Automatic calibration device and method for soil moisture content sensor

Abstract

The invention discloses a soil moisture content sensor automatic calibration device which comprises a soil sample cylinder, a support, a to-be-calibrated soil moisture content sensor, a wireless transmission module, a power supply module, a weighing module and a measurement and control host, the soil sample cylinder is placed on the weighing module through the support, and the soil sample cylinder is filled with a soil sample used for calibrating the to-be-calibrated soil moisture content sensor; a to-be-calibrated soil moisture content sensor penetrates through the soil sample cylinder and is inserted into a soil sample, the wireless transmission module is electrically connected with the to-be-calibrated soil moisture content sensor and wirelessly transmits collected real-time data to the measurement and control host, and meanwhile continuous and uniform moisture control is conducted on the soil sample through an external air pump and a temperature and humidity adjusting device. The actual moisture content of the soil sample is measured by the weighing module, and the measurement and control host collects weighing data in real time and calibrates the soil moisture content sensor to be calibrated inserted into the soil sample. The method has the advantages that the calibration process of the soil moisture content sensor is accurate and efficient, and original physical characteristics of soil can be kept.

Description

Technical Field

[0001] The present invention relates to the technical field of soil moisture monitoring, and particularly to an automatic calibration device and method for a soil moisture sensor. Background Art

[0002] Soil moisture directly affects crop growth. Monitoring soil moisture not only helps optimize irrigation decisions and reduce water resource waste, but also enables early warning of drought conditions and provides a scientific basis for agricultural production. Against the backdrop of climate change, achieving accurate monitoring of soil moisture plays an irreplaceable role in ensuring food security and coping with extreme weather events.

[0003] Since the dielectric constant of soil itself is relatively low while that of water is relatively high, in a mixture of soil and water, the moisture content can be indirectly measured by the dielectric constant, which is also the basic principle of most current soil moisture sensors. As the physical and chemical properties of soil have a direct impact on the sensor readings and there are differences in dielectric characteristics among different regions and soil types, calibration is required to establish an accurate relationship between the sensor readings and the actual soil moisture content. Currently, the commonly used calibration method is to use a standard soil sample with a known moisture content or the drying method to determine the soil moisture content, and then compare and analyze it with the sensor readings to establish a calibration formula. However, this method often needs to destroy the original physical properties of the soil. For example, it is difficult to restore the bulk density of the natural soil mass during the process of preparing a soil sample with a known moisture content, which is a key conversion factor for realizing the conversion between the volumetric moisture content measured by the sensor and the gravimetric moisture content measured by the drying method. The uncontrollability of this factor greatly affects the calibration result of the sensor. Therefore, there is an urgent need to develop a simple and efficient laboratory automatic calibration device for soil moisture sensors that does not damage the original physical properties of the soil. Summary of the Invention

[0004] Object of the Invention: The object of the present invention is to provide a simple and efficient laboratory automatic calibration device and method for a soil moisture sensor that does not damage the original physical properties of the soil.

[0005] Technical Solution: In a first aspect of the present invention, there is provided an automatic calibration device for a soil moisture sensor, including a soil sample cylinder, a bracket, a soil moisture sensor to be calibrated, a wireless transmission module, a power supply module, a weighing module, and a measurement and control host. The soil sample cylinder is placed on the weighing module through the bracket. The soil sample cylinder is filled with a soil sample for calibrating the soil moisture sensor to be calibrated. The soil moisture sensor to be calibrated passes through the soil sample cylinder and is inserted into the soil sample. The wireless transmission module is electrically connected to the soil moisture sensor to be calibrated and wirelessly transmits the collected real-time data to the measurement and control host. The power supply module supplies power to the soil moisture sensor to be calibrated and the wireless transmission module. The weighing module is electrically connected to the measurement and control host.

[0006] Further, the soil sample cylinder is a cylindrical shell composed of a cylinder body and a cylinder cover. Protruding shafts are provided at the center of the outer side of the bottom of the cylinder body and at the center of the outer side of the cylinder cover. Rotating bearings matching the protruding shafts are provided on the bracket, and the protruding shafts are installed in the rotating bearings. The main body of the soil sample cylinder is made of a hard material that absorbs water and is permeable, and the outside of the soil sample cylinder is covered with a water absorption and evaporation layer, which is made of a material with multiple capillary pores and a high specific surface area.

[0007] Further, it also includes a sealed housing, an air pipe and an air pump. The sealed housing is a cube and two or more of its faces have opening areas. Sealing covers are provided outside the opening areas, and air pipe connectors are provided on the outer sides of the sealing covers. The air pipe is connected to the air pipe connector and the air pump, so that a circulating air path is formed between the sealed housing and the air pump.

[0008] Further, it also includes an air humidity adjustment device and / or an air temperature adjustment device. The air humidity adjustment device is connected in series on the air pipe and is electrically connected to the measurement and control host.

[0009] Further, it also includes an air temperature and humidity sensor, which is installed in the downstream air pipe of the air humidity adjustment device and the air temperature adjustment device and is electrically connected to the measurement and control host.

[0010] Further, it also includes a soil sample temperature sensor, which is inserted into the soil sample and is electrically connected to the measurement and control host.

[0011] Further, it also includes a speed control motor. The output shaft of the speed control motor is connected to the protruding shaft at the center of the outer side of the bottom of the soil sample cylinder body and is electrically connected to the measurement and control host.

[0012] Further, it also includes an electromagnetic torque transmission module, which is composed of a driving disk and a driven disk. The center of the driving disk is connected to the output shaft of the speed control motor. One or more magnet Ns are uniformly arranged on the driving disk with the center as the center. The driven disk is provided with magnet Ss with the same number and corresponding positions as the magnet Ns. The two poles of the magnet N and the magnet S attract each other, and the center of the driven disk is connected to the protruding shaft at the center of the outer side of the bottom of the soil sample cylinder body.

[0013] The second aspect of the present invention provides a method for automatically calibrating a soil moisture sensor, which can adopt the soil moisture sensor automatic calibration device as described above, and specifically includes the following steps:

[0014] S1: Install an empty soil sample cylinder, a soil moisture sensor to be calibrated, a wireless transmission module, a power supply module, and a soil sample temperature sensor on the bracket together, and use the weighing module to measure the weight Wk of the above components

[0015] S2: Given that the volume of the soil sample cylinder is V, take a soil sample and fill it into the soil sample cylinder, cover it, and immerse it in water until the weight no longer increases;

[0016] S3: Install the soil sample cylinder on the bracket, insert the soil moisture sensor to be calibrated and the soil sample temperature sensor, and connect components such as the sealed housing, air pump, air temperature controller, air humidity controller, and air temperature and humidity sensor through an air pipe;

[0017] S4: The measurement and control host controls the start of the speed-regulating motor to drive the rotation of the soil sample cylinder, so that the gravitational water in it is evenly distributed inside the soil sample. At the same time, start the air pump, air humidity adjustment device, and air temperature adjustment device, and feedback-adjust the air temperature and humidity output according to the monitoring values returned by the air temperature and humidity sensor. The adjusted air flow blows out from the air pipe. When the air flow passes through the water-absorbing evaporation layer outside the soil sample cylinder, it takes away the surface moisture, thereby controllably reducing the moisture in the soil sample through different air flow temperature and humidity controls;

[0018] S5: While S4 is running continuously, the measurement and control host simultaneously collects the data Ws recorded by the weighing module and the data of the soil moisture sensor to be calibrated and the soil sample temperature sensor collected through the wireless transmission module at a set cycle. During this process, to avoid the influence of the soil sample temperature fluctuation on the measurement accuracy of the soil moisture sensor to be calibrated, the measurement and control host can feedback-adjust the air temperature adjustment device through the real-time data collected by the soil sample temperature sensor to keep the soil sample temperature stable;

[0019] S6: The measurement and control host compares the data Ws - Wk recorded by the weighing module at each moment with the weight Wt corresponding to the field water holding capacity of the soil sample. When Ws - Wk is lower than Wt, it means that there is no gravitational water in the soil sample, and the measurement and control host controls the speed-regulating motor to stop rotating;

[0020] S7: The measurement and control host compares the data Ws - Wk recorded by the weighing module at each moment with the weight Wl corresponding to the set minimum water holding capacity of the soil sample. When Ws - Wk is lower than Wl, the calibration process ends, and the measurement and control host stops the operation of the air pump, air temperature adjustment device, and air humidity adjustment device, and exports the weighing data and the data collected by the soil moisture sensor to be calibrated during the whole calibration process;

[0021] S8: Take out the soil sample cylinder, pour out all the soil samples into a container, send them into an oven to dry, record the dry soil weight as Wgt, reinstall the empty soil sample cylinder, the soil moisture sensor to be calibrated, the wireless transmission module, the power supply module, and the soil sample temperature sensor on the bracket, and use the weighing module to re-measure the weight Wk1 of the above components for further correction of Wk in subsequent calibration.

[0022] Beneficial effects: Compared with the prior art, the present invention has the following advantages: (1) The present invention can achieve accurate and high-efficiency calibration of the soil moisture sensor in the laboratory, avoiding various interference factors in the process of calibrating by preparing soil samples with determined moisture content in the laboratory; (2) The present invention can quickly realize the change from saturated soil to relatively dry soil through the scheduling of the equipped temperature and humidity regulation and monitoring device, and can form continuous monitoring and calibration throughout the whole process from wet to dry, avoiding the problem of limited sample quantity for calibration by preparing soil samples with determined moisture content; (3) The present invention can also, under the known specific soil moisture condition, turn off the air humidity controller and adjust the air temperature controller through the feedback of the soil sample temperature sensor to realize the research on the influence of temperature on the soil moisture sensor. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a schematic internal view of the overall structure of the present invention;

[0024] Figure 2 It is a schematic view of the overall structure of the present invention;

[0025] Figure 3 It is a schematic view of the opening area after removing the sealing cover of the sealing shell of the present invention;

[0026] Figure 4 It is a schematic view of the structure of the electromagnetic torque transmission module of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0027] The technical solution of the present invention will be further described below with reference to the drawings.

[0028] As Figure 1-2 shown, an automatic calibration device for a soil moisture sensor of the present invention includes a soil sample cylinder 1, a bracket 2, a soil moisture sensor to be calibrated 3, a wireless transmission module 4, a power supply module 5, a weighing module 6, and a measurement and control host 7. The soil sample cylinder 1 is placed on the weighing module 6 through the bracket 2. The soil sample cylinder 1 is filled with soil samples for calibrating the soil moisture sensor to be calibrated. The soil moisture sensor to be calibrated 3 passes through the soil sample cylinder 1 and is inserted into the soil sample. The wireless transmission module 4 is electrically connected to the soil moisture sensor to be calibrated 3 and wirelessly transmits the collected real-time data to the measurement and control host 7. The power supply module 5 supplies power to the soil moisture sensor to be calibrated 3 and the wireless transmission module 4. The weighing module 6 is electrically connected to the measurement and control host 7.

[0029] In order to make the moisture in the soil sample change uniformly, in some embodiments, the soil sample cylinder 1 is a cylindrical shell composed of a cylinder body and a cylinder cover. Convex shafts are provided at the center of the outer bottom of the cylinder body and the center of the outer side of the cylinder cover. Rotating bearings matching the convex shafts are provided on the bracket, and the convex shafts are installed in the rotating bearings. The main body of the soil sample cylinder is made of a hard material that absorbs and permeates water. An absorption and evaporation layer is covered outside the soil sample cylinder, and the absorption and evaporation layer is made of a material with multiple capillary pores and a high specific surface area.

[0030] To achieve continuous and controllable change of moisture in the soil sample, in some embodiments, the device is further provided with a sealed housing 8, an air pipe 9 and an air pump 10, as Figure 3 shown, the sealed housing is a cube and two or more of its faces have an opening area. A sealing cover 11 is provided outside the opening area. An air pipe joint is arranged on the outside of the sealing cover 11. The air pipe 9 is connected to the air pipe joint and the air pump 10, so that a circulating air path is formed by the sealed housing 11 and the air pump 10.

[0031] To achieve continuous and controllable change of moisture in the soil sample, in some embodiments, the device is further provided with an air humidity regulating device 12, an air temperature regulating device 13 and an air temperature and humidity sensor 14. The air humidity regulating device 12, the air temperature regulating device 13 and the air temperature and humidity sensor 14 are connected in series downstream of the air pipe and are electrically connected to the measurement and control host.

[0032] To avoid the influence of soil sample temperature fluctuation on the measurement accuracy of the soil moisture sensor to be calibrated, in some embodiments, the device is further provided with a soil sample temperature sensor 15. The soil sample temperature sensor 15 is inserted into the soil sample. The measurement and control host can feedback and adjust the air temperature regulating device through the real-time data collected by the soil sample temperature sensor to keep the soil sample temperature stable.

[0033] To achieve wireless power drive of the soil sample cylinder, in some embodiments, the device is further provided with a speed regulating motor 16 and an electromagnetic torque transmission module 17, as Figure 4 shown, the electromagnetic torque transmission module 17 is composed of a driving disk and a driven disk. The center of the driving disk is connected to the output shaft of the speed regulating motor. One or more magnets N are uniformly arranged on the driving disk with the center of the circle as the center. The driven disk is provided with magnets S with the same number and corresponding positions as the magnets N. The two poles of the magnets N and S attract each other. The center of the driven disk is connected to the protruding shaft at the center of the outer side of the bottom of the soil sample cylinder body.

[0034] An automatic calibration method for a soil moisture sensor according to the present invention can adopt the device in any of the above embodiments, and includes the following steps:

[0035] S1: Install an empty soil sample cylinder, the soil moisture sensor to be calibrated, a wireless transmission module, a power supply module, and a soil sample temperature sensor on the bracket together, and measure the weight Wk of the above components by using a weighing module;

[0036] S2: Given that the volume of the soil sample cylinder is V, take soil samples and fill them into the soil sample cylinder, cover it, and immerse it in water until the weight no longer increases;

[0037] S3: Install the soil sample cylinder on the bracket, insert the soil moisture sensor to be calibrated and the soil sample temperature sensor, and connect components such as the sealed housing, the air pump, the air temperature controller, the air humidity controller, and the air temperature and humidity sensor through the air pipe;

[0038] S4: The measurement and control host controls the start of the speed-regulating motor to drive the soil sample cylinder to rotate, so that the gravitational water in it is evenly distributed inside the soil sample. At the same time, the air pump, the air humidity regulating device, and the air temperature regulating device are started, and the air temperature and humidity output are feedback-regulated according to the monitoring values returned by the air temperature and humidity sensors. The adjusted air flow blows out from the air pipe. When the air flow passes through the water-absorbing evaporation layer outside the soil sample cylinder, it takes away the surface moisture, so that the moisture in the soil sample can be controllably reduced through different air temperature and humidity regulations;

[0039] S5: While S4 is running continuously, the measurement and control host simultaneously collects the data Ws recorded by the weighing module and the data of the soil moisture sensor to be calibrated and the data of the soil sample temperature sensor collected through the wireless transmission module at a set period. During this process, to avoid the influence of the soil sample temperature fluctuation on the measurement accuracy of the soil moisture sensor to be calibrated, the measurement and control host can feedback-regulate the air temperature regulating device through the real-time data collected by the soil sample temperature sensor to keep the soil sample temperature stable;

[0040] S6: The measurement and control host compares the data Ws - Wk recorded by the weighing module at each moment with the weight Wt corresponding to the field water holding capacity of the soil sample. When Ws - Wk is lower than Wt, it means that there is no gravitational water in the soil sample, and the measurement and control host controls the speed-regulating motor to stop rotating;

[0041] S7: The measurement and control host compares the data Ws - Wk recorded by the weighing module at each moment with the weight Wl corresponding to the set minimum water holding rate of the soil sample. When Ws - Wk is lower than Wl, the calibration process ends, and the measurement and control host stops the operation of the air pump, the air temperature regulating device, and the air humidity regulating device, and exports the weighing data and the data collected by the soil moisture sensor to be calibrated during the whole calibration process;

[0042] S8: Take out the soil sample cylinder, pour out all the soil samples into a container, send them into an oven for drying, record the dry soil weight as Wgt, reinstall the empty soil sample cylinder, the soil moisture sensor to be calibrated, the wireless transmission module, the power supply module, and the soil sample temperature sensor on the bracket, and use the weighing module to re-measure the weight Wk1 of the above components for further correction of Wk in the subsequent calibration;

[0043] S9: Through multiple experiments, the actual weight Wkn of the soil sample cylinder and the water-absorbing evaporation layer under different soil water contents can be obtained for further correction of Wk.

[0044] Preferably, under the known specific soil moisture condition, the air humidity controller is turned off, and the air temperature controller is feedback-regulated through the soil sample temperature sensor, so as to realize the research on the influence of temperature on the soil moisture sensor.

Claims

1. An automatic calibration device for soil moisture sensors, characterized in that, It includes a soil sample cylinder (1), a bracket (2), a soil moisture sensor to be calibrated (3), a wireless transmission module (4), a power supply module (5), a weighing module (6) and a measurement and control host (7). The soil sample cylinder (1) is placed on the weighing module (6) through the bracket (2). The soil sample cylinder (1) is filled with a soil sample for calibrating the soil moisture sensor to be calibrated (3). The soil moisture sensor to be calibrated (3) passes through the soil sample cylinder (1) and is inserted into the soil sample. The wireless transmission module (4) is electrically connected to the soil moisture sensor to be calibrated (3) and wirelessly transmits the collected real-time data to the measurement and control host (7). The weighing module (6) is electrically connected to the measurement and control host (7).

2. The automatic calibration device for soil moisture sensors according to claim 1, characterized in that The soil sample cylinder (1) is a cylindrical shell composed of a cylinder body and a cylinder cover. There are protruding shafts at the center of the outer bottom of the cylinder body and at the center of the outer side of the cylinder cover. The bracket is provided with a rotating bearing matching the protruding shaft, and the protruding shaft is installed in the rotating bearing. The main body of the soil sample cylinder is made of a hard material that absorbs and permeates water. The outside of the soil sample cylinder is covered with a water-absorbing and evaporating layer, and the water-absorbing and evaporating layer is made of a material with multiple capillary pores and a high specific surface area.

3. The automatic calibration device for soil moisture sensors according to claim 1, characterized in that It further includes a sealed housing (8), an air pipe (9) and an air pump (10). The sealed housing (8) is a cube and two or more of its faces have opening areas. Sealing covers (11) are provided outside the opening areas. An air pipe joint is arranged on the outside of the sealing cover (11). The air pipe (9) is connected to the air pipe joint and the air pump (10) to form a circulating air path for the sealed housing (8) and the air pump.

4. The automatic calibration device for soil moisture sensors according to claim 3, characterized in that, It further includes an air humidity adjusting device (12) and / or an air temperature adjusting device (13). The air humidity adjusting device (12) and / or the air temperature adjusting device (13) are connected in series on the air pipe (9) and are electrically connected to the measurement and control host (7).

5. The automatic calibration device for soil moisture sensors according to claim 4, characterized in that It further includes an air temperature and humidity sensor (14). The air temperature and humidity sensor (14) is installed in the downstream air pipe of the air humidity adjusting device (12) and the air temperature adjusting device (13) and is electrically connected to the measurement and control host (7).

6. The automatic calibration device for soil moisture sensors according to claim 5, characterized in that, It further includes a soil sample temperature sensor (15). The soil sample temperature sensor (15) is inserted into the soil sample and is electrically connected to the measurement and control host (7).

7. The automatic calibration device for soil moisture sensors according to claim 2, characterized in that It further includes a speed-regulating motor (16). The output shaft of the speed-regulating motor (16) is connected to the protruding shaft at the center of the outer bottom of the cylinder body of the soil sample cylinder (1) and is electrically connected to the measurement and control host (7).

8. The automatic calibration device for soil moisture sensors according to claim 7, characterized in that It further includes an electromagnetic torque transmission module (17). The electromagnetic torque transmission module (17) includes a driving disk and a driven disk. The center of the driving disk is connected to the output shaft of the speed-regulating motor (16). One or more magnets N are evenly arranged on the driving disk with the center as the center. The driven disk is provided with magnets S having the same number and corresponding positions as the magnets N. The two poles of the magnets N and S attract each other. The center of the driven disk is connected to the protruding shaft at the center of the outer bottom of the cylinder body of the soil sample cylinder (1).

9. An automatic calibration method for soil moisture sensors, characterized in that, Using the device according to any one of claims 1-8, it includes the following steps: S1: Mount an empty soil sample cylinder together with the soil moisture sensor to be calibrated, a wireless transmission module, a power supply module, and a soil sample temperature sensor on a bracket, and use a weighing module to measure the weight Wk of the above components. S2: Given that the volume of the soil sample cylinder is V, take soil samples and fill them into the soil sample cylinder, cover it, and immerse it in water until the weight no longer increases. S3: Install the soil sample cylinder on the bracket, insert the soil moisture sensor to be calibrated and the soil sample temperature sensor, and connect components such as a sealed housing, an air pump, an air temperature controller, an air humidity controller, and an air temperature and humidity sensor through an air pipe. S4: The measurement and control host controls the speed-regulating motor to start, drives the soil sample cylinder to rotate, so that the gravitational water in it is evenly distributed inside the soil sample. At the same time, start the air pump, the air humidity adjustment device, and the air temperature adjustment device, and feedback-adjust the air temperature and humidity output according to the monitoring values returned by the air temperature and humidity sensor. The adjusted air flow blows out from the air pipe. When the air flow passes through the water-absorbing evaporation layer outside the soil sample cylinder, it takes away the surface moisture, so that the moisture in the soil sample can be controllably reduced through different air flow temperature and humidity regulations. S5: While S4 is running continuously, the measurement and control host simultaneously collects the data Ws recorded by the weighing module and the data of the soil moisture sensor to be calibrated and the soil sample temperature sensor collected through the wireless transmission module at a set period. During this process, to avoid the influence of soil sample temperature fluctuations on the measurement accuracy of the soil moisture sensor to be calibrated, the measurement and control host feedback-adjusts the air temperature adjustment device through the real-time data collected by the soil sample temperature sensor to keep the soil sample temperature stable. S6: The measurement and control host compares the data Ws - Wk recorded by the weighing module at each moment with the weight Wt corresponding to the field water holding capacity of the soil sample. When Ws - Wk is lower than Wt, it means that there is no gravitational water in the soil sample, and the measurement and control host controls the speed-regulating motor to stop rotating. S7: The measurement and control host compares the data Ws - Wk recorded by the weighing module at each moment with the weight Wl corresponding to the set lowest water holding capacity of the soil sample. When Ws - Wk is lower than Wl, the calibration process ends. The measurement and control host stops the operation of the air pump, the air temperature adjustment device, and the air humidity adjustment device, and exports the weighing data and the data collected by the soil moisture sensor to be calibrated during the whole calibration process. S8: Take out the soil sample cylinder, pour out all the soil samples into a container, send them to an oven for drying, record the dry soil weight as Wgt, reinstall the empty soil sample cylinder together with the soil moisture sensor to be calibrated, a wireless transmission module, a power supply module, and a soil sample temperature sensor on the bracket, and use the weighing module to re-measure the weight Wk1 of the above components for further correction of Wk in subsequent calibration.

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