A simple PM2.5 sensor calibration system and method

Abstract

The present application discloses a simple PM2.5 sensor calibration system and method, belonging to the technical field of particulate matter sensor calibration. The method relies on the USB direct communication architecture of the host computer, saves the CANOE calibration software and multi-level protocol conversion hardware, and reduces the cost of device construction and use. The method sets 850 μg / m 3 to 30 μg / m 3 10 dense concentration gradients, realizes automatic degradation of concentration steps through the linkage of exhaust electromagnetic valves and stirring fans, and triggers synchronous sampling by adopting double determination logic of target concentration ± 5% and 2 min of continuous stability based on the value of the TSI standard detector. After collecting data and removing abnormal values through median filtering, the calibration coefficient is automatically fitted through a quadratic polynomial model, and then written into the sensor register through USB communication one key, realizing the whole process automation closed loop calibration from cabin purification, aerosol generation, concentration control, data acquisition, algorithm fitting to parameter rewriting.

Description

Technical Field

[0001] This invention relates to the field of particulate matter sensor calibration technology, specifically to a simple PM2.5 sensor calibration system and method. Background Technology

[0002] With the increasing demand for air quality monitoring, PM2.5 sensors are widely used in various environmental monitoring equipment. Due to individual differences in core sensor components (such as laser diodes and photodetectors), and the significant impact of environmental factors (such as temperature, humidity, and dust type) on measurement results, the output signal must be calibrated using a high-precision calibration system before the sensor leaves the factory or during the R&D phase. Currently, the industry primarily uses a simple calibration device for PM2.5 sensors in R&D and small-batch verification scenarios, consisting of a sealed chamber, an aerosol generator, a manual sampling port, and a reference instrument. Operators manually inject aerosol (such as cigarette smoke or standard particles) into the chamber and manually turn on a small fan for mechanical stirring. After the reference instrument readings stabilize, the raw data from the sensor under test is read through a serial port acquisition board, and finally, manual calculation and analysis are performed on an external computer.

[0003] In terms of hardware structure, existing PM2.5 sensor calibration systems are mostly large-scale industrial equipment, which are expensive and have fixed structures, making them difficult to adapt to the rapid verification of small batches of samples in the R&D stage. Their communication architecture generally relies on expensive external calibration engineering software such as CANOE, or uses multi-level protocol conversion links such as RS-485 to Ethernet and CAN, which are complex and costly to deploy. Most calibration chambers only operate at room temperature and cannot cover performance drift compensation across the entire temperature range. At the same time, the environmental control accuracy inside the calibration chamber is limited, and particulate matter often produces measurement deviations due to poor suspension uniformity and lack of humidity pretreatment.

[0004] In terms of process control, existing calibration methods suffer from low levels of automation and integration. Data acquisition, result calculation, and parameter write-back are disconnected, resulting in cumbersome procedures and heavy reliance on manual intervention. Concentration gradients often rely on a few fixed points (e.g., 5 concentration values) or manual mixing, making it difficult to achieve automatic degradation and stability determination for wide-range, dense gradients. Calibration results often remain at the level of numerical output or offline fitting, failing to automatically fit data from standard equipment in real time and write parameters back to the sensor register with a single click to form a hardware closed loop. This leads to long calibration cycles and low efficiency, making it difficult to meet the needs of rapid verification and precise optimization of structural designs and software algorithms during sensor development. Summary of the Invention

[0005] The present invention aims to solve the above-mentioned technical problems by providing a simple PM2.5 sensor calibration system and method.

[0006] To solve the above-mentioned technical problems, the technical solution provided by the present invention is as follows:

[0007] A simplified PM2.5 sensor calibration system includes a hardware layer and a control layer; the hardware layer includes a particulate matter generation unit, a calibration chamber, a standard detection unit, and a group of sensors to be tested.

[0008] The control layer is a host computer equipped with automated calibration software;

[0009] The particulate matter generating unit includes a particulate matter generator, a dryer filter, and an intake solenoid valve;

[0010] The particulate matter generator outlet is connected to the dryer filter, and the pipeline at the rear end of the dryer filter is connected to the calibration chamber inlet. The inlet solenoid valve is located between the pipelines to control the aerosol flow.

[0011] The calibration chamber has air inlets and exhaust outlets arranged vertically opposite each other on both sides, and the exhaust outlets are equipped with adjustable exhaust solenoid valves.

[0012] The cabin is equipped with multiple distributed stirring fans, air purifiers, and temperature and humidity sensors;

[0013] The standard testing unit and the sensor group under test are placed horizontally at the bottom of the calibration chamber;

[0014] The standard detection unit is a high-precision TSI particulate matter detector, used to output a PM2.5 standard concentration benchmark;

[0015] The host computer is bidirectionally connected to the TSI particulate matter detector, the sensor under test, the intake solenoid valve, the exhaust solenoid valve, the stirring fan, the air purifier, and the temperature and humidity sensor via multiple USB communication interfaces, without any intermediate protocol conversion hardware.

[0016] Preferably, the calibration chamber can be made of acrylic or stainless steel to achieve temperature drift compensation calibration across the entire temperature range of -40℃ to 70℃.

[0017] Preferably, the particulate matter generator uses cigarettes as the source of combustion aerosols, and removes water vapor from the aerosols through a drying filter to eliminate the interference of humidity on the light scattering calibration results.

[0018] This invention also provides a simple PM2.5 sensor calibration method, characterized by the following steps:

[0019] S1: Environmental purification: Place the sample to be calibrated into the chamber and seal the calibration chamber. The host computer starts the purifier, exhaust valve, stirring fan and TSI particulate matter detector. The purification and exhaust will be automatically shut off after the concentration is lower than 10μg / m³.

[0020] S2: Particulate matter Note: The host computer controls the opening of the air inlet and instructs the particulate matter generator to inject the smoke, which has been dried by the dryer filter, into the calibration chamber at a uniform speed.

[0021] S3: Stirring: Start all the stirring fans in the chamber to stir thoroughly, so that the particulate matter is mixed evenly with the air in the chamber and kept suspended. At this time, the calibration sample enters the working mode and begins real-time monitoring.

[0022] S4: Concentration gradient adjustment and stabilization: Adjust the opening of the exhaust valve to reduce the concentration in the chamber to the target gradient value, and then close the exhaust valve and let it stand for 2 minutes.

[0023] S5: Stable sampling: When the TSI concentration is stable at ±5% of the target value for 2 minutes, the system determines that the environment has reached quasi-static equilibrium and simultaneously records the standard concentration and the original signal of the sensor under test.

[0024] S6: Multi-point cyclic calibration: Repeat S4-S5 to complete the data acquisition of all 10 concentration gradient levels in sequence;

[0025] S7: Calculation and parameter write-back: After the acquisition of 10 points, median filtering is used to remove abnormal data, and the fitting coefficients of each sample are automatically calculated through the fitting algorithm. The coefficients are written to the sensor register via USB communication.

[0026] The fitting algorithm formula is y=p1x 2 +p2x+p3; where x is the original scattering signal of the sensor to be calibrated; Y is the reference value of PM2.5 concentration of the standard instrument; p1 is the coefficient of the quadratic term, with a value range of (-0.1, 0.1); p2 is the coefficient of the linear term, with a value range of (-0.5, 0.5); p3 is the intercept term, with a value range of (-50, 0).

[0027] Preferably, it also includes a high and low temperature full-range temperature drift compensation extension process, the steps of which are:

[0028] S01: Replace the stainless steel calibration chamber and place it entirely into the high and low temperature test chamber. The host computer will control the temperature of the test chamber in conjunction with the main computer.

[0029] S02: Sequentially set multiple temperature levels: -40℃, -30℃, -20℃, 50℃, 60℃, and 70℃. After each temperature level stabilizes, complete the S1~S7 room temperature calibration process.

[0030] S03: The host computer summarizes the calibration coefficients under multiple temperatures and calculates the temperature drift compensation parameters corresponding to each temperature.

[0031] S04: Write the temperature drift compensation coefficients into the sensor register in batches to complete the full temperature range accuracy compensation.

[0032] Preferably, the target gradient value, from high to low, has a concentration gradient of 850 μg / m³. 3 750μg / m 3 650μg / m 3 550μg / m 3 450μg / m 3 350μg / m 3 250μg / m 3 150μg / m 3 70μg / m 3 30μg / m 3 .

[0033] With the above structure, the present invention has the following advantages:

[0034] This invention features a low-cost and simple architecture, making deployment convenient. It eliminates the need for expensive CANOE calibration software and RS485 / CAN multi-level protocol conversion hardware. All devices use USB direct connection to the host computer for bidirectional communication, significantly reducing hardware setup costs. The miniaturized, sealed cabin occupies little space, making it suitable for small-batch, rapid verification scenarios in R&D laboratories.

[0035] This invention provides an aerosol drying pretreatment that eliminates humidity interference at the source. A drying and filtering device is added to the air inlet of the particulate generator to pre-dehumidify combustion-type smoke aerosols, preventing water vapor from altering the light scattering characteristics of the particulate matter. This completely solves the calibration reference drift caused by high humidity aerosols and improves the stability of calibration data. This pretreatment structure is an innovative structure that is not available in existing calibration devices.

[0036] This invention employs multi-point distributed stirring and multi-level precise concentration gradient control, with multiple fans working together to mix particulate matter within the chamber, significantly improving the uniformity of particulate matter concentration. Through the coordinated control of the exhaust solenoid valve, fans, and intake valve, a concentration of 850~30μg / m³ can be achieved. 3 With a total of 10 levels of dense wide-range gradient degradation, coupled with dual stability judgment logic of ±5% concentration and 2min duration, the reliability of each set of calibration point data is greatly improved, which is better than the traditional 5-point sparse calibration scheme.

[0037] This invention features a fully automated closed-loop calibration system that eliminates human error. The entire process, from cabin purification, aerosol generation, concentration adjustment, data acquisition, anomaly filtering, curve fitting to writing calibration parameters into the sensor register, is executed automatically without manual recording, offline calculation, or manual parameter burning. It truly achieves one-click calibration, supports parallel testing of multi-channel sensors, significantly improves R&D verification throughput, and shortens the calibration cycle.

[0038] This invention is compatible with full-temperature-range temperature drift compensation calibration, and has strong expandability. The calibration chamber can be replaced with stainless steel and placed in a high and low temperature test chamber, covering the extreme working temperature range of -40℃ to 70℃. It automatically calculates the temperature drift compensation coefficient at multiple temperatures and writes it into the sensor, solving the pain points of traditional calibration equipment that can only be calibrated at room temperature and has poor measurement accuracy in extreme temperature ranges, and improving the consistency of the sensor under all working conditions. Attached Figure Description

[0039] Figure 1 This is a flowchart of the present invention.

[0040] Figure 2 This is a graph showing the fitting results of the present invention.

[0041] Figure 3 This is a system diagram of the present invention. Detailed Implementation

[0042] The present invention will now be described in further detail with reference to the full text.

[0043] Combined with appendix Figures 1-3 A simplified PM2.5 sensor calibration system includes a hardware layer and a control layer; the hardware layer includes a particulate matter generation unit, a calibration chamber, a standard detection unit, and a group of sensors to be tested.

[0044] Specifically, the sensor calibration system based on fully automatic closed-loop control provided by this invention consists of a hardware layer and a control layer. The hardware layer includes a calibration chamber, a particulate matter generator, a standard testing instrument (TSI device), and a sample to be calibrated; the control layer consists of a host computer control terminal and built-in automated calibration software. The connection relationships of each component are as follows: the particulate matter generator is connected to the air inlet of the calibration chamber through a pipeline; the standard testing instrument and the sample to be calibrated are both placed inside the calibration chamber; the host computer control terminal establishes bidirectional data links with the standard testing instrument, the sample to be calibrated, and the control elements of the calibration chamber through a USB communication interface, realizing command issuance and real-time data acquisition.

[0045] High-sealing calibration chamber: Constructed of acrylic glass or stainless steel, the chamber integrates air inlets and exhaust outlets, which are vertically distributed on opposite sides to optimize airflow. Multiple small stirring fans are integrated inside the chamber, achieving uniform suspension of particulate matter through multi-point coordination. Temperature and humidity sensors and adjustable one-way control solenoid valves are integrated into the chamber walls. The temperature and humidity sensors are attached to the vertical inner wall, while the samples to be calibrated and standard testing instruments are placed horizontally at the bottom of the chamber.

[0046] Particulate matter generator with drying function: It uses combustible substances (such as cigarette smoke) as particulate matter source and is equipped with a drying and filtering device at the front end of the intake valve. After drying, the smoke is injected into the calibration chamber through the intake pipe to ensure that the calibration environment is not affected by high humidity.

[0047] Standard testing instruments: High-precision TSI equipment is used to monitor the PM2.5 mass concentration in the cabin in real time, and this value is used as the standard reference value for automated calibration.

[0048] The host computer software system features automated communication and closed-loop control functions, supporting TSI device control, real-time acquisition of multi-channel data, automatic recording of CSV format logs, data fitting algorithm processing, and automatic parameter write-back. The software interface integrates modules for calibration point setting, process visualization monitoring, and completion status determination.

[0049] The control layer is a host computer equipped with automated calibration software;

[0050] The particulate matter generating unit includes a particulate matter generator, a dryer filter, and an intake solenoid valve;

[0051] The particulate matter generator outlet is connected to the dryer filter, and the pipeline at the rear end of the dryer filter is connected to the calibration chamber inlet. The inlet solenoid valve is located between the pipelines to control the aerosol flow.

[0052] The calibration chamber has air inlets and exhaust outlets arranged vertically opposite each other on both sides, and the exhaust outlets are equipped with adjustable exhaust solenoid valves.

[0053] The cabin is equipped with multiple distributed stirring fans, air purifiers, and temperature and humidity sensors;

[0054] The standard testing unit and the sensor group under test are placed horizontally at the bottom of the calibration chamber;

[0055] The standard detection unit is a high-precision TSI particulate matter detector, used to output a PM2.5 standard concentration benchmark;

[0056] The host computer is bidirectionally connected to the TSI particulate matter detector, the sensor under test, the intake solenoid valve, the exhaust solenoid valve, the stirring fan, the air purifier, and the temperature and humidity sensor via multiple USB communication interfaces, without any intermediate protocol conversion hardware.

[0057] The calibration chamber can be made of acrylic or stainless steel, enabling temperature drift compensation calibration across the entire temperature range of -40℃ to 70℃.

[0058] The particulate matter generator uses cigarettes as a combustion aerosol source and removes water vapor from the aerosol through a drying filter to eliminate the interference of humidity on the light scattering calibration results.

[0059] This invention also provides a simple PM2.5 sensor calibration method, characterized by the following steps:

[0060] S1: Environmental purification: Place the sample to be calibrated into the chamber and seal the calibration chamber. The host computer starts the purifier, exhaust valve, stirring fan and TSI particulate matter detector. The purification and exhaust will be automatically shut off after the concentration is lower than 10μg / m³.

[0061] Specifically, the sample to be calibrated is placed inside the chamber and sealed. The host computer activates the purifier and air outlet, and simultaneously runs the stirring fan and TSI device. When the concentration inside the chamber drops to 10 μg / m³, the calibration is initiated. 3 The air purifier and air outlet will automatically shut off when the following conditions are met.

[0062] S2: Particulate matter Note: The host computer controls the opening of the air inlet and instructs the particulate matter generator to inject the smoke, which has been dried by the dryer filter, into the calibration chamber at a uniform speed.

[0063] S3: Stirring: Start all the stirring fans in the chamber to stir thoroughly, so that the particulate matter is mixed evenly with the air in the chamber and kept suspended. At this time, the calibration sample enters the working mode and begins real-time monitoring.

[0064] Specifically, the host computer software controls the fan to start and thoroughly stir the particles, so that they are evenly mixed with the air in the chamber and kept suspended. At this time, the sample to be calibrated enters the working mode and begins real-time monitoring.

[0065] S4: Concentration gradient adjustment and stabilization: Adjust the opening of the exhaust valve to reduce the concentration in the chamber to the target gradient value, and then close the exhaust valve and let it stand for 2 minutes.

[0066] Specifically, the host computer software controls the opening of the gas outlet and adjusts the valve opening to reduce the concentration to the first calibration point set value (850μg / m³). Then, the gas outlet is closed, and after the mixture is stirred evenly, the fan is turned off, and the system is left to stand for another 2 minutes.

[0067] S5: Stable sampling: When the TSI concentration is stable at ±5% of the target value for 2 minutes, the system determines that the environment has reached quasi-static equilibrium and simultaneously records the standard concentration and the original signal of the sensor under test.

[0068] Specifically, the host computer monitors the TSI concentration fluctuation rate in real time, when the concentration value is 850 μg / m³. 3 After the concentration of ±5% is maintained for more than 2 minutes, the system determines that the environment has reached quasi-static equilibrium, and the host computer automatically records the TSI standard concentration value and the number of particles detected in the sample to be calibrated at that point.

[0069] S6: Multi-point cyclic calibration: Repeat S4-S5 to complete the data acquisition of all 10 concentration gradient levels in sequence;

[0070] Specifically, repeat steps 4 to 5, and complete the data collection for the remaining 9 points in sequence according to the preset gradient (750→650→550→450→350→250→150→70→30μg / m³).

[0071] S7: Calculation and parameter write-back: After the acquisition of 10 points, median filtering is used to remove abnormal data, and the fitting coefficients of each sample are automatically calculated through the fitting algorithm. The coefficients are written to the sensor register via USB communication.

[0072] Specifically, after data collection at 10 points is completed, the host computer uses a median filtering algorithm to remove abnormal data, then automatically calculates the fitting coefficients of each sample using a fitting algorithm formula, and automatically writes the generated calibration parameters into the sensor register to achieve closed-loop configuration.

[0073] The fitting algorithm formula is y=p1x 2 +p2x+p3; where x is the original scattering signal of the sensor to be calibrated; Y is the reference value of PM2.5 concentration of the standard instrument; p1 is the coefficient of the quadratic term, with a value range of (-0.1, 0.1); p2 is the coefficient of the linear term, with a value range of (-0.5, 0.5); p3 is the intercept term, with a value range of (-50, 0).

[0074] It also includes an extended process for temperature drift compensation across the entire high and low temperature range, with the following steps:

[0075] S01: Replace the stainless steel calibration chamber and place it entirely into the high and low temperature test chamber. The host computer will control the temperature of the test chamber in conjunction with the main computer.

[0076] S02: Sequentially set multiple temperature levels: -40℃, -30℃, -20℃, 50℃, 60℃, and 70℃. After each temperature level stabilizes, complete the S1~S7 room temperature calibration process.

[0077] S03: The host computer summarizes the calibration coefficients under multiple temperatures and calculates the temperature drift compensation parameters corresponding to each temperature.

[0078] S04: Write the temperature drift compensation coefficients into the sensor register in batches to complete the full temperature range accuracy compensation.

[0079] Specifically, to address the issue of sensor performance consistency across the entire operating temperature range, this invention supports extended calibration applications:

[0080] Hardware adaptation: The calibration chamber is made of stainless steel and placed inside the high and low temperature environment test chamber.

[0081] Full-temperature calibration: Under different set temperature conditions (-40℃, -30℃, -20℃, 50℃, 60℃, 70℃), repeat the above 10-point calibration process. The host computer automatically calculates the offset compensation coefficient at different temperatures using multiple sets of temperature data and writes the compensation coefficient into the sensor to complete the temperature compensation configuration, ensuring the sensor's detection accuracy in extreme environments.

[0082] The standard calibration conditions for the system are: temperature 25±5°C, relative humidity 50±10%RH. During extended calibration, the environmental parameters of the test chamber can be flexibly adjusted according to the operating temperature range defined in the sensor specifications.

[0083] The target concentration gradient, from high to low, is 850 μg / m³. 3 750μg / m 3 650μg / m 3 550μg / m 3 450μg / m 3 350μg / m 3 250μg / m 3 150μg / m 3 70μg / m 3 30μg / m 3 .

[0084] This invention presents a highly integrated, fully automated closed-loop calibration system architecture. Unlike traditional manual calibration and schemes relying on expensive external calibration engineering software such as CANOE and RS-485 multi-level protocol conversion, this invention innovatively proposes a closed-loop control system where host computer software uniformly schedules particulate matter generation, environmental adjustment, standard equipment calibration, synchronous data acquisition, and automatic parameter writing. The system establishes a bidirectional data link between the host computer, standard instruments, the sample to be calibrated, and the calibration chamber control components via a direct USB communication interface, eliminating the need for intermediate protocol conversion. This achieves deep collaboration between the hardware and control layers, eliminating operational errors caused by manual intervention.

[0085] This invention features a particulate matter pretreatment and conveying technology with a drying mechanism. Addressing the issue of large humidity fluctuations and hygroscopicity in combustion-related particulate matter sources (such as cigarette smoke), which can lead to deviations in light scattering measurements, this system integrates a drying and filtering device at the front end of the particulate matter generator. This pretreatment of the particulate matter source before injection into the calibration chamber ensures extremely high physical stability of the injected particulate matter, eliminating interference from humidity factors on the calibration benchmark of the light scattering sensor at the source and improving the purity of the calibration source—a feature not found in existing particulate matter calibration schemes.

[0086] This invention presents a gradient concentration precision adjustment and automated stable control algorithm. Unlike existing calibration methods that only use 5 fixed concentration values ​​or 17 concentration ranges + 8 preset values, this invention achieves precise, stepwise degradation of concentration from high to low by controlling the linkage of "solenoid valve opening + stirring fan + air outlet" via a host computer, covering 850→30μg / m³. 3 With a total of 10 calibration points, the measurement range is wider and the gradient is denser. The innovation lies in its stability determination logic: based on the real-time monitoring value of the high-precision TSI device, when the TSI detection value enters the set threshold (±5%) and remains stable for 2 minutes, the system automatically triggers sampling to ensure the reliability of the data at each calibration point.

[0087] This invention relates to an automatic fitting and closed-loop configuration technology for calibration parameters. Unlike existing calibration methods that only output calibration results and whose parameter writing is disconnected from hardware operation, this system achieves a direct conversion from data acquisition to hardware configuration. The host computer first uses a median filtering algorithm to remove outliers from multi-point acquired data, then automatically fits and generates compensation coefficients based on the particle number and TSI standard concentration value. These coefficients are then written back to the sensor register via USB with a single click, achieving a complete closed loop at the hardware level and enabling one-click calibration to produce a finished product during production / R&D.

[0088] This invention presents an extended calibration scheme for temperature drift compensation compatible with both high and low temperature environments. It innovatively proposes a calibration chamber design with a replaceable material (stainless steel), allowing the entire chamber to be placed within a high and low temperature test chamber. By repeating the automated calibration process across different temperature gradients throughout the full temperature range of -40℃ to 70℃, the system can automatically calculate the temperature drift compensation coefficient of the sensor at different temperatures and write it back to the sensor, solving the problem of maintaining the accuracy of PM2.5 sensors across the entire operating temperature range and overcoming the limitation of existing calibration devices that are only suitable for ambient temperature environments.

[0089] Example 1: Implementation of fully automated calibration of a room temperature multi-channel PM2.5 sensor.

[0090] 1. Preparations before calibration:

[0091] A high-sealed calibration chamber made of acrylic material is used, and the calibration hardware includes: a particulate matter generator with a built-in cigarette aerosol source, and a drying and filtering device connected in series at the outlet; intake solenoid valves and adjustable exhaust solenoid valves are arranged opposite each other on both sides of the calibration chamber; two distributed stirring fans, an air purifier, and built-in temperature and humidity sensors are installed inside the chamber; a TSI standard detector and four identical laser scattering PM2.5 sensors are placed at the bottom of the chamber; the host computer is directly connected to the TSI detector, the four sensors under test, the intake solenoid valve, the exhaust solenoid valve, the stirring fan, the air purifier, and the temperature and humidity sensors via USB cables, without intermediate protocol conversion modules such as CAN and RS485; the host computer is pre-installed with the automated calibration software of this invention, preset to 850μg / m³.3 ~30μg / m 3 There are 10 concentration gradients in total. The stability judgment threshold is ±5% of the target concentration, and the stability is maintained for 2 minutes. Standard operating conditions: ambient temperature 25℃, relative humidity 50%RH.

[0092] The steps are as follows:

[0093] S1 Chamber Purification: Four sensors to be tested are horizontally fixed to the bottom of the chamber, and the calibration chamber is sealed; the host computer automatically turns on the air purifier, exhaust valve, dual stirring fan, and real-time reading of the TSI detector; residual particulate matter in the chamber is continuously purged, and the TSI real-time concentration is stabilized below 10 μg / m³. 3 The system automatically shuts down the purifier and the exhaust solenoid valve.

[0094] S2 Dry Aerosol Introduction: The host computer opens the air intake solenoid valve, starts the particulate generator to burn cigarette smoke to produce aerosol. After all the smoke flows through the drying and filtering device to remove moisture, it is introduced into the calibration chamber at a uniform speed to avoid interference from high humidity aerosols with the light scattering measurement benchmark.

[0095] S3 Particulate Matter Mixing and Suspension: Dual stirring fans run synchronously and continuously for 5 minutes to ensure that the dry aerosol is evenly distributed in the chamber. Four sensors under test are powered on simultaneously and continuously output the original scattering signal x to the host computer.

[0096] S4 Gradient Adjustment and Static Setting: The host computer opens the exhaust solenoid valve and adjusts the valve opening to dilute the aerosols in the chamber, reducing the concentration to the first target level of 850 μg / m³. 3 Close the exhaust valve, run the fan briefly, then stop and let it stand still for 2 minutes.

[0097] S5 Stability Assessment and Synchronous Sampling: The host computer continuously reads the TSI standard concentration, and the value is maintained between 807.5 and 892.5 μg / m³. 3 If the range is within a continuous 2-minute interval without any fluctuations, the system automatically and synchronously records the TSI standard concentration y and the original scattering signals x of each of the four sensors.

[0098] S6 Multi-point Loop Acquisition: Executes steps S4 and S5 in a loop to sequentially acquire data from the remaining 9 calibration points at 750, 650, 550, 450, 350, 250, 150, 70, and 30 μg / m³. All 10 sets of data are automatically saved as a CSV log file.

[0099] S7 Filtering Fitting and Parameter Write-back: The software uses median filtering to remove outliers in the data at each point and calculates the calibration coefficients for the four sensors respectively; the host computer writes the three sets of coefficients into the built-in register of each sensor in batches via USB channel, and the room temperature calibration process ends automatically.

[0100] The entire calibration process is completed without human intervention, with the total time for calibrating four sensors in parallel being 36 minutes. After calibration, the sensors were retested, and the measurement error within the range of 30~850μg / m³ at room temperature (25℃) was ≤±6μg / m³. Compared with the traditional manual calibration scheme, the testing efficiency is improved by more than 70%, and the operational errors caused by manual reading and offline calculation are completely eliminated.

[0101] The present invention and its embodiments have been described above. This description is not restrictive, and the embodiments shown throughout are only one of the embodiments of the present invention. The actual structure is not limited to this. In conclusion, if those skilled in the art are inspired by this description and design similar structures and embodiments without departing from the spirit of the present invention, they should all fall within the protection scope of the present invention.

Claims

1. A simple PM2.5 sensor calibration system, characterized in that, It includes a hardware layer and a control layer; the hardware layer includes a particulate matter generation unit, a calibration chamber, a standard detection unit, and a group of sensors to be tested; The control layer is a host computer equipped with automated calibration software; The particulate matter generating unit includes a particulate matter generator, a dryer filter, and an intake solenoid valve; The particulate matter generator outlet is connected to the dryer filter, and the pipeline at the rear end of the dryer filter is connected to the calibration chamber inlet. The inlet solenoid valve is located between the pipelines to control the aerosol flow. The calibration chamber has air inlets and exhaust outlets arranged vertically opposite each other on both sides, and the exhaust outlets are equipped with adjustable exhaust solenoid valves. The cabin is equipped with multiple distributed stirring fans, air purifiers, and temperature and humidity sensors; The standard testing unit and the sensor group under test are placed horizontally at the bottom of the calibration chamber; The standard detection unit is a high-precision TSI particulate matter detector, used to output a PM2.5 standard concentration benchmark; The host computer is bidirectionally connected to the TSI particulate matter detector, the sensor under test, the intake solenoid valve, the exhaust solenoid valve, the stirring fan, the air purifier, and the temperature and humidity sensor via multiple USB communication interfaces, without any intermediate protocol conversion hardware.

2. The simplified PM2.5 sensor calibration system according to claim 1, characterized in that: The calibration chamber can be made of acrylic or stainless steel, enabling temperature drift compensation calibration across the entire temperature range of -40℃ to 70℃.

3. The simplified PM2.5 sensor calibration system according to claim 1, characterized in that: The particulate matter generator uses cigarettes as a combustion aerosol source and removes water vapor from the aerosol through a drying filter to eliminate the interference of humidity on the light scattering calibration results.

4. A simplified method for calibrating a PM2.5 sensor, characterized in that, The steps are as follows: S1: Environmental purification: Place the sample to be calibrated into the chamber and seal the calibration chamber. The host computer starts the purifier, exhaust valve, stirring fan and TSI particulate matter detector. The purification and exhaust will be automatically shut off after the concentration is lower than 10μg / m³. S2: Particulate matter Note: The host computer controls the opening of the air inlet and instructs the particulate matter generator to inject the smoke, which has been dried by the dryer filter, into the calibration chamber at a uniform speed. S3: Stirring: Start all the stirring fans in the chamber to stir thoroughly, so that the particulate matter is mixed evenly with the air in the chamber and kept suspended. At this time, the calibration sample enters the working mode and begins real-time monitoring. S4: Concentration gradient adjustment and stabilization: Adjust the opening of the exhaust valve to reduce the concentration in the chamber to the target gradient value, and then close the exhaust valve and let it stand for 2 minutes. S5: Stable sampling: When the TSI concentration is stable at ±5% of the target value for 2 minutes, the system determines that the environment has reached quasi-static equilibrium and simultaneously records the standard concentration and the original signal of the sensor under test. S6: Multi-point cyclic calibration: Repeat S4-S5 to complete the data acquisition of all 10 concentration gradient levels in sequence; S7: Calculation and parameter write-back: After the acquisition of 10 points, median filtering is used to remove abnormal data, and the fitting coefficients of each sample are automatically calculated through the fitting algorithm. The coefficients are written to the sensor register via USB communication.

5. The simplified PM2.5 sensor calibration method according to claim 4, characterized in that: The fitting algorithm formula is y=p1x 2 +p2x+p3; where x is the original scattering signal of the sensor to be calibrated; Y is the reference value of PM2.5 concentration of the standard instrument; p1 is the coefficient of the quadratic term, with a value range of (-0.1, 0.1); p2 is the coefficient of the linear term, with a value range of (-0.5, 0.5); p3 is the intercept term, with a value range of (-50, 0).

6. The simplified PM2.5 sensor calibration method according to claim 4, characterized in that: It also includes an extended process for temperature drift compensation across the entire high and low temperature range, with the following steps: S01: Replace the stainless steel calibration chamber and place it entirely into the high and low temperature test chamber. The host computer will control the temperature of the test chamber in conjunction with the main computer. S02: Sequentially set multiple temperature levels: -40℃, -30℃, -20℃, 50℃, 60℃, and 70℃. After each temperature level stabilizes, complete the S1~S7 room temperature calibration process. S03: The host computer summarizes the calibration coefficients under multiple temperatures and calculates the temperature drift compensation parameters corresponding to each temperature. S04: Write the temperature drift compensation coefficients into the sensor register in batches to complete the full temperature range accuracy compensation.

7. The simplified PM2.5 sensor calibration method according to claim 4, characterized in that: The target concentration gradient, from high to low, is 850 μg / m³. 3 750μg / m 3 650μg / m 3 550μg / m 3 450μg / m 3 350μg / m 3 250μg / m 3 150μg / m 3 70μg / m 3 30μg / m 3 .

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