Volume water content type soil moisture characteristic curve measuring system and method

Abstract

A kind of volumetric water content type soil moisture characteristic curve measurement system and method, belong to soil physical property measurement field, including centrifugal rotor, centrifugal tube, calibration module and the drive module of driving centrifugal rotor to operate at different speeds;Centrifugal rotor is equipped with multiple insertion slots for inserting centrifugal tube;Centrifugal tube includes outer tube and inner tube, inner tube is nested in outer tube, inner tube is used to hold soil sample, and its bottom wall is filter membrane structure;Outer wall of outer tube is marked with millimeter scale, and scale is increasing from bottom to top along the axial direction of outer tube;The detection end of calibration module is arranged on the outer circumferential side of centrifugal rotor, and it is towards the outer wall of outer tube, for collecting image frame containing outer wall scale of outer tube, liquid level position in outer tube and upper boundary and lower boundary of soil column in inner tube after centrifugal rotor operates at different speeds for different time, and completing dynamic self-calibration of pixel and actual length with millimeter scale of outer wall of outer tube as internal standard, to calculate the soil column volume and dehydration volume of soil sample.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of soil physical property measurement, and particularly relates to a volumetric water content type soil water characteristic curve measurement system and method. BACKGROUND

[0002] At present, the mainstream soil water characteristic curve measurement methods at home and abroad include the pressure membrane method, the tensiometer method and the centrifugal method. The centrifugal method has become the preferred technical solution for laboratory scale measurement due to the advantages of high measurement efficiency, wide suction range and small sample requirement.

[0003] In the actual application of the centrifugal method measurement technology, the core operation process of the traditional measurement system is developed around the cycle mode of "centrifugation - shutdown - sampling - measurement - reinstallation". Specifically, the existing technology usually adopts a single speed gradient mode for centrifugation during operation. In terms of device structure, the combination of centrifuge tubes, filter membranes and water receiving trays is mainly adopted.

[0004] After completing the centrifugation process at one speed level, the centrifuge device must be shut down, and then the centrifuge tube and the water receiver are taken out of the device. Next, the staff need to calculate the dehydration volume data of the soil by manually weighing, and also need to measure the soil column volume; in some cases, the change of the soil column volume is also ignored, and only the initial volume of the soil sample is used for calculation to obtain the soil water content. After completing the above data acquisition work, the staff need to reinstall the centrifuge tube and the water receiving tray into the centrifuge device, and then adjust the device to the next preset speed, and continue the subsequent centrifugation measurement steps, and so on, until the measurement at all preset speed levels is completed.

[0005] As can be seen, the above-mentioned cycle process is not only complicated to operate, but also needs to be stopped and disassembled after completing each speed level, which greatly reduces the measurement efficiency and is difficult to adapt to batch sample detection requirements. Moreover, the dehydration volume is calculated by manual weighing and the soil column volume is measured, which has large operation error, and in some cases, the change of the soil column volume is ignored and the initial volume is directly used to calculate the water content, which further affects the data accuracy. In addition, frequent start and stop of the equipment increases the part wear and tear, and improper installation of the centrifuge tube and the water receiving tray during manual disassembly and assembly may cause imbalance during the second centrifugation, which poses a safety hazard. Moreover, data can only be obtained after the device is stopped, and the dynamic changes of the soil column and the dehydration volume during the centrifugation process cannot be tracked in real time, which is difficult to capture details and is not conducive to accurate analysis of soil water properties. SUMMARY

[0006] Therefore, the application provides a volumetric water content type soil water characteristic curve measurement system and method, which aims to improve the accuracy, efficiency and safety of soil water characteristic curve measurement.

[0007] To achieve the above object, the present application mainly provides the following technical solutions:

[0008] In an aspect of the present application, a volume water content type soil water characteristic curve measurement system is provided, comprising a centrifugal rotor, a centrifugal tube, a calibration module and a driving module for driving the centrifugal rotor to operate at different rotating speeds;

[0009] A plurality of slots are provided on the centrifugal rotor, and the slots are used for inserting the centrifugal tube;

[0010] The centrifugal tube comprises an outer tube and an inner tube, the inner tube is used for containing a soil sample, the bottom wall of the inner tube is a filter membrane structure, and the inner tube is nested in the outer tube;

[0011] A millimeter scale is marked on the outer wall of the outer tube, and the millimeter scale increases from bottom to top along the axial direction of the outer tube;

[0012] The detection end of the calibration module is arranged on the outer circumferential side of the centrifugal rotor, and the detection direction is towards the outer wall of the outer tube, the calibration module is used for collecting image frames containing the outer wall scale of the outer tube, the liquid level position in the outer tube, and the upper boundary and lower boundary of the soil column in the inner tube after the centrifugal rotor operates at different rotating speeds for different time, and completing dynamic self-calibration of pixels and actual length by taking the millimeter scale of the outer wall of the outer tube as an internal standard, and then calculating the soil column volume and dehydration volume of the soil sample under corresponding rotating speed and operating time.

[0013] Optionally, the centrifugal rotor comprises a shaft and a disc body arranged coaxially; one end of the shaft is in transmission connection with the driving module, and is used for driving the disc body to rotate under the driving of the driving module; a plurality of slots are uniformly arranged on the disc body along the circumferential direction of the shaft.

[0014] Optionally, the disc body comprises a first disc and a second disc arranged in parallel and at intervals, and the first disc and the second disc are fixed and coaxial with the shaft; the slots are correspondingly arranged on the first disc and the second disc to jointly clamp the centrifugal tube inserted in the slots; the interval distance between the first disc and the second disc is arranged so that the detection end of the calibration module can collect the image frames of the outer wall scale of the outer tube, the liquid level position in the outer tube, and the upper boundary and lower boundary of the soil column in the inner tube without obstruction.

[0015] Optionally, among the plurality of slots, the slots symmetrically distributed with the slots inserted with the centrifugal tubes are inserted with balance tubes, and the balance tubes are used for balancing the centrifugal force when the centrifugal rotor operates.

[0016] Optionally, the centrifugal tube further comprises a sealing cover, the sealing cover is used to cover the tube opening of the outer tube, and a side of the sealing cover facing the inner side of the outer tube is provided with a positioning structure for fixing the inner tube, the positioning structure is used to limit axial movement or radial deviation of the inner tube relative to the outer tube during operation of the centrifugal rotor.

[0017] Optionally, the calibration module comprises an image acquisition unit and an analysis processing unit; the image acquisition unit is arranged on the outer circumferential side of the centrifugal rotor, and an acquisition end of the image acquisition unit faces the outer wall of the outer tube, and is used to acquire image frames containing millimeter scale of the outer wall of the outer tube, liquid level in the outer tube, and upper boundary and lower boundary of the soil column in the inner tube after the centrifugal rotor is operated at different rotational speeds for different time; the analysis processing unit is in communication connection with the image acquisition unit, and is used to dynamically self-calibrate pixels and actual length of the image frames acquired by the image acquisition unit by taking the millimeter scale of the outer wall of the outer tube as an internal standard, and then calculate the soil column volume and dehydration volume of the soil sample under corresponding rotational speed and operation time.

[0018] Optionally, the volume water content type soil water characteristic curve measurement system further comprises a centrifugal cavity with a top opening; the centrifugal rotor is arranged in the internal space of the centrifugal cavity; the image acquisition unit of the calibration module is fixedly arranged on the inner wall of the centrifugal cavity, and an acquisition end of the image acquisition unit faces the central region of the centrifugal cavity; the centrifugal cavity is provided with a hinged door at the top opening, and the hinged door is used to seal with the opening edge of the centrifugal cavity, so that the internal space of the centrifugal cavity can form a relatively closed space when the hinged door is closed.

[0019] In another aspect of the present application, a volume water content type soil water characteristic curve measurement method is provided, which adopts the volume water content type soil water characteristic curve measurement system described in any one of the above, and the method comprises the following steps:

[0020] A target soil sample is obtained, weighed, filled into the inner tube to form a soil column, and saturated by a bottom permeation method, and after standing until no air bubbles escape, the soil column is suspended and drained until no visible water droplets are generated, the outer tube is emptied and wiped dry, the inner tube is reset and sealed;

[0021] According to a preset multi-stage centrifugal rotational speed sequence, a target rotational speed of each stage and a corresponding operation time are set;

[0022] The driving module is started in sequence, so that the centrifugal rotor rotates at the target rotational speed of each stage for the corresponding operation time, and after the operation at each target rotational speed ends, the driving module is paused, and the calibration module is used to acquire image frames containing millimeter scale of the outer wall of the outer tube, liquid level position in the outer tube, and upper boundary and lower boundary of the soil column in the inner tube;

[0023] Based on the millimeter scale of the outer wall of the outer tube as an internal standard, the collected image frames are dynamically self-calibrated from pixels to actual length, and then the actual volume of the soil column in the current state and the volume of water discharged since the last state are identified and calculated;

[0024] According to the total water content in the initial saturated state and the cumulative water volume discharged in each level of centrifugation, the residual water volume in the soil column at the end of each level of centrifugation is determined, and combined with the actual volume of the soil column determined based on image recognition at the end of the current centrifugation level, the volume water content under the corresponding centrifugal force is calculated; wherein the centrifugal force is converted into equivalent matrix suction according to the rotation speed and effective rotation radius;

[0025] The volume water content and the corresponding equivalent matrix suction data of all test points are summarized, and the soil water characteristic curve is drawn and generated.

[0026] Optionally, before saturating the soil column by the bottom permeation method, the step of pre-wetting the inner tube and the filter membrane structure at the bottom of the inner tube is further included.

[0027] Optionally, the image frames are collected after the centrifugal rotor stops rotating.

[0028] By the above technical solution, the present application has at least the following beneficial effects:

[0029] The volume water content type soil water characteristic curve measurement system and method provided in the embodiments of the present application can realize dynamic and continuous measurement, without stopping and disassembling the centrifugal tube, and can avoid the position deviation of the centrifugal tube caused by repeated disassembly and assembly, and eliminate the systematic measurement error caused by uneven compression deformation of the soil column. In addition, the measurement accuracy and reliability can be improved, manual operation can be replaced by automatic image acquisition and data calculation, human errors such as scale reading error and sample remixing can be reduced, the influence of experience difference of the operator on the result can be avoided, and the measurement repeatability can be greatly improved. Furthermore, the efficiency and safety can be considered, the cycle process of “centrifugation-stopping-taking sample-reloading” can be saved, the measurement efficiency can be improved, the centrifugal tube does not need to be repeatedly disassembled and assembled, the risk of decreasing the fitting precision of the centrifugal tube and the slot can be reduced, the centrifugal tube can be prevented from loosening, falling off or breaking during high-speed centrifugation, and the safety of the equipment and the personnel can be ensured. BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1 FIG. 1 is a structural schematic diagram of a volume water content type soil water characteristic curve measurement system according to an optional embodiment of the present application;

[0031] Figure 2Structure diagram of centrifugal rotor for an optional embodiment of the present application;

[0032] Figure 3 Structure diagram of centrifugal tube for an optional embodiment of the present application;

[0033] Figure 4 Structure diagram of filter membrane structure for an optional embodiment of the present application;

[0034] Figure 5 Structure diagram of image acquisition unit for an optional embodiment of the present application;

[0035] Figure 6 Flow chart of volumetric water content type soil moisture characteristic curve measurement method for an optional embodiment of the present application.

[0036] The reference signs are represented as:

[0037] 1, centrifugal rotor; 11, rotating shaft; 12, first disc; 13, second disc; 2, centrifugal tube; 21, outer tube; 211, millimeter scale; 22, inner tube; 221, filter membrane structure; 23, sealing cover; 3, image acquisition unit; 4, centrifugal cavity; 5, opening and closing door. DETAILED DESCRIPTION

[0038] In the description of the present application, it is to be understood that the terms "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise" and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, and therefore cannot be understood as indicating or implying that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as limiting the present application.

[0039] In addition, the terms "first", "second" are only for description purpose, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the technical features referred to. Therefore, the features defined with "first", "second" can explicitly or implicitly include one or more of the features. In the description of the present application, the meaning of "multiple" is two or more, unless otherwise specifically limited.

[0040] In this application, unless specifically defined and limited otherwise, the terms "mount", "connect", "connection", "fixed", and like terms should be construed as broadly as possible, for example, can be fixed connection, can also be detachable connection, or integrally connected; can be mechanical connection, can also be electrical connection; can be directly connected, can also be indirectly connected through an intermediate medium, can be internal communication of two elements. For those skilled in the art, the specific meanings of the above terms in this application can be understood according to the specific circumstances.

[0041] The preferred embodiments of the present application are described below in conjunction with the accompanying drawings, it should be understood that the preferred embodiments described here are only used to illustrate and explain the present application, and are not used to limit the present application.

[0042] In conjunction with Figures 1 to 5 As shown, according to the embodiments of the present application, a volumetric water content type soil water characteristic curve measurement system is provided, which comprises a centrifugal rotor 1, a centrifugal tube 2, a calibration module and a driving module for driving the centrifugal rotor 1 to operate at different speeds; the centrifugal rotor 1 is provided with a plurality of slots, and the slots are used for inserting and assembling the centrifugal tube 2; the centrifugal tube 2 comprises an outer tube 21 and an inner tube 22, the inner tube 22 is used for containing soil samples, the bottom wall of the inner tube 22 is a filter membrane structure 221, and the inner tube 22 is nested in the outer tube 21; the outer wall of the outer tube 21 is marked with a millimeter scale 211, and the millimeter scale 211 increases from bottom to top along the axial direction of the outer tube 21; the detection end of the calibration module is arranged on the outer circumferential side of the centrifugal rotor 1, and the detection direction is towards the outer wall of the outer tube 21; the calibration module is used for collecting image frames containing the scale of the outer wall of the outer tube 21, the liquid level position in the outer tube 21 and the upper and lower boundaries of the soil column in the inner tube 22 after the centrifugal rotor 1 operates at different speeds for different time, and completing dynamic self-calibration of pixels and actual length with the millimeter scale 211 of the outer wall of the outer tube 21 as an internal standard, and then calculating the soil column volume and dehydration volume of the soil sample under the corresponding speed and operating time.

[0043] The volume water content type soil water characteristic curve measurement system provided in the embodiments of the present application can realize dynamic continuous measurement without stopping and disassembling the centrifugal tube 2, can acquire the scale, liquid level and soil column boundary images of the outer tube 21 in real time through the calibration module, can calculate data by self-calibration of the millimeter scale 211, can avoid the position deviation of the centrifugal tube 2 caused by repeated disassembly, and can eliminate the systematic measurement error caused by uneven compression deformation of the soil column. On the other hand, the measurement accuracy and reliability can be improved, manual operation can be replaced by automatic image acquisition and data calculation, human errors such as scale reading error and sample remixing can be reduced, the influence of experience difference of the operator on the result can be avoided, and the measurement repeatability can be greatly improved. In addition, the efficiency and safety can also be considered, the "centrifugation-stopping-sampling-reloading" circulation process can be omitted, the measurement efficiency can be improved, the centrifugal tube 2 does not need to be repeatedly disassembled, the risk of reduction of the cooperation precision of the centrifugal tube 2 and the slot can be reduced, the centrifugal tube 2 can be prevented from loosening, falling off or breaking during high-speed centrifugation, and the safety of the equipment and the personnel can be ensured.

[0044] The driving module is a power source for rotating the centrifugal rotor 1, and has two functions: one is to provide rotating power for the centrifugal rotor 1, to drive the centrifugal rotor 1 and the centrifugal tube 2 inserted into the slot of the centrifugal rotor 1 to rotate synchronously; the other is to control the rotating speed of the centrifugal rotor 1, to set and maintain different target rotating speeds according to the measurement requirements. The centrifugal force is proportional to the square of the rotating speed, so different rotating speeds will correspond to different centrifugal forces, and these different centrifugal forces can simulate different suction conditions of the soil in the natural environment, to provide a basis for subsequent measurement of the soil moisture characteristics under different suction.

[0045] Specifically, in some examples, the driving module includes a variable frequency motor and a transmission mechanism, the input current frequency is adjusted through a frequency converter or a servo driver, the stepless speed change of the motor is realized, and the measurement requirements of different centrifugal forces are met. The power of the motor is transmitted to the centrifugal rotor 1 through a belt drive, a gear drive or a direct coupling, to ensure the stable rotation of the centrifugal rotor 1. In other examples, the driving module includes a stepping motor and a speed reducer or a speed increaser, the stepping motor controls the rotating angle through a pulse signal, to realize the rotating speed gear shifting, and the centrifugal rotor 1 is driven by the speed reducer or the speed increaser.

[0046] The centrifugal rotor 1 can be used as a carrier for the centrifugal tube 2.

[0047] Specifically, a plurality of slots are formed on the centrifugal rotor 1, each slot is used to fix a centrifugal tube 2, a plurality of groups of soil samples can be measured at the same time, and the system is suitable for large-scale requirements.

[0048] The centrifugal tube 2 is a component directly contacting the soil sample, and can have a double-layer structure. In the embodiment, the centrifugal tube 2 includes an inner tube 22 and an outer tube 21.

[0049] Specifically, the inner tube 22 is used to hold the soil sample, and the bottom thereof is a filter membrane structure 221, which is preferably a hydrophilic PTFE filter membrane with a pore size of 0.45 µm to allow water to pass through but block soil particles, thereby achieving water-soil separation. The outer tube 21 is sleeved outside the inner tube 22 to collect the water seeping from the filter membrane structure 221 of the inner tube 22, and the outer wall thereof is engraved with a millimeter scale 211 with increasing numbers from bottom to top, which is a scale for subsequent volume calculation.

[0050] The calibration module is used to realize automatic measurement, and the detection end thereof is installed outside the centrifugal rotor 1 and aligned with the outer wall of the outer tube 21 to capture images and automatically calculate data.

[0051] Specifically, in actual application, the working principle of the volume water content type soil moisture characteristic curve measurement system is as follows: first, the inner tube 22 containing the soil sample is nested into the outer tube 21 to form a complete centrifugal tube 2, and then the same is inserted into the insertion slot of the centrifugal rotor 1; after the driving module is started, the centrifugal rotor 1 operates at a set speed, and after operating at a certain speed for a certain time, the calibration module located at the outer peripheral side of the centrifugal rotor 1 automatically captures an image of the outer tube 21, which contains the millimeter scale 211 of the outer wall of the outer tube 21, the liquid surface position of the water collected in the outer tube 21, and the upper and lower boundaries of the soil column in the inner tube 22; then, the calibration module takes the millimeter scale 211 of the outer tube 21 as a reference to automatically establish a corresponding relationship between the image pixels and the actual length, and then calculates the soil column volume according to the soil column boundaries and the dehydration volume according to the liquid surface position, to finally obtain the soil moisture data under the soil suction corresponding to the speed; subsequently, only by adjusting the speed of the centrifugal rotor 1 through the driving module and repeating the steps of “operation → collection → calculation”, a series of data under different suctions can be obtained, so as to generate a soil moisture characteristic curve.

[0052] In some possible implementation embodiments of the present application, as shown in Figure 1 and Figure 2 The centrifugal rotor 1 comprises a shaft 11 and a disc body arranged coaxially; one end of the shaft 11 is in transmission connection with the driving module, and is used to drive the disc body to rotate under the driving of the driving module; a plurality of insertion slots are uniformly arranged on the disc body in the circumferential direction of the shaft 11.

[0053] In this embodiment, by arranging the rotating shaft 11 coaxially with the disc body and directly connecting one end of the rotating shaft 11 with the driving module, the power of the driving module can be stably and non-deviatedly transmitted to the disc body, avoiding the shaking of the disc body during rotation caused by different transmission axes, and ensuring the uniform centrifugal force on the soil sample during centrifugation. At the same time, the disc body is uniformly provided with a plurality of insertion slots along the circumferential direction of the rotating shaft 11, so that the inserted centrifuge tubes 2 are symmetrically distributed on the disc body, further balancing the centrifugal force during rotation of the disc body, reducing the vibration noise during high-speed rotation, reducing equipment loss and improving operation safety. Moreover, the plurality of insertion slots can simultaneously load a plurality of groups of centrifuge tubes 2, meeting the laboratory scale parallel measurement demand, and indirectly improving the overall measurement efficiency.

[0054] In the above embodiment, referring to Figure 2 As shown in the figure, the disc body includes a first disc 12 and a second disc 13 arranged in parallel and at intervals, and the first disc 12 and the second disc 13 are fixed with and coaxial with the rotating shaft 11. The first disc 12 and the second disc 13 are provided with insertion slots corresponding thereto to jointly hold the centrifuge tubes 2 inserted in the insertion slots. The interval distance between the first disc 12 and the second disc 13 is set so that the detection end of the calibration module can unobstructedly collect the image frames of the scale on the outer wall of the outer tube 21, the liquid level position in the outer tube 21, and the upper boundary and lower boundary of the soil column in the inner tube 22.

[0055] Here, the first disc 12 and the second disc 13 arranged in parallel and at intervals and provided with insertion slots corresponding thereto can jointly hold the centrifuge tubes 2 from the upper and lower ends, avoiding the radial inclination or axial deviation of the centrifuge tubes 2 during high-speed rotation, ensuring the uniform centrifugal force on the soil sample, and reducing the measurement error caused by shaking of the centrifuge tubes 2. At the same time, the interval distance of the two discs is accurately set to reserve sufficient shooting space for the detection end of the calibration module, which can unobstructedly collect complete image frames of the scale, liquid level position, and soil column boundary of the outer tube 21, ensuring the accuracy of subsequent image analysis and data calculation, and further improving the stability and reliability of the entire measurement system.

[0056] Among them, the first disc 12 and the second disc 13 are fixedly connected with the rotating shaft 11, and the axes of the three are completely coincident. Based on this, it can be ensured that the disc will not produce eccentric shaking when rotating with the rotating shaft 11, providing a basis for stable centrifugation.

[0057] The first disc 12 and the second disc 13 have corresponding slots. When the centrifuge tube 2 is inserted, it passes through the corresponding slots on both discs simultaneously, and the two discs clamp the centrifuge tube 2 together. This firmly secures the centrifuge tube 2, preventing radial tilting or axial displacement due to centrifugal force during high-speed rotation, ensuring uniform force on the soil sample and reducing measurement deviation. It should be noted that the aperture of the slot is matched to the outer diameter of the centrifuge tube 2, with a small gap, such as 0.5mm to 1mm, to ensure smooth insertion of the centrifuge tube 2 while preventing excessive gaps that could cause shaking. When the centrifuge tube 2 is inserted, it must pass through the slots on the first disc 12 and the corresponding slots on the second disc 13 in sequence. At this time, the inner walls of the slots on the two discs form radial constraints on the centrifuge tube 2 from the top and bottom, respectively. That is, the outer wall of the centrifuge tube 2 fits against the walls of the two slots, limiting radial tilting or displacement of the centrifuge tube 2.

[0058] The first disk 12 and the second disk 13 are both positioned outside the millimeter-level scale 211 on the outer wall of the outer tube 21, ensuring that the scale area is not obstructed by either disk 12 or the second disk 13. This provides sufficient field of view for the calibration module's detection end, ensuring that during centrifugation, the millimeter-level scale on the outer wall of the outer tube 21, the liquid level inside the tube, and the upper and lower boundaries of the soil column in the inner tube 22 can be completely and unobstructed, providing clear and accurate original images for subsequent image analysis and data calculation.

[0059] In some possible embodiments disclosed in this application, when the multiple slots of the centrifugal rotor 1 are not filled with centrifugal tubes 2 and the inserted centrifugal tubes 2 are asymmetrically distributed on the rotor, a balance tube is inserted in the slots that are symmetrically distributed with the slots where centrifugal tubes 2 are inserted. The balance tube is used to balance the centrifugal force when the centrifugal rotor 1 is running.

[0060] In this embodiment, when the centrifuge rotor 1 slot is not full of centrifuge tubes 2, a balance tube is inserted into the corresponding symmetrical slot. The weight of the balance tube can counteract the eccentric torque generated by the asymmetrical centrifuge tubes 2, ensuring that the centrifuge rotor 1 is subjected to uniform circumferential force when rotating at high speed. This avoids severe vibration or abnormal noise caused by the center of gravity shift, and reduces wear and tear on components such as the drive module. At the same time, the stable rotation state ensures that the centrifugal force on the soil sample is always uniform, preventing soil column deformation or liquid surface sloshing caused by vibration, avoiding the introduction of additional measurement errors, and ensuring the accuracy of soil column volume and dewatering volume calculations. In addition, it can effectively avoid the risk of centrifuge tubes 2 loosening, falling off, or even breaking due to centrifugal force imbalance, further improving the safety of laboratory operations and adapting to the measurement needs of different sample numbers.

[0061] The balance pipe can adopt the same pipe body structure as the centrifugal pipe 2, and inert substances such as clean water, quartz sand, and glass beads are filled in the balance pipe to balance the centrifugal force.

[0062] In some possible implementation embodiments disclosed in the present application, referring to Figure 3 As shown in the figure, the centrifugal pipe 2 further comprises a sealing cover 23, which is used to cover the pipe opening of the outer pipe 21, and the side of the sealing cover 23 facing the inside of the outer pipe 21 is provided with a positioning structure for fixing the inner pipe 22, which is used to limit the axial movement or radial deviation of the inner pipe 22 relative to the outer pipe 21 during the operation of the centrifugal rotor 1.

[0063] In this embodiment, by setting the sealing cover 23 to cover the pipe opening of the outer pipe 21, the water in the outer pipe 21 can be prevented from splashing and overflowing due to high-speed rotation during the centrifugation process, and the distortion of the dehydration volume measurement data can be avoided. At the same time, by setting the positioning structure on the side of the sealing cover 23 facing the inside of the outer pipe 21, the inner pipe 22 can be firmly fixed during the operation of the centrifugal rotor 1, the axial movement or radial deviation of the inner pipe 22 relative to the outer pipe 21 can be limited, and the stable position of the inner pipe 22 in the outer pipe 21 can be ensured. The deviation of the soil column boundary and the liquid surface position from the shooting field of view of the calibration module due to the displacement of the inner pipe 22 can be avoided, or the abnormal deformation of the soil column due to uneven stress can be avoided, which provides reliable conditions for the accurate measurement of the volume of the soil column and the dehydration volume, and further improves the accuracy and repeatability of the soil moisture data.

[0064] The sealing cover 23 and the outer pipe 21 can be connected by screw threads.

[0065] Specifically, the outer wall of the pipe opening of the outer pipe 21 is provided with external threads, and the inner wall of the sealing cover 23 is provided with internal threads matched with the external threads, and the sealing cover 23 and the pipe opening of the outer pipe 21 are tightly covered by screwing the internal and external threads. Based on this, the sealing cover 23 and the outer pipe 21 can be kept in stable connection during the high-speed rotation of the centrifugal rotor 1, which can prevent the sealing cover 23 from falling off due to the centrifugal force, and can enhance the sealing performance of the outer pipe 21 by the tight engagement of the threads to prevent the water in the pipe from splashing and overflowing, and at the same time, it is convenient for the operator to quickly disassemble and assemble to complete the filling and replacement of the soil sample.

[0066] The positioning structure of the sealing cover 23 for fixing the inner pipe 22 on the side facing the inside of the outer pipe 21 can be a concentric annular protrusion, and the concentric annular protrusion and the inner pipe 22 can also be connected by screw threads.

[0067] Specifically, the outer wall of the nozzle of the inner tube 22 is provided with external threads, and the inner wall of the concentric annular protrusion is provided with internal threads matched with the external threads. The inner tube 22 is firmly pulled by the concentric annular protrusion through the screw connection between the internal threads and the external threads of the nozzle of the inner tube 22, so as to prevent axial movement of the nozzle under the action of centrifugal force. Meanwhile, the detachable screw connection facilitates the assembly and disassembly of the inner tube 22 and the replacement of the soil sample.

[0068] In some possible implemented embodiments disclosed in the present application, referring to Figure 1 As shown in the figure, the calibration module includes an image acquisition unit 3 and an analysis processing unit. The image acquisition unit 3 is arranged on the outer periphery of the centrifugal rotor 1, and the acquisition end of the image acquisition unit 3 faces the outer wall of the outer tube 21. The image acquisition unit 3 is used to acquire image frames containing the millimeter scale 211 on the outer wall of the outer tube 21, the liquid surface in the outer tube 21, and the upper boundary and lower boundary of the soil column in the inner tube 22 after the centrifugal rotor 1 operates at different speeds for different time. The analysis processing unit is in communication connection with the image acquisition unit 3, and is used to dynamically self-calibrate the pixels and actual length of the image frames acquired by the image acquisition unit 3 by taking the millimeter scale 211 on the outer wall of the outer tube 21 as an internal standard, and then calculate the soil column volume and dehydration volume of the soil sample under the corresponding speed and operating time.

[0069] In this embodiment, by arranging the image acquisition unit 3 and the analysis processing unit, the automation and accuracy of measurement are improved.

[0070] The image acquisition unit 3 can be a complementary metal oxide semiconductor (CMOS) camera. The CMOS camera is small in size, strong in adaptability, and convenient to install on the outer periphery of the centrifugal rotor 1. The CMOS camera can stably cope with environmental interference in the centrifugal process, and ensure that clear image frames meeting the analysis requirements can be acquired under different speeds and different operating time nodes, thereby providing a high-quality image basis for subsequent data calculation of the analysis processing unit.

[0071] Specifically, the image acquisition unit 3 can be arranged in multiple numbers, and the multiple image acquisition units 3 are uniformly distributed along the circumference of the centrifugal rotor 1.

[0072] The analysis processing unit can be a processor. The processor has data receiving, image analysis and operation processing functions, can receive the image frames transmitted by the image acquisition unit 3 through a communication link, then automatically complete dynamic calibration of the pixels and actual length of the image by taking the millimeter scale 211 on the outer wall of the outer tube 21 in the image as a reference, extract key features such as the upper boundary and lower boundary of the soil column and the liquid surface position in the outer tube 21 through an embedded image recognition algorithm, and then calculate the soil column volume and dehydration volume, and associate the corresponding speed and operating time, and finally output the moisture data of the soil sample under the condition.

[0073] Specifically, the analysis processing unit can integrate preset algorithm logic to perform parallel processing on multiple groups of image frames synchronously transmitted by the multiple image acquisition units 3: on the one hand, by comparing the volume changes of the soil columns at different rotation speeds and different time nodes, combined with the accumulated data of the dehydration volume in the outer tube 21, the water loss rule of the soil sample under the corresponding centrifugal force is established; on the other hand, abnormal data caused by image blur, scale recognition deviation and other problems can be eliminated, and the effective data is smoothed to ensure the stability of the output results. In addition, the analysis processing unit can also store a series of soil moisture data calculated in order according to the rotation speed gradient, providing structured data support for subsequent automatic generation of soil moisture characteristic curve. The whole process does not need manual intervention, which not only reduces the error caused by human operation, but also significantly improves the efficiency of the whole process from image acquisition to curve generation through algorithm optimization and parallel processing capability, so that the system can quickly adapt to the measurement requirements of multiple samples and multiple gradient suction.

[0074] In some possible implemented embodiments disclosed in the present application, referring to Figure 1 As shown in the figure, the volume water content type soil moisture characteristic curve measurement system also includes a centrifugal cavity 4 with a top opening; the centrifugal rotor 1 is arranged in the inner space of the centrifugal cavity 4; the image acquisition unit 3 of the calibration module is fixedly arranged on the inner wall of the centrifugal cavity 4, and the acquisition end of the image acquisition unit 3 faces the central area of the centrifugal cavity 4; the centrifugal cavity 4 is provided with an opening and closing door 5 at the top opening, and the opening and closing door 5 is used for sealing cooperation with the opening edge of the centrifugal cavity 4, so that when the opening and closing door 5 is closed, the inside of the centrifugal cavity 4 can form a relatively closed space.

[0075] In this embodiment, the relatively closed space formed by closing the centrifugal rotor 1 in the centrifugal cavity 4 after closing the opening and closing door 5 can isolate external airflow, light and dust interference, avoid environmental factors causing the images taken by the image acquisition unit 3 to appear reflection, blur or pollution, and ensure the clarity of scale and boundary recognition; at the same time, the closed space can buffer the noise and vibration generated by the high-speed rotation of the centrifugal rotor 1, reduce the influence on the surrounding equipment, and prevent the safety hazards caused by the liquid splashing or accidental falling of the centrifugal tube 2 during centrifugation; in addition, the image acquisition unit 3 is fixed to the inner wall of the centrifugal cavity 4 and the acquisition end faces the center, which can ensure the stability of the relative position of the image acquisition unit 3 and the centrifugal rotor 1, avoid the deviation of the shooting angle caused by external collision, and further ensure the consistency of the length reference during dynamic self-calibration, providing a reliable environmental basis for the accurate calculation of the volume of the soil column and the dehydration volume.

[0076] It should be noted that in the present embodiment, the measurement system can be adapted to the structural depth of a conventional centrifuge, wherein the centrifugal cavity 4 for accommodating the centrifugal rotor 1 can be specifically adopted as the internal cavity of the centrifuge housing; and the driving module for providing rotational power for the centrifugal rotor 1, the centrifugal rotor 1 for carrying the centrifugal tube 2, and the opening and closing door 5 for achieving the isolation between the inside and outside of the cavity can also be directly reused as the original components of the centrifuge. Based on this, there is no need to separately develop the above-mentioned structure for the measurement system, but to rely on the mature hardware framework of the centrifuge, such as the driving module as the power core of the centrifuge, which can directly drive the centrifugal rotor 1 to stably rotate in the internal cavity of the centrifuge housing, i.e. the centrifugal cavity 4; the opening and closing door 5 is sealed with the opening of the centrifuge housing, and when closed, it provides a closed and protected environment for the operation of the centrifugal rotor 1; at the same time, the image acquisition unit 3 of the calibration module only needs to be fixed on the inner wall of the internal cavity of the centrifuge housing, which can complete the acquisition of the information of the centrifugal tube 2, which not only simplifies the overall structural design of the measurement system and reduces the development and assembly cost, but also can further guarantee the reliability and stability of the measurement process by means of the verified power output, stable rotation and safety protection performance of the centrifuge itself.

[0077] Here, in order to facilitate the operator to monitor the measurement process in real time, adjust the parameters and view the results, an operation display screen can be provided on the side of the centrifuge housing, which is in communication connection with the analysis and processing unit. Based on this, the operation display screen can receive the information transmitted by the analysis and processing unit, such as the real-time display of the current rotational speed and running time of the centrifugal rotor 1, as well as the calculated soil column volume, dehydration volume and soil moisture data, and also allows the operator to input instructions through the screen and feed the instructions back to the analysis and processing unit for linkage control of the running state of the driving module and the image acquisition unit 3; at the same time, the operation display screen can also store historical measurement data, which is convenient for the operator to subsequently call, view or export the data, and further improves the operation convenience and human-computer interaction experience of the measurement system.

[0078] Further, in order to clarify the operation process of the aforementioned volume moisture content type soil moisture characteristic curve measurement system, the embodiments of the present application also provide a volume moisture content type soil moisture characteristic curve measurement method, which adopts any one of the volume moisture content type soil moisture characteristic curve measurement systems described above, as shown in Figure 6 The method comprises the following steps:

[0079] Step S1: Obtain a target soil sample, weigh it and fill it into the inner tube 22 to form a soil column, and saturate the soil column by the bottom permeation method, and after standing until no air bubbles escape, suspend and drop to drain until no visible water droplets, empty and wipe dry the outer tube 21, reset the inner tube 22 and seal it.

[0080] In the process of obtaining the target soil sample, the original soil sample collected in the field can be pretreated, and the wet screening and compounding operations can be completed according to the following steps: first, remove the impurities such as stones and plant residues from the undisturbed soil sample or disturbed soil sample collected in the field, then add deionized water and stir until a paste is formed to form a soil suspension; then, select a standard sieve that meets the experimental particle size requirements, slowly pour the soil suspension into the sieve, and continuously rinse the sieve with deionized water at the same time, so that the soil particles meeting the particle size requirements pass through the sieve, and the impurities with a particle size larger than the sieve are intercepted, and the wet screening process is completed; then, the soil particles obtained after wet screening are placed in a constant temperature oven and dried to a constant weight, and then cooled to room temperature and weighed, and the mass of each particle size component is recorded; finally, according to the preset requirements of the target soil sample in the experiment, the soil particles of different particle size components are mixed and compounded in proportion, and stirring and sieving are required during the mixing process to ensure uniform distribution of each component, and finally the target soil sample meeting the experimental requirements in terms of particle size and texture is obtained, which lays a foundation for subsequent filling of the inner tube 22 to form a uniform soil column.

[0081] The purpose of weighing is to calculate the initial dry soil mass combined with the soil density, so as to provide basic data for subsequent water content calculation. Specifically, the mass of the target soil sample obtained by weighing, combined with the soil saturated water content obtained by soil physical and chemical property determination, can further calculate the total water content of the soil column in the initial saturated state, i.e. the product of the dry soil mass and the saturated water content. This total water content value is the basis for subsequent calculation of the remaining water volume. After each stage of centrifugal operation, the total amount of water remaining in the current soil column can be obtained by subtracting the cumulative water volume from the total water content in the initial saturated state; then, combining the total amount of remaining water with the actual volume of the current soil column obtained by image recognition, the volume water content in the corresponding state can be calculated according to the logic that the volume water content is equal to the remaining water volume divided by the actual volume of the current soil column.

[0082] In the process of saturating the soil column, a top-down infiltration method can be used: first, ensure that the filter membrane structure 221 is assembled at the bottom of the inner tube 22, then slowly inject deaerated water into the outer tube 21, and control the water level during the injection process so that the water surface in the outer tube 21 always maintains a water head height of 2-5 cm; maintain this water head state for 24-48 hours, and observe whether there are bubbles escaping from the soil column during this period, until the soil column no longer produces bubbles, which indicates that the internal pores of the soil column have been fully filled with water, and the saturation process is completed, providing a soil sample in the initial saturated state for subsequent centrifugal dewatering experiments.

[0083] Wherein, after the saturation of the soil column is completed, the inner tube 22 containing the saturated soil column can be taken out first, and is placed in suspension, so that the excess free water not adsorbed by the soil in the inner tube 22 is naturally drained through the bottom filter membrane structure 221 until no visible water droplets are observed; then the residual water in the outer tube 21 is emptied, and the inner wall of the outer tube 21 is wiped clean with a clean and dry cloth or filter paper; finally, the inner tube 22 after the drainage is completed is placed back in the outer tube 21.

[0084] Step S2: According to the preset multi-stage centrifugal speed sequence, set the target speed of each stage and the corresponding running time.

[0085] Here, by presetting a multi-stage speed sequence, the water characteristics of the soil under different suction can be simulated.

[0086] Wherein, when setting the centrifugal parameters, the multi-stage target speed can be preset according to the type of the target soil sample to form a multi-stage centrifugal speed sequence covering different centrifugal force ranges. For example, for the measurement requirements of most soil samples, a speed interval from 300 rpm / min to 14000 rpm / min can be designed, and the interval of every two adjacent stages is set to 500 rpm / min, thereby forming a complete speed sequence of 300 rpm / min, 800 rpm / min, 1300 rpm / min, and so on to 14000 rpm / min; if the soil is clay with strong water holding capacity, the number of stages in the low speed interval can be appropriately increased, such as starting from 200 rpm / min, with an interval of 300 rpm / min for each stage; if the soil is sandy with weak water holding capacity, the coverage of the high speed interval can be focused on, and through such a speed sequence design that fits the characteristics of the soil, it is ensured that the water release law of different soils under corresponding suction can be accurately captured, thereby providing comprehensive data support for the subsequent correlation calculation of the volume moisture content and the equivalent matrix suction.

[0087] Wherein, while setting the multi-stage centrifugal speed, the corresponding running time for each target speed needs to be matched to ensure that the water in the target soil sample reaches a dehydration steady state under the speed. The time can be set differently according to the speed: for example, for low speed stages such as 300 rpm / min and 800 rpm / min, the soil water migration speed is relatively slow due to the small centrifugal force, and a running time of 30 minutes can meet the water balance requirement; for high speed stages such as 13500 rpm / min and 14000 rpm / min, although the centrifugal force is stronger and the water release rate is faster, the running time can be appropriately extended, such as 60 minutes, to avoid that the water in the deep pores of the soil is not fully migrated to the outer tube 21. Through such adaptive time setting of low speed for short time and high speed for long time, the problem of incomplete water release due to insufficient running time can be effectively avoided, the dehydration amount and the volume moisture content in the subsequent calculation are prevented from being deviated, and the accuracy of the measurement data of each stage is ensured.

[0088] Step S3: sequentially start the driving module to make the centrifugal rotor 1 rotate at each target speed for a corresponding running time, and pause the driving module after each target speed running ends, and use the calibration module to collect image frames containing the millimeter scale 211 on the outer wall of the outer tube 21, the liquid level inside the outer tube 21, and the upper and lower boundaries of the soil column in the inner tube 22.

[0089] Among them, the driving module sequentially drives the centrifugal rotor 1 to rotate at each target speed, and forces the water in the soil column to seep out through the inner tube 22 filter membrane structure 221 to the outer tube 21 by centrifugal force.

[0090] Among them, after each target speed running ends, the driving module is paused to avoid image blurring caused by the rotation of the centrifugal rotor 1, and at this time the image acquisition unit 3 of the calibration module captures the image of the outer tube 21, which contains the millimeter scale 211 on the outer wall of the outer tube 21, the liquid level inside the outer tube 21, and the upper and lower boundaries of the soil column in the inner tube 22, providing a visual basis for subsequent calculations.

[0091] Step S4: Based on the millimeter scale 211 on the outer wall of the outer tube 21 as an internal standard, dynamically self-calibrate the collected image frames from pixels to actual length, and then identify and calculate the actual volume of the soil column under the current state and the volume of water discharged since the last state.

[0092] Among them, when analyzing the collected image frames, first establish a conversion relationship with the millimeter scale 211 on the outer wall of the outer tube 21 as a reference, for example, 1 millimeter corresponds to 10 pixels in the image, to achieve accurate association between image pixels and actual length, and automatically correct measurement deviation caused by small changes in shooting angle and distance; On this basis, the distance between the upper and lower boundaries of the soil column in the inner tube 22 is extracted through image recognition technology, that is, the height of the soil column, and the actual volume of the soil column is obtained by combining the known cross-sectional area of the inner tube 22 and the volume formula of the cylinder; For the volume of water discharged from the outer tube 21, the scale difference corresponding to the liquid level in the outer tube 21 of the current level and the last level is identified, and the cross-sectional area of the outer tube 21 is combined to calculate the volume of the cylinder, so that the data of the change in the volume of the soil column and the amount of water discharged is accurately obtained.

[0093] Step S5: According to the total water content under the initial saturated state and the cumulative water volume discharged in each centrifugal process, determine the remaining water volume in the soil column at the end of each centrifugal process, and combine the actual volume of the soil column determined based on image recognition at the end of the current centrifugal level to calculate the volume water content under the corresponding centrifugal force; wherein the centrifugal force is converted into equivalent matrix suction according to the speed and effective rotating radius.

[0094] Wherein, in the calculation of the soil moisture parameter, firstly, the residual water volume of the soil column is determined, which is the water volume retained in the current soil column, and the total water content in the initial saturated state is calculated by multiplying the volume of the soil column in the saturated state by the saturated water content of the soil, and then the cumulative water volume is subtracted; then the volume water content is calculated, which is equal to the residual water volume of the current soil column divided by the actual volume of the current soil column; finally, the conversion between the centrifugal force and the matrix suction is carried out, according to the physical formula, the centrifugal force is equal to the water mass multiplied by the effective rotating radius, and then multiplied by the square of the angular velocity, wherein the effective rotating radius refers to the distance from the center of the centrifugal tube 2 to the rotor shaft 11, and the angular velocity is related to the rotating speed, the current rotating speed is first converted into the centrifugal force, and then the centrifugal force is converted into the matrix suction unit commonly used in soil science, such as kilopascal, so as to establish the corresponding relationship between the centrifugal force and the actual water absorption capacity of the soil.

[0095] Step S6: The volume water content and the corresponding equivalent matrix suction data of all test points are summarized, and the soil moisture characteristic curve is drawn and generated.

[0096] Here, the volume water content data measured by all centrifugal levels and the equivalent matrix suction data corresponding to each level are collected, and each set of volume water content and equivalent matrix suction forms an independent data point; then the data points are connected into a curve by means of a drawing tool, wherein the horizontal axis of the curve represents the matrix suction, and the vertical axis represents the volume water content. From the shape of the curve, the water holding capacity of the soil under different suction conditions can be directly judged, for example, the curve trend of clay soil is relatively flat, which indicates that the water holding capacity fluctuates less when the suction changes, and the curve trend of sandy soil is relatively steep, which indicates that the water holding capacity changes more obviously with the suction.

[0097] In the above embodiment, before the soil column is saturated by the bottom permeation method, the step of pre-wetting the inner tube 22 and the filter membrane structure 221 at the bottom of the inner tube 22 is further included.

[0098] Here, before the soil column is saturated by the bottom permeation method, the pre-wetting step of the inner tube 22 and the filter membrane structure 221 at the bottom of the inner tube 22 is added, which can improve the uniformity and fullness of the soil column saturation. On the one hand, pre-wetting can make the filter membrane structure 221 absorb water in advance and eliminate the water absorption capacity of the filter membrane structure 221 itself; on the other hand, the inner wall of the pre-wetted inner tube 22 and the filter membrane can form a continuous water film, reducing the resistance in the water permeation process, making the degassed water pass through the filter membrane into the soil column pores more smoothly, and avoiding the situation that the water permeation is not smooth and the pores are left with bubbles due to the dryness of the filter membrane.

[0099] Wherein, when the filter membrane structure 221 and the inner tube 22 are pre-wetted, degassed water can be selected, and deionized water or an isotonic solution is preferred.

[0100] In the above embodiments, the image frames are captured after the centrifugal rotor 1 stops rotating.

[0101] Here, the selection of capturing the image frames after the centrifugal rotor 1 stops rotating can significantly improve the clarity and accuracy of the image information, provide reliable visual basis for subsequent data calculation, thereby reducing the shooting error of the image acquisition unit 3 due to the capture of high-speed moving targets, making the subsequent image-based dynamic self-calibration, volume calculation and other links more accurate, and finally providing high-quality data support for the generation of the soil moisture characteristic curve.

[0102] Those skilled in the art can easily understand that the above advantageous modes can be freely combined and superimposed without conflict.

[0103] The above is only a preferred embodiment of the present application, and is not intended to limit the present application. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present application shall be included in the protection scope of the present application. The above is only a preferred embodiment of the present application, and it should be pointed out that, for ordinary skilled in the art, without departing from the technical principles of the present application, a number of improvements and modifications can be made, which should be regarded as the protection scope of the present application.

Claims

1. A volumetric water content type soil moisture characteristic curve measuring system, characterized by, The centrifugal rotor, the centrifugal tube, the calibration module and the driving module for driving the centrifugal rotor to operate at different rotating speeds are included. A plurality of slots are arranged on the centrifugal rotor, and the slots are used for inserting the centrifugal tube. The centrifugal tube includes an outer tube and an inner tube, the inner tube is used for containing the soil sample, the bottom wall of the inner tube is a filter membrane structure, and the inner tube is nested in the outer tube. A millimeter scale is marked on the outer wall of the outer tube, and the millimeter scale is increased from bottom to top along the axial direction of the outer tube. The detection end of the calibration module is arranged on the outer circumferential side of the centrifugal rotor, and the detection direction is towards the outer wall of the outer tube. The centrifugal rotor includes a shaft and a disc body arranged coaxially. The shaft is in transmission connection with the driving module at one end, and is used for driving the disc body to rotate under the driving of the driving module.

2. The volumetric water content type soil moisture characteristic curve measuring system according to claim 1, characterized in that, The disc body includes a first disc and a second disc arranged in parallel and at intervals.

3. The volumetric water content type soil moisture characteristic curve measuring system according to claim 1, characterized in that, The first disc and the second disc are fixed and coaxial with the shaft.

4. The volumetric water content type soil moisture characteristic curve measuring system according to claim 1, characterized in that, The first disc and the second disc are arranged correspondingly with the slots to jointly hold the centrifugal tube inserted in the slots. The spacing distance between the first disc and the second disc is arranged so that the detection end of the calibration module can collect the image frames of the outer wall scale of the outer tube, the liquid level in the outer tube, and the upper and lower boundaries of the soil column in the inner tube without obstruction. The centrifugal tube further includes a sealing cover for covering the pipe opening of the outer tube. The side of the sealing cover towards the inside of the outer tube is provided with a positioning structure for fixing the inner tube. The positioning structure is used for limiting the axial movement or radial deviation of the inner tube relative to the outer tube during the operation of the centrifugal rotor. The calibration module includes an image acquisition unit and an analysis processing unit. The image acquisition unit is arranged on the outer circumferential side of the centrifugal rotor, and the acquisition end of the image acquisition unit is towards the outer wall of the outer tube. The analysis processing unit is in communication connection with the image acquisition unit. The analysis processing unit is used for dynamically self-calibrating the pixels and actual length of the image frames collected by the image acquisition unit with the millimeter scale on the outer wall of the outer tube as an internal standard, and further calculating the soil column volume and dehydration volume of the soil sample under the corresponding rotating speed and operation time. The calibration module includes an image acquisition unit and an analysis processing unit. The image acquisition unit is arranged on the outer circumferential side of the centrifugal rotor, and the acquisition end of the image acquisition unit is towards the outer wall of the outer tube. The analysis processing unit is in communication connection with the image acquisition unit. The analysis processing unit is used for dynamically self-calibrating the pixels and actual length of the image frames collected by the image acquisition unit with the millimeter scale on the outer wall of the outer tube as an internal standard, and further calculating the soil column volume and dehydration volume of the soil sample under the corresponding rotating speed and operation time.

5. The volumetric water content type soil moisture characteristic curve measuring system according to claim 4, characterized in that, It also includes a centrifuge chamber with a top opening; the centrifuge rotor is disposed in the internal space of the centrifuge chamber; the image acquisition unit of the calibration module is fixedly disposed on the inner wall of the centrifuge chamber, and the acquisition end of the image acquisition unit faces the central area of ​​the centrifuge chamber; the top opening of the centrifuge chamber is provided with an opening and closing door, which is used to seal and cooperate with the opening edge of the centrifuge chamber so that when the opening and closing door is closed, the interior of the centrifuge chamber can form a relatively closed space.

6. A volumetric water content type soil water characteristic curve measurement method characterized by, The method using the volumetric water content type soil moisture characteristic curve measurement system as described in any one of claims 1-5 includes the following steps: Obtain the target soil sample, weigh it, fill it into the inner tube to form a soil column, and saturate the soil column by bottom permeation. After standing until no air bubbles escape, suspend and drip until no visible water droplets are discharged. Empty and wipe the outer tube dry, then reset and seal the inner tube. Based on the preset multi-stage centrifugal speed sequence, set the target speed and corresponding running time for each stage; The drive modules are started sequentially, causing the centrifugal rotor to rotate at each target speed for the corresponding running time. After each target speed is completed, the drive modules are paused. The calibration module is used to collect image frames containing millimeter-level scales on the outer wall of the outer tube, the liquid level in the outer tube, and the upper and lower boundaries of the soil column in the inner tube. Based on the millimeter-level scale on the outer wall of the outer tube as an internal standard, the acquired image frames are dynamically self-calibrated from pixels to actual length, thereby identifying and calculating the actual volume of the soil column in the current state and the volume of water released since the previous state. Based on the total water content under initial saturation and the cumulative water volume removed during each centrifugation stage, the remaining water volume in the soil column at the end of each centrifugation stage is determined. Combined with the actual volume of the soil column determined by image recognition at the end of the current centrifugation stage, the volumetric water content under the corresponding centrifugal force is calculated. The centrifugal force is converted into equivalent matrix suction based on the rotational speed and effective rotation radius. Summarize the volumetric water content and corresponding equivalent matrix suction data of all test points, and plot and generate soil moisture characteristic curves.

7. The volumetric water content type soil moisture characteristic curve measuring method according to claim 6, characterized in that, Before saturating the soil column by bottom permeation, the process includes a step of pre-wetting the inner tube and the filter membrane structure at the bottom of the inner tube.

8. The volumetric water content type soil moisture characteristic curve measuring method according to claim 6, characterized by, The image frames were acquired after the centrifugal rotor stopped rotating.

Images