CN116007801A - A kind of soft contact earth pressure sensor and earth pressure sensor calibration method - Google Patents

Abstract

The invention discloses a soft contact type soil pressure sensor and a calibration method thereof, wherein the soil pressure sensor comprises: soft contact layer, piezoresistance sensitive element, sensor main casing, pagoda type anti-breaking structure and screw thread protection casing. According to the invention, the contact surface of the soil pressure sensor and the soil body adopts a soft contact mode, 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 to form a shape flush with the sensor main shell under the influence of the upper layer filled soil layer, 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 an aluminum alloy material and a stainless steel material, the soft contact layer adopts the high-elasticity material, so that the problem of rigidity matching between the soil pressure sensor and a soil medium can be effectively reduced, the testing precision of the soil pressure sensor is improved, and the soil pressure data measured by the soil pressure sensor has higher accuracy and reliability.

Description

A kind of soft contact earth pressure sensor and earth pressure sensor calibration method

technical field

The invention relates to the technical field of earth pressure sensors, in particular to a soft-contact earth pressure sensor and a calibration method for the earth pressure sensor.

Background technique

The high-gravity centrifugal model test relies on the high-speed rotation of the geotechnical centrifuge to generate high centrifugal force, compensates for the stress loss of the soil layer or rock-soil structure in the high-gravity centrifugal model, and reaches a stress level similar to or equal to the prototype. When the stable high centrifugal acceleration condition is reached (such as 50g~100g), by applying compressive seismic loads (with "high frequency 10~300Hz", "instantaneous ≤ 1s", "strong vibration up to 30g~60g"), the actual prototype dynamic characteristics and Failure mechanism is also an important research method in the field of geotechnical engineering, which plays an important role in basic theoretical research and engineering application research.

However, due to the small size of the supergravity centrifugal model (mostly 700 (length) * 300 (width) * 400mm (height)), the miniature earth pressure sensor is used as a method to monitor the earth pressure and lateral soil pressure in saturated/unsaturated soil. The key measurement sensor of pressure is quite different from the measurement medium of conventional pressure sensors such as air pressure and water pressure (soil is a non-uniform and inelastic medium, gas and liquid are homogeneous media), affected by the embedded effect, contact interface, size Influenced by many factors such as the effect, waterproof structure, etc., there are large errors in the accuracy and reliability of the earth pressure data measured by the miniature earth pressure sensor in the supergravity centrifuge test (the highest error can reach 50%).

Contents of the invention

In view of this, the present invention discloses a soft-contact earth pressure sensor and an earth pressure sensor calibration method to improve the test accuracy of the earth pressure sensor, so that the earth pressure data measured by the earth pressure sensor has higher accuracy and reliability .

A soft-contact earth pressure sensor, comprising: a soft-contact layer, a piezoresistive sensitive element, a sensor main housing, a pagoda-type anti-break structure and a threaded protective housing;

The soft contact layer, as the direct contact between the soil pressure sensor and the soil, is made of highly elastic material, and is used to install at the front window of the main housing of the sensor, and directly transmits the physical changes of the soil pressure to the piezoresistive Type sensitive components;

The piezoresistive sensitive element is used as the core part of the earth pressure sensor for converting the physical change of the earth pressure into a voltage signal output;

The main housing of the sensor has an internal thread for matching with the threaded protective shell through the internal thread to install and protect the piezoresistive sensitive element; it is also used as a carrier for the soft contact layer;

The pagoda-type break-proof structure is used to match with the main housing of the sensor to install a Teflon waterproof pipe.

Optionally, the contact surface between the soft contact layer and the soil is a circular arc surface, and the contact surface with the piezoresistive sensitive element is a parallel surface;

The circular arc surface is used for deforming to disperse the extra additional stress when the earth pressure is detected, and transmit it to the parallel surface.

Optionally, the piezoresistive sensitive element includes: a high pressure chamber, a sensitive diaphragm, a vacuum chamber, gold wires, stress-free glue, terminal blocks, a conversion circuit board and a silicon diaphragm protective case;

The high-pressure chamber is a transparent pressure chamber for contacting with the measured soil pressure;

The vacuum chamber is a transparent pressure chamber, which is used to output a zero point with the vacuum environment as a reference;

The two sides of the sensitive diaphragm are respectively provided with the high-pressure chamber and the vacuum chamber, which are used to generate strain changes when the pressures on the high-pressure chamber and the vacuum chamber are different, and convert the strain changes into Voltage signal output;

The gold wire is used to connect a plurality of equivalent resistances arranged in the sensitive diaphragm to form a Wheatstone bridge;

The connecting terminal is arranged on the conversion circuit board and connected with the gold wire;

The conversion circuit board is used for fixed connection with the four-core shielded cable outside the piezoresistive sensitive element;

The front side of the silicon diaphragm protection case has windows and a cavity structure inside, the cavity structure is used to install the high pressure chamber, the sensitive diaphragm and the vacuum chamber, and fill the surrounding and surface with the Stress glue acts as a protective layer.

Optionally, the sensor main housing includes: soft contact layer positioning groove, soft contact layer support beam, sensitive element installation cavity and sensitive element positioning groove, wherein the internal thread is provided inside the sensitive element installation cavity;

The positioning groove of the soft contact layer is used for positioning the soft contact layer;

The soft contact layer support beam is used to support the soft contact layer;

The sensitive element installation cavity is used to place the piezoresistive sensitive element, and position the piezoresistive sensitive element in combination with the sensitive element positioning groove, and after the piezoresistive sensitive element is positioned and installed , fill the remaining space with epoxy resin.

Optionally, the thread protection housing includes: connecting the external thread and the support column of the sensitive element;

The thread protection housing is matched with the sensor main housing through the connecting external thread, and the piezoresistive sensitive element is supported and fixed through the sensitive element supporting column.

Optionally, it also includes: four-core shielded cable;

The four-core shielded cable is fixedly connected to the piezoresistive sensitive element.

Optionally, it also includes: the Teflon waterproof pipe.

Optionally, the piezoresistive sensitive element is a miniature high-frequency piezoresistive sensitive diaphragm.

A method for calibrating an earth pressure sensor, applied to a data acquisition instrument, where the data acquisition instrument is connected to the above-mentioned earth pressure sensor, and the method for calibrating the earth pressure comprises:

Divide the maximum theoretical earth pressure value of the measured soil layer required by the earth pressure sensor to be calibrated into M levels, where M is a positive integer;

When the earth pressure sensor to be calibrated is buried to the depth of the soil layer corresponding to the actual test, based on the M levels, apply the centrifugal acceleration load to the earth pressure sensor to be calibrated step by step to a preset value, and obtain each The theoretical earth pressure value corresponding to the output voltage signal of the earth pressure sensor to be calibrated under the above-mentioned level and the depth of the soil layer under each centrifugal acceleration;

Based on the theoretical earth pressure values corresponding to each of the levels, using the least squares curve fitting method, the earth pressure output voltage signals of the various levels of the earth pressure sensor to be calibrated and the theoretical earth pressure under the corresponding centrifugal acceleration conditions are obtained The average calibration coefficient of the value;

Multiplying the earth pressure output voltage signals of each level of the earth pressure sensor to be calibrated by the corresponding average calibration coefficient to obtain the measured output earth pressure value of the earth pressure sensor to be calibrated at each of the levels;

calculating the deviation between the measured output earth pressure value corresponding to each level of the earth pressure sensor to be calibrated and the corresponding theoretical earth pressure value;

A calibrated target coefficient of the earth pressure sensor to be calibrated is determined based on each of the deviations.

It can be seen from the above technical solution that the present invention discloses a soft-contact earth pressure sensor and a calibration method for the earth pressure sensor. The earth pressure sensor includes: Broken structure and threaded protection shell, the soft contact layer is used as the contact body between the soil pressure sensor and the soil directly. It is made of high elastic material and installed at the front window of the main shell of the sensor to directly transmit the physical changes of the soil pressure to the piezoresistor. The piezoresistive sensitive element is the core part of the earth pressure sensor, which converts the physical change of the earth pressure into a voltage signal output. The main shell of the sensor can not only be used as the carrier of the soft contact layer, but also through the inner thread and the threaded protective shell. Matching to install and protect the piezoresistive sensitive components, reduce the impact of external force on the piezoresistive sensitive components, the pagoda-type anti-break structure matches the main housing of the sensor to install the Teflon waterproof tube. In the present invention, the contact surface between the soil pressure sensor and the soil body adopts a soft contact method, and the main housing of the sensor is filled with an arc-shaped column through the front window, and the soft contact layer on the surface of the soil pressure sensor is deformed and deflected by the upper filling soil layer. The curved shape is flush with the main shell of the sensor, so that the earth pressure acts on the piezoresistive sensitive element; the soft contact layer of the earth pressure sensor is made of high elastic material, and the density of the high elastic material is between dry sand and saturated sand. Compared with aluminum alloy and stainless steel, the high elastic material used 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 sensor The measured earth pressure data has high accuracy and reliability.

Description of drawings

In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings that need to be used in the description of the embodiments or the prior art. Obviously, the accompanying drawings in the following description are only It is an embodiment of the present invention. For those skilled in the art, other drawings can also be obtained according to the disclosed drawings without creative work.

Fig. 1 is an exploded view of the main structure of a soft-contact earth pressure sensor disclosed in an embodiment of the present invention;

Fig. 2 is an exploded diagram of the main structure of another soft-contact earth pressure sensor disclosed in the embodiment of the present invention;

Fig. 3 is a front view of the main structure of a soft-contact earth pressure sensor disclosed in an embodiment of the present invention;

Fig. 4 is a cross-sectional view of the main structure of a soft-contact earth pressure sensor disclosed in an embodiment of the present invention;

Fig. 5 is a front view of a soft contact layer disclosed by an embodiment of the present invention;

Fig. 6 is a side view of a soft contact layer disclosed by an embodiment of the present invention;

Fig. 7 is a schematic diagram of the connection between a piezoresistive sensitive element and a four-core shielded cable disclosed in an embodiment of the present invention;

Fig. 8 is a cross-sectional view of a piezoresistive sensitive element disclosed in an embodiment of the present invention;

Fig. 9 is a schematic diagram of the connection between a sensor main housing and a pagoda-type anti-break structure disclosed in an embodiment of the present invention;

Fig. 10 is a perspective view of the connection between a sensor main housing and a pagoda-type anti-break structure disclosed in an embodiment of the present invention;

Fig. 11 is a cross-sectional view of the connection between a sensor main housing and a pagoda-type anti-break structure disclosed in an embodiment of the present invention;

Fig. 12 is a schematic structural view of a threaded protective casing disclosed in an embodiment of the present invention;

Fig. 13 is a kind of Fujian standard quartz sand grain size distribution curve diagram disclosed by the embodiment of the present invention;

Fig. 14(a) is a layout diagram of a soft-contact earth pressure sensor disclosed in an embodiment of the present invention;

Fig. 14(b) is a schematic diagram of centrifugal acceleration staged loading disclosed in the embodiment of the present invention;

Fig. 15(a) is a diagram of the centrifugal acceleration verification result of a soft-contact earth pressure sensor T1 disclosed in the embodiment of the present invention;

Fig. 15(b) is a diagram of a theoretical earth pressure calibration result of a soft-contact earth pressure sensor T1 disclosed in an embodiment of the present invention;

Fig. 15(c) is a diagram of the centrifugal acceleration verification result of a soft-contact earth pressure sensor T2 disclosed in the embodiment of the present invention;

Fig. 15(d) is a diagram of a theoretical earth pressure calibration result of a soft-contact earth pressure sensor T2 disclosed in an embodiment of the present invention;

Fig. 15(e) is a diagram of the centrifugal acceleration verification result of a soft-contact earth pressure sensor T3 disclosed in the embodiment of the present invention;

Fig. 15(f) is a diagram of a theoretical earth pressure calibration result of a soft-contact earth pressure sensor T3 disclosed in an embodiment of the present invention;

Fig. 16 is a flowchart of a method for calibrating an earth pressure sensor disclosed in an embodiment of the present invention.

Detailed ways

The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only some, not all, embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without making creative efforts belong to the protection scope of the present invention.

The embodiment of the invention discloses a soft-contact earth pressure sensor and a calibration method for the earth pressure sensor. The earth pressure sensor includes: a soft-contact layer, a piezoresistive sensitive element, a sensor main shell, a pagoda-type anti-break structure and a thread protection The shell, the soft contact layer is used as the direct contact body between the soil pressure sensor and the soil. It is made of high elastic material and installed on the front window of the main shell of the sensor. It directly transmits the physical changes of the soil pressure to the piezoresistive sensitive element. As the core part of the earth pressure sensor, the resistive sensitive element converts the physical change of earth pressure into a voltage signal output. The main shell of the sensor can not only serve as the carrier of the soft contact layer, but also match the threaded protective shell through the internal thread to install and Protect piezoresistive sensitive components and reduce the impact of external force on piezoresistive sensitive components. The pagoda-type anti-break structure matches the main housing of the sensor to install a Teflon waterproof tube. In the present invention, the contact surface between the soil pressure sensor and the soil body adopts a soft contact method, and the main housing of the sensor is filled with an arc-shaped column through the front window, and the soft contact layer on the surface of the soil pressure sensor is deformed and deflected by the upper filling soil layer. The curved shape is flush with the main shell of the sensor, so that the earth pressure acts on the piezoresistive sensitive element; the soft contact layer of the earth pressure sensor is made of high elastic material, and the density of the high elastic material is between dry sand and saturated sand. Compared with aluminum alloy and stainless steel, the high elastic material used 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 sensor The measured earth pressure data has high accuracy and reliability.

Referring to Fig. 1, an exploded view of the main structure of a soft-contact earth pressure sensor disclosed in an embodiment of the present invention, the earth pressure sensor includes: soft-contact layer 01, piezoresistive sensitive element 02, sensor main housing 04, pagoda-type Anti-breaking structure 05 and threaded protection shell 07.

Among them, the soft contact layer 01 is used as the direct contact between the soil pressure sensor and the soil. It is made of high elastic material and is used to install at the front window of the main housing 04 of the sensor. It directly transmits the physical changes of the soil pressure to the piezoresistive sensor Element 02.

The main function of the soft contact layer 01 in the present invention is to be installed on the front window of the sensor main housing 04, which is the contact body between the sensor and the soil body directly. High elastic silicone material), has good high temperature resistance, high pressure resistance, water and oil resistance, strong corrosion resistance, electrical insulation, high dielectric strength and other characteristics, and its density can be adjusted according to the soil type. The range is 1.7g ~ 2.5g/cm ^3. The Shore hardness can be selected from 45 to 65, and the shear and tensile strengths are ≥2.0Mpa. The density of dry sand with soil particle gradation in the range of 0.08mm to 2.0mm is about 1.4g/cm ³ to 1.7g/cm ³ , and the density of saturated sand is about 1.8g/cm ³ to 2.1g/cm ³ . Therefore, the density of highly elastic materials is between dry sand and saturated sand, and is comparable to aluminum alloy (density about 2.7g/cm ³ , Rockwell hardness about 90) and stainless steel (density about 7.8g/cm ^{3 )} . , Rockwell hardness is about 201), compared with the highly elastic material used on the front of the earth pressure sensor can effectively reduce the stiffness matching problem with the soil medium.

The soft contact layer 01 in the present invention is an elastic body with a small micro-stiffness, which can directly physically change the earth pressure to the piezoresistive sensitive element 02, thereby improving the sensitivity and frequency response rate of the earth pressure sensor. In addition, the soft contact layer 01 is made of highly elastic silicone rubber, so the matching error with the soil itself is small, which can reduce the stress redistribution phenomenon of the original sand stress field, thereby improving the test accuracy of the earth pressure sensor.

As the core part of the earth pressure sensor, the piezoresistive sensitive element 02 is used to convert the physical change of earth pressure into a voltage signal output.

The sensor main housing 04 has an internal thread for matching with the threaded protective shell 07 to install and protect the piezoresistive sensitive element 02 and reduce the influence of external force on the piezoresistive sensitive element 02 .

The main sensor housing 04 also serves as a carrier for the soft contact layer 01 .

It should be noted that the sensor main housing 04 is an arc-shaped cylinder.

The pagoda-type break-proof structure 05 is used to match the sensor main housing 04 to install a Teflon waterproof pipe.

In summary, the present invention discloses a soft-contact earth pressure sensor, comprising: a soft-contact layer 01, a piezoresistive sensitive element 02, a sensor main housing 04, a pagoda-type anti-break structure 05 and a threaded protection housing 07 , the soft contact layer 01 is used as the contact body between the soil pressure sensor and the soil directly. It is made of high elastic material and installed at the front window of the sensor main housing 04, and directly transmits the physical changes of the soil pressure to the piezoresistive sensitive element 02. As the core part of the earth pressure sensor, the piezoresistive sensitive element 02 converts the physical change of the earth pressure into a voltage signal output. The main housing 04 of the sensor can not only be used as the carrier of the soft contact layer 01, but also through the internal thread and the threaded protective shell 07 Matching to install and protect the piezoresistive sensitive element 02, and reduce the impact of external force on the piezoresistive sensitive element 02. The pagoda-style anti-break structure 05 is matched with the sensor main housing 04 to install a Teflon waterproof tube. In the present invention, the contact surface between the soil pressure sensor and the soil adopts a soft contact method, and the main sensor housing 04 of the arc-shaped column is filled through the front window, and the soft contact layer 01 on the surface of the soil pressure sensor is affected by the upper filling soil layer Deformation and deflection form a shape flush with the main housing 04 of the sensor, so that the earth pressure acts on the piezoresistive sensitive element 02; the soft contact layer 01 of the earth pressure sensor is made of high elastic material, and the density of the high elastic material is between dry sand and Among saturated sands, compared with aluminum alloy and stainless steel, the high elastic material used in the soft contact layer 01 can effectively reduce the stiffness matching problem between the earth pressure sensor and the soil medium, thus improving the test performance of the earth pressure sensor. Accuracy, so that the earth pressure data measured by the earth pressure sensor has high accuracy and reliability.

In order to further optimize the above embodiment, see Fig. 2, an exploded diagram of the main structure of another soft-contact earth pressure sensor disclosed in the embodiment of the present invention. On the basis of the embodiment shown in Fig. 1, the earth pressure sensor may also include : four-core shielded cable 03, the four-core shielded cable 03 is fixedly connected to the piezoresistive sensitive element 02.

In order to further optimize the above embodiment, the earth pressure sensor may also include: Teflon waterproof pipe 06;

The pagoda-type anti-break structure 05 is matched with the sensor main housing 04 to install the Teflon waterproof pipe 06.

Wherein, the connection relationship between the main structures of the earth pressure sensor in the embodiment shown in FIG. 2 can also refer to the front view and sectional view of the main structures of the earth pressure sensor shown in FIG. 3 and FIG. 4 respectively.

The following is a detailed description of each main structure of the earth pressure sensor, as follows:

Referring to Fig. 5 and Fig. 6, they are respectively a front view and a side view of a soft contact layer disclosed in an embodiment of the present invention. The contact surface of is the parallel surface 012;

The arc surface 011 is used for deforming to disperse the extra additional stress when the earth pressure is detected, and transfer it to the parallel surface 012 .

In the present invention, the soft contact layer 01 can effectively reduce the "arch effect" phenomenon of the original sand stress field through the arc-shaped design (that is, the arc surface 011) and the selection of materials (high elastic materials), thereby improving the performance of the earth pressure sensor. Test accuracy.

Specifically, when the overlying soil layer is filled, the soil will be disturbed. At this time, the soil pressure sensor will bear more stress in the soil. The contact surface between the soft contact layer 01 and the soil is designed with an arc surface 011, so that the overlying soil When the pressure directly acts on the arc surface 011, the arc surface 011 can disperse the additional additional stress through its own slight deflection (the arc is reduced, but only limited to the slight deformation of the contact surface), and evenly applied to the earth pressure The soft contact layer 01 of the sensor is then transferred to the parallel surface 012. This process can reduce the stress concentration phenomenon and cause the sensor measurement data to be too large, and protect the internal piezoresistive sensitive element 02 of the earth pressure sensor from damage; secondly, compared with the use of Aluminum alloy and stainless steel (high rigidity, easy to cause insensitive response of sensitive elements), soft contact layer 01 (small rigidity, elastic body) can directly physically change the earth pressure to the piezoresistive sensitive element 02, thereby improving the earth pressure sensor sensitivity and frequency response rate.

Referring to FIG. 7 , a schematic diagram of the connection between a piezoresistive sensitive element and a four-core shielded cable disclosed in an embodiment of the present invention, combined with the sectional view of the piezoresistive sensitive element shown in FIG. 8 , it can be seen that the piezoresistive sensitive element 02 is used as The core part of the earth pressure sensor includes: high pressure chamber 021, sensitive diaphragm 022, vacuum chamber 023, gold wire 024, stress-free glue 025, terminal 026, conversion circuit board 027 and silicon diaphragm protective case 028.

The high-pressure chamber 021 is a transparent pressure chamber for contacting with the measured soil pressure.

The vacuum chamber 023 is a transparent pressure chamber for outputting a zero point with the vacuum environment as a reference.

In practical application, the material of the high pressure chamber 021 and the vacuum chamber 023 can be puffed glass.

The sensitive diaphragm 022 is a semiconductor material (silicon), and the two sides of the sensitive diaphragm 022 are respectively provided with a high-pressure chamber 021 and a vacuum chamber 023, which are used to generate strain changes when the pressures on the high-pressure chamber 021 and the vacuum chamber 023 are different, and the The strain change is converted into a voltage signal output.

The gold wire 024 is used to connect a plurality of equivalent resistances arranged in the sensitive diaphragm 022 to form a Wheatstone bridge.

The connection terminal 026 is arranged on the conversion circuit board 027 and connected with the gold wire 024 .

The conversion circuit board 027 is used for fixed connection with the four-core shielded cable 03 outside the piezoresistive sensitive element 02 .

The silicon diaphragm protection case 028 has a window on the front and a cavity structure inside. The cavity structure is used to install the high pressure chamber 021, the sensitive diaphragm 022 and the vacuum chamber 023, and the non-stress glue 025 is filled around and on the surface as a protective layer.

Preferably, the piezoresistive sensitive element 02 can be a miniature high-frequency piezoresistive sensitive diaphragm, and the natural frequency can be as high as 700kHz.

Specifically, the sensitive diaphragm 022 is used to generate strain changes when the pressures on the high-pressure chamber 021 and the vacuum chamber 023 are different, and convert the strain changes into voltage signal output. equal-value resistors (for example, four equivalent-value resistors R ₁ =R ₂ =R ₃ =R ₄ =5kΩ), and use the gold wire 024 to connect the four equivalent-value resistors to form a Wheatstone bridge, and then connect the gold The wire 024 is connected to the connection terminal 026 on the conversion circuit board 027, and then the internal cable of the conversion circuit board 028 and the external four-core shielded cable 03 are soldered. When the pressure (change in earth pressure) on the high-pressure chamber 021 and the vacuum chamber 023 on both sides of the sensitive diaphragm 022 is different, the strain change of the sensitive diaphragm 022 diaphragm will be converted into a voltage signal output; the silicon diaphragm protection The shell 028 has a window on the front and a cavity structure inside. The cavity structure is used to install the high pressure chamber 021, the sensitive diaphragm 022, and the vacuum chamber 023, and fill the surrounding and surface with stress-free glue 025 as a protective layer, stress-free glue 025 The upper surface is bonded to the parallel surface 012 of the soft contact layer 01, so that the force on the entire cavity surface is uniform.

In summary, it can be seen that the sensing element of the earth pressure sensor in the present invention can be selected from a miniature high-frequency piezoresistive sensitive diaphragm, and a plurality of equivalent resistances (such as four equivalent resistances) are provided by utilizing an ion implantation process on the sensitive diaphragm 022. resistance), and use gold wire 024 to connect multiple equivalent circuits to form a Wheatstone bridge. Two pressure chambers, a high pressure chamber 021 and a vacuum chamber 023, are arranged on both sides of the sensitive diaphragm 022. When the two pressure chambers are subjected to When the pressure is different, the sensitive diaphragm 022 produces strain, thereby improving the frequency response performance and sensitivity of the earth pressure sensor.

In addition, through the design in this embodiment and the miniaturization of the piezoresistive sensitive diaphragm, the volume of the earth pressure sensor can be reduced, the diameter can be controlled within 10 mm, and the output voltage signal can reach more than 100 mV.

Further, the present invention uses the design of the inner chamber of the housing to fix the sensitive diaphragm 022, and covers a layer of stress-free protective glue 025 on the surface of the sensitive diaphragm 022 and its surroundings, which can not only reduce the impact caused by the compaction of the overlying soil layer. "Stress concentration" damages the sensitive diaphragm 022 and avoids direct contact between the soil and the sensitive diaphragm 022, thereby improving the life cycle of the earth pressure sensor, and making the entire inner chamber surface evenly stressed, thereby improving the earth pressure sensor. Test accuracy.

Referring to Figures 9 to 11, they are respectively a schematic diagram of the connection between the sensor main housing and the pagoda-type anti-breakage structure disclosed in the embodiment of the present invention, a perspective view of the connection between the sensor main housing and the pagoda-type anti-breakage structure, and the sensor main shell The sectional view of the connection between the body and the pagoda-type anti-break structure, the sensor main housing 04 includes: soft contact layer positioning groove 041, soft contact layer support beam 042, sensitive element installation cavity 043 and sensitive element positioning groove 044, wherein the sensitive element is installed Internal threads 045 are provided inside the cavity 043 .

The soft contact layer positioning groove 041 is used for positioning the soft contact layer 01 .

The soft contact layer supporting beam 042 is used to support the soft contact layer 01 .

The sensitive element installation cavity 043 is used to place the piezoresistive sensitive element 02, and position the piezoresistive sensitive element 02 in combination with the sensitive element positioning groove 044, and fill the remaining space after the piezoresistive sensitive element 02 is positioned and installed The epoxy resin further fixes and waterproofs the inside of the piezoresistive sensitive element 02, and isolates the influence of the additional lateral stress on the piezoresistive sensitive element 02. .

Specifically, the sensor main housing 04 is matched with the pagoda-type anti-break structure 05 to install the Teflon waterproof tube 06, thereby protecting the four-core shielded cable 03 from breakage and the cable waterproof function.

To sum up, it can be seen that the cable fixing and sealing method of the earth pressure sensor in the present invention adopts the pagoda-type anti-break structure 05 design, which can effectively improve the shear strength and tensile strength of the cable of the earth pressure sensor, and can also improve the earth pressure sensor. Excellent sealing effect; and with the Teflon material cable protection layer, it can protect the exposed cables and reduce the interference to the original flow field and stress field and the wear of the sensor cable.

Referring to FIG. 12 , it is a schematic structural diagram of a thread protection housing disclosed in an embodiment of the present invention. The thread protection housing 07 mainly includes: connecting external threads 071 and sensitive element support columns 072 .

The thread protection housing 07 matches with the sensor main housing 04 by connecting the external thread 071 , and supports and fixes the piezoresistive sensitive element 02 through the sensitive element supporting column 072 .

It should be noted that the split structure of the thread protection housing 07 and the main sensor housing 04 is adopted in the present invention, which can increase the maintenance capability of the earth pressure sensor and improve the utilization rate of the piezoresistive sensitive element 02 .

In order to improve the reliability of the earth pressure sensor, the earth pressure sensor needs to be calibrated before use, and a geotechnical centrifuge can be used for calibration during calibration.

Referring to Fig. 16, a flow chart of an earth pressure sensor calibration method disclosed in an embodiment of the present invention, the method is applied to a data acquisition instrument connected to the earth pressure sensor in the above embodiment, and the earth pressure calibration method may include:

Step S101 , dividing the maximum theoretical earth pressure value of the measured soil layer required by the earth pressure sensor to be calibrated into M levels.

The maximum theoretical earth pressure is: the maximum earth pressure value corresponding to the depth of the prototype under the preset centrifugal acceleration condition.

Wherein, M is a positive integer.

In practical applications, each level corresponds to a calibrated earth pressure output voltage signal.

Step S102, determining the theoretical earth pressure value corresponding to the output voltage signal of the earth pressure sensor to be calibrated at each level and the depth of the soil layer under each centrifugal acceleration.

Specifically, when the earth pressure sensor to be calibrated is buried to the depth of the soil layer corresponding to the actual test, based on M levels, the centrifugal acceleration load is applied to the earth pressure sensor to be calibrated step by step to the preset value, and the to-be-calibrated The output voltage signal of the earth pressure sensor corresponds to the theoretical earth pressure value corresponding to the depth of the soil layer under each centrifugal acceleration.

Wherein, the value of the preset value is determined according to actual needs, which is not limited in the present invention.

Step S103, based on the theoretical earth pressure values corresponding to each level, use the least squares curve fitting method to obtain the average calibration coefficient of the earth pressure output voltage signals of each level of the earth pressure sensor to be calibrated and the theoretical earth pressure value under the corresponding centrifugal acceleration condition .

Among them, the average calibration coefficient is the ratio of the theoretical earth pressure value (kPa) at each level to the earth pressure sensor to be calibrated (mV).

Step S104: Multiply the earth pressure output voltage signals of each level of the earth pressure sensor to be calibrated by the corresponding average calibration coefficient to obtain the measured output earth pressure values of the earth pressure sensor to be calibrated at each level.

Step S105 , calculating the deviation between the measured output earth pressure value corresponding to each level of the earth pressure sensor to be calibrated and the corresponding theoretical earth pressure value.

Step S106: Determine the target coefficient after calibration of the earth pressure sensor to be calibrated based on each deviation.

In summary, the present invention connects the earth pressure sensor to be calibrated with the data acquisition instrument, and the data acquisition instrument processes the data collected from the earth pressure sensor to be calibrated to obtain the measured output earth pressure corresponding to each level of the earth pressure sensor to be calibrated The deviation between the value and the corresponding theoretical earth pressure value, so that the target coefficient of the earth pressure sensor to be calibrated is obtained based on each deviation, and the calibration of the earth pressure sensor to be calibrated is completed to further improve the test accuracy of the earth pressure sensor. The earth pressure data measured by the pressure sensor has higher accuracy and reliability.

The calibration process of the earth pressure sensor 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 Fujian standard quartz sand as an example. The particle size gradation curve of Fujian standard quartz sand is shown in Figure 13 , the basic physical parameters are shown in Table 1, as follows:

Table 1 Main physical parameters of Fujian standard quartz sand

The relative density D _r of sand and soil is 55%, and the dry sand model is laid out in 5 layers in the model box. ), 450mm (number T5), and a soft-contact earth pressure sensor to be calibrated is arranged at the center of each layer, a total of 5 sensors are arranged, and the direction of each sensor is vertically upward; then the model box , soft-contact soil pressure sensor and cables are hoisted to the geotechnical centrifuge and connected to the data acquisition instrument.

2) After preheating the five soft-contact earth pressure sensors for 60 minutes, set the sampling rate of the data acquisition instrument to 5 Hz, set the initial calibration factor (ICF) of the soft-contact earth pressure sensor to 1.0, and set The initial value of the soft-contact earth pressure sensor is "NULL" (that is, the balance is cleared); after the soft-contact earth pressure sensor completes the "NULL" setting, the soft-contact earth pressure to be calibrated will be monitored in real time on the display screen of the data acquisition instrument. Sensor, and then check whether the output voltage signal of the soft-contact earth pressure sensor is in a stable state and whether it is disturbed by noise.

3) The geotechnical centrifuge will load the centrifugal acceleration in stages (gradation number ≥ 5), which are 5g, 10g, 15g, 20g, 30g, 40g, 50g respectively. The output voltage of the contact earth pressure sensor reaches a stable state, and then apply the next level of centrifugal acceleration, as shown in Figure 14(a) and 14(b), repeat the application of centrifugal acceleration 2 to 3 times, and obtain the softness under the condition of each level of centrifugal acceleration The average output voltage value of the contact earth pressure sensor.

4) Finally, use the formula (1) to calculate the calibration coefficient ACF (unit: kPa/mV) of the soft-contact earth pressure sensor (that is, draw the output voltage value (abscissa) of the soft-contact earth pressure sensor recorded by the data acquisition instrument and the calibration comparison curve of the theoretical earth pressure value (ordinate) corresponding to each soil layer under each level of centrifugal acceleration), and based on the calibration curve, the curve fitting and conversion correlation coefficient R ² are obtained, and Figure 15(a)-Figure 15 (f) Calibration results for representative soft-contact earth pressure transducers numbered T1, T2, and T3 shown.

In the formula, N is the centrifugal acceleration of each level, ρ is the density of each soil layer (kg/m ² ), g _c is the acceleration of gravity (m/s ² ) (take 9.8), h is the buried height of the soft-contact earth pressure sensor (m), N is the number of measuring points recorded during the calibration process; X is the output voltage signal of the soft-contact earth pressure sensor, in mV; Y is the theoretical earth pressure value corresponding to each soil layer under each level of centrifugal acceleration, in units is kPa.

Finally, it should also be noted that in this text, relational terms such as first and second etc. are only used to distinguish one entity or operation from another, and do not necessarily require or imply that these entities or operations, any such actual relationship or order exists. Furthermore, the term "comprises", "comprises" or any other variation thereof is intended to cover a non-exclusive inclusion such that a process, method, article, or apparatus comprising a set of elements includes not only those elements, but also includes elements not expressly listed. other elements of or also include elements inherent in such a process, method, article, or device. Without further limitations, an element defined by the phrase "comprising a ..." does not exclude the presence of additional identical elements in the process, method, article or apparatus comprising said element.

Each embodiment in this specification is described in a progressive manner, each embodiment focuses on the difference from other embodiments, and the same and similar parts of each embodiment can be referred to each other.

The above description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those 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 invention. Therefore, the present invention will not 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 (9)

1. A soft touch soil pressure sensor, comprising: soft contact layer, piezoresistance sensitive element, sensor main shell, pagoda type breaking preventing structure and screw 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 internal threads, and the internal threads are matched with the threaded protective shell so as to install and protect the piezoresistive sensitive element; and 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.

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: the high-voltage cavity, the sensitive membrane, the vacuum cavity, the gold wire, the stress-free glue, the wiring terminal, the conversion circuit board and the 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.

4. The soil pressure sensor of claim 1, wherein the sensor main housing comprises: the sensor comprises a soft contact layer positioning groove, a soft contact layer supporting beam, a sensor mounting cavity and a sensor positioning groove, wherein the inner thread is arranged in the sensor 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, wherein the threaded protective housing comprises: connecting the external thread with the 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.

6. 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.

7. The soil pressure sensor of claim 1, further comprising: the teflon waterproof pipe.

8. The soil pressure sensor of claim 1, wherein the piezoresistive sensor is a miniature high frequency response piezoresistive sensor diaphragm.

9. A method for calibrating a soil pressure sensor, characterized by being applied to a data acquisition instrument, the data acquisition instrument being connected to the soil pressure sensor according to any one of claims 1 to 8, the method comprising:

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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