A grain condition measurement and control system based on a hydrophilic conjugated small molecule humidity sensor

Abstract

This invention discloses a grain condition monitoring and control system based on a hydrophilic conjugated small molecule humidity sensor, belonging to the field of grain storage monitoring technology. The system includes a hydroxyethyl side-chain modified PDI hydrophilic conjugated small molecule humidity-sensitive material, an FBG-based fiber optic humidity sensor, a multi-parameter sensor array, a signal demodulation module, a data transmission unit, a cloud platform, and an early warning module. The humidity-sensitive material uses PDI as the core, introducing hydroxyethyl groups to form reversible hydrogen bonds with water molecules, regulating molecular aggregation and spectral response, with batch-to-batch variation ≤0.1% RH; the sensor detection range is 10%–98% RH, response time <10s, sensitivity ≥0.05nm / % RH; system node coverage ≤1m³ / node, transmission delay ≤1s, early warning response ≤5min, passive operation with no circuit fire hazard, and long-term drift ≤3%. This invention solves the bottlenecks of large batch-to-batch variation and poor reproducibility in traditional fiber optic humidity sensors, achieving highly stable, high-precision, and long-life grain condition monitoring and control, suitable for intelligent and safe storage in large grain warehouses, ensuring national food security.

Description

Technical Field

[0001] This invention relates to the field of grain storage monitoring technology, specifically to a grain condition monitoring and control system based on a hydrophilic conjugated small molecule humidity sensor. Background Technology

[0002] During grain storage, environmental humidity directly affects grain quality. High humidity significantly enhances grain respiration and accelerates internal metabolism. When the grain moisture content exceeds 20%, localized high-temperature mold spots easily form inside the grain pile and rapidly spread to surrounding areas, ultimately leading to widespread mold, rot, and spoilage, causing significant grain loss and economic damage, and seriously threatening national grain reserve security. Therefore, real-time, accurate, and stable monitoring of the internal humidity and moisture content of grain piles is a core technical means to prevent grain mold and ensure safe grain storage.

[0003] With the development of information and sensing technologies, grain condition monitoring and control is gradually shifting from manual point measurement to automated, intelligent, and networked monitoring. Wireless grain condition monitoring and control systems based on embedded systems, ARM processors, GPRS, the Internet, Zigbee, and other technologies have been developed both domestically and internationally, achieving remote monitoring of parameters such as temperature, humidity, and pests in grain warehouses to a certain extent. However, the traditional humidity sensors used in existing systems generally suffer from problems such as large size, cumbersome installation and operation, low detection accuracy, and poor long-term operational stability, making it difficult to meet the high-precision, long-cycle monitoring and control needs of large grain depots.

[0004] In recent years, fiber optic humidity sensors have received widespread attention in the field of grain condition monitoring due to their unique advantages, including passive detection, safe operation, flexible form factor, resistance to electromagnetic interference, and the ability to achieve large-capacity networking and distributed measurement. Fiber optic humidity sensors eliminate the need for power supply circuits inside and around grain silos, fundamentally avoiding fire hazards caused by circuit failures and significantly improving storage safety. However, the current humidity-sensitive materials used in fiber optic humidity sensors are mainly hydrophilic polymers or two-dimensional nanomaterials such as graphene oxide, polyimide, and polyvinyl alcohol. These materials suffer from technical bottlenecks such as disordered molecular structure, poor batch consistency, weak reproducibility, large hysteresis error, and susceptibility to aging after long-term use. This results in significant batch variations and insufficient performance stability in fiber optic humidity sensors, severely restricting their large-scale application in grain condition monitoring and control systems.

[0005] Perylene diimide (PDI) and its derivatives, as typical conjugated organic small molecule materials, possess characteristics such as well-defined molecular structure, high molecular rigidity, good arrangement regularity, and excellent photothermal stability. Compared with traditional polymer materials, they have natural advantages in batch consistency and performance reproducibility. However, conventional PDI molecules themselves are strongly hydrophobic and cannot interact effectively with water molecules, making them unsuitable for use as humidity-sensitive materials. Current technologies have not yet achieved controllable hydrophilic modification of PDI-like small molecules, nor have they established fiber optic humidity sensing mechanisms and grain condition monitoring and control systems based on hydrophilic PDI conjugated small molecules. This fails to solve the common industry problems of large batch variations, poor stability, and poor reproducibility in existing fiber optic humidity sensors.

[0006] Therefore, it is of great practical significance and engineering application value to develop a hydrophilic conjugated small molecule humidity sensor with low batch variation, high sensitivity, high stability and long service life, and to construct a matching grain condition monitoring and control system. Summary of the Invention

[0007] In view of this, the present invention provides a grain condition monitoring and control system based on a hydrophilic conjugated small molecule humidity sensor to solve or alleviate one of the technical problems existing in the prior art, and at least provides a beneficial alternative.

[0008] The technical solution of this invention is implemented as follows: a grain condition monitoring and control system based on a hydrophilic conjugated small molecule humidity sensor, comprising a hydroxyethyl side chain modified perylene diimide (PDI) hydrophilic conjugated small molecule humidity-sensitive material, a single-mode fiber Bragg grating (FBG) substrate fiber optic humidity sensor, a multi-parameter sensing array, a signal demodulation module, a data transmission unit, a cloud platform data management system, and a grain condition risk early warning module; The hydrophilic conjugated small molecule humidity-sensitive material uses PDI as the conjugated core and connects hydroxyethyl side chains through chemical bonds. The hydroxyl groups can form reversible hydrogen bonds with water molecules, reversibly regulating the molecular aggregation and thin film absorption spectrum under humidity changes. The fiber optic humidity sensor uses spin coating or drop coating to coat a 50–200 nm thick humidity-sensitive active layer on the surface of a fiber Bragg grating. The multi-parameter sensing array includes the fiber optic humidity sensor, a PT100 temperature sensor, and... and Gas sensors are distributed at a density of ≤1m³ / node in the upper, middle, bottom, and corner positions of the grain pile. The signal demodulation module uses an STM32 chip and wavelet transform noise reduction algorithm to achieve high-precision demodulation of humidity signals. The data transmission unit uses a combination of fiber optic bus and wireless gateway to achieve low-latency data transmission. The cloud platform data management system enables real-time visualization of grain pile temperature, humidity, and gas concentration parameters, as well as historical data tracing and storage. The grain condition risk early warning module can quickly identify condensation and early mold growth in the grain pile and output linkage control commands.

[0009] Furthermore, the hydroxyethyl side-chain modified PDI hydrophilic conjugated small molecule humidity-sensitive material is prepared by reacting perylene tetrahydric anhydride with N-(3-aminopropyl)diethanolamine or N-(3-aminopropyl)diethylamine in DMF solvent at 130°C for 3 hours to generate an intermediate product, which is then quaternized with 2-bromoethanol in toluene at 40°C. By controlling the number of hydroxyethyl side chains, the hydrophilicity, molecular packing mode, particle size distribution, and optical absorption characteristics of the material can be changed. Under humid conditions, the material exhibits a decrease in molecular order induced by water molecules, resulting in a characteristic red shift in the absorption spectrum. The moisture absorption and dehumidification processes are completely reversible and do not involve any chemical structural changes. The batch variation of the humidity-sensitive material is ≤0.1%RH, demonstrating high reproducibility and long-term stability.

[0010] Furthermore, the fiber optic humidity sensor uses a single-mode fiber Bragg grating as the sensing substrate. The humidity-sensitive active layer is prepared by fully dispersing hydroxyethyl-modified PDI small molecules in tetrahydrofuran, chloroform, or ethanol solvents. During the film formation process, the crystallinity, porosity, and surface roughness of the film are controlled by spin coating speed of 1000-3000 r / min and annealing temperature of 40-80℃, optimizing the water molecule penetration path and response rate. The sensor operates stably in the relative humidity range of 10%-98% RH, with a response time of <10s, a recovery time of ≤30s, a sensitivity of ≥0.05nm / % RH, an error of ≤2% after 30 cycles of moisture absorption and dehumidification, low temperature cross-interference, and a complete software compensation scheme.

[0011] Furthermore, the multi-parameter sensor array adopts a layered distributed deployment strategy in both flat warehouses and vertical silos. The fiber optic humidity sensor and temperature sensor are arranged at different depths inside the grain pile, with a sensor node coverage accuracy of ≤1m³ / node. It can simultaneously collect multi-dimensional parameters such as temperature, humidity, and gas concentration inside the grain pile. The fiber optic humidity sensor is a passive sensing structure, and there is no need to lay power supply circuits inside and around the grain warehouse, which can effectively avoid fire hazards caused by circuit failures and is suitable for complex storage conditions such as grain ventilation, compaction, and fumigation.

[0012] Furthermore, the signal demodulation module acquires and demodulates the spectral drift signal of the fiber optic humidity sensor in real time, and filters out noise signals caused by grain pile vibration, dust, and electromagnetic interference through wavelet transform algorithm. The final humidity measurement error is ≤±1% RH, the data transmission delay is ≤1s, the cloud platform data refresh frequency is ≥1 time / min, and it can store historical monitoring data for a long time and support remote access, viewing, exporting and analysis by multiple terminals.

[0013] Furthermore, the grain condition risk early warning module has a built-in grain condition risk assessment model, which can assess risks based on the rate of change in humidity, Concentration thresholds and abnormal temperature increases are used to provide early warnings of condensation and mold growth. A sudden increase in humidity ≥5% / h is considered a risk of condensation. A concentration ≥0.15% is considered a risk of early mold growth. The system's early warning response time is ≤5 minutes, and it automatically outputs control commands for starting and stopping ventilation equipment and linking circulation fumigation, forming a complete closed-loop monitoring and control system of perception, analysis, early warning, and regulation.

[0014] Furthermore, the fiber optic humidity sensor operated continuously and stably for 3 months in a simulated grain warehouse environment with temperatures ranging from 0-35℃ and humidity from 50%-85%RH, with an overall drift of ≤3%. It maintained good linear response and high sensitivity within the 10%-90%RH test range, and its hysteresis error was far lower than that of traditional polymer and graphene oxide-based fiber optic humidity sensors. This meets the high-precision monitoring requirements of large grain depots that require long-term unattended operation.

[0015] Furthermore, the method includes the following steps: using PDI as the molecular core, selecting PDI units with strong molecular rigidity and planar structure; Hydroxyethyl side chains are introduced as hydrophilic functional groups, and the strength of hydrogen bonding between the material and water molecules is controlled by adjusting the number of hydroxyl groups. Starting with perylenetetraanic anhydride, N-(3-aminopropyl)diethanolamine was reacted in DMF at 130°C for 3 h to obtain an intermediate product containing an amino side chain. The intermediate product was reacted with 2-bromoethanol in toluene solvent at 40 °C to undergo a quaternization reaction to obtain the target hydroxyethyl-modified PDI small molecule; The aggregation state, absorption spectrum, and optical band gap of the material were systematically characterized by ultraviolet-visible absorption spectroscopy, atomic force microscopy, transmission electron microscopy, and synchrotron grazing incidence wide-angle X-ray scattering, and the molecular structure and synthesis process with optimal humidity sensitivity were determined.

[0016] Furthermore, the method includes the following steps: using a single-mode fiber Bragg grating as a substrate, dissolving hydroxyethyl-modified PDI small molecules in tetrahydrofuran, chloroform, or ethanol solvents to form a uniform dispersion. A 50-200 nm humidity-sensitive active layer was prepared in the grating region by spin coating or drop coating; the film quality was optimized by adjusting the spin coating speed to 1000-3000 r / min and the annealing temperature to 40-80℃. Sensor sensitivity, response / recovery time, repeatability, hysteresis characteristics, and temperature cross-sensitivity were tested within a humidity range of 10%-90%RH. The hydrogen bonding mechanism was analyzed by FTIR, and the chemical state changes before and after moisture absorption were characterized by XPS. The accuracy of humidity measurement was verified by constant weight method at 105℃ according to GB5497-85 standard, thus forming a standardized and repeatable sensor preparation process.

[0017] Furthermore, the overall technical specifications of the system meet the following requirements: humidity response time <10s, humidity-sensitive active layer prepared by solution processing, humidity detection range 10%–98% RH, batch difference of humidity-sensitive material <0.1% RH, and sensor drift ≤3% after 3 months of continuous operation. It can be widely used for long-term storage monitoring of various grains such as wheat, rice, and corn, significantly reducing grain spoilage and loss, and improving the intelligent, digital, and safe operation level of grain depots.

[0018] The embodiments of the present invention have the following advantages due to the adoption of the above technical solutions: This invention uses hydroxyethyl side-chain modified PDI hydrophilic conjugated small molecules as humidity-sensitive functional materials. The molecular structure is well-defined and the arrangement is regular and orderly. This solves the problems of large batch differences and poor reproducibility of traditional humidity-sensitive materials such as polymers and graphene oxide from the material level. The batch difference of humidity-sensitive materials is ≤0.1% RH, which greatly improves the consistency and interchangeability of sensors and reduces the cost of large-scale application.

[0019] The sensor's humidity response is based on the reversible hydrogen bonding between hydroxyl groups and water molecules. The entire process involves only changes in the molecular aggregation state, without chemical reactions, material structure damage, or performance degradation. This effectively extends the sensor's lifespan, improves long-term operational stability, has low hysteresis error, and exhibits excellent cyclic performance.

[0020] The fiber optic humidity sensor has a passive fiber optic structure, eliminating the need for power supply circuits and electronic components inside the grain silo. This completely eliminates fire hazards such as short circuits and electrical sparks. It can withstand complex working conditions such as grain silo fumigation, dust, humidity, and ventilation disturbances, and its safety and adaptability are far superior to traditional electronic humidity sensors.

[0021] The system humidity measurement error is ≤±1% RH, and the sensor node coverage accuracy is ≤1m³ / node, enabling all-round coverage monitoring of the upper, middle, bottom and corner areas of the grain pile; the data transmission delay is ≤1s, and the cloud platform data refresh frequency is ≥1 time / min; the early warning response time for grain pile condensation and early mold growth is ≤5min, which can identify risks in advance and automatically trigger control measures to minimize grain spoilage.

[0022] The system is adaptable to various warehouse types, such as flat warehouses and vertical silos, and meets the storage and monitoring needs of mainstream grain varieties such as wheat, rice, and corn. The overall technology has reached the advanced level in China, and it has important social and economic benefits for promoting the digital, intelligent, and safe upgrading of the grain storage industry and ensuring national food security.

[0023] The above overview is for illustrative purposes only and is not intended to be limiting in any way. In addition to the illustrative aspects, embodiments, and features described above, further aspects, embodiments, and features of the invention will become readily apparent from the accompanying drawings and the following detailed description. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the grain condition monitoring system based on a fiber optic humidity sensor according to the present invention; Figure 2 This is a schematic diagram illustrating the changes in the aggregation state / absorption spectrum of the PDI-type humidity-sensitive material of the present invention with ambient humidity. Figure 3 This is a schematic diagram of the molecular structure of the PDI-type humidity-sensitive material of the present invention and its hydrogen bonding interaction with water molecules; Figure 4 This is the synthetic route for the target humidity-sensitive material of the present invention. Detailed Implementation

[0025] Example 1: Synthesis and Characterization of Hydroxyethyl Side-Chain Modified PDI Hydrophilic Conjugated Small Molecule Humidity Sensing Material This embodiment details the preparation method and characterization process of a monohydroxyethyl modified PDI hydrophilic conjugated small molecule humidity-sensitive material.

[0026] Perylenetetraanic anhydride was used as the starting material and N-(3-aminopropyl)diethanolamine was added to DMF solvent at a molar ratio of 1:1.2. The mixture was heated to 130°C under nitrogen protection and reacted at this temperature for 3 hours. After the reaction was completed, the mixture was cooled to room temperature, and the solvent was removed by vacuum distillation. The product was then purified by column chromatography to obtain a PDI intermediate with an amino side chain. This intermediate was then added to toluene solvent at a molar ratio of 1:1.5 and subjected to a quaternization reaction at 40°C for 4 hours. After the reaction was completed, the product was rotary evaporated, washed, and vacuum dried to obtain a hydrophilic conjugated small molecule humidity-sensitive material modified with a monohydroxyethyl side chain.

[0027] The optical properties of the material under different humidity environments were tested using ultraviolet-visible absorption spectroscopy. The results showed that as the ambient humidity increased from 10%RH to 98%RH, the molecular aggregation order of the PDI film decreased due to the intervention of water molecules, resulting in a significant characteristic redshift in the absorption spectrum. The magnitude of the redshift showed a good linear relationship with the humidity change. The morphology and aggregation state of the material film were characterized using atomic force microscopy (AFM), high-resolution transmission electron microscopy (TEM), and synchrotron radiation grazing incidence wide-angle X-ray scattering (GIWAXS). The results showed that the hydroxyethyl side chain significantly improved the hydrophilicity and film uniformity of the material. The film surface was smooth and free of obvious defects, with high molecular arrangement regularity. Under humidity changes, only reversible aggregation adjustment occurred, without significant phase separation or structural damage. After repeated preparation and testing in multiple batches, the batch-to-batch variation of this humidity-sensitive material was ≤0.1%RH, demonstrating excellent batch consistency and reproducibility, meeting the requirements of fiber optic humidity sensors for functional materials.

[0028] Example 2: Fabrication and Performance Testing of an Fiber Optic Humidity Sensor Based on Hydroxyethyl-Modified PDI This embodiment discloses the fabrication process, optimization conditions, and full-parameter performance testing of a fiber Bragg grating humidity sensor based on hydrophilic PDI small molecules.

[0029] A single-mode fiber Bragg grating (FBG) with a center wavelength in the communication band was selected as the sensing substrate. The hydroxyethyl-modified PDI hydrophilic conjugated small molecule prepared in Example 1 was dissolved in chloroform to prepare a uniformly concentrated dispersion. A humidity-sensitive active layer was then coated onto the FBG region using spin coating. The spin coating speed was set to 2000 r / min, and the active layer thickness was precisely controlled to 100 nm by controlling the solution concentration and spin coating time. After coating, the layer was annealed at 60℃ under vacuum for 60 min to eliminate solvent residue and improve the adhesion between the film and the fiber substrate, ultimately obtaining the fiber optic humidity sensor.

[0030] The sensor performance was comprehensively tested using a self-made humidity testing system. The humidity range was set to 10%-98%RH, and the temperature was maintained at a constant 25℃. The test results show that: (1) Sensitivity: The center wavelength drift of the sensor has a good linear relationship with the humidity change, and the sensitivity reaches 0.052nm / %RH, which meets the design specification of ≥0.05nm / %RH; (2) Response and recovery speed: The sensor's moisture absorption response time is <8s and the dehumidification recovery time is ≤25s, both of which are better than the design requirement of 30s; (3) Cyclic stability: After 30 consecutive moisture absorption and desiccation cycle tests, the maximum error of the output signal is ≤1.8%, which shows excellent repeatability; (4) Long-term stability: After running continuously for 3 months in a simulated grain warehouse with a temperature range of 0-35℃ and a humidity range of 50%-85%RH, the overall drift of the sensor is ≤2.7%, which meets the long-term unattended monitoring requirements of the grain warehouse. (5) Accuracy verification: Based on the national standard GB5497-85 Grain and oilseed inspection moisture determination method, the sensor measurement results were compared and verified by the 105℃ constant weight method. The measurement error was ≤±0.9% RH, and the accuracy met the requirements of grain condition monitoring and control.

[0031] Fourier transform infrared spectroscopy (FTIR) was used to analyze the hydrogen bonding mechanism, confirming that reversible hydrogen bonds are formed between hydroxyl groups and water molecules. X-ray photoelectron spectroscopy (XPS) was used to characterize the changes in the chemical state of the material before and after moisture absorption, proving that the material does not undergo chemical structural changes during the humidity response process, but only physical aggregation state adjustments, further verifying the stability and reversibility of the sensing mechanism.

[0032] Example 3: Integration and Application Testing of Grain Condition Monitoring and Control System Based on Hydrophilic Conjugated Small Molecule Humidity Sensor This embodiment discloses the construction method, layout scheme, system integration and debugging, and actual storage scenario verification of a complete grain condition monitoring and control system.

[0033] Using the fiber optic humidity sensor prepared in Example 2 as the core sensing unit, and paired with a PT100 temperature sensor, and Gas sensors are used to construct a multi-parameter distributed sensor array. For a 100-ton simulated flat warehouse, a layered distributed deployment strategy is adopted, with sensor nodes placed in the upper, middle, and lower layers of the grain pile, as well as at the four corners. The node coverage accuracy is ≤1m³ / node, achieving full-area monitoring without blind spots inside the grain pile.

[0034] The system hardware employs a high-speed signal demodulation module based on STM32 to acquire and demodulate the spectral drift signal from the fiber optic sensor in real time. Wavelet transform denoising algorithms are used to filter out noise from grain pile vibration, dust, and external electromagnetic interference, improving measurement accuracy. Data transmission utilizes a combination of fiber optic bus and wireless gateway, ensuring data transmission latency of ≤1s and guaranteeing real-time signal performance. The software system is a cloud platform data management system that enables real-time visualization of parameters such as temperature, humidity, and gas concentration, with a data refresh rate of ≥1 time / min. It also features historical data storage, querying, exporting, and curve analysis functions.

[0035] An agricultural risk assessment model is embedded in the cloud platform, with early warning thresholds set: a sudden increase in humidity ≥5% / h is considered a risk of condensation; when... When the concentration is ≥0.15%, it is judged as an early risk of mold growth. The system will automatically issue an audible and visual warning and send a command to the control terminal to activate the ventilation equipment for dehumidification and air exchange.

[0036] A 90-day system integration test was conducted on a 100-ton wheat storage simulation platform, and the results showed: (1) The system humidity measurement range is 10%-98% RH, the measurement error is ≤±1% RH, and the response time is <10s; (2) The sensor works stably under conditions such as grain pile compaction, intermittent ventilation, and simulated fumigation, without failure or excessive drift; (3) The system's early warning response time for local condensation and early mold growth is ≤4 min, and the early warning is accurate and reliable; (4) The system operates stably as a whole, with no data loss or transmission interruption, and can achieve long-term stable automated measurement and control.

[0037] This system can effectively reduce grain spoilage caused by abnormal humidity, significantly reducing grain storage losses annually. It has significant economic, social, and environmental benefits and can be widely used in national grain depots, local grain depots, and large grain processing enterprises for warehouse monitoring.

[0038] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any person skilled in the art can easily conceive of various variations or substitutions within the technical scope disclosed in the present invention, and these should all be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A grain condition monitoring and control system based on a hydrophilic conjugated small molecule humidity sensor, characterized in that: This includes hydrophilic conjugated small molecule humidity-sensitive material with hydroxyethyl side chain modified perylene diimide (PDI), a single-mode fiber Bragg grating (FBG) substrate fiber optic humidity sensor, a multi-parameter sensing array, a signal demodulation module, a data transmission unit, a cloud platform data management system, and a grain condition risk early warning module; The hydrophilic conjugated small molecule humidity-sensitive material uses PDI as the conjugated core and connects hydroxyethyl side chains through chemical bonds. The hydroxyl groups can form reversible hydrogen bonds with water molecules, reversibly regulating the molecular aggregation and thin film absorption spectrum under humidity changes. The fiber optic humidity sensor uses spin coating or drop coating to coat a 50–200 nm thick humidity-sensitive active layer on the surface of a fiber Bragg grating. The multi-parameter sensing array includes the fiber optic humidity sensor, a PT100 temperature sensor, and... and Gas sensors are distributed at a density of ≤1m³ / node in the upper, middle, bottom, and corner positions of the grain pile. The signal demodulation module uses an STM32 chip and wavelet transform noise reduction algorithm to achieve high-precision demodulation of humidity signals. The data transmission unit uses a combination of fiber optic bus and wireless gateway to achieve low-latency data transmission. The cloud platform data management system enables real-time visualization of grain pile temperature, humidity, and gas concentration parameters, as well as historical data tracing and storage. The grain condition risk early warning module can quickly identify condensation and early mold growth in the grain pile and output linkage control commands.

2. The grain condition monitoring and control system based on a hydrophilic conjugated small molecule humidity sensor according to claim 1, characterized in that: The hydroxyethyl side-chain modified PDI hydrophilic conjugated small molecule humidity-sensitive material is prepared by reacting perylene tetrahydric anhydride with N-(3-aminopropyl)diethanolamine or N-(3-aminopropyl)diethylamine in DMF solvent at 130°C for 3 hours to generate an intermediate product, which is then quaternized with 2-bromoethanol in toluene at 40°C. By controlling the number of hydroxyethyl side chains, the hydrophilicity, molecular packing mode, particle size distribution and optical absorption characteristics of the material can be changed. Under humid conditions, the material exhibits a decrease in molecular order induced by water molecules and a characteristic red shift in the absorption spectrum. The moisture absorption and dehumidification processes are completely reversible and do not involve any chemical structural changes. The batch variation of the humidity-sensitive material is ≤0.1%RH, and it has high reproducibility and long-term stability.

3. The grain condition monitoring and control system based on a hydrophilic conjugated small molecule humidity sensor according to claim 1, characterized in that: The fiber optic humidity sensor uses a single-mode fiber Bragg grating as the sensing substrate. The humidity-sensitive active layer is prepared by fully dispersing hydroxyethyl-modified PDI small molecules in tetrahydrofuran, chloroform, or ethanol solvents. During the film formation process, the crystallinity, porosity, and surface roughness of the film are controlled by spin coating speed of 1000-3000 r / min and annealing temperature of 40-80℃ to optimize the water molecule penetration path and response rate. The sensor operates stably in the relative humidity range of 10%-98% RH, with a response time of <10s, a recovery time of ≤30s, a sensitivity of ≥0.05nm / % RH, and an error of ≤2% after 30 cycles of moisture absorption and dehumidification. It has low temperature cross-interference and a complete software compensation scheme.

4. The grain condition monitoring and control system based on a hydrophilic conjugated small molecule humidity sensor according to claim 1, characterized in that: The multi-parameter sensor array adopts a layered distributed deployment strategy in both flat and vertical silos. The fiber optic humidity and temperature sensors are arranged at different depths inside the grain pile, with a sensor node coverage accuracy of ≤1m³ / node. It can simultaneously collect multi-dimensional parameters such as temperature, humidity, and gas concentration inside the grain pile. The fiber optic humidity sensor is a passive sensing structure, and there is no need to lay power supply circuits inside and around the grain silo, which can effectively avoid fire hazards caused by circuit failures. It is suitable for complex storage conditions such as grain ventilation, compaction, and fumigation.

5. A grain condition monitoring and control system based on a hydrophilic conjugated small molecule humidity sensor according to claim 1, characterized in that: The signal demodulation module acquires and demodulates the spectral drift signal of the fiber optic humidity sensor in real time. It filters out noise signals caused by grain pile vibration, dust, and electromagnetic interference through wavelet transform algorithm. The final humidity measurement error is ≤±1%RH, the data transmission delay is ≤1s, the cloud platform data refresh frequency is ≥1 time / min, and it can store historical monitoring data for a long time and support remote access, viewing, exporting and analysis by multiple terminals.

6. The grain condition monitoring and control system based on a hydrophilic conjugated small molecule humidity sensor according to claim 1, characterized in that: The grain condition risk early warning module has a built-in grain condition risk assessment model, which can be based on the rate of change in humidity, Concentration thresholds and abnormal temperature increases are used to provide early warnings of condensation and mold growth. A sudden increase in humidity ≥5% / h is considered a risk of condensation. A concentration ≥0.15% is considered a risk of early mold growth. The system's early warning response time is ≤5 minutes, and it automatically outputs control commands for starting and stopping ventilation equipment and linking circulation fumigation, forming a complete closed-loop monitoring and control system of perception, analysis, early warning, and regulation.

7. The grain condition monitoring and control system based on a hydrophilic conjugated small molecule humidity sensor according to claim 1, characterized in that: The fiber optic humidity sensor operated continuously and stably for 3 months in a simulated grain warehouse environment with a temperature of 0-35℃ and a humidity of 50%-85%RH. The overall drift was ≤3%. It maintained good linear response and high sensitivity within the 10%-90%RH test range. The hysteresis error was much lower than that of traditional polymer and graphene oxide-based fiber optic humidity sensors, which can meet the high-precision monitoring requirements of large grain depots for long-term unattended operation.

8. A grain condition monitoring and control system based on a hydrophilic conjugated small molecule humidity sensor according to claim 1, characterized in that: Includes the following steps: Using PDI as the molecular core, PDI units with strong molecular rigidity and planar structure were selected; Hydroxyethyl side chains are introduced as hydrophilic functional groups, and the strength of hydrogen bonding between the material and water molecules is controlled by adjusting the number of hydroxyl groups. Starting with perylenetetraanic anhydride, N-(3-aminopropyl)diethanolamine was reacted in DMF at 130°C for 3 h to obtain an intermediate product containing an amino side chain. The intermediate product was reacted with 2-bromoethanol in toluene solvent at 40 °C to undergo a quaternization reaction to obtain the target hydroxyethyl-modified PDI small molecule; The aggregation state, absorption spectrum, and optical band gap of the material were systematically characterized by ultraviolet-visible absorption spectroscopy, atomic force microscopy, transmission electron microscopy, and synchrotron grazing incidence wide-angle X-ray scattering, and the molecular structure and synthesis process with optimal humidity sensitivity were determined.

9. A grain condition monitoring and control system based on a hydrophilic conjugated small molecule humidity sensor according to claim 1, characterized in that: Includes the following steps: Using a single-mode fiber Bragg grating as a substrate, hydroxyethyl-modified PDI small molecules are dissolved in tetrahydrofuran, chloroform or ethanol solvents to form a uniform dispersion. A 50-200 nm humidity-sensitive active layer was prepared in the grating region by spin coating or drop coating; the film quality was optimized by adjusting the spin coating speed to 1000-3000 r / min and the annealing temperature to 40-80℃. Sensor sensitivity, response / recovery time, repeatability, hysteresis characteristics, and temperature cross-sensitivity were tested within a humidity range of 10%-90%RH. The hydrogen bonding mechanism was analyzed by FTIR, and the chemical state changes before and after moisture absorption were characterized by XPS. The accuracy of humidity measurement was verified by constant weight method at 105℃ according to GB5497-85 standard, thus forming a standardized and repeatable sensor preparation process.

10. A grain condition monitoring and control system based on a hydrophilic conjugated small molecule humidity sensor according to claim 1, characterized in that: The overall technical specifications of the system meet the following requirements: humidity response time <10s, humidity-sensitive active layer prepared by solution processing, humidity detection range 10%–98% RH, batch difference of humidity-sensitive material <0.1% RH, and sensor drift ≤3% after 3 months of continuous operation. It can be widely used for long-term storage monitoring of various grains such as wheat, rice, and corn, significantly reducing grain spoilage and loss, and improving the intelligent, digital, and safe operation level of grain depots.

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