in 10cm, 20cm and 40cm horizontal planes below the ground surface as an example, and comprises the following steps:
(1) three groups of probes are arranged on the outer wall of the conduit from top to bottom by 10cm, 20cm and 40cm according to the depth of soil to be measured, which is 10cm, 20cm and 40 cm;
(2) drilling a hole with the depth of 40cm in the measured soil, wherein the diameter of the hole is slightly smaller than the diameter of the outer wall of the guide pipe by 10 cm;
(3) the sensor is inserted into a drilled hole of the soil to be measured, and the soil and the outer wall of the conduit of the sensor are tightly attached to the three-layer three-needle type annular needle body after about one month of sedimentation;
(4) the BNC joint at the other end of the coaxial cable is connected with a TDR host machine, and the characterization dielectric constant of a mixed medium formed by soil and a material for manufacturing a conduit is measured;
(5) by passing
Calculating to obtain the characteristic dielectric constant of the tested soil by using an operation formula;
(6) and calculating by using a TOPP formula to obtain the water content of the soil to be detected.
Through comparison of the laboratory measurement data and the field measurement data with a manual method, parameters such as soil moisture content and the like can be accurately measured by using the conduit type annular structure sensor.
Claims (6)
1. A ducted annular structure sensor, characterized by: it comprises a catheter and more than one group of probes;
the probe consists of an impedance converter, a straight needle body, an annular needle body and a coaxial cable;
the impedance converter is tubular and is arranged in the catheter, a straight needle body is arranged in the impedance converter along the axial direction of the impedance converter, and one end of the coaxial cable is connected with the straight needle body;
the annular needle body comprises a central annular needle body and side annular needle bodies which are positioned on two sides of the central annular needle body and are arranged in parallel with the central annular needle body, the side annular needle bodies are all in a non-closed annular shape and are attached to the outer wall of the catheter, and one non-closed end of the central annular needle body is connected with the straight needle body; the non-closed end of each side annular needle body is provided with a right-angle bend which is vertical to the annular plane of the annular needle body;
the side wall of the catheter is provided with a through hole, and the impedance converter is inserted into the through hole and is fixedly connected with the right-angle bent end of the side needle body attached to the outer wall of the catheter.
2. The ducted annular structure sensor according to claim 1, wherein: the impedance converter is a T-shaped sleeve and consists of a tubular component and a T-shaped pipe cap, the pipe cap end of the T-shaped pipe cap is fixedly inserted with the tubular component, the sleeve is inserted in the tubular component, and the straight needle body is inserted in the sleeve.
3. The ducted annular structure sensor according to claim 1, wherein: the front end of the straight needle body is provided with an insertion hole, and one end of a coaxial cable is inserted into the insertion hole and connected with the straight needle body.
4. The ducted annular structure sensor according to claim 1, wherein: the tail end of the tube wall of the impedance converter is provided with a notch, and one non-closed end of the central annular needle body is aligned with the notch at the tail end of the tube wall of the impedance converter and is connected with the rear end of the straight needle body.
5. The ducted annular structure sensor according to claim 1, wherein: the conduit and the sleeve are made of high-molecular low-dielectric-constant materials.
6. The ducted annular structure sensor according to claim 1, wherein: the straight needle body, the central annular needle body, the side annular needle bodies, the tubular member and the T-shaped pipe cap are all made of metal materials.
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