Real-time monitoring device for moisture of materials in grain storage bin

Abstract

The invention discloses a real-time monitoring device for moisture of materials in a grain storage bin, which comprises a device seat body, a plurality of pairs of detection electrodes, an environment monitoring sensor group and a data acquisition and processing unit, at least one grain sealing cavity and a plurality of open cavities are formed in the device seat body; open cavities are formed in the two sides of the closed cavity. A pair of detection electrodes is mounted in each of the closed cavity and the open cavity; gas can be communicated between the closed cavity and the adjacent space; the environment monitoring sensor is mounted in the closed cavity; the data acquisition and processing unit comprises a microcontroller and a moisture acquisition circuit; and all sensors included in the moisture acquisition circuit and the environment monitoring sensor group are connected with the microcontroller through an IIC bus. By arranging the closed cavity, the detection element in the closed cavity can provide data such as reference capacitance parameters, temperature, humidity and carbon dioxide concentration, data generated by the detection electrode in the open cavity can be corrected, environmental interference can be reduced, and data accuracy can be improved.

Description

Technical Field

[0001] The present invention relates to the technical field of grain monitoring in grain storage silos, and in particular to a device for real-time monitoring of moisture content of materials in grain storage silos. Background Art

[0002] During grain storage, real-time monitoring of material moisture is crucial to ensuring food safety and quality. Traditional methods for grain moisture testing are mainly divided into two categories: destructive testing and non-destructive testing. Destructive testing usually measures grain moisture content through sampling and drying. Although highly accurate, it has problems such as complex operation, long time consumption, inability to monitor in real time, and damage to the grain. For example, the direct drying method requires placing the sample in an oven for a long time to heat it, and the difference in quality before and after measurement is used to determine the moisture content. This method is not only inefficient, but also fails to meet the needs of real-time monitoring in modern granaries.

[0003] In recent years, nondestructive testing (NDT) has become a mainstream approach for grain moisture testing due to its speed, efficiency, and safety. Common NDT methods include capacitance, resistance, near-infrared spectroscopy, and low-field magnetic resonance (LFR). For example, capacitance measures changes in the grain's dielectric constant to estimate moisture content, offering advantages such as low cost and fast response, but its accuracy and stability require improvement. While near-infrared spectroscopy and LFR offer high accuracy, they require complex equipment and are more expensive, making them more suitable for laboratory environments.

[0004] Currently, some granaries have begun using online monitoring devices to measure grain moisture in real time. For example, rod-type moisture sensors require a probe to be inserted into the grain. While they can detect moisture in layers (surface, middle, and bottom), their mechanical structure is complex, prone to wear and tear, and requires frequent maintenance. These sensors are also difficult to adapt to the frequent movement and vibration of mobile equipment. Furthermore, existing online moisture monitoring methods based on millimeter-wave radars enable non-contact monitoring but are sensitive to environmental interference.

[0005] In summary, existing technologies for monitoring moisture content in grain storage silos still have shortcomings in terms of real-time performance, non-destructiveness, and accuracy. Developing a device that can achieve non-destructive, real-time, and high-precision monitoring is of great significance for improving grain storage management and ensuring food security.

[0006] In the prior art, patent CN103940858A discloses an online grain moisture detection device based on the principle of parallel plate floating capacitance, which evenly transports grains to the measuring chamber through a feed controller and realizes static measurement in combination with a temperature compensation algorithm. Another patent CN112198199A proposes to use IQ modulation technology to separate the capacitance component and realize moisture detection in combination with a temperature sensor. Its technical core lies in eliminating the interference of the resistance component through orthogonal signal processing and building a distributed detection network using a wireless communication module. None of the above technical solutions can solve the problem of synchronization between the collected environmental parameters such as temperature and humidity and the temperature and humidity at the detection location. The environmental sensor is either far away from the detection location and cannot fully reflect the temperature and humidity data at the detection location, resulting in inaccurate correction of the moisture content. If the environmental sensor is installed at the detection location, it is easily affected by grain wear and tear, which reduces its lifespan. Furthermore, while the solution in patent CN103940858A can address the issue of varying porosity within grain piles, it relies on a mechanical feeding mechanism to achieve uniform filling. This not only makes the equipment bulky and difficult to integrate into storage environments, but also limits real-time monitoring efficiency due to the switching between dynamic feeding and static measurement, making it unsuitable for multi-point, continuous monitoring within the grain silo. The solution in patent CN112198199A utilizes a single-point capacitive sensor design, which is susceptible to differences in material compactness within the complex media distribution environment within the grain pile. In particular, when gaps exist on the contact surface of the detection electrodes, the capacitance detection value can exhibit significant deviations. Summary of the Invention

[0007] Purpose of the invention: In order to overcome the deficiencies in the prior art, the present invention provides a real-time monitoring device for moisture content in grain storage bins, which can accurately collect environmental data, avoid sensor damage, and avoid the influence of void ratio on moisture content detection without relying on sampling.

[0008] Technical Solution: To achieve the above-mentioned purpose, the present invention provides a real-time monitoring device for moisture content in a grain storage bin, which includes a device base and multiple pairs of detection electrodes, as well as an environmental monitoring sensor group and a data acquisition and processing unit. The environmental monitoring sensor is used to monitor environmental data such as temperature, humidity, and carbon dioxide concentration in the storage bin;

[0009] The device base has at least one closed cavity and a plurality of open cavities; both sides of the closed cavity have the open cavities; a pair of detection electrodes are respectively installed in the closed cavity and the open cavity;

[0010] The closed cavity and the adjacent space can communicate with each other, and food materials cannot enter the closed cavity. The space adjacent to the closed cavity includes the adjacent closed cavity and the external space of the device base. In this way, the temperature, humidity and carbon dioxide concentration in the closed cavity can be consistent with the environmental parameters of the external space. Since the closed cavity is open, the open cavity can communicate with the external space of the device base.

[0011] The environmental monitoring sensor is installed in the closed cavity;

[0012] The data acquisition and processing unit includes a microcontroller and a moisture acquisition circuit, as well as a data storage circuit, a power supply circuit, a communication circuit and a communication power supply; the moisture acquisition circuit, the data storage circuit and all sensors included in the environmental monitoring sensor group are connected to the microcontroller via an IIC bus.

[0013] When in use, the monitoring device is placed in a grain storage bin, and the grain fills all the open chambers. Since the moisture content of grains with different moisture contents is different, the capacitance parameters of the paired detection electrodes will change, based on which the moisture content can be calculated. A pair of detection electrodes placed in a closed cavity will be affected by the environment in the storage bin and will also generate a baseline capacitance parameter for the system to refer to. Combined with the environmental data generated by the environmental monitoring sensor, the data generated by the detection electrodes in the open chamber can be adjusted and corrected to make the generated data more accurate.

[0014] Furthermore, the open cavity has a structure with walls on all four sides and is connected vertically. The partitions between the closed cavity and the open cavity, and between the closed cavity and the external space, each have an inclined hole for communication. The end of the inclined hole closest to the closed cavity is higher, and the other end is lower. The aperture of the inclined hole is smaller than the grain particle size. This ensures gas flow while preventing impurities from entering the closed cavity and preventing grain from blocking the inclined hole. A large hole is provided on the partition between the open cavity and the external space to facilitate grain circulation.

[0015] This makes it easier to insert the monitoring device into the grain storage bin for multi-position detection. In actual use, the monitoring device can also be installed in the storage bin first, and then the grain can be piled up in the storage bin, and it can be used as needed.

[0016] Furthermore, the detection electrode includes an electrode body and an equipotential protection ring arranged around the electrode body;

[0017] The moisture collection circuit includes a harmonic drive circuit connected to the two electrode bodies corresponding to the two detection electrodes. A 0-ohm resistor is provided on the connection line between the electrode body and the harmonic drive circuit. The 0-ohm resistor is a protective resistor and provides a short return path for the high-frequency signal to reduce signal interference. The moisture collection circuit also includes an inductor L and a capacitor C connected in parallel between the two electrode bodies. The harmonic drive circuit is connected to a frequency-digital conversion circuit, and the frequency-digital conversion circuit is connected to an IIC bus.

[0018] An equipotential driving circuit is connected between the electrode body of each detection electrode and the potential protection ring.

[0019] Furthermore, the equipotential driving circuit includes an operational amplifier U1, which is a high-frequency rail-to-rail operational amplifier. The electrode body is connected to the non-inverting input terminal of the operational amplifier U1 through a resistor R10, and the equipotential protection ring is connected to the output terminal of the operational amplifier U1 through a resistor R20. The inverting input terminal of the operational amplifier U1 is connected to the output terminal.

[0020] The principle of the moisture collection circuit is: when there are grains with different moisture contents in the open cavity, the dielectric constant between the parallel plates changes, resulting in a change in the capacitive parameters of the parallel plate capacitors, thereby changing the frequency of the LC oscillation circuit. The frequency-to-digital conversion circuit collects and analyzes the frequency and converts it into data, and provides the frequency data representing the current moisture content of the grain to the microcontroller through the IIC interface.

[0021] Each detection electrode in the circuit is independently equipped with an equipotential driving circuit. The equipotential driving circuit obtains the signal from the corresponding electrode body and drives the equipotential protection ring. The equipotential protection ring can shield external electromagnetic interference and significantly improve the stability of the device in complex environments.

[0022] Furthermore, a strain gauge is installed on the inner side of the top plate of the closed cavity, the strain gauge is connected to a strain acquisition circuit, and the strain acquisition circuit establishes data exchange with the microcontroller through an SPI interface; the strain gauge has a strain bridge, which is a voltage DC Wheatstone bridge, and the strain bridge is used to extract the strain signal of the strain gauge body;

[0023] The strain acquisition circuit includes:

[0024] Bridge conversion circuit, used to achieve resistance matching of single bridge, half bridge and full bridge and self-calibration function of strain gauge bridge;

[0025] A signal processing circuit, used for amplifying and filtering the analog strain signal;

[0026] a signal conversion circuit, configured to convert the analog strain signal processed by the signal processing circuit into a digital signal;

[0027] a microprocessor, configured to read the digital signal from the signal conversion circuit and manage the coordinated operation of other circuits;

[0028] Self-calibration circuit, used to calibrate the system voltage measurement accuracy;

[0029] Self-balancing circuit, used to offset the initial strain output value;

[0030] A bridge excitation circuit, used for providing an excitation voltage for the strain gauge bridge;

[0031] The power module is used to provide power to each circuit.

[0032] Furthermore, the bridge conversion circuit includes a bridge signal processing circuit and a calibration circuit;

[0033] The calibration circuit includes a switch K102 and a resistor R107. The microprocessor can control the switch K102 to determine whether the two ends of the resistor R107 are connected to the two ends of the strain gauge. When the switch K102 is turned on, the microprocessor can perform a strain measurement calibration procedure.

[0034] The bridge conversion circuit further includes a resistor R108, a resistor R109, and a switch K101. The midpoint of a series connection formed by the resistors R108 and R109 is connected to one terminal of the switch K101, and the two ends of the series connection are respectively connected to the positive excitation terminal and the negative excitation terminal of the strain gauge bridge. The switch K101 can selectively connect the midpoint of the series connection or the positive output terminal of the strain gauge bridge to the positive input terminal of the bridge signal processing circuit; the negative output terminal of the strain gauge bridge is directly connected to the negative input terminal of the bridge signal processing circuit.

[0035] A switch K103 is further provided between the negative excitation terminal of the strain bridge and the resistor R109. The switch K103 can select to directly connect the negative excitation terminal to the resistor R109 or select to connect a resistor of at least one resistance value between the negative excitation terminal and the resistor R109.

[0036] The switch K101 , the switch K102 , and the switch K103 can all be controlled by the microprocessor to change their states.

[0037] When the strain gauge bridge is a full bridge, switch K101 directly connects the positive output of the strain gauge bridge to the positive input of the bridge signal processing circuit. When the strain gauge bridge is a half bridge or single bridge, switch K101 connects the positive input of the bridge signal processing circuit to the midpoint of the resistor divider network composed of resistors R108 and R109. In single-bridge and half-bridge strain measurements, these two resistors, along with the strain gauge and matching resistors, form the full bridge for strain measurement. Switch K103 is primarily used to select matching resistors. When the top terminal of the switch is turned on, the negative excitation terminal of the strain gauge bridge is directly output, corresponding to the full-bridge configuration. When switch K103 turns on the other three terminals, resistors R105, R106, and Rx can be matched to single-bridge measurements.

[0038] Furthermore, the signal processing circuit includes an instrumentation amplifier U201 and a precision amplifier U202, wherein U201 plays an amplifying role and U202 is designed as an inverse proportional operational amplifier circuit to play an attenuating role;

[0039] The input end of the instrument amplifier U201 is connected to the strain signal of the strain bridge, and the output end is connected to the inverting input end of the precision amplifier U202 through the resistor R203; the non-inverting input end of the precision amplifier U202 is grounded, and its output end is connected to the signal filtering and acquisition circuit; resistors R204 and R205 are connected between the inverting input end and the output end of the precision amplifier U202, and a switch K203 is connected in parallel between the two ends of the resistor R205. The microprocessor can control the on and off of the switch K203;

[0040] A plurality of parallel resistor branches are connected between the G1 and G2 terminals of the instrument amplifier U201, each resistor branch has a resistor and a switch, and the switch is connected to the microprocessor;

[0041] Typically, the magnification factors in strain measurement systems are 1x, 10x, and 100x. When measuring strain, the microprocessor controls switch K203 to be disconnected, meaning the signal is not attenuated. When measuring voltage signals, the measurement range can reach ±15V. However, typical ADC chips are insufficient to measure such a wide range, so switch K203 is turned on to attenuate the signal before feeding it into subsequent circuits.

[0042] Furthermore, the self-balancing circuit includes an instrumentation amplifier U301 and a precision amplifier U302;

[0043] The input end of the instrument amplifier U301 is connected to the strain bridge signal, and the output end is connected to the signal processing and acquisition circuit;

[0044] The precision op amp U302 drives the Vref pin of the instrument op amp U301; the non-inverting input terminal of the precision op amp U302 is connected to the DAC via a resistor R303 and is grounded via a resistor R304; the DAC and the signal processing and acquisition circuit are both connected to a microprocessor;

[0045] The inverting input terminal and the output terminal of the precision operational amplifier U302 are directly connected to a resistor R302 , and the inverting input terminal is connected to a power supply V301 through a resistor R301 .

[0046] During bridge balancing, the initial strain values that need to be eliminated can be both positive and negative. However, typical DACs are unipolar, meaning they can only output positive or negative voltages. To achieve this balance, a subtraction circuit is formed using U302 and resistors R301, R302, R303, and R304. The specific process for automatic strain bridge balancing is as follows: After the strain gauges are properly installed, the microprocessor controls the DAC to output a certain voltage value, ensuring that the balanced voltage output by U302 is 0V. The microprocessor then reads the value from the signal processing and acquisition circuit. If the value is not 0, the DAC is driven to output the corresponding voltage, and the signal acquisition circuit is read again to control the DAC output. This cycle repeats until the signal processing and acquisition circuit reads 0, stopping the DAC output adjustment. At this point, automatic balancing of the strain bridge is complete.

[0047] Furthermore, the power supply circuit includes the above-mentioned system power supply and communication power supply; the power supply circuit is connected to a 24V DC input voltage, and the power supply circuit includes a rectifier bridge B1. The rectifier bridge B1 is designed to realize external DC 24V access without distinguishing between positive and negative poles, facilitate on-site wiring, and reduce damage to the circuit due to reverse positive and negative connection of the power supply to a certain extent. A varistor M1 is connected between the two input ends of the rectifier bridge B1 to protect subsequent circuits from high-voltage shocks. The output end of the rectifier bridge B1 is connected to an electrolytic capacitor C1 and a first LC filter circuit composed of an inductor L1 and a capacitor C2. The electrolytic capacitor C1 can reduce the voltage ripple after rectification, and the first LC filter circuit can suppress high-frequency interference; the output end of the rectifier bridge B1 is connected to two parallel voltage output circuits located on the rear side of the LC filter circuit, and each voltage output circuit includes an isolated DC-DC voltage conversion module, an LC filter circuit and a tantalum capacitor.

[0048] Furthermore, the communication circuit includes an RS485 interface circuit and a CAN interface circuit, both of which are powered by the communication power supply; the RS485 interface circuit includes a single-channel high-speed RS-485 isolation transceiver U1, which has its own isolation power supply and can achieve secondary isolation, so that the communication cable connection part is electrically isolated from the communication circuit, and the RXD end and TXD end of the single-channel high-speed RS-485 isolation transceiver U1 are respectively connected to the RXD485 and TXD485 signals output by the microcontroller after optical coupling isolation, and the same-direction signals R485 and T485; the single-channel high-speed RS-485 isolation transceiver U1 is connected to the RXD485 and TXD485 signals output by the microcontroller after optical coupling isolation. The VCC and GND terminals of the transceiver U1 are connected to the 5V communication power supply and ground respectively, and a power supply filter capacitor C7 is connected between the two ports; the single-channel high-speed RS-485 isolation transceiver U1 is also connected to a current limiting resistor R1, a current limiting resistor R2, a pull-up resistor R3, a pull-down resistor R4 and a bidirectional low-capacitance ESD electrostatic protector D1; the current limiting resistor is used to protect the single-channel high-speed RS-485 isolation transceiver U1, the pull-up resistor R3 and the pull-down resistor R4 are used to improve the driving capability of the communication signal, and the bidirectional low-capacitance ESD electrostatic protector D1 is used to improve the adaptability of the communication circuit to the on-site environment.

[0049] The CAN interface circuit includes a single-channel high-speed CAN isolation transceiver U2, the RXD and TXD terminals of the single-channel high-speed CAN isolation transceiver U2 are respectively connected to the same-direction signals C_R and C_T of the CAN_R and CAN_T signals output by the microcontroller after optical coupling isolation; the VCC and GND terminals of the isolation transceiver U2 are respectively connected to a 5V communication power supply and ground, and a power supply filter capacitor C8 is connected between the two ports; the CANH and CANL terminals of the single-channel high-speed CAN isolation transceiver U2 are respectively connected to a bidirectional low-capacitance ESD electrostatic protector D2 through current limiting resistors R5 and R6, and the bidirectional low-capacitance ESD electrostatic protector D2 is also connected to the CANG port of the single-channel high-speed CAN isolation transceiver U2.

[0050] Beneficial effects: The real-time monitoring device for moisture content in grain storage bins of the present invention has the following advantages:

[0051] Beneficial effects:

[0052] (1) The present invention provides an open cavity inside the device base, thereby providing a closed cavity that is inaccessible to grain materials, and installing detection electrodes and environmental monitoring sensors in the closed cavity. The detection elements in the closed cavity can provide reference capacitance parameters, temperature, humidity, carbon dioxide concentration and other data, and correct the data generated by the detection electrodes in the open cavity, thereby reducing environmental interference, improving data accuracy, and providing reliable support for grain storage.

[0053] (2) Multiple detection electrodes in the closed cavity provide multiple sets of reference capacitance parameters, which can be fused to obtain more accurate moisture content data.

[0054] (3) The moisture collection circuit shields external electromagnetic interference through the equipotential protection ring of the detection electrode, improving stability in complex environments. A harmonic drive circuit and LC oscillation circuit achieve precise measurement of the relationship between frequency changes and grain moisture. The frequency-to-digital conversion circuit converts the frequency signal into digital data and transmits it via the IIC bus, ensuring efficient real-time monitoring. The 0-ohm resistor reduces high-frequency signal interference, and the equipotential drive circuit precisely controls the potential difference through an operational amplifier, further improving measurement accuracy. The overall design significantly enhances the device's anti-interference ability and the accuracy of moisture monitoring.

[0055] (4) The bridge conversion circuit in the strain acquisition circuit achieves flexible adaptation to various configurations such as full-bridge, half-bridge, and single-bridge through switches K101, K102, and K103 controlled by the microprocessor, significantly improving the versatility and compatibility of the real-time monitoring device for moisture content in grain storage bins. The design of the calibration circuit allows for precise strain measurement calibration, effectively improving measurement accuracy. In addition, switch K103 can select different matching resistors, further enhancing the adaptability to various strain gauges. Overall, the circuit optimizes monitoring accuracy and reliability through automated control and flexible configuration.

[0056] (5) The signal processing circuit in the strain acquisition circuit accurately amplifies the strain signal through the instrument operational amplifier U201, and the precision operational amplifier U202 flexibly attenuates the signal. The microprocessor adjusts the amplification factor and attenuation function to adapt to different measurement requirements, thereby improving the accuracy and applicability of the real-time monitoring device for material moisture in the grain storage bin, and supporting ±15V voltage range measurement.

[0057] (6) The design of the self-balancing circuit solves the problems existing in the traditional bridge balancing method. The traditional bridge balancing method uses the potentiometer method. Although the potentiometer method is relatively low in cost, it has the disadvantages of being difficult to adjust and being easily affected by mechanical vibration, temperature and humidity changes, etc., which leads to drift and reduced accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0058] Figure 1 This is a structural diagram of a real-time moisture monitoring device for materials in a grain storage bin;

[0059] Figure 2 This is the combined structure diagram of the top plate and strain gauge;

[0060] Figure 3 It is a schematic diagram of the connection between the data acquisition and processing unit and each sensor;

[0061] Figure 4 This is the structural diagram of the moisture collection circuit;

[0062] Figure 5 is the structural diagram of the detection electrode;

[0063] Figure 6 It is the structural diagram of the equipotential driving circuit;

[0064] Figure 7 Schematic diagram of the electric field of the detection electrode in the present invention;

[0065] Figure 8 Schematic diagram of the electric field of a traditional detection electrode;

[0066] Figure 9 Schematic diagram of the strain acquisition circuit;

[0067] Figure 10 It is a schematic diagram of the bridge conversion circuit;

[0068] Figure 11 is a schematic diagram of a signal processing circuit;

[0069] Figure 12 is a schematic diagram of a self-balancing circuit;

[0070] Figure 13 is a schematic diagram of the microcontroller and its peripheral circuits;

[0071] Figure 14 is a schematic diagram of the power supply circuit;

[0072] Figure 15 This is a schematic diagram of the RS485 interface circuit;

[0073] Figure 16 This is a schematic diagram of the CAN interface circuit;

[0074] Figure 17 Schematic diagram of wireless communication circuit.

[0075] In the figure: 1-device base; 11-top plate; 1a-closed cavity; 1b-open cavity; 1c-inclined hole; 1d-large hole; 2-detection electrode; 21-electrode body; 22-equipotential protection ring; 23-equipotential protection layer; 24-equipotential pad; 25-electrode pad; 3-data acquisition and processing unit; 4-strain gauge. DETAILED DESCRIPTION

[0076] The present invention will be further described below with reference to the accompanying drawings.

[0077] like Figure 1 The device for real-time monitoring of moisture content in a grain storage bin shown in the figure comprises a device base 1 and multiple pairs of detection electrodes 2, as well as an environmental monitoring sensor group and a data acquisition and processing unit 3. The environmental monitoring sensor is used to monitor environmental data such as temperature, humidity, and carbon dioxide concentration in the storage bin;

[0078] The device body 1 has at least one closed cavity 1a and multiple open cavities 1b; both sides of the closed cavity 1a have open cavities 1b; a pair of detection electrodes 2 are installed in each of the closed cavity 1a and the open cavity 1b;

[0079] The closed cavity 1a and the adjacent space can communicate with each other, and food materials cannot enter the closed cavity 1a. The space adjacent to the closed cavity 1a includes the adjacent closed cavity 1a and the external space of the device base 1, so that the temperature, humidity and carbon dioxide concentration in the closed cavity 1a can be consistent with the environmental parameters of the external space; because the closed cavity 1a is open, the open cavity 1b can communicate with the external space of the device base 1.

[0080] The environmental monitoring sensor is installed in the closed cavity 1a;

[0081] like Figure 3 As shown, the data acquisition and processing unit 3 includes a microcontroller and a moisture acquisition circuit, as well as a data storage circuit, a power supply circuit, a communication circuit and a communication power supply; the moisture acquisition circuit, the data storage circuit and all sensors included in the environmental monitoring sensor group are connected to the microcontroller through an IIC bus.

[0082] When in use, the monitoring device is placed in a grain storage bin, and the grain fills all the open chambers 1b. Since the moisture content of grains with different moisture contents is different, the capacitance parameters of the paired detection electrodes 2 will change, based on which the moisture content can be calculated. Among them, a pair of detection electrodes 2 placed in the closed cavity 1a are affected by the environment in the storage bin and will also generate a baseline capacitance parameter for the system reference. Combined with the environmental data generated by the environmental monitoring sensor, the data generated by the detection electrode 2 in the open chamber 1b can be adjusted and corrected to make the generated data more accurate.

[0083] The present invention sets a closed cavity 1a which is inaccessible to grain materials outside an open cavity 1b in the device base 1, and installs a detection electrode 2 and an environmental monitoring sensor in the closed cavity. The detection element in the closed cavity 1a can provide reference capacitance parameters, temperature, humidity, carbon dioxide concentration and other data, and correct the data generated by the detection electrode 2 in the open cavity 1b, which can reduce environmental interference, improve data accuracy, and provide reliable support for grain storage.

[0084] The detection electrodes 2 in the multiple closed cavities 1a provide multiple sets of reference capacitance parameters, which can be integrated to obtain more accurate moisture content data.

[0085] The communication circuit is configured with RS485 and CAN communication interface circuits, which communicate with the UART and CAN ports of the microcontroller respectively, and can adapt to the requirements of low-speed and high-speed communication systems.

[0086] The system power supply supplies power to all parts except the communication circuit, and its output voltage is 3.3V. The communication power supply supplies power to the communication circuit, and its output voltage is 5V.

[0087] The circuit design uses a dual-isolation design, isolating the communication power supply and system power supply from the external input power supply, and the communication power supply and system power supply are also isolated from each other. The RS485 and CAN interface circuits are isolated from the microprocessor system. The dual-isolation circuit design further enhances the system's anti-interference capabilities.

[0088] Considering the need for moisture monitoring during grain storage, the microcontroller uses STMicroelectronics' 32-bit low-power microprocessor STM32L4x1 series, which has high performance -M4 32-bit RISC core ultra-low power microprocessor, operating frequency up to 80MHz, supports single-precision floating-point calculations and DSP instructions, meeting the system data calculation and analysis needs. Figure 13 As shown, C01 and R01 constitute the microcontroller power-on reset and startup area selection circuit; R02 and R03 are IIC bus pull-up resistors, cooperating with the processor to realize bus drive; XT1, C03, and C04 constitute the microprocessor clock system resonant source with a frequency of 8MHz; TXD485 and RXD485 are the data sending and receiving pins for communication between the microprocessor and the RS485 communication circuit; CAN_R and CAN_T are the data sending and receiving pins for communication between the microprocessor and the CAN communication circuit.

[0089] Data storage uses non-volatile FeRAM, which has low power consumption, high-speed reading and writing, and no write waiting time, matching the system's high-speed data processing requirements.

[0090] Preferably, the open chamber 1b has walls on all four sides and is connected vertically. The partition between the closed chamber 1a and the open chamber 1b, and the partition between the closed chamber 1a and the outside space, both have an oblique hole 1c for communication. The end of the oblique hole 1c closest to the closed chamber 1a is higher, and the other end is lower. The aperture of the oblique hole 1c is smaller than the grain particle size. This ensures gas flow while preventing impurities from entering the closed chamber 1a and preventing grain from blocking the oblique hole 1c. A large hole 1d is provided on the partition between the open chamber 1b and the outside space to facilitate grain circulation.

[0091] This makes it easier to insert the monitoring device into the grain storage bin for multi-position detection. In actual use, the monitoring device can also be installed in the storage bin first, and then the grain can be piled up in the storage bin, and it can be used as needed.

[0092] Preferably, if Figure 5 As shown, the detection electrode 2 includes an electrode body 21 and an equipotential protection ring 22 arranged around the electrode body 21. Preferably, the detection electrode 2 includes four layers of substrates. In the direction from the outside to the inside, the first layer of substrate (shown as layer ① in the figure) is an insulating substrate, and the second layer of substrate (shown as layer ② in the figure) is electroplated with the above-mentioned electrode body 21 and equipotential protection ring 22, and there is an annular gap between the electrode body 21 and the equipotential protection ring 22; the third layer of substrate (shown as layer ③ in the figure) is electroplated with an equipotential protection layer 23, and the outer contour of the equipotential protection layer 23 is consistent with the outer contour of the equipotential protection ring 22, and the outer contour of the equipotential protection layer is plated with a copper layer within its outer contour; the fourth layer of substrate (shown as layer ④ in the figure) is provided with an equipotential pad 24 and an electrode pad 25, and the equipotential pad is conductive to the equipotential protection ring 22 and the equipotential protection layer, and the electrode pad is conductive to the electrode body 21. With the above structure, the equipotential protection ring 22 and the equipotential protection layer can shield interference signals in all directions to ensure the accuracy of moisture monitoring. In addition, as shown in FIG. Figure 7 As shown, the length and width of the electrode body 21 of one detection electrode are smaller than the length and width of the electrode body 21 of the other detection electrode. Figure 7 As shown, the electric field of the detection electrode in the present invention is compared with Figure 8 As for the electric field of the traditional detection electrode shown, the edge effect is effectively reduced and the electric field distribution is optimized, thereby ensuring the accuracy of capacitance detection.

[0093] like Figure 5 As shown, the moisture collection circuit includes a harmonic drive circuit connected to the two electrode bodies 21 corresponding to the two detection electrodes 2. A 0-ohm resistor is provided on the connection line between the electrode body 21 and the harmonic drive circuit. The 0-ohm resistor is a protective resistor and provides a short return path for high-frequency signals to reduce signal interference. The moisture collection circuit also includes an inductor L and a capacitor C connected in parallel between the two electrode bodies 21. The harmonic drive circuit is connected to a frequency-digital conversion circuit, and the frequency-digital conversion circuit is connected to the IIC bus.

[0094] An equipotential driving circuit is connected between the electrode body 21 and the potential protection ring 22 of each detection electrode 2 .

[0095] Preferably, if Figure 6 As shown, the equipotential driving circuit includes an operational amplifier U1, which is a high-frequency rail-to-rail operational amplifier. The electrode body 21 is connected to the non-inverting input terminal of the operational amplifier U1 through a resistor R10, and the equipotential protection ring 22 is connected to the output terminal of the operational amplifier U1 through a resistor R20. The inverting input terminal of the operational amplifier U1 is connected to the output terminal.

[0096] The two detection electrodes 2 of the same pair above form a parallel plate capacitor C X , whose values are:

[0097]

[0098] Where ε0 is the dielectric constant of vacuum; ε r is the relative dielectric constant of the medium to be measured, that is, the relative dielectric constant of grains with different moisture content; S and d are the electrode area and spacing, respectively; when the sampling plates are filled with grains with different moisture content, the relative dielectric constant ε between the electrodes r The values of are different. From the above formula, we can know that the parallel plate capacitance C X It will also change accordingly.

[0099] In the moisture collection circuit, the parallel plate capacitor is connected in parallel with the inductor L and the capacitor C to form an LC oscillation circuit. Under the drive of the resonant drive circuit, the oscillation frequency is kept stable. The frequency f is:

[0100]

[0101] Combining the previous two equations, we can get:

[0102]

[0103] In the above formula, except ε r All other parameters except ε are constant, so the frequency f of the LC oscillation circuit is only related to ε r Related, that is, related to the moisture content of the grain in the channel.

[0104] The principle of the moisture collection circuit is: when there are grains with different moisture contents in the open cavity 1b, the dielectric constant between the parallel plates changes, resulting in a change in the capacitive parameters of the parallel plate capacitors, thereby changing the frequency of the LC oscillation circuit. The frequency-to-digital conversion circuit collects and analyzes the frequency and converts it into data, and the IIC interface provides the microcontroller with frequency data representing the current moisture content of the grain.

[0105] Each detection electrode 2 in the circuit is independently equipped with an equipotential driving circuit. The equipotential driving circuit obtains the signal from the corresponding electrode body 21 and drives the equipotential protection ring 22. The equipotential protection ring 22 can shield external electromagnetic interference and significantly improve the stability of the device in complex environments.

[0106] The moisture collection circuit shields the detection electrodes from external electromagnetic interference through an equipotential guard ring, improving stability in complex environments. A harmonic drive circuit and LC oscillator circuit accurately measure the correlation between frequency changes and grain moisture. A frequency-to-digital conversion circuit converts the frequency signal into digital data, which is transmitted via the IIC bus to ensure efficient real-time monitoring. A 0-ohm resistor reduces high-frequency signal interference, and the equipotential drive circuit precisely controls the potential difference through an operational amplifier, further improving measurement accuracy. The overall design significantly enhances the device's anti-interference capabilities and moisture monitoring accuracy.

[0107] Preferably, if Figure 2 As shown, a strain gauge 4 is mounted on the inner side of the top plate 11 of the enclosed chamber 1a. This strain gauge 4 is connected to a strain acquisition circuit, which exchanges data with the microcontroller via an SPI interface. The top plate 11 is tilted so that as the grain storage compartment decreases, it does not accumulate on the top plate 11, affecting the accuracy of the data collected by the strain gauge 4. The data generated by the strain gauge 4, the thickness of the grain accumulated on the top plate 11, and the basic parameters of the grain can be used to calculate the grain's porosity. This porosity can then be used to correct the moisture content, further improving the accuracy of the resulting moisture content.

[0108] The strain gauge 4 has a strain bridge, which is a voltage DC type Wheatstone bridge, and the strain bridge is used to extract the strain signal of the strain gauge body;

[0109] like Figure 9 As shown, the strain acquisition circuit includes:

[0110] Bridge conversion circuit, used to achieve resistance matching of single bridge, half bridge and full bridge and self-calibration function of strain gauge bridge;

[0111] A signal processing circuit, used for amplifying and filtering the analog strain signal;

[0112] a signal conversion circuit, configured to convert the analog strain signal processed by the signal processing circuit into a digital signal;

[0113] a microprocessor, configured to read the digital signal from the signal conversion circuit and manage the coordinated operation of other circuits;

[0114] Self-calibration circuit, used to calibrate the system voltage measurement accuracy;

[0115] Self-balancing circuit, used to offset the initial strain output value;

[0116] A bridge excitation circuit, used for providing an excitation voltage for the strain gauge bridge;

[0117] The power module is used to provide power to each circuit.

[0118] Preferably, if Figure 10 As shown, the bridge conversion circuit includes a bridge signal processing circuit and a calibration circuit;

[0119] The calibration circuit includes a switch K102 and a resistor R107. The microprocessor can control the switch K102 to be on or off to determine whether the two ends of the resistor R107 are connected to the two ends of the strain gauge 4. When the switch K102 is turned on, the microprocessor can perform a strain measurement calibration procedure.

[0120] The bridge conversion circuit further includes a resistor R108, a resistor R109, and a switch K101. The midpoint of a series connection formed by the resistors R108 and R109 is connected to one terminal of the switch K101, and the two ends of the series connection are respectively connected to the positive excitation terminal and the negative excitation terminal of the strain gauge bridge. The switch K101 can selectively connect the midpoint of the series connection or the positive output terminal of the strain gauge bridge to the positive input terminal of the bridge signal processing circuit; the negative output terminal of the strain gauge bridge is directly connected to the negative input terminal of the bridge signal processing circuit.

[0121] A switch K103 is further provided between the negative excitation terminal of the strain gauge bridge and the resistor R109. The switch K103 can select to directly connect the negative excitation terminal to the resistor R109 or to connect at least one resistor of different resistance values between the negative excitation terminal and the resistor R109. In this embodiment, in addition to directly connecting the negative excitation terminal to the resistor R109, the switch K103 can also select among the resistors R105, R106, and Rx.

[0122] The switch K101 , the switch K102 , and the switch K103 can all be controlled by the microprocessor to change their states.

[0123] When the strain gauge bridge is a full bridge, switch K101 directly connects the positive output of the strain gauge bridge to the positive input of the bridge signal processing circuit. When the strain gauge bridge is a half bridge or single bridge, switch K101 connects the positive input of the bridge signal processing circuit to the midpoint of the resistor divider network composed of resistors R108 and R109. In single-bridge and half-bridge strain measurements, these two resistors, along with the strain gauge and matching resistors, form the full bridge for strain measurement. Switch K103 is primarily used to select matching resistors. When the top terminal of the switch is turned on, the negative excitation terminal of the strain gauge bridge is directly output, corresponding to the full-bridge configuration. When switch K103 turns on the other three terminals, resistors R105, R106, and Rx can be matched to single-bridge measurements.

[0124] The bridge conversion circuit in the strain acquisition circuit, through microprocessor-controlled switches K101, K102, and K103, enables flexible adaptation to various configurations, including full-bridge, half-bridge, and single-bridge configurations. This significantly enhances the versatility and compatibility of the real-time moisture monitoring device for grain storage bins. The calibration circuit design allows for precise strain measurement calibration, effectively improving measurement accuracy. Furthermore, switch K103 allows for the selection of different matching resistors, further enhancing compatibility with various strain gauges. Overall, this circuit optimizes monitoring accuracy and reliability through automated control and flexible configuration.

[0125] like Figure 11 As shown, the signal processing circuit includes an instrumentation amplifier U201 and a precision amplifier U202, wherein U201 plays an amplifying role, and U202 is designed as an inverse proportional operational amplifier circuit, which plays an attenuating role;

[0126] The input end of the instrument amplifier U201 is connected to the strain signal of the strain bridge, and the output end is connected to the inverting input end of the precision amplifier U202 through the resistor R203; the non-inverting input end of the precision amplifier U202 is grounded, and its output end is connected to the signal filtering and acquisition circuit; resistors R204 and R205 are connected between the inverting input end and the output end of the precision amplifier U202, and a switch K203 is connected in parallel between the two ends of the resistor R205. The microprocessor can control the on and off of the switch K203;

[0127] A plurality of parallel resistor branches are connected between the G1 and G2 terminals of the instrumentation amplifier U201. Each resistor branch has a resistor and a switch, and the switch is connected to the microprocessor. In this embodiment, two resistor branches are included, one of which includes a resistor R201 and a switch K201, and the other includes a resistor R202 and a switch K202. By turning on switch K201 or switch K202, the resistance value R between the G1 and G2 terminals can be changed. G , thereby changing the amplification factor of the instrumentation amplifier U201.

[0128] Typically, the magnification factors in strain measurement systems are 1x, 10x, and 100x. When measuring strain, the microprocessor controls switch K203 to be disconnected, meaning the signal is not attenuated. When measuring voltage signals, the measurement range can reach ±15V. However, typical ADC chips are insufficient to measure such a wide range, so switch K203 is turned on to attenuate the signal before feeding it into subsequent circuits.

[0129] The signal processing circuit in the strain acquisition circuit accurately amplifies the strain signal through the instrument op amp U201, and the precision op amp U202 flexibly attenuates the signal. The microprocessor adjusts the amplification factor and attenuation function to adapt to different measurement requirements, thereby improving the accuracy and applicability of the real-time moisture monitoring device for materials in grain storage bins, and supports measurement in the ±15V voltage range.

[0130] like Figure 13 As shown, the self-balancing circuit includes an instrumentation amplifier U301 and a precision amplifier U302;

[0131] The input end of the instrument amplifier U301 is connected to the strain bridge signal, and the output end is connected to the signal processing and acquisition circuit;

[0132] The precision op amp U302 drives the Vref pin of the instrument op amp U301; the non-inverting input terminal of the precision op amp U302 is connected to the DAC via a resistor R303 and is grounded via a resistor R304; the DAC and the signal processing and acquisition circuit are both connected to a microprocessor;

[0133] The inverting input terminal and the output terminal of the precision operational amplifier U302 are directly connected to a resistor R302 , and the inverting input terminal is connected to a power supply V301 through a resistor R301 .

[0134] During bridge balancing, the initial strain values that need to be eliminated can be both positive and negative. However, typical DACs are unipolar, meaning they can only output positive or negative voltages. To achieve this balance, a subtraction circuit is formed using U302 and resistors R301, R302, R303, and R304. The specific process for automatic strain bridge balancing is as follows: After the strain gauges are properly installed, the microprocessor controls the DAC to output a certain voltage value, ensuring that the balanced voltage output by U302 is 0V. The microprocessor then reads the value from the signal processing and acquisition circuit. If the value is not 0, the DAC is driven to output the corresponding voltage, and the signal acquisition circuit is read again to control the DAC output. This cycle repeats until the signal processing and acquisition circuit reads 0, stopping the DAC output adjustment. At this point, automatic balancing of the strain bridge is complete.

[0135] The design of the self-balancing circuit solves the problems existing in the traditional bridge balancing method, that is, the traditional bridge balancing method uses the potentiometer method. Although the potentiometer method is relatively low in cost, it has the disadvantages of being difficult to adjust and being easily affected by mechanical vibration, temperature and humidity changes, etc., which leads to drift and reduced accuracy.

[0136] Preferably, the power supply circuit includes the above-mentioned system power supply and communication power supply; Figure 14As shown, the power supply circuit is connected to a 24V DC input voltage. The power supply circuit includes a rectifier bridge B1. The rectifier bridge B1 is designed to enable external DC 24V access without distinguishing between positive and negative poles, facilitate on-site wiring, and reduce damage to the circuit due to reverse connection of the positive and negative poles of the power supply to a certain extent. A varistor M1 is connected between the two input ends of the rectifier bridge B1 to protect subsequent circuits from high-voltage shocks. The output end of the rectifier bridge B1 is connected to an electrolytic capacitor C1 and a first LC filter circuit composed of an inductor L1 and a capacitor C2. The electrolytic capacitor C1 can reduce the voltage ripple after rectification, and the first LC filter circuit can suppress high-frequency interference; the output end of the rectifier bridge B1 is connected to two parallel voltage output circuits located on the rear side of the LC filter circuit, and each voltage output circuit is connected to the rectifier bridge B1. It includes an isolated DC-DC voltage conversion module, an LC filter circuit and a tantalum capacitor. Specifically, among the two voltage output circuits, one voltage output circuit includes an isolated DC-DC voltage conversion module P1 and a second LC filter circuit composed of a capacitor C3 and an inductor L2, and also includes a tantalum capacitor C4. The second LC filter circuit suppresses high-frequency interference on the 3.3V voltage, and the tantalum capacitor C4 eliminates ripple on the 3.3V voltage to ensure stable power supply voltage; the other voltage output circuit includes an isolated DC-DC voltage conversion module P2 and a third LC filter circuit composed of a capacitor C5 and an inductor L3, and also includes a tantalum capacitor C6. The third LC filter circuit suppresses high-frequency interference on the 5V voltage, and the tantalum capacitor C4 eliminates ripple on the 5V voltage to ensure stable power supply voltage.

[0137] Preferably, the communication circuit includes an RS485 interface circuit and a CAN interface circuit, both of which are powered by the communication power supply; Figure 15 As shown, the RS485 interface circuit includes a single-channel high-speed RS-485 isolation transceiver U1, which has its own isolated power supply and can achieve secondary isolation, so that the communication cable connection part is electrically isolated from the communication circuit. The RXD terminal and TXD terminal of the single-channel high-speed RS-485 isolation transceiver U1 are respectively connected to the RXD485 and TXD485 signals output by the microcontroller after optical coupling isolation of the same-direction signals R485 and T485; the VCC terminal and GND terminal of the single-channel high-speed RS-485 isolation transceiver U1 are respectively connected to 5V Communication power supply and ground, and a power supply filter capacitor C7 is connected between the two ports; the single-channel high-speed RS-485 isolation transceiver U1 is also connected to a current limiting resistor R1, a current limiting resistor R2, a pull-up resistor R3, a pull-down resistor R4 and a bidirectional low-capacitance ESD electrostatic protector D1; the current limiting resistor is used to protect the single-channel high-speed RS-485 isolation transceiver U1, the pull-up resistor R3 and the pull-down resistor R4 are used to improve the driving capability of the communication signal, and the bidirectional low-capacitance ESD electrostatic protector D1 is used to improve the adaptability of the communication circuit to the on-site environment.

[0138] like Figure 16As shown, the CAN interface circuit includes a single-channel high-speed CAN isolation transceiver U2, and the RXD terminal and TXD terminal of the single-channel high-speed CAN isolation transceiver U2 are respectively connected to the same-direction signals C_R and C_T after the CAN_R and CAN_T signals output by the microcontroller are isolated by optical couplers; the VCC terminal and GND terminal of the isolation transceiver U2 are respectively connected to the 5V communication power supply and the ground, and a power supply filter capacitor C8 is connected between the two ports; the CANH terminal and CANL terminal of the single-channel high-speed CAN isolation transceiver U2 are respectively connected to the bidirectional low-capacitance ESD electrostatic protector D2 through the current limiting resistor R5 and the current limiting resistor R6, and the bidirectional low-capacitance ESD electrostatic protector D2 is also connected to the CANG port of the single-channel high-speed CAN isolation transceiver U2.

[0139] To monitor moisture levels during grain storage, wiring within the grain pile is impractical. Moisture monitoring devices are independently located at different locations within the grain pile. Therefore, this moisture monitoring device provides a wireless communication interface and module. The wireless communication circuitry is housed as a separate unit within the wireless communication module housing and connected via the moisture monitoring device's input and output interface plugs.

[0140] Wireless communication inside the grain pile requires high penetration capability of the wireless module, such as Figure 17 As shown in the figure, this design uses a 433MHz wireless bidirectional transparent transmission module to communicate with the RS485 serial port of the microcontroller in the moisture monitoring device's internal circuit. The module is equipped with a lithium battery pack and a charge-discharge circuit. Through the discharge circuit, the lithium battery not only powers the wireless communication module but also provides 3.3V power to the moisture monitoring device's internal circuitry. When the moisture monitoring device is not operating, the module can be removed and charged through the charging port.

[0141] In order to ensure the battery power supply time, when using wireless communication, the moisture monitoring device sends moisture data once at a fixed interval and is in sleep mode for the rest of the time to reduce power consumption.

[0142] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A real-time moisture monitoring device for materials in a grain storage bin, comprising a device base, multiple pairs of detection electrodes, an environmental monitoring sensor group, and a data acquisition and processing unit; The device base has at least one closed cavity and a plurality of open cavities; both sides of the closed cavity have the open cavities; a pair of detection electrodes are respectively installed in the closed cavity and the open cavity; The closed cavity and the adjacent space can communicate with each other; The environmental monitoring sensor is installed in the closed cavity; The data acquisition and processing unit includes a microcontroller and a moisture acquisition circuit; the moisture acquisition circuit and all sensors included in the environmental monitoring sensor group are connected to the microcontroller via an IIC bus.

2. The real-time monitoring device for moisture content in a grain storage bin according to claim 1 is characterized in that: The open cavity is a structure that is through-connected from top to bottom.

3. The real-time monitoring device for moisture content in a grain storage bin according to claim 1 is characterized in that: The detection electrode includes an electrode body and an equipotential protection ring arranged around the electrode body; The moisture collection circuit includes a harmonic drive circuit connected to the two electrode bodies corresponding to the two detection electrodes, and a 0-ohm resistor is provided on the connection line between the electrode body and the harmonic drive circuit; the moisture collection circuit also includes an inductor L and a capacitor C connected in parallel between the two electrode bodies, the harmonic drive circuit is connected to the frequency-digital conversion circuit, and the frequency-digital conversion circuit is connected to the IIC bus; An equipotential driving circuit is connected between the electrode body of each detection electrode and the potential protection ring.

4. The real-time monitoring device for moisture content in a grain storage bin according to claim 3 is characterized in that: The equipotential driving circuit includes an operational amplifier U1, the electrode body is connected to the non-inverting input terminal of the operational amplifier U1 through a resistor R10, the equipotential protection ring is connected to the output terminal of the operational amplifier U1 through a resistor R20, and the inverting input terminal of the operational amplifier U1 is connected to the output terminal.

5. The real-time monitoring device for moisture content in a grain storage bin according to claim 1 is characterized in that: A strain gauge is installed on the inner side of the top plate of the closed cavity, and the strain gauge is connected to a strain acquisition circuit, and the strain acquisition circuit establishes data interaction with the microcontroller through an SPI interface; The strain gauge has a strain bridge; The strain acquisition circuit includes: Bridge conversion circuit, used to achieve resistance matching of single bridge, half bridge and full bridge and self-calibration function of strain gauge bridge; A signal processing circuit, used for amplifying and filtering the analog strain signal; a signal conversion circuit, configured to convert the analog strain signal processed by the signal processing circuit into a digital signal; a microprocessor, configured to read the digital signal from the signal conversion circuit and manage the coordinated operation of other circuits; Self-calibration circuit, used to calibrate the system voltage measurement accuracy; Self-balancing circuit, used to offset the initial strain output value; A bridge excitation circuit, used for providing an excitation voltage for the strain gauge bridge; The power module is used to provide power to each circuit.

6. The real-time monitoring device for moisture content in a grain storage bin according to claim 5, characterized in that: The bridge conversion circuit includes a bridge signal processing circuit and a calibration circuit; The calibration circuit includes a switch K102 and a resistor R107. The microprocessor can control the switch K102 to be on or off to determine whether the two ends of the resistor R107 are connected to the two ends of the strain gauge; The bridge conversion circuit further includes a resistor R108, a resistor R109, and a switch K101. The midpoint of a series connection formed by the resistors R108 and R109 is connected to one terminal of the switch K101, and the two ends of the series connection are respectively connected to the positive excitation terminal and the negative excitation terminal of the strain gauge bridge. The switch K101 can selectively connect the midpoint of the series connection or the positive output terminal of the strain gauge bridge to the positive input terminal of the bridge signal processing circuit. A switch K103 is further provided between the negative excitation terminal of the strain bridge and the resistor R109. The switch K103 can select to directly connect the negative excitation terminal to the resistor R109 or select to connect a resistor of at least one resistance value between the negative excitation terminal and the resistor R109. The switch K101 , the switch K102 , and the switch K103 can all be controlled by the microprocessor to change their states.

7. The real-time monitoring device for moisture content in a grain storage bin according to claim 5, characterized in that: The signal processing circuit includes an instrumentation amplifier U201 and a precision amplifier U202; The input end of the instrument amplifier U201 is connected to the strain signal of the strain bridge, and the output end is connected to the inverting input end of the precision amplifier U202 through the resistor R203; the non-inverting input end of the precision amplifier U202 is grounded, and its output end is connected to the signal filtering and acquisition circuit; resistors R204 and R205 are connected between the inverting input end and the output end of the precision amplifier U202, and a switch K203 is connected in parallel between the two ends of the resistor R205. The microprocessor can control the on and off of the switch K203; A plurality of parallel resistor branches are connected between the G1 terminal and the G2 terminal of the instrumentation amplifier U201. Each resistor branch has a resistor and a switch, and the switch is connected to the microprocessor.

8. The real-time monitoring device for moisture content in a grain storage bin according to claim 5, characterized in that: The self-balancing circuit includes an instrumentation amplifier U301 and a precision amplifier U302; The input end of the instrument amplifier U301 is connected to the strain bridge signal, and the output end is connected to the signal processing and acquisition circuit; The precision op amp U302 drives the Vref pin of the instrument op amp U301; the non-inverting input terminal of the precision op amp U302 is connected to the DAC via a resistor R303 and is grounded via a resistor R304; the DAC and the signal processing and acquisition circuit are both connected to a microprocessor; The inverting input terminal and the output terminal of the precision operational amplifier U302 are directly connected to a resistor R302 , and the inverting input terminal is connected to a power supply V301 through a resistor R301 .

9. The real-time monitoring device for moisture content in a grain storage bin according to claim 1, characterized in that: The data acquisition and processing unit also includes a power supply circuit and a communication circuit. The power supply circuit includes the above-mentioned system power supply and communication power supply. The power supply circuit is connected to a 24V DC input voltage. The power supply circuit includes a rectifier bridge B1. A varistor M1 is connected between the two input ends of the rectifier bridge B1. The output end of the rectifier bridge B1 is connected to an electrolytic capacitor C1 and a first LC filter circuit composed of an inductor L1 and a capacitor C2. The output end of the rectifier bridge B1 is connected to two parallel voltage output circuits located on the rear side of the LC filter circuit. Each voltage output circuit includes an isolated DC-DC voltage conversion module, an LC filter circuit and a tantalum capacitor.

10. The real-time monitoring device for moisture content in a grain storage bin according to claim 9, characterized in that: The communication circuit includes an RS485 interface circuit and a CAN interface circuit, both of which are powered by the communication power supply; the RS485 interface circuit includes a single-channel high-speed RS-485 isolation transceiver U1, and the RXD terminal and TXD terminal of the single-channel high-speed RS-485 isolation transceiver U1 are respectively connected to the same-direction signals R485 and T485 after the RXD485 and TXD485 signals output by the microcontroller are isolated by optical couplers; the VCC terminal and GND terminal of the single-channel high-speed RS-485 isolation transceiver U1 are respectively connected to the 5V communication power supply and ground, and a power supply filter capacitor C7 is connected between the two ports; the single-channel high-speed RS-485 isolation transceiver U1 is also connected to a current limiting resistor R1, a current limiting resistor R2, a pull-up resistor R3, a pull-down resistor R4 and a bidirectional low-capacitance ESD electrostatic protector D1; The CAN interface circuit includes a single-channel high-speed CAN isolation transceiver U2, the RXD and TXD terminals of the single-channel high-speed CAN isolation transceiver U2 are respectively connected to the same-direction signals C_R and C_T of the CAN_R and CAN_T signals output by the microcontroller after optical coupling isolation; the VCC and GND terminals of the isolation transceiver U2 are respectively connected to a 5V communication power supply and ground, and a power supply filter capacitor C8 is connected between the two ports; the CANH and CANL terminals of the single-channel high-speed CAN isolation transceiver U2 are respectively connected to a bidirectional low-capacitance ESD electrostatic protector D2 through current limiting resistors R5 and R6, and the bidirectional low-capacitance ESD electrostatic protector D2 is also connected to the CANG port of the single-channel high-speed CAN isolation transceiver U2.

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