Integrated micro pore pressure sensor

Abstract

The present invention discloses an integrated micro-pore pressure sensor. In the sensor: a filter installation slot, a sensing element installation slot, and a ventilation duct are sequentially arranged in the main shell along the axial direction, a porous filter is installed in the filter installation slot, a sensing element is installed in the sensing element installation slot, and a sensor cable at the tail end of the sensing element extends out of the main shell through the ventilation duct to connect with the ventilation cable; the sensing element includes an annular packaging shell, a piezoresistive core, a positioning plate, and a sensor cable, the positioning plate and the annular packaging shell constitute a concave core installation slot, and the piezoresistive core is arranged on the positioning plate; the concave core installation slot is filled and smeared with stress-free glue; the place where the sensing element installation slot and the ventilation duct meet constitutes a step surface for axial positioning of the sensing element; the sensing element is fixedly connected to the sensing element installation slot by an adhesive. The micro-pore pressure sensor can be applied to geotechnical centrifuge tests, and has a low failure rate, high stability, and strong anti-interference performance.

Description

Technical Field

[0001] The invention relates to the technical field of geotechnical test sensors, and in particular to an integrated micro pore pressure sensor. Background Art

[0002] Geotechnical centrifuge test: With the help of geotechnical centrifuge, the stress loss of soil or geotechnical structures in various parts of the centrifugal model is compensated to achieve a stress level close to or equal to that of the prototype. When an over-compression dynamic load is applied, the dynamic characteristics and failure mechanism of the actual prototype can be presented more accurately.

[0003] Pore ​​water pressure: generally refers to the water pressure when the pore medium of saturated soil is filled with water. It is a positive pressure above the atmospheric pressure. Pore water pressure is divided into static pore water pressure and excess static pore water pressure.

[0004] Static pore water pressure: caused by the deadweight of groundwater in the foundation soil, that is, the pore water pressure below the static groundwater is the static pore water pressure.

[0005] Excess pore water pressure: The part of pore water pressure that exceeds the static pore water pressure due to dynamic loads such as seismic waves, blasting, and traffic loads is called excess pore water pressure.

[0006] Pore ​​pressure sensor: Pore pressure sensor is a key measurement sensor for monitoring the growth and dissipation of excess pore water pressure in saturated / unsaturated soil. It can directly reflect the stress state and stability of soil in geotechnical engineering physical models, geotechnical structures, construction site foundations, etc.

[0007] Integrated pore pressure sensor: The main housing of the pore pressure sensor is an integral part, and the porous filter at the front end of the sensor cannot be freely disassembled.

[0008] Porous filter: used to separate soil particles and pore fluid, allowing the pore fluid to freely enter and exit the sensor to act on the sensor sensing element, thereby causing changes in the pore fluid pressure.

[0009] In the field of geotechnical earthquake engineering, accurate measurement of pore water pressure is an important research direction of engineering tests, which can directly reflect the softening and liquefaction disaster process of soil in the site foundation, geotechnical structures and geotechnical model tests. Due to the large differences between the porous filter and ventilation cable of the integrated micro pore pressure sensor and the conventional pressure sensor, the test accuracy of the integrated micro pore pressure sensor is affected by many factors. More importantly, unlike the conventional vibration table and on-site in-situ test, the geotechnical centrifuge test compensates for the stress loss of the soil under the environment of N times high centrifugal acceleration, and then applies the super-compression dynamic load (frequency of tens to hundreds of Hz, load duration less than 1s). The excess static pore water pressure in the soil is accompanied by the vibration acceleration. The acceleration completes the rapid growth process in an "instant". In the geotechnical centrifuge test, the integrated micro pore pressure sensor is often required to have the characteristics of high frequency response, good stability, low failure rate, and strong anti-interference ability to ensure the accuracy and reliability of its test results, which further illustrates the importance of the integrated micro pore pressure sensor with excellent performance to geotechnical tests.

[0010] Before 2010, the international standard pore water pressure sensor PDCR-81 was a "high-precision, high-frequency response, high-stability" integrated micro pore pressure sensor widely used in geotechnical centrifuge tests at home and abroad, and was considered the "standard" sensor for pore water pressure measurement in geotechnical centrifuge tests. However, due to the low sales volume of PDCR-81 compared with other types of sensors from Druck, since the British Druck company announced the discontinuation of the PDCR-81 integrated micro pore pressure sensor in 2010, geotechnical testing units around the world have lost their main source of high-precision, high-frequency response integrated pore pressure sensors. Ten years have passed since then, and as the inventory of PDCR-81 integrated pore pressure sensors in various geotechnical engineering research units has been almost exhausted, the demand for the development of an alternative integrated pore pressure sensor to PDCR-81 has become increasingly strong.

[0011] In recent years, the integrated pore pressure sensors developed by many domestic manufacturers have defects in their structural design, packaging and waterproof structure, resulting in problems such as low frequency response performance, low measurement accuracy, high failure rate, poor stability and poor anti-interference performance. They are not suitable for the "high frequency response, high precision" geotechnical centrifuge test pore water pressure measurement needs; and although the newly developed integrated sensors by foreign manufacturers have higher frequency response performance and measurement accuracy, they still have many problems in failure rate, anti-interference performance and waterproof performance.

[0012] Specifically, the disadvantages of the integrated miniature air pressure sensor in the prior art are as follows:

[0013] (1) In terms of sensor component packaging

[0014] In the prior art, the internal sensing elements of the HC-25 integrated pore pressure sensor are all installed on the circular glass ring inside the shell. Although this can effectively reduce the stress on both sides of the sensor, the pore fluid is still mixed with fine soil particles and other materials. The sensor sensing element is in direct contact with the measured pore fluid, which can easily cause irreversible damage and destruction to the sensing element. This is also one of the main reasons for the high failure rate of sensors in the prior art. The KYB integrated pore pressure sensor is modified from the soil pressure sensor. The strain sensing membrane is encapsulated on the inner side of the shell pressure sensing surface with adhesive, and the pore fluid pressure is measured through its deformation and deflection. However, its response speed is lower than that of the HC-25 sensor, and it cannot adapt to and meet the measurement requirements of geotechnical centrifuge tests.

[0015] (2) In terms of porous filter installation method

[0016] In the prior art, the porous filters of the integrated micro pore pressure sensors such as HC-25 and KYB are directly fixed by adhesives. When the integrated micro pore pressure sensors in the prior art are in saturated fluid monitoring environments such as geotechnical centrifuge tests, rock and soil structures, and site foundations for a long time, the porous filters of the sensors are easily caused to fall off, thereby causing the sensors to malfunction.

[0017] (3) In terms of sensor waterproof sealing method

[0018] The waterproof structure at the tail of the HC-25 and KYB integrated micro pore pressure sensors in the prior art is mainly used to connect with the ventilation cable to provide waterproof sealing for the cable. However, after a large number of experimental results, it was found that although the waterproof structure can achieve a certain sealing effect, it is found that a large amount of water vapor is easily accumulated inside the sensor ventilation cable in saturated fluid under high centrifugal acceleration environment for a long time, which in turn affects the accuracy and reliability of the pore pressure data measured by the integrated micro pore pressure sensor. More seriously, it may cause water vapor to directly block the ventilation cable, causing the integrated pore pressure sensor to fail to work properly.

[0019] (4) Sensor without cavity structure design

[0020] In the prior art, traditional domestic sensors such as HC-25 and KYB integrated micro pore pressure sensors do not take into account the sensor cavity structure design (the "cavity" refers to the cavity gap between the porous filter and the sensing element provided by the present invention), which causes impurities such as tiny soil particles in the pore fluid inside the soil to enter the sensor through the porous filter, which may directly cause a bridge between the porous filter and the sensing element, thereby causing stress concentration in the sensing element, resulting in larger sensor test data, and more seriously, directly causing irreversible damage to the sensing element.

[0021] Therefore, there is an urgent need to develop a new type of integrated micro pore pressure sensor that can be suitable for high-frequency response, high-precision geotechnical centrifuge tests, and has a low failure rate, high stability, and strong anti-interference performance. This is of great practical significance for solving related "bottleneck" technical problems. Summary of the invention

[0022] In view of this, the purpose of the present invention is to provide an integrated micro pore pressure sensor with a novel structure and excellent performance, which can be applied to high-frequency response and high-precision geotechnical centrifuge tests, and has a low failure rate, high stability and strong anti-interference performance.

[0023] To achieve the above object, the present invention provides the following technical solutions:

[0024] An integrated micro pore pressure sensor, comprising a porous filter, a sensing element, a main housing and a ventilation cable, wherein:

[0025] The main housing is provided with a filter installation slot, a sensor element installation slot and a ventilation pipe in sequence along the axial direction, the porous filter is installed in the filter installation slot, the sensor element is installed in the sensor element installation slot, and the sensor cable at the tail end of the sensor element extends out of the main housing through the ventilation pipe to be connected with the ventilation cable;

[0026] The sensing element comprises an annular packaging shell, a piezoresistive core, a positioning plate and the sensor cable, wherein the positioning plate is fixedly connected to one end of the annular packaging shell so that a concave core installation groove is formed in the annular packaging shell, the piezoresistive core is located in the concave core installation groove and is arranged on the side of the positioning plate, the sensor cable is connected to the piezoresistive core and passes through the positioning plate and extends into the ventilation duct, and a connecting hole is arranged on the positioning plate;

[0027] The concave core body installation groove is filled and coated with stress-free glue;

[0028] The place where the sensor element installation groove and the ventilation pipe meet constitutes a step surface for axially positioning the sensor element;

[0029] The side of the positioning plate away from the annular packaging shell is fixedly connected to the step surface by an adhesive, and / or the outer wall of the annular packaging shell is fixedly connected to the sensor element installation groove by an adhesive.

[0030] Optionally, in the above-mentioned integrated micro pore pressure sensor, the through hole in the sensing element installation groove is a first stepped hole, and in the first stepped hole:

[0031] The hole section close to the porous filter is a first hole section adapted to the annular packaging shell;

[0032] The hole section close to the ventilation duct is a second hole section adapted to the positioning plate;

[0033] The hole diameter of the first hole segment is smaller than the hole diameter of the second hole segment.

[0034] Optionally, in the above-mentioned integrated micro pore pressure sensor, a spacing groove is provided inwardly protruding between the filter mounting groove and the sensing element mounting groove, wherein:

[0035] The aperture of the spacing groove is smaller than the end diameter of the porous filter so as to axially limit the porous filter;

[0036] The annular inner wall surface of the spacing groove and the porous filter and the sensing element located on both sides of the spacing groove form a cavity structure with a thickness of 0.1 mm to 0.5 mm.

[0037] Optionally, in the above-mentioned integrated micro pore pressure sensor, the aperture of the spacing groove is smaller than the aperture of the first hole section.

[0038] Optionally, in the above-mentioned integrated micro pore pressure sensor, the filter mounting slot is provided with: an end opening (040) adapted to the shape of the porous filter, a sealing ring positioning groove adapted to the positioning sealing ring, and a filter glue sealing groove for filling with sealing grease in sequence along the axial direction.

[0039] Optionally, in the above-mentioned integrated micro pore pressure sensor, the aperture of the end opening (040) is D1, the aperture of the sealing ring positioning groove is D2, and the aperture of the filter glue sealing groove is D3, and D2>D3>D1.

[0040] Optionally, in the above-mentioned integrated micro pore pressure sensor, one end of the porous filter is a cylindrical side wall structure, and the other end is a conical side wall structure, the positioning sealing ring is adapted to the cylindrical side wall structure, and the conical side wall structure is located in the filter glue sealing groove.

[0041] Optionally, in the above-mentioned integrated micro pore pressure sensor, a barb pagoda head structure for connecting the ventilation cable is provided on the main shell, a through hole connected to the ventilation pipe is provided in the barb pagoda head structure, and a barb step is provided on the outer side of the barb pagoda head structure.

[0042] Optionally, in the above-mentioned integrated micro pore pressure sensor, a sealing groove for filling with sealing grease is provided on the end of the main shell for connecting the ventilation cable, and the barbed pagoda head structure connection end is located at the bottom of the sealing groove.

[0043] Optionally, in the above-mentioned integrated micro pore pressure sensor, the through hole in the ventilation pipe is a second stepped hole, and in the second stepped hole, the hole section adjacent to the sensing element mounting groove is a third hole section, and the hole section connected to the barbed pagoda head structure is a fourth hole section, and the aperture of the third hole section is larger than the aperture of the fourth hole section.

[0044] It can be seen from the above technical scheme that in the integrated micro pore pressure sensor provided by the present invention, the sensor chip-level packaging is realized by stress-free glue and adhesive, and the device-level packaging is realized by the main shell. The sensor as a whole realizes electromagnetic shielding, electrical insulation, side stress isolation, thermal isolation and other treatments for the sensing elements in the sensor. Moreover, the annular packaging shell can protect the piezoresistive core from the stress on both sides of the sensor to the greatest extent, ensuring the normal operation of the piezoresistive core; the stress-free glue can directly avoid direct contact between the sensing element and the pore fluid, thereby effectively preventing impurities such as fine particles in the saturated fluid from damaging the sensing element, greatly reducing the failure rate of the sensor. Therefore, the integrated micro pore pressure sensor provided by the present invention has high long-term stability and anti-interference performance, and can be applied to high-frequency response and high-precision geotechnical centrifuge tests. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0046] Figure 1 A first exploded structural axonometric diagram of the integrated micro pore pressure sensor provided in an embodiment of the present invention;

[0047] Figure 2 A second exploded structural axonometric diagram of the integrated micro pore pressure sensor provided by an embodiment of the present invention;

[0048] Figure 3 A first overall structural axonometric diagram of the integrated micro pore pressure sensor provided in an embodiment of the present invention;

[0049] Figure 4 A second overall structural axonometric diagram of the integrated micro pore pressure sensor provided in an embodiment of the present invention;

[0050] Figure 5 A front view of an integrated micro pore pressure sensor provided by an embodiment of the present invention;

[0051] Figure 6 A cross-sectional view of an integrated micro pore pressure sensor provided by an embodiment of the present invention;

[0052] Figure 7 An axonometric view of a porous filter provided by an embodiment of the present invention;

[0053] Figure 8 A side view of a porous filter provided by an embodiment of the present invention;

[0054] Fig. 9 A schematic diagram of the structure of a sealing ring provided in an embodiment of the present invention;

[0055] Fig.10 A first isometric view of a sensing element provided by an embodiment of the present invention;

[0056] Fig.11 A second isometric view of a sensing element provided by an embodiment of the present invention;

[0057] Fig.12 A first perspective isometric view of a main housing provided with a barbed pagoda head structure provided in an embodiment of the present invention;

[0058] Fig.13 A second perspective isometric view of a main housing provided with a barbed pagoda head structure provided in an embodiment of the present invention;

[0059] Fig.14 A cross-sectional view of a main housing provided with a barbed pagoda head structure provided in an embodiment of the present invention;

[0060] Fig.15 A schematic structural diagram of a ventilation cable provided in an embodiment of the present invention.

[0061] in:

[0062] 01-porous filter, 02-positioning seal ring, 03-sensing element, 04-stainless steel main shell,

[0063] 05-barb pagoda head structure, 06-ventilation cable;

[0064] 011 - side surface of the porous filter, 012 - trapezoidal end surface of the porous filter;

[0065] 031-ring packaging shell, 032-piezoresistive core, 033-concave core installation groove,

[0066] 034-positioning plate, 035-sensor cable, 036-vent;

[0067] 040-end opening, 041-seal ring positioning groove, 042-filter glue sealing groove,

[0068] 043-sensor cavity structure, 044-sensor element installation groove, 045-ventilation duct,

[0069] 046-sealing groove;

[0070] 051-Barbed stairs. DETAILED DESCRIPTION

[0071] The invention discloses an integrated micro pore pressure sensor with a novel structure and excellent performance, which can be applied to high-frequency response and high-precision geotechnical centrifuge tests and has a low failure rate, high stability and strong anti-interference performance.

[0072] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0073] See also Figures 1 to 15 , Figure 1 A first exploded structural axonometric diagram of the integrated micro pore pressure sensor provided in an embodiment of the present invention; Figure 2 A second exploded structural axonometric diagram of the integrated micro pore pressure sensor provided by an embodiment of the present invention; Figure 3 A first overall structural axonometric diagram of the integrated micro pore pressure sensor provided in an embodiment of the present invention; Figure 4 A second overall structural axonometric diagram of the integrated micro pore pressure sensor provided in an embodiment of the present invention; Figure 5 A front view of an integrated micro pore pressure sensor provided by an embodiment of the present invention; Figure 6 A cross-sectional view of an integrated micro pore pressure sensor provided by an embodiment of the present invention; Figure 7 An axonometric view of a porous filter provided by an embodiment of the present invention; Figure 8 A side view of a porous filter provided by an embodiment of the present invention; Fig. 9 A schematic diagram of the structure of a sealing ring provided in an embodiment of the present invention; Fig.10 A first isometric view of a sensing element provided by an embodiment of the present invention; Fig.11 A second isometric view of a sensing element provided by an embodiment of the present invention; Fig.12 A first perspective isometric view of a main housing provided with a barbed pagoda head structure provided in an embodiment of the present invention; Fig.13 A second perspective isometric view of a main housing provided with a barbed pagoda head structure provided in an embodiment of the present invention; Fig.14 A cross-sectional view of a main housing provided with a barbed pagoda head structure provided in an embodiment of the present invention; Fig.15 A schematic structural diagram of a ventilation cable provided in an embodiment of the present invention.

[0074] The embodiment of the present invention provides an integrated micro pore pressure sensor (also referred to as an "integrated micro pore pressure sensor", or simply referred to as a "sensor") with a novel structure and excellent performance. The integrated micro pore pressure sensor includes a porous filter 01, a sensing element 03, a main housing 04 and a ventilation cable 06, and further includes a positioning seal ring 02 and a barbed pagoda head structure 05.

[0075] Specifically, in the above-mentioned integrated micro pore pressure sensor, a filter mounting slot, a sensing element mounting slot 044 and a ventilation pipe 045 are sequentially arranged in the main shell 04 along the axial direction, the porous filter 01 is installed in the filter mounting slot, the sensing element 03 is installed in the sensing element mounting slot 044, and the sensor cable 035 at the tail end of the sensing element 03 extends out of the main shell 04 through the ventilation pipe 045 to be connected to the ventilation cable 06.

[0076] Specifically, in the above-mentioned integrated micro-pore pressure sensor, the sensing element 03 includes an annular packaging shell 031, a piezoresistive core 032, a positioning plate 034 and a sensor cable 035. The positioning plate 034 is fixedly connected to one end of the annular packaging shell 031 so that a concave core mounting groove 033 is formed in the annular packaging shell 031. The piezoresistive core 032 is located in the concave core mounting groove 033 and is arranged on the side of the positioning plate 034. The sensor cable 035 is connected to the piezoresistive core 032 and passes through the positioning plate 034 and extends into the ventilation duct 045. A connecting hole 036 is provided on the positioning plate 034.

[0077] in:

[0078] The annular packaging shell 031 is used to protect the piezoresistive core 032 from stress on both sides of the sensor, ensuring that the piezoresistive core 032 can work normally;

[0079] The piezoresistive core 032 is mainly used to sense the pressure value of the pore fluid inside the measured saturated / unsaturated soil, and through the built-in four equal-value diffused silicon resistors, a Wheatstone bridge circuit is formed to convert the pore fluid pressure value into a voltage change output;

[0080] The concave core installation groove 033 has a window on the front side, and is filled and coated with stress-free glue inside. The stress-free glue serves as an edge isolation protection layer of the piezoresistive core 032 to prevent impurities such as tiny soil particles in the pore fluid inside the soil from directly acting on the piezoresistive core 032 and causing irreversible damage to the piezoresistive core 032.

[0081] The sensing element installation groove 044 is used to install and position the sensing element 03 to prevent the sensing element 03 from changing its position, wherein the place where the sensing element installation groove 044 and the ventilation pipe 045 meet constitutes a step surface 0441 for axially positioning the sensing element 03;

[0082] The side of the positioning plate 034 away from the annular packaging shell 031 is fixedly connected to the step surface 0441 through an adhesive to fix the sensing element 03, and / or the outer wall of the annular packaging shell 031 is fixedly connected to the sensing element mounting groove 044 through an adhesive to fix the sensing element 03;

[0083] The main function of the connecting hole 036 and the ventilation pipe 045 is to connect the piezoresistive core 032 to the external atmospheric pressure, so that the sensor uses the atmospheric pressure as a reference to measure the external pressure change. For the sensor to work normally, the connecting hole 036 and the ventilation pipe 045 must not be blocked.

[0084] It can be seen from the above technical scheme that in the integrated micro pore pressure sensor provided by the embodiment of the present invention, the sensor chip-level packaging is realized by stress-free glue and adhesive, and the device-level packaging is realized by the main shell 04. The sensor as a whole realizes electromagnetic shielding, electrical insulation, side stress isolation, thermal isolation and other treatments for the sensing element 03 in the sensor. Moreover, the annular packaging shell 031 can protect the piezoresistive core 032 from the stress on both sides of the sensor to the greatest extent, ensuring the normal operation of the piezoresistive core 032; the stress-free glue can directly prevent the sensing element 03 from direct contact with the pore fluid, thereby effectively preventing impurities such as fine particles in the saturated fluid from damaging the sensing element 03, greatly reducing the failure rate of the sensor. Therefore, the above-mentioned integrated micro pore pressure sensor provided by the embodiment of the present invention has high long-term stability and anti-interference performance, and can be applied to high-frequency response and high-precision geotechnical centrifuge tests.

[0085] Specifically, the main housing 04 is a stainless steel housing. The ventilation cable 06 is made of silicone wire, which has good pressure resistance, wear resistance, corrosion resistance and other characteristics. It is used to protect the sensor cable 035, and the inside of the sensor cannot be blocked when the sensor is working. Figures 11 to 14 .

[0086] Preferably, in the sensing element 03, the diameter of the annular encapsulating shell 031 is smaller than the diameter of the positioning plate 034. Therefore, correspondingly, the through hole in the sensing element mounting groove 044 is a first stepped hole, in which: the hole section close to the porous filter 01 is a first hole section adapted to the annular encapsulating shell 031; the hole section close to the ventilation pipe 045 is a second hole section adapted to the positioning plate 034, and the aperture of the first hole section is smaller than the aperture of the second hole section.

[0087] Specifically, during the production process, the sensing element 03 is installed in the sensing element installation groove 044 by electron beam welding.

[0088] In order to further optimize the above technical solution, in the above integrated micro pore pressure sensor, a spacing groove 043 is provided inwardly protruding between the filter mounting groove and the sensing element mounting groove 044. Figure 6 and Fig.14 .in:

[0089] The aperture of the spacing groove 043 is smaller than the end diameter of the porous filter 01 so as to limit the axial position of the porous filter 01;

[0090] The annular inner wall of the spacing groove 043 and the porous filter 01 and the sensing element 03 on both sides of the spacing groove 043 form a cavity structure a with a thickness of 0.1 mm to 0.5 mm. Generally, the concave core mounting groove 033 is filled with stress-free glue, that is, the stress-free glue and the porous filter 01 maintain a cavity structure a with a thickness of 0.1 mm to 0.5 mm. In other words, the gap distance between the porous filter and the sensing element is controlled within 0.5 mm, preferably 0.1 mm to 0.5 mm.

[0091] During use, the porous filter 01 separates soil particles and pore fluid from each other, allowing the pore fluid in the soil to freely enter and exit the above-mentioned cavity structure a, and then act on the sensing element 03.

[0092] The cavity structure design can ensure that the sensing element 03 is not affected by stress on both sides of the sensor to the greatest extent, and directly avoid the contact between the sensing element 03 and the porous fluid, thereby effectively preventing impurities such as fine particles in the saturated fluid from damaging the sensing element 03. In other words, the cavity structure design can effectively prevent the tiny soil particles and other impurities in the pore fluid inside the soil from causing the bridging of the porous filter 01 and the sensing element 03, and effectively protect the sensing element 03 of the sensor. (The integrated micro pore pressure sensor in the prior art often does not have this cavity structure, so that the tiny soil particles and other impurities in the pore fluid inside the soil can easily cause the bridging of the porous filter and the sensing element, thereby causing stress concentration, resulting in a large deviation between the sensor's measurement data and the actual situation.)

[0093] Specifically, the aperture of the spacing groove 043 is smaller than the aperture of the first hole section of the sensing element installation groove 044 , thereby being able to play an axial limiting role on the sensing element 03 .

[0094] In a specific embodiment, the filter installation slot in the above-mentioned integrated micro-pore pressure sensor is provided in sequence along the axial direction with: an end opening 040 adapted to the shape of the porous filter 01, a sealing ring positioning groove 041 adapted to the positioning sealing ring 02 (such as an "O-ring"), and a filter glue sealing groove 042 for filling sealing grease. Among them, the aperture of the end opening 040 is D1, the aperture of the sealing ring positioning groove 041 is D2, and the aperture of the filter glue sealing groove 042 is D3, and D2>D3>D1.

[0095] Thus, when the porous filter 01 is installed in the filter installation slot: the above-mentioned end opening 040 can circumferentially position the porous filter 01 to prevent it from shaking; the positioning sealing ring 02 is installed in the sealing ring positioning groove 041, which plays a role in positioning and sealing the porous filter 01; the filter glue sealing groove 042 is filled with sealing grease (also called sealant), and the sealing grease is in full contact with the end of the porous filter 01 (specifically the conical side wall structure 012 mentioned below), thereby further realizing the sealing between the main shell 04 and the porous filter 01, and fixing the porous filter 01.

[0096] It can be seen that the integrated micro pore pressure sensor is provided with a sealing ring positioning groove 041 and a positioning sealing ring 02, and the cooperation between the filter glue sealing groove 042 and the sealant can effectively prevent the porous filter from falling off due to the sensor being in the saturated fluid for a long time.

[0097] Specifically, the positioning seal ring 02 is made of fluorine rubber, which has good characteristics of high temperature resistance, high pressure resistance, water resistance, oil resistance, and strong corrosion resistance. Its main function is to cooperate with the porous filter side 011 to position and fix the porous filter 01. Fig. 9 shown.

[0098] Specifically, before conducting geotechnical tests, the integrated micro pore pressure sensor can select a suitable porous filter 01 according to the permeability of different soil types in field tests or geotechnical physical model tests. The porous filter 01 that can be configured with the integrated micro pore pressure sensor is mainly stainless steel sintered filter, fine sintered bronze filter, and porous ceramic filter type, and the filter particle size range can be selected from 20um to 0.2mm.

[0099] Preferably, if Figure 7 and Figure 8As shown: one end of the porous filter 01 is a cylindrical side wall structure 011, and the other end is a conical side wall structure 012. The positioning seal ring 02 is adapted to the cylindrical side wall structure 011, and the conical side wall structure 012 is located in the filter seal groove 042. The sealant filled in the filter seal groove is bonded and fixed to the conical side wall structure 012, which is conducive to expanding the contact seal area, thereby further playing the role of fixing the porous filter, so as to ensure that the porous filter is not easy to loosen and fall off when the integrated micro pore pressure sensor is in a saturated fluid long-term monitoring environment such as geotechnical centrifuge test, geotechnical structure, site foundation, etc., thereby reducing the failure rate of the integrated micro pore pressure sensor.

[0100] See also Figure 6 ,as well as Figure 12 to Figure 14 In order to further optimize the above technical solution, in the above integrated micro pore pressure sensor, a barb pagoda head structure 05 for connecting the ventilation cable 06 is provided on the main housing 04, a through hole communicating with the ventilation pipe 045 is provided in the barb pagoda head structure 05, and a barb step 051 is provided on the outside of the barb pagoda head structure 05. The end of the ventilation cable 06 connected to the barb pagoda head structure 05 has a larger outer diameter, and its internal through hole is adapted to the barb pagoda head structure 05 and tightly connected.

[0101] See also Figure 2 , Figure 6 , Figure 12 to Figure 14 In a specific embodiment, a sealing groove 046 is provided on the main housing 04 of the above-mentioned integrated micro-pore pressure sensor at the end for connecting the ventilation cable 06, and the connecting end of the barbed pagoda head structure 05 is located at the bottom of the sealing groove 046. The sealing groove 046 is used to fill with sealing grease, thereby sealing the connection between the main housing 04 and the ventilation cable 06. The waterproof structure composed of the sealing groove 046, the barbed pagoda head structure 05 and the sealing grease mainly connects the main housing of the sensor with the ventilation cable, and plays the role of waterproofing and sealing the cable. Among them, the barbed pagoda head structure 05 is used to further cooperate closely with the ventilation cable 06 to ensure that water does not enter the sensor and to ensure that the ventilation pipe 045 is connected to the atmospheric pressure.

[0102] It can be seen that in the above-mentioned integrated micro pore pressure sensor, a new waterproof sealing structure composed of a barbed pagoda head structure and sealing grease is adopted, which can effectively improve the sealing performance of the sensor cable and is better suitable for the long-term monitoring needs of saturated fluid in geotechnical centrifuge tests.

[0103] Specifically, in the above-mentioned integrated micro-pore pressure sensor, the through hole in the ventilation pipe 045 is a second stepped hole. In the second stepped hole, the hole section adjacent to the sensing element installation groove 044 is the third hole section, and the hole section connected to the barbed pagoda head structure 05 is the fourth hole section, and the aperture of the third hole section is larger than the aperture of the fourth hole section.

[0104] In addition, the specific steps of using the integrated micro pore pressure sensor provided by the embodiment of the present invention are as follows:

[0105] (1) Soak the integrated micro pore pressure sensor in 95% alcohol for 2 hours. Then, take out the integrated micro pore pressure sensor and place it in heated 100℃ airless water for boiling and cleaning for 5 minutes until no bubbles emerge on the porous filter surface of the integrated micro pore pressure sensor. Repeat the above steps 3 to 5 times to complete the cleaning of the integrated micro pore pressure sensor.

[0106] (2) Place the cleaned integrated micro pore pressure sensor in a vacuum saturation tank, slowly inject saturated fluid, airless water, and evacuate and saturate for 1.0 h. Then open the saturation tank and stir appropriately to facilitate the discharge of bubbles in the water. Vacuum and saturate again for 0.5 h. Repeat the above steps 8 to 10 times to complete the saturation process of the porous filter in the integrated micro pore pressure sensor.

[0107] (3) Place the integrated micro pore pressure sensor in the calibration device, connect the sensor ventilation cable to the data acquisition instrument, and calibrate the various performance indicators of the sensor (static performance: sensitivity, static correlation coefficient, linearity and other parameters. Dynamic performance: response time, frequency response rate, dynamic correlation coefficient and other parameters) according to the relevant national standards and industry specifications "Pressure Sensor Performance Test Method" (GB / T 15478-2015) and "Geotechnical Centrifuge Model Test Technical Specification" (DL / T 5102-2013).

[0108] (4) Take out the calibrated integrated micro pore pressure sensor from the calibration device and place it in a saturated fluid for immersion until the sensor needs to be deployed in the geotechnical test. Apply a layer of vaseline on the porous filter surface of the integrated micro pore pressure sensor to prevent the porous filter from contacting the air.

[0109] In summary, the integrated micro pore pressure sensor provided by the embodiment of the present invention has the following advantages:

[0110] (1)Sensor element packaging method:

[0111] The integrated micro pore pressure sensor provided in the embodiment of the present invention is an integrated geotechnical test integrated micro pore pressure sensor, whose internal sensing element is installed inside the annular packaging shell, which can effectively reduce the stress on both sides of the sensor;

[0112] The concave core installation groove of the sensing element is filled and coated with stress-free glue as an insulating isolation protective layer, which can effectively prevent impurities such as tiny soil particles in the pore fluid inside the soil from directly acting on the piezoresistive core and causing irreversible damage to the piezoresistive core.

[0113] Furthermore, through the annular packaging shell, and the filling and coating of stress-free glue, double protection is formed for the sensor sensing element, so that the piezoresistive core can minimize strong and weak electromagnetic interference and stress on both sides compared with the previous packaging method of traditional sensors, and improve thermal isolation and electrical insulation strength to adapt to various harsh working environments such as geotechnical centrifuge tests, so as to reduce the failure rate and damage of the integrated micro pore pressure sensor.

[0114] (2)Porous filter installation method:

[0115] In the integrated micro pore pressure sensor provided by the embodiment of the present invention, the porous filter is installed with an O-ring through the sealing ring positioning groove, and then the position of the porous filter is positioned by the O-ring; the filter glue sealing groove is used to fill the sealing grease, and the tapered side wall structure at the end of the porous filter is fully bonded, thereby expanding the contact glue sealing area, and further playing the role of fixing the porous filter, so as to ensure that the porous filter is not easy to loosen or fall off when the integrated micro pore pressure sensor is in a saturated fluid long-term monitoring environment such as geotechnical centrifuge test, rock and soil structure, site foundation, etc., thereby reducing the failure rate of the integrated micro pore pressure sensor.

[0116] (3).Sensor waterproof sealing method:

[0117] In the integrated micro pore pressure sensor provided by the embodiment of the present invention, a sealing groove is provided at one end of the main shell body for filling with sealing grease to seal the ventilation cable; further, the barbed pagoda head structure is closely matched with the ventilation cable to ensure that water vapor and water droplets will not enter the sensor and accumulate, and ensure that the ventilation duct is connected to the atmospheric pressure, so that the sensor can work normally. The combination of the sealing groove, sealing grease and barbed pagoda head structure can provide good waterproof sealing and pressure bearing for the ventilation cable. And through a large number of experimental results, it is proved that the waterproof structure provided by the present invention has a better waterproof sealing effect than the waterproof structure of the traditional sensor. When the saturated soil is in the high centrifugal acceleration environment of the geotechnical centrifuge test for a long time, no water vapor accumulation is found inside the sensor ventilation cable, ensuring the accuracy and reliability of the integrated micro pore pressure sensor in measuring the pore water pressure value.

[0118] (4). Sensor cavity structure design:

[0119] In the integrated micro pore pressure sensor provided in the embodiment of the present invention, a cavity structure (i.e. Figure 6The cavity structure a between the porous filter 01 and the sensing element 03 shown in FIG. 1 ). When impurities such as tiny soil particles in the pore fluid inside the soil enter the sensor through the porous filter, the presence of the cavity structure can avoid the stress concentration caused by the bridging of the porous filter and the sensing element caused by the tiny soil particles, thereby avoiding damage to the sensor. However, considering that the frequency response rate of the sensor is proportional to the size of the cavity structure, the cavity structure should not be too large, and a large cavity is prone to accumulate a large number of bubbles, which in turn causes the frequency response lag and amplitude attenuation of the sensor. Therefore, the thickness of the cavity structure in the integrated micro pore pressure sensor provided in the embodiment of the present invention (i.e., the gap distance between the porous filter and the sensing element) is controlled within 0.5 mm.

[0120] Finally, it should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the sentence "comprise a ..." do not exclude the presence of other identical elements in the process, method, article or device including the elements.

[0121] The various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referenced to each other.

[0122] The above description of the disclosed embodiments enables one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. An integrated micro pore pressure sensor, characterized in that: The integrated micro pore pressure sensor comprises a porous filter (01), a sensing element (03), a main housing (04) and a ventilation cable (06), wherein: The main housing (04) is provided with a filter installation slot, a sensing element installation slot (044) and a ventilation pipe (045) in sequence along the axial direction, the porous filter (01) is installed in the filter installation slot, the sensing element (03) is installed in the sensing element installation slot (044), and the sensor cable (035) at the tail end of the sensing element (03) extends out of the main housing (04) through the ventilation pipe (045) to be connected to the ventilation cable (06); The sensing element (03) comprises an annular packaging shell (031), a piezoresistive core (032), a positioning plate (034) and the sensor cable (035); the positioning plate (034) is fixedly connected to one end of the annular packaging shell (031) so that a concave core installation groove (033) is formed in the annular packaging shell (031); the piezoresistive core (032) is located in the concave core installation groove (033) and is arranged on the side of the positioning plate (034); the sensor cable (035) is connected to the piezoresistive core (032) and passes through the positioning plate (034) to extend into the ventilation duct (045); and a connecting hole (036) is arranged on the positioning plate (034); The concave core body installation groove (033) is filled with and coated with stress-free glue; The place where the sensing element installation groove (044) and the ventilation pipe (045) meet constitutes a step surface (0441) for axially positioning the sensing element (03); The side of the positioning plate (034) away from the annular packaging shell (031) is fixedly connected to the step surface (0441) by means of an adhesive, and / or the outer wall of the annular packaging shell (031) is fixedly connected to the sensor element installation groove (044) by means of an adhesive; The through hole in the sensing element installation groove (044) is a first stepped hole, wherein: The hole section close to the porous filter (01) is a first hole section adapted to the annular packaging shell (031); The hole section close to the ventilation pipe (045) is a second hole section adapted to the positioning plate (034); The aperture of the first hole segment is smaller than the aperture of the second hole segment; A spacing groove (043) is provided inwardly protruding between the filter installation groove and the sensor element installation groove (044), wherein: The aperture of the spacing groove (043) is smaller than the end diameter of the porous filter (01), so as to axially limit the porous filter (01); the aperture of the spacing groove (043) is smaller than the aperture of the first hole section of the sensing element installation groove (044), so as to play an axial limiting role for the sensing element (03); The annular inner wall surface of the spacing groove (043) and the porous filter (01) and the sensing element (03) located on both sides of the spacing groove (043) form a cavity structure with a thickness of 0.1 mm to 0.5 mm; The filter installation notch is provided with: an end opening (040) adapted to the shape of the porous filter (01), a sealing ring positioning groove (041) adapted to the positioning sealing ring (02), and a filter glue sealing groove (042) for filling sealing grease in sequence along the axial direction; The aperture of the end opening (040) is D1, the aperture of the sealing ring positioning groove (041) is D2, and the aperture of the filter glue sealing groove (042) is D3, D2>D3>D1; One end of the porous filter (01) is a cylindrical side wall structure (011), and the other end is a conical side wall structure (012); the positioning seal ring (02) is adapted to the cylindrical side wall structure (011), and the conical side wall structure (012) is located in the filter glue sealing groove (042).

2. The integrated micro pore pressure sensor according to claim 1, characterized in that: The aperture of the spacing groove (043) is smaller than the aperture of the first hole section.

3. The integrated micro pore pressure sensor according to claim 1, characterized in that: The main shell (04) is provided with a barbed pagoda head structure (05) for connecting the ventilation cable (06), a through hole connected to the ventilation duct (045) is provided inside the barbed pagoda head structure (05), and a barbed step (051) is provided on the outer side of the barbed pagoda head structure (05).

4. The integrated micro pore pressure sensor according to claim 3, characterized in that: The end of the main shell (04) for connecting the ventilation cable (06) is provided with a sealing groove (046) for filling with sealing grease, and the connecting end of the barbed pagoda head structure (05) is located at the bottom of the sealing groove (046).

5. The integrated micro pore pressure sensor according to claim 3, characterized in that: The through hole in the ventilation duct (045) is a second stepped hole. In the second stepped hole, the hole section adjacent to the sensor element mounting groove (044) is a third hole section, and the hole section connected to the barbed pagoda head structure (05) is a fourth hole section. The aperture of the third hole section is larger than the aperture of the fourth hole section.

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