CN116007801B - A soft-contact soil pressure sensor and soil pressure sensor calibration method - Google Patents
A soft-contact soil pressure sensor and soil pressure sensor calibration methodInfo
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- CN116007801B CN116007801B CN202310072589.5A CN202310072589A CN116007801B CN 116007801 B CN116007801 B CN 116007801B CN 202310072589 A CN202310072589 A CN 202310072589A CN 116007801 B CN116007801 B CN 116007801B
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Abstract
本发明公开了一种软接触式的土压传感器及土压传感器校准方法，土压传感器包括：软接触层、压阻式敏感元件、传感器主壳体、宝塔式防断结构和螺纹保护壳体。本发明中土压传感器与土体接触面采用软接触方式，通过正面开窗填入圆弧状柱体的传感器主壳体，土压传感器表面的软接触层受上层填筑土层影响变形挠曲形成与传感器主壳体齐平形状，使土压力作用于压阻式敏感元件；土压传感器的软接触层采用高弹性材料，高弹性材料的密度介于干砂与饱和砂之间，与铝合金材质和不锈钢材质相比，软接触层采用高弹性材料可有效减小土压传感器与土体介质之间的刚度匹配问题，从而提高土压传感器测试精度，使土压传感器测量的土压力数据具有较高的准确性和可靠性。
The present invention discloses a soft-contact earth pressure sensor and an earth pressure sensor calibration method. The earth pressure sensor includes: a soft contact layer, a piezoresistive sensitive element, a sensor main shell, a pagoda-shaped anti-breakage structure, and a threaded protective shell. In the present invention, the earth pressure sensor and the soil contact surface adopt a soft contact method. The arc-shaped columnar sensor main shell is filled in through a window on the front. The soft contact layer on the surface of the earth pressure sensor is affected by the upper filling soil layer and deformed and flexed to form a shape flush with the sensor main shell, so that the earth pressure acts on the piezoresistive sensitive element. The soft contact layer of the earth pressure sensor is made of a high-elastic material. The density of the high-elastic material is between dry sand and saturated sand. Compared with aluminum alloy and stainless steel materials, the use of a high-elastic material in the soft contact layer can effectively reduce the stiffness matching problem between the earth pressure sensor and the soil medium, thereby improving the test accuracy of the earth pressure sensor and making the earth pressure data measured by the earth pressure sensor have higher accuracy and reliability.
Description
Technical Field
The invention relates to the technical field of soil pressure sensors, in particular to a soft contact type soil pressure sensor and a soil pressure sensor calibration method.
Background
The high-gravity centrifugal model test is based on high-speed rotation of a geotechnical centrifuge to generate high centrifugal force, compensates stress loss of soil layers or rock and soil structures in the hypergravity centrifugal model, achieves stress level similar to or equal to that of a prototype, and plays an important role in basic theoretical research and engineering application research by applying compressive seismic load (with high frequency of 10-300 Hz, instantaneous less than or equal to 1s and strong vibration of 30-60 g) when achieving stable high centrifugal acceleration condition (such as 50-100 g).
However, because the size of the supergravity centrifugal model is smaller (most 700 (long) and 300 (wide) and 400mm (high)), the micro soil pressure sensor is used as a key measurement sensor for monitoring soil pressure and lateral soil pressure in saturated/unsaturated soil, has larger difference with conventional pressure sensor measuring media (such as air pressure, water pressure and the like (the soil is a non-uniform and non-elastic medium, and the air and the liquid are uniform mediums), is influenced by various factors such as embedding effect, contact interface, size effect, waterproof structure and the like, and the accuracy and the reliability of the soil pressure data measured by the micro soil pressure sensor in the supergravity centrifugal test have larger errors (the maximum error can reach 50%).
Disclosure of Invention
In view of the above, the invention discloses a soft contact type soil pressure sensor and a calibration method thereof, so as to improve the test precision of the soil pressure sensor and ensure that the soil pressure data measured by the soil pressure sensor has higher accuracy and reliability.
A soft contact type soil pressure sensor comprises a soft contact layer, a piezoresistance sensitive element, a sensor main shell, a pagoda type breaking preventing structure and a thread protecting shell;
the soft contact layer is used as a contact body between the soil pressure sensor and soil body, and is made of high-elasticity materials and is used for being arranged at a front window of the sensor main shell so as to directly transmit the physical change of the soil pressure to the piezoresistive sensitive element;
the piezoresistive sensitive element is used as a core part of the soil pressure sensor and is used for converting the physical change of the soil pressure into voltage signals for output;
The sensor main shell is provided with an internal thread, is matched with the thread protective shell through the internal thread to mount and protect the piezoresistive sensitive element, and is also used as a carrier of the soft contact layer;
the pagoda-type anti-breaking structure is used for being matched with the sensor main shell so as to install the teflon waterproof pipe.
Optionally, the contact surface of the soft contact layer and the soil body is an arc surface, and the contact surface of the soft contact layer and the piezoresistive sensitive element is a parallel surface;
The circular arc surface is used for dispersing additional stress when the soil pressure is detected and transmitting the additional stress to the parallel surface.
Optionally, the piezoresistive sensitive element comprises a high-voltage cavity, a sensitive membrane, a vacuum cavity, a gold wire, stress-free glue, a wiring terminal, a conversion circuit board and a silicon membrane protective shell;
the high-pressure cavity is a transparent pressure cavity and is used for being contacted with the soil pressure to be measured;
the vacuum cavity is a transparent pressure cavity and is used for taking a vacuum environment as a reference output zero point;
the high-pressure cavity and the vacuum cavity are respectively arranged on two sides of the sensitive diaphragm, and are used for generating strain change when the pressure born by the high-pressure cavity and the vacuum cavity is different, and converting the strain change into voltage signals to be output;
the gold wire is used for connecting a plurality of equivalent resistors arranged in the sensitive membrane to form a Wheatstone bridge;
The wiring terminal is arranged on the conversion circuit board and is connected with the gold wire lead;
the conversion circuit board is used for being fixedly connected with a four-core shielding cable outside the piezoresistive sensitive element;
The front side of the silicon diaphragm protective housing is windowed, and a cavity structure is arranged inside the silicon diaphragm protective housing, and is used for installing the high-pressure cavity, the sensitive diaphragm and the vacuum cavity, and the stress-free glue is filled around and on the surface of the cavity structure to serve as a protective layer.
Optionally, the sensor main shell comprises a soft contact layer positioning groove, a soft contact layer supporting beam, a sensitive element mounting cavity and a sensitive element positioning groove, wherein the internal thread is arranged in the sensitive element mounting cavity;
the soft contact layer positioning groove is used for positioning the soft contact layer;
the soft contact layer supporting beam is used for supporting the soft contact layer;
the sensor mounting cavity is used for placing the piezoresistive sensor, positioning the piezoresistive sensor by combining the sensor positioning groove, and filling epoxy resin in the residual space after the piezoresistive sensor is positioned and mounted.
Optionally, the thread protection shell comprises a connecting external thread and a sensitive element support column;
The thread protection shell is matched with the sensor main shell through the connecting external thread, and supports and fixes the piezoresistive sensitive element through the sensitive element support column.
Optionally, the cable also comprises a four-core shielding cable;
The four-core shielding cable is fixedly connected with the piezoresistive sensitive element.
Optionally, the water-proof pipe also comprises the teflon waterproof pipe.
Optionally, the piezoresistive sensor is a micro high-frequency piezoresistive sensor membrane.
The method for calibrating the soil pressure sensor is applied to a data acquisition instrument, wherein the data acquisition instrument is connected with the soil pressure sensor, and the method for calibrating the soil pressure comprises the following steps of:
Dividing the maximum theoretical soil pressure value of a soil layer required to be measured by the soil pressure sensor to be calibrated into M grades, wherein M is a positive integer;
when the soil pressure sensor to be calibrated is buried to the soil layer depth corresponding to the actual test, applying centrifugal acceleration load to the soil pressure sensor to be calibrated step by step to a preset value based on M grades, and obtaining a theoretical soil pressure value corresponding to the output voltage signal of the soil pressure sensor to be calibrated at each grade and the soil layer depth under each centrifugal acceleration;
based on the theoretical soil pressure value corresponding to each level, obtaining average calibration coefficients of each level of soil pressure output voltage signal of the soil pressure sensor to be calibrated and the theoretical soil pressure value under the corresponding centrifugal acceleration condition by using a least square method curve fitting method;
multiplying each level of soil pressure output voltage signal of the soil pressure sensor to be calibrated by the corresponding average calibration coefficient to obtain an actually measured output soil pressure value of the soil pressure sensor to be calibrated at each level;
Calculating the deviation amount of the actually measured output soil pressure value corresponding to each level of the soil pressure sensor to be calibrated and the corresponding theoretical soil pressure value;
And determining target coefficients after the soil pressure sensor to be calibrated is calibrated based on the deviation amounts.
According to the technical scheme, the soft contact type soil pressure sensor and the soil pressure sensor calibration method are disclosed, the soil pressure sensor comprises a soft contact layer, a piezoresistance type sensing element, a sensor main shell, a pagoda type anti-breaking structure and a thread protection shell, wherein the soft contact layer is used as a contact body of the soil pressure sensor and soil body, is made of high-elasticity materials, is arranged at a front window of the sensor main shell, directly transmits physical changes of the soil pressure to the piezoresistance type sensing element, the piezoresistance type sensing element is used as a core part of the soil pressure sensor, converts the physical changes of the soil pressure into voltage signals to be output, and the sensor main shell can be used as a carrier of the soft contact layer and can also be matched with a thread protection shell through internal threads so as to install and protect the piezoresistance type sensing element, and reduce the influence of external force on the piezoresistance type sensing element. According to the invention, a soft contact mode is adopted at the contact surface of the soil pressure sensor and the soil body, the front window is filled into the sensor main shell of the circular arc cylinder, the soft contact layer on the surface of the soil pressure sensor is deformed and deflected under the influence of the upper layer filled soil layer to form a flush shape with the sensor main shell, so that the soil pressure acts on the piezoresistive sensitive element, the soft contact layer of the soil pressure sensor adopts a high-elasticity material, the density of the high-elasticity material is between that of dry sand and saturated sand, and compared with that of an aluminum alloy material and a stainless steel material, the high-elasticity material adopted by the soft contact layer can effectively reduce the problem of rigidity matching between the soil pressure sensor and the soil body medium, thereby improving the test precision of the soil pressure sensor and ensuring that the soil pressure data measured by the soil pressure sensor has higher accuracy and reliability.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings that are required in the embodiments or the description of the prior art will be briefly described, and it is obvious that the drawings in the following description are only embodiments of the present invention, and that other drawings can be obtained according to the disclosed drawings without inventive effort for a person skilled in the art.
FIG. 1 is an exploded view of a main structure of a soft contact soil pressure sensor according to an embodiment of the present invention;
FIG. 2 is an exploded view showing the main structure of another soft contact soil pressure sensor according to an embodiment of the present invention;
FIG. 3 is a front view showing the main structure of a soft contact soil pressure sensor according to an embodiment of the present invention;
FIG. 4 is a cross-sectional view of a main structure of a soft contact soil pressure sensor according to an embodiment of the present invention;
FIG. 5 is a front view of a soft contact layer according to an embodiment of the present invention;
FIG. 6 is a side view of a soft contact layer according to an embodiment of the present invention;
FIG. 7 is a schematic diagram of a piezoresistive sensor connected to a four-core shielded cable according to an embodiment of the present invention;
FIG. 8 is a cross-sectional view of a piezoresistive sensor according to an embodiment of the present invention;
FIG. 9 is a schematic diagram illustrating connection between a sensor main housing and a pagoda-type anti-breakage structure according to an embodiment of the present invention;
FIG. 10 is a perspective view of a sensor main housing and pagoda-type break resistant structure connection as disclosed in an embodiment of the present invention;
FIG. 11 is a cross-sectional view of a connection between a sensor main housing and a pagoda-type anti-breakage structure in accordance with an embodiment of the present invention;
FIG. 12 is a schematic view of a screw thread protecting housing according to an embodiment of the present invention;
FIG. 13 is a graph showing particle size grading of standard silica sand for Fujian according to an embodiment of the present invention;
FIG. 14 (a) is a layout diagram of a soft contact soil pressure sensor according to an embodiment of the present invention;
FIG. 14 (b) is a schematic diagram of a centrifugal acceleration staged loading according to an embodiment of the present invention;
fig. 15 (a) is a diagram showing a centrifugal acceleration calibration result of a soft-contact soil pressure sensor T1 according to an embodiment of the present invention;
fig. 15 (b) is a diagram showing a theoretical soil pressure calibration result of a soft contact soil pressure sensor T1 according to an embodiment of the present invention;
Fig. 15 (c) is a diagram showing a centrifugal acceleration calibration result of a soft-contact soil pressure sensor T2 according to an embodiment of the present invention;
FIG. 15 (d) is a diagram showing the theoretical soil pressure calibration result of a soft contact soil pressure sensor T2 according to an embodiment of the present invention;
fig. 15 (e) is a diagram showing a centrifugal acceleration calibration result of a soft-contact soil pressure sensor T3 according to an embodiment of the present invention;
FIG. 15 (f) is a diagram showing the theoretical soil pressure calibration result of a soft contact soil pressure sensor T3 according to an embodiment of the present invention;
fig. 16 is a flowchart of a method for calibrating a soil pressure sensor according to an embodiment of the present invention.
Detailed Description
The following description of the embodiments of the present invention will be made clearly and completely with reference to the accompanying drawings, in which it is apparent that the embodiments described are only some embodiments of the present invention, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
The embodiment of the invention discloses a soft contact type soil pressure sensor and a calibration method thereof, wherein the soil pressure sensor comprises the following components: the soft contact layer is used as a contact body between the soil pressure sensor and soil, is made of high-elasticity materials and is arranged at a front window of the sensor main shell, the soil pressure physical change is directly transmitted to the piezoresistive sensor, the piezoresistive sensor is used as a core part of the soil pressure sensor, the soil pressure physical change is converted into voltage signals to be output, the sensor main shell can be used as a carrier of the soft contact layer and can be matched with a threaded protective shell through internal threads to install and protect the piezoresistive sensor, the influence of external force on the piezoresistive sensor is reduced, and the pagoda type anti-breaking structure is matched with the sensor main shell to install the teflon waterproof pipe. According to the invention, a soft contact mode is adopted at the contact surface of the soil pressure sensor and the soil body, the front window is filled into the sensor main shell of the circular arc cylinder, the soft contact layer on the surface of the soil pressure sensor is deformed and deflected under the influence of the upper layer filled soil layer to form a flush shape with the sensor main shell, so that the soil pressure acts on the piezoresistive sensitive element, the soft contact layer of the soil pressure sensor adopts a high-elasticity material, the density of the high-elasticity material is between that of dry sand and saturated sand, and compared with that of an aluminum alloy material and a stainless steel material, the high-elasticity material adopted by the soft contact layer can effectively reduce the problem of rigidity matching between the soil pressure sensor and the soil body medium, thereby improving the test precision of the soil pressure sensor and ensuring that the soil pressure data measured by the soil pressure sensor has higher accuracy and reliability.
Referring to fig. 1, an exploded view of a main structure of a soft contact type soil pressure sensor according to an embodiment of the present invention includes a soft contact layer 01, a piezoresistive sensor 02, a sensor main housing 04, a pagoda type breaking preventing structure 05, and a screw thread protecting housing 07.
The soft contact layer 01 is used as a contact body between the soil pressure sensor and soil body, and is made of high-elasticity materials and used for being arranged at a front window of the sensor main shell 04 to directly transmit physical changes of the soil pressure to the piezoresistive sensor 02.
The soft contact layer 01 of the invention mainly has the function of being arranged at the front window of the sensor main shell 04, is a contact body between the sensor and soil body, adopts high-elasticity material, and mainly comprises silicon rubber (namely, the invention is preferably high-elasticity silica gel material), and has the characteristics of good high temperature resistance, high pressure resistance, water resistance, oil resistance, strong corrosion resistance, electric insulation, high dielectric strength and the like, the density can be adjusted to be 1.7 g-2.5 g/cm 3 according to the soil body type, the Shore hardness can be selected to be 45-65, and the shearing resistance and the tensile strength are more than or equal to 2.0Mpa. And the dry sand density of the soil body grain composition of 0.08-2.0 mm is about 1.4g/cm 3～1.7g/cm3, and the saturated sand density is about 1.8g/cm 3～2.1g/cm3. Therefore, the density of the high-elasticity material is between that of dry sand and saturated sand, and compared with that of aluminum alloy materials (the density is about 2.7g/cm 3 and the Rockwell hardness is about 90) and stainless steel materials (the density is about 7.8g/cm 3 and the Rockwell hardness is about 201), the high-elasticity material adopted by the front surface of the soil pressure sensor can effectively reduce the problem of rigidity matching with soil media.
The elastomer with small micro-rigidity of the soft contact layer 01 can directly and physically change the soil pressure to the piezoresistive sensitive element 02, so that the sensitivity and the frequency response rate of the soil pressure sensor are improved. In addition, the soft contact layer 01 is made of high-elasticity silicon rubber, so that the matching error between the soft contact layer and the rigidity of the soil body is small, the stress redistribution phenomenon of the original sand stress field can be reduced, and the testing precision of the soil pressure sensor is improved.
The piezoresistive sensor 02 is used as a core part of the soil pressure sensor and is used for converting physical change of the soil pressure into voltage signal output.
The sensor main shell 04 is provided with internal threads, and is used for being matched with the threaded protective shell 07 through the internal threads so as to install and protect the piezoresistive sensor 02 and reduce the influence of external force on the piezoresistive sensor 02.
The sensor main housing 04 also serves as a carrier for the soft contact layer 01.
The sensor main case 04 is a circular arc cylinder.
The pagoda-type breaking preventing structure 05 is used for matching with the sensor main shell 04 to install a teflon waterproof pipe.
In summary, the invention discloses a soft contact type soil pressure sensor, which comprises a soft contact layer 01, a piezoresistive sensitive element 02, a sensor main shell 04, a pagoda type anti-breaking structure 05 and a thread protection shell 07, wherein the soft contact layer 01 is used as a contact body of the soil pressure sensor and soil body, is made of high-elasticity materials, is arranged at a front window of the sensor main shell 04, directly transmits physical changes of the soil pressure to the piezoresistive sensitive element 02, the piezoresistive sensitive element 02 is used as a core part of the soil pressure sensor, converts the physical changes of the soil pressure into voltage signals for output, and the sensor main shell 04 can be used as a carrier of the soft contact layer 01 and can also be matched with the thread protection shell 07 through internal threads so as to be arranged and protect the piezoresistive sensitive element 02, and the pagoda type anti-breaking structure 05 is matched with the sensor main shell 04 so as to reduce the influence of external force on the piezoresistive sensitive element 02 and install a teflon waterproof pipe. According to the invention, a soft contact mode is adopted on the contact surface of the soil pressure sensor and a soil body, the front window is filled into the sensor main shell 04 of the circular arc cylinder, the soft contact layer 01 on the surface of the soil pressure sensor is deformed and deflected to form a flush shape with the sensor main shell 04 under the influence of an upper layer filled soil layer, so that soil pressure acts on the piezoresistive sensitive element 02, the soft contact layer 01 of the soil pressure sensor is made of a high-elasticity material, the density of the high-elasticity material is between that of dry sand and saturated sand, and compared with that of an aluminum alloy material and a stainless steel material, the high-elasticity material adopted by the soft contact layer 01 can effectively reduce the problem of rigidity matching between the soil pressure sensor and the soil body medium, thereby improving the test precision of the soil pressure sensor and ensuring that soil pressure data measured by the soil pressure sensor have higher accuracy and reliability.
In order to further optimize the above embodiment, referring to fig. 2, the explosion diagram of the main structure of another soft contact soil pressure sensor disclosed in the embodiment of the present invention may further include a four-core shielding cable 03, where the four-core shielding cable 03 is fixedly connected with the piezoresistive sensor 02 on the basis of the embodiment shown in fig. 1.
To further optimize the above embodiment, the soil pressure sensor may further comprise a teflon waterproof pipe 06;
the pagoda-type breaking preventing structure 05 is matched with the main shell 04 of the sensor to install the teflon waterproof pipe 06.
The connection relationship between the main structures of the soil pressure sensor in the embodiment shown in fig. 2 may also be referred to as a front view and a cross-sectional view of the main structures of the soil pressure sensor shown in fig. 3 and 4, respectively.
The following describes each main structure of the soil pressure sensor in detail, specifically as follows:
referring to fig. 5 and fig. 6, which are respectively a front view and a side view of a soft contact layer disclosed in the embodiment of the present invention, a contact surface between the soft contact layer 01 and a soil body is an arc surface 011, and a contact surface between the soft contact layer 01 and the piezoresistive sensor 02 is a parallel surface 012;
The circular arc face 011 is used for deformation to disperse additional stress upon detection of soil pressure, and transmits to the parallel face 012.
According to the invention, the soft contact layer 01 can effectively reduce the arch effect phenomenon of the original sand stress field through the arc-shaped design (namely the arc surface 011) and the selection of the material (high-elasticity material), so that the test precision of the soil pressure sensor is improved.
Specifically, when the upper soil covering layer is filled, soil is disturbed, at the moment, the soil pressure sensor bears more stress in the soil, the contact surface of the soft contact layer 01 and the soil is designed to be an arc surface 011, so that when the upper soil covering pressure directly acts on the arc surface 011, the arc surface 011 can disperse additional stress through micro deflection deformation (the arc degree is reduced, but only limited by micro deformation of the contact surface), and the additional stress is uniformly applied to the soft contact layer 01 of the soil pressure sensor and then transferred to the parallel surface 012, the process can reduce the phenomenon of stress concentration to cause the sensor to measure the larger data and protect the piezoresistive sensor 02 in the soil pressure sensor from being damaged, and secondly, compared with the process of adopting aluminum alloy and stainless steel materials (high rigidity and easy reaction of the sensor to be insensitive), the soft contact layer 01 (low rigidity and elastomer) can directly change the soil pressure to the piezoresistive sensor 02, so that the sensitivity and the frequency response rate of the soil pressure sensor are improved.
Referring to fig. 7, a connection schematic diagram of a piezoresistive sensor and a four-core shielding cable according to an embodiment of the present invention is disclosed, and as can be seen from a cross-sectional view of the piezoresistive sensor shown in fig. 8, the piezoresistive sensor 02 is used as a core part of a soil pressure sensor, and includes a high-pressure chamber 021, a sensitive diaphragm 022, a vacuum chamber 023, a gold wire 024, a stress-free adhesive 025, a connection terminal 026, a conversion circuit board 027 and a silicon diaphragm protective housing 028.
The high pressure cavity 021 is a transparent pressure cavity for contacting with the soil pressure to be measured.
The vacuum chamber 023 is a transparent pressure chamber for outputting zero point with the vacuum environment as a reference.
In practical applications, the high-pressure chamber 021 and the vacuum chamber 023 may be made of expanded glass.
The sensitive diaphragm 022 is made of semiconductor material (silicon), and a high-pressure cavity 021 and a vacuum cavity 023 are respectively arranged on two sides of the sensitive diaphragm 022 and are used for generating strain change when the pressure born by the high-pressure cavity 021 and the vacuum cavity 023 is different, and converting the strain change into voltage signal output.
The gold wire 024 is used to connect a plurality of equivalent resistors disposed in the sensitive membrane 022 to form a wheatstone bridge.
The connection terminal 026 is provided on the conversion circuit board 027 and is connected to the gold wire 024.
The conversion circuit board 027 is used for fixedly connecting with the four-core shielding cable 03 outside the piezoresistive sensor 02.
The front of the silicon diaphragm protective housing 028 is windowed and is internally provided with a cavity structure which is used for installing the high-pressure cavity 021, the sensitive diaphragm 022 and the vacuum cavity 023, and the periphery and the surface are filled with stress-free glue 025 as a protective layer.
Preferably, the piezoresistive sensitive element 02 can be a micro high-frequency piezoresistive sensitive diaphragm, and the natural frequency can be up to 700kHz.
Specifically, the sensitive membrane 022 is configured to generate a strain change when the pressures applied to the high-voltage cavity 021 and the vacuum cavity 023 are different, convert the strain change into a voltage signal and output the voltage signal, and set a plurality of equivalent resistors (for example, four equivalent resistors R 1＝R2＝R3＝R4 =5kΩ) on the sensitive membrane 022 by using an ion implantation process, connect the four equivalent resistors by using a gold wire 024 to form a wheatstone bridge, then connect the gold wire 024 with a connection terminal 026 on the conversion circuit board 027, and then solder the internal cable of the conversion circuit board 028 with an external four-core shielding cable 03. When the pressure (soil pressure change) of the high-pressure cavity 021 and the vacuum cavity 023 on two sides of the sensitive diaphragm 022 are different, the sensitive diaphragm 022 generates strain change and converts the strain change into voltage signal output, the front surface of the silicon diaphragm protective shell 028 is windowed and is internally provided with a cavity structure, the cavity structure is used for installing the high-pressure cavity 021, the sensitive diaphragm 022 and the vacuum cavity 023, and the periphery and the surface are filled with non-stress glue 025 as protective layers, and the upper surface of the non-stress glue 025 is bonded with the parallel surface 012 of the soft contact layer 01, so that the stress of the whole cavity surface is uniform.
As can be seen from the above, the sensing element of the soil pressure sensor of the present invention may be a micro high-frequency piezoresistive sensing diaphragm, in which a plurality of equivalent resistors (for example, four equivalent resistors) are disposed on the sensing diaphragm 022 by using an ion implantation process, and a plurality of equivalent circuits are connected by using a gold wire 024 to form a wheatstone bridge, two pressure chambers including a high-pressure chamber 021 and a vacuum chamber 023 are disposed on two sides of the sensing diaphragm 022, and when the pressures of the two pressure chambers are different, the sensing diaphragm 022 generates strain, thereby improving the frequency response performance and sensitivity of the soil pressure sensor.
In addition, through the design and adoption of the piezoresistive sensitive membrane in the embodiment, the volume of the soil pressure sensor can be reduced, the diameter can be controlled within 10mm, and the output voltage signal can reach more than 100 mV.
Furthermore, the invention utilizes the design of the cavity in the shell to fix the sensitive diaphragm 022, and covers a layer of stress-free protective glue 025 on the surface and the periphery of the sensitive diaphragm 022, thereby not only reducing the damage to the sensitive diaphragm 022 caused by the stress concentration generated by filling and compacting the upper soil covering layer and avoiding the direct contact between the soil body and the sensitive diaphragm 022, further improving the service life cycle of the soil pressure sensor, and ensuring the uniform stress of the whole inner cavity surface, thereby improving the test precision of the soil pressure sensor.
Referring to fig. 9-11, a schematic connection diagram of a sensor main housing and a pagoda-type anti-breaking structure, a perspective connection diagram of the sensor main housing and the pagoda-type anti-breaking structure, and a cross-sectional connection diagram of the sensor main housing and the pagoda-type anti-breaking structure are disclosed in the embodiment of the invention, the sensor main housing 04 includes a soft contact layer positioning groove 041, a soft contact layer supporting beam 042, a sensing element mounting cavity 043, and a sensing element positioning groove 044, wherein an internal thread 045 is disposed inside the sensing element mounting cavity 043.
Soft contact layer positioning slots 041 are used to position soft contact layer 01.
The soft contact layer support beam 042 is used to support the soft contact layer 01.
The sensor mounting cavity 043 is used for placing the piezoresistive sensor 02, positioning the piezoresistive sensor 02 by combining the sensor positioning groove 044, and filling epoxy resin into the residual space after the piezoresistive sensor 02 is positioned and mounted, so as to further fix and waterproof the inside of the piezoresistive sensor 02 and isolate the influence of lateral additional stress on the piezoresistive sensor 02. .
Specifically, the sensor main housing 04 is matched with the pagoda type anti-breaking structure 05 so as to install the teflon waterproof tube 06, and further the four-core shielding cable 03 is protected from breaking and the cable is protected from water.
In summary, the cable fixing and sealing mode of the soil pressure sensor adopts the design of the pagoda type anti-breaking structure 05, so that the shearing strength and the tensile strength of the cable of the soil pressure sensor can be effectively improved, the sealing effect of the soil pressure sensor can be improved, the cable exposed outside can be protected by matching with the teflon material cable protection layer, and the interference effect on the original flow field and the stress field and the abrasion of the cable of the sensor can be reduced.
Referring to fig. 12, a schematic structural view of a screw thread protecting housing according to an embodiment of the present invention is disclosed, and the screw thread protecting housing 07 mainly includes a connecting external screw thread 071 and a sensing element supporting column 072.
The screw protection housing 07 mates with the sensor main housing 04 by connecting external screw threads 071 and supports and secures the piezoresistive sensor 02 by the sensor support post 072.
In particular, the split structure of the thread protection casing 07 and the sensor main casing 04 is adopted in the invention, so that the maintenance capability of the soil pressure sensor can be increased, and the utilization rate of the piezoresistive sensor 02 can be improved.
In order to improve the reliability of the soil pressure sensor, the soil pressure sensor needs to be calibrated before use, and the soil pressure sensor can be calibrated by adopting a geotechnical centrifuge during calibration.
Referring to fig. 16, a flowchart of a method for calibrating a soil pressure sensor according to an embodiment of the present invention is disclosed, and the method is applied to a data acquisition device, where the data acquisition device is connected to the soil pressure sensor in the foregoing embodiment, and the method for calibrating soil pressure may include:
and S101, dividing the maximum theoretical soil pressure value of the soil layer required to be measured by the soil pressure sensor to be calibrated into M levels.
The maximum theoretical soil pressure is the maximum soil pressure value of the corresponding prototype depth under the preset centrifugal acceleration condition.
Wherein M is a positive integer.
In practical applications, each level corresponds to a calibration soil pressure output voltage signal.
Step S102, determining theoretical soil pressure values corresponding to the soil layer depths under the centrifugal acceleration of output voltage signals of the soil pressure sensors to be calibrated under each level.
Specifically, when the soil pressure sensor to be calibrated is buried to the soil layer depth corresponding to the actual test, centrifugal acceleration load is applied to the soil pressure sensor to be calibrated step by step to a preset value based on M grades, and a theoretical soil pressure value corresponding to the output voltage signal of the soil pressure sensor to be calibrated at each grade and the soil layer depth under each centrifugal acceleration is obtained.
The preset value is determined according to actual needs, and the invention is not limited herein.
And step S103, obtaining average calibration coefficients of all levels of soil pressure output voltage signals of the soil pressure sensor to be calibrated and theoretical soil pressure values under the corresponding centrifugal acceleration conditions by utilizing a least square method curve fitting method based on the theoretical soil pressure values corresponding to all levels.
Wherein the average calibration coefficient is the ratio of each stage of theoretical soil pressure value (kPa) to the soil pressure sensor (mV) to be calibrated.
And step S104, multiplying all levels of soil pressure output voltage signals of the soil pressure sensor to be calibrated by corresponding average calibration coefficients to obtain actual measurement output soil pressure values of the soil pressure sensor to be calibrated at all levels.
Step 105, calculating the deviation between the measured output soil pressure value corresponding to each level of the soil pressure sensor to be calibrated and the corresponding theoretical soil pressure value.
And S106, determining target coefficients after the soil pressure sensor to be calibrated is calibrated based on the deviation amounts.
In summary, according to the invention, the soil pressure sensor to be calibrated is connected with the data acquisition instrument, the data acquired from the soil pressure sensor to be calibrated is processed by the data acquisition instrument, so that the deviation amount of the actually measured output soil pressure value corresponding to each level of the soil pressure sensor to be calibrated and the corresponding theoretical soil pressure value is obtained, the target coefficient after the calibration of the soil pressure sensor to be calibrated is obtained based on each deviation amount, the calibration of the soil pressure sensor to be calibrated is completed, the test precision of the soil pressure sensor is further improved, and the soil pressure data measured by the soil pressure sensor has higher accuracy and reliability.
The soil pressure sensor calibration process is illustrated as follows:
1) The soil sample material can be selected according to the actual test soil type, in this embodiment, the soil sample material is taken as a Fujian standard quartz sand as an example, the grain size grading curve of the Fujian standard quartz sand is shown in fig. 13, and the basic physical parameters are shown in table 1, as follows:
TABLE 1 Main physical parameters of Fujian Standard Quartz Sand
The sand relative density D r is 55%, the dry sand model is distributed in 5 layers in the model box, the embedded depths of the sensors are respectively 50mm (number T1), 150mm (number T2), 250mm (number T3), 350mm (number T4) and 450mm (number T5), 1 soft-contact soil pressure sensor to be calibrated is distributed at the right center of each layer, 5 sensors are distributed in total, the distribution direction of each sensor is vertical upwards, and then the model box, the soft-contact soil pressure sensor and the cable are hoisted to a geotechnical centrifuge and are connected with a data acquisition instrument.
2) After preheating 5 soft-contact soil pressure sensors for 60min, setting the sampling rate of a data acquisition instrument to be 5Hz, setting the initial calibration coefficient (ICF) of the soft-contact soil pressure sensors to be 1.0, setting the initial value of the soft-contact soil pressure sensors to be NULL (namely balance zero clearing) on the data acquisition instrument, monitoring the soft-contact soil pressure sensors to be calibrated on a display screen of the data acquisition instrument in real time after the soft-contact soil pressure sensors are set to be NULL, and checking whether output voltage signals of the soft-contact soil pressure sensors are in a stable state and are affected by noise.
3) The geotechnical centrifuge loads centrifugal acceleration (the number of stages is more than or equal to 5) in a grading manner, namely 5g, 10g, 15g, 20g, 30g, 40g and 50g respectively, after the centrifugal acceleration of each stage is kept more than or equal to 5min, after the soil layer reaches a stable state and the output voltage of the soft contact soil pressure sensor reaches a stable state, the centrifugal acceleration of the next stage is applied, as shown in fig. 14 (a) and 14 (b), the centrifugal acceleration is repeatedly applied for 2-3 times, and the average output voltage value of the soft contact soil pressure sensor under the condition of the centrifugal acceleration of each stage is obtained.
4) Finally, calculating a calibration coefficient ACF (unit: kPa/mV) of the soft-contact soil pressure sensor by using the formula (1) (namely, drawing a calibration contrast curve of an output voltage value (abscissa) of the soft-contact soil pressure sensor recorded by a data acquisition instrument and a theoretical soil pressure value (ordinate) corresponding to each soil layer under each level of centrifugal acceleration), and performing curve fitting and conversion correlation coefficient R 2 based on the calibration curve to obtain representative soft-contact soil pressure sensor serial numbers T1, T2 and T3 calibration results shown in fig. 15 (a) -15 (f).
Wherein N is centrifugal acceleration of each stage, ρ is density of each soil layer (kg/m 2),gc is gravity acceleration (m/s 2) (9.8 is taken), h is embedded height (m) of the soft contact soil pressure sensor, N is the number of measuring points recorded in the calibration process, X is output voltage signals of the soft contact soil pressure sensor, the unit is mV, and Y is a theoretical soil pressure value corresponding to each soil layer under each stage of centrifugal acceleration, and the unit is kPa.
Finally, it is further noted that relational terms such as first and second, and the like are used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. Moreover, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising one does not exclude the presence of other like elements in a process, method, article, or apparatus that comprises an element.
In the present specification, each embodiment is described in a progressive manner, and each embodiment is mainly described in a different point from other embodiments, and identical and similar parts between the embodiments are all enough to refer to each other.
The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.
Claims (8)
1. The soft contact type soil pressure sensor is characterized by comprising a soft contact layer, a piezoresistance type sensitive element, a sensor main shell, a pagoda type anti-breaking structure and a thread protection shell;
The soft contact layer is used as a contact body between the soil pressure sensor and soil body, and is made of high-elasticity materials, wherein the density of the high-elasticity materials is between that of dry sand and saturated sand, and the high-elasticity materials are used for being arranged at a front window of the sensor main shell and directly transmitting the physical change of the soil pressure to the piezoresistive sensitive element;
the piezoresistive sensitive element is used as a core part of the soil pressure sensor and is used for converting the physical change of the soil pressure into voltage signals for output;
The sensor main shell is provided with an internal thread, is matched with the thread protective shell through the internal thread to mount and protect the piezoresistive sensitive element, and is also used as a carrier of the soft contact layer;
the pagoda type anti-breaking structure is used for being matched with the sensor main shell so as to install a teflon waterproof pipe;
the thread protection shell comprises a connecting external thread and a sensitive element support column;
The thread protection shell is matched with the sensor main shell through the connecting external thread, and supports and fixes the piezoresistive sensitive element through the sensitive element support column.
2. The soil pressure sensor according to claim 1, wherein the contact surface of the soft contact layer and the soil body is an arc surface, and the contact surface of the soft contact layer and the piezoresistive sensor is a parallel surface;
The circular arc surface is used for dispersing additional stress when the soil pressure is detected and transmitting the additional stress to the parallel surface.
3. The soil pressure sensor of claim 1, wherein the piezoresistive sensor comprises a high pressure chamber, a sensor diaphragm, a vacuum chamber, a gold wire, a stress free adhesive, a connection terminal, a conversion circuit board, and a silicon diaphragm protective case;
the high-pressure cavity is a transparent pressure cavity and is used for being contacted with the soil pressure to be measured;
the vacuum cavity is a transparent pressure cavity and is used for taking a vacuum environment as a reference output zero point;
the high-pressure cavity and the vacuum cavity are respectively arranged on two sides of the sensitive diaphragm, and are used for generating strain change when the pressure born by the high-pressure cavity and the vacuum cavity is different, and converting the strain change into voltage signals to be output;
the gold wire is used for connecting a plurality of equivalent resistors arranged in the sensitive membrane to form a Wheatstone bridge;
The wiring terminal is arranged on the conversion circuit board and is connected with the gold wire lead;
the conversion circuit board is used for being fixedly connected with a four-core shielding cable outside the piezoresistive sensitive element;
The front side of the silicon diaphragm protective housing is windowed, and a cavity structure is arranged inside the silicon diaphragm protective housing, and is used for installing the high-pressure cavity, the sensitive diaphragm and the vacuum cavity, and the stress-free glue is filled around and on the surface of the cavity structure to serve as a protective layer.
4. The soil pressure sensor according to claim 1, wherein the sensor main housing comprises a soft contact layer positioning groove, a soft contact layer supporting beam, a sensitive element mounting cavity and a sensitive element positioning groove, wherein the internal thread is arranged in the sensitive element mounting cavity;
the soft contact layer positioning groove is used for positioning the soft contact layer;
the soft contact layer supporting beam is used for supporting the soft contact layer;
the sensor mounting cavity is used for placing the piezoresistive sensor, positioning the piezoresistive sensor by combining the sensor positioning groove, and filling epoxy resin in the residual space after the piezoresistive sensor is positioned and mounted.
5. The soil pressure sensor of claim 1, further comprising a four-core shielded cable;
The four-core shielding cable is fixedly connected with the piezoresistive sensitive element.
6. The soil pressure sensor of claim 1, further comprising the Teflon waterproof tube.
7. The soil pressure sensor of claim 1, wherein the piezoresistive sensor is a miniature high frequency response piezoresistive sensor diaphragm.
8. A method for calibrating a soil pressure sensor, characterized in that the method is applied to a data acquisition instrument, the data acquisition instrument is connected with the soil pressure sensor according to any one of claims 1 to 7, and the method for calibrating the soil pressure comprises the following steps:
Dividing the maximum theoretical soil pressure value of a soil layer required to be measured by the soil pressure sensor to be calibrated into M grades, wherein M is a positive integer;
when the soil pressure sensor to be calibrated is buried to the soil layer depth corresponding to the actual test, applying centrifugal acceleration load to the soil pressure sensor to be calibrated step by step to a preset value based on M grades, and obtaining a theoretical soil pressure value corresponding to the output voltage signal of the soil pressure sensor to be calibrated at each grade and the soil layer depth under each centrifugal acceleration;
based on the theoretical soil pressure value corresponding to each level, obtaining average calibration coefficients of each level of soil pressure output voltage signal of the soil pressure sensor to be calibrated and the theoretical soil pressure value under the corresponding centrifugal acceleration condition by using a least square method curve fitting method;
multiplying each level of soil pressure output voltage signal of the soil pressure sensor to be calibrated by the corresponding average calibration coefficient to obtain an actually measured output soil pressure value of the soil pressure sensor to be calibrated at each level;
Calculating the deviation amount of the actually measured output soil pressure value corresponding to each level of the soil pressure sensor to be calibrated and the corresponding theoretical soil pressure value;
And determining target coefficients after the soil pressure sensor to be calibrated is calibrated based on the deviation amounts.
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| CN110987707A (en) * | 2019-12-09 | 2020-04-10 | 中国人民解放军军事科学院国防工程研究院工程防护研究所 | Manufacturing method of rock-soil pressure sensor bag body |
| CN111122657B (en) * | 2019-12-11 | 2021-05-04 | 武汉大学 | A ground-based GNSS-R sensing method for soil moisture under vegetation using a three-channel receiver |
| CN111928991B (en) * | 2020-09-10 | 2025-03-18 | 中国地震局工程力学研究所 | Integrated micro pore pressure sensor |
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| CN1987385A (en) * | 2005-12-23 | 2007-06-27 | 昆山双桥传感器测控技术有限公司 | Pressure resistance type soil stress sensor |
| CN104792615A (en) * | 2015-04-02 | 2015-07-22 | 长沙理工大学 | Soil pressure testing device and soil pressure testing correction calculation method |
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