PID sensor calibration system, method and device

Abstract

The invention discloses a PID sensor calibration system, method and device, and the system comprises a storage container which is provided with a liquid storage cavity, and the liquid storage cavity is filled with organic liquid; the capillary tube is communicated with an outlet of the liquid storage cavity; the gas path switching device is used for closing or opening a gas path between the capillary tube and the PID sensor; and the temperature sensing control device is used for detecting the temperature in the liquid storage cavity and maintaining the temperature in the liquid storage cavity within a constant preset temperature range. The organic liquid in the storage container is used as the VOC volatilization source for calibration, and high-pressure steel cylinder standard gas is not needed, so that the calibration cost is greatly reduced, and the overall architecture of the system is simplified. In addition, the temperature sensing control device can detect in real time and maintain the temperature in the liquid storage cavity to be within a constant preset range, in combination with precise control of the capillary tube on the steam diffusion rate, it is ensured that the organic liquid can be stably volatilized to form steam with the constant concentration, a traceable stable reference signal is provided for the PID sensor, and the calibration precision is guaranteed.

Description

Technical Field

[0001] This invention relates to the field of sensor technology, and in particular to a PID sensor calibration system, method and apparatus. Background Technology

[0002] Volatile organic compounds (VOCs) are one of the main pollutants in the atmospheric environment, and their accurate detection is of great significance for environmental protection, industrial production safety, and human health. Photoionization detectors (PIDs), with their advantages of high sensitivity and rapid response, have become the core sensor in the field of VOC detection, and are widely used in portable monitoring devices, Internet of Things (IoT) environmental monitoring nodes, and industrial process control.

[0003] The detection principle of a PID sensor is to use photons emitted by a high-energy ultraviolet lamp to ionize the VOC molecules being measured. The gas concentration is then inverted by measuring the ion current generated by ionization. Its detection accuracy is highly dependent on the stability of the photon energy output by the ultraviolet lamp. However, in practical use, the ultraviolet lamp, the core component of the PID sensor, inevitably ages over time, causing a gradual decrease in photon output energy and resulting in a drift in the PID sensor's sensitivity (i.e., gain). If this drift is not corrected, it will directly lead to deviations in subsequent VOC concentration detection data, severely affecting the accuracy and reliability of the detection results. Therefore, it is essential to periodically calibrate the PID sensor to correct the errors caused by gain drift.

[0004] Currently, the calibration solutions for PID sensors in the industry are mainly divided into two categories, but both have significant technical defects and are difficult to meet the current application requirements of miniaturization, automation and low cost of equipment: One type is the traditional calibration scheme based on high-pressure gas cylinders. This scheme uses a known concentration of standard gas (such as 100 ppm isobutylene) encapsulated in a high-pressure gas cylinder as a calibration reference source. Calibration is completed by passing the standard gas into a PID sensor and comparing the sensor's measured value with the standard gas concentration value. However, this scheme has several problems: First, the purchase, transportation, and storage costs of high-pressure gas cylinders are high, and the capacity of the standard gas inside the cylinder is limited, requiring frequent replacement to maintain the continuity of calibration work, resulting in high long-term operating costs; second, high-pressure gas cylinders pose certain safety hazards, and strict adherence to safety regulations is required during handling, storage, and use, increasing operational complexity; more importantly, high-pressure gas cylinders are large in size and weight, making them unsuitable for integration into portable devices or small IoT monitoring nodes, and completely lacking the automatic and continuous calibration capabilities required for field or embedded systems, greatly limiting their application scenarios.

[0005] Another type is the dynamic gas mixing calibration scheme based on permeation tubes. This scheme slowly releases the calibration substance through the permeation tube, diluting it with a carrier gas to a standard gas of a specific concentration, which is then used for PID sensor calibration. However, the stable operation of the permeation tube depends on precise temperature control and a constant carrier gas flow rate: on the one hand, a dedicated temperature control device is required to maintain the temperature of the permeation tube to ensure a constant permeation rate; on the other hand, a flow controller is needed to precisely control the carrier gas flow rate to achieve accurate gas mixing at the target concentration. The above design results in a complex and bulky calibration system, and the system requires a long temperature and flow stabilization process during startup, resulting in a slow response speed. This makes it difficult to adapt to portable devices with high integration requirements, and it also fails to meet the needs of IoT monitoring nodes for rapid start-up of the calibration process, making it extremely unsuitable for automated and miniaturized application scenarios.

[0006] With the rapid development of IoT technology and portable testing equipment, the market has placed new demands on PID sensor calibration technology. Calibration devices need to be integrated into the equipment to achieve automatic calibration on demand, while also possessing the characteristics of simple structure, small size, low power consumption, and low cost. However, neither of the existing calibration solutions can balance the requirements of calibration accuracy with miniaturization and low cost. Traditional high-pressure cylinder solutions, while ensuring calibration accuracy, completely lack integration and automation capabilities. Permeation tube solutions, although capable of dynamic gas distribution, are difficult to miniaturize due to their high system complexity, and suffer from slow start-up and high power consumption, making them unsuitable for IoT and portable device applications.

[0007] In summary, a new calibration technology is urgently needed to overcome the aforementioned technical bottlenecks. Summary of the Invention

[0008] The purpose of this invention is to overcome the shortcomings of the prior art and provide a PID sensor calibration system, method and apparatus, which aims to solve the problem that existing PID sensor calibration methods cannot simultaneously meet the requirements of high calibration accuracy and simple and compact structure.

[0009] To achieve the above objectives, the present invention adopts the following technical solution: In a first aspect, the present invention provides a PID sensor calibration system, comprising: A storage container is provided with a liquid storage chamber, the liquid storage chamber being filled with organic liquid; A capillary tube is connected to the outlet of the liquid storage chamber; An air path switching device is used to close or open the air path between the capillary and the PID sensor; A temperature-sensing control device is used to detect the temperature inside the liquid storage chamber and maintain the temperature inside the liquid storage chamber within a constant preset temperature range.

[0010] Furthermore, the liquid storage cavity is filled with a porous material.

[0011] Furthermore, the gas path switching device includes a first branch, which is connected between the capillary tube and the PID sensor, and the first branch is provided with at least one on / off first gas path valve.

[0012] Furthermore, a gas pipeline is provided between the first branch and the capillary, with the end of the capillary away from the storage container connected to the gas pipeline, and the first branch connected to one end of the gas pipeline.

[0013] Furthermore, the gas path switching device also includes a second branch, one end of which is connected to the sampling gas inlet and the other end of which is connected to the PID sensor. At least one second gas path valve is provided on the second branch.

[0014] Furthermore, the temperature control device includes a heating and cooling element and a temperature sensor. The temperature sensor is used to detect the temperature inside the liquid storage chamber, and the heating and cooling element is used to heat or cool the liquid storage chamber.

[0015] Furthermore, a breathable membrane is provided inside the liquid storage chamber, and the breathable membrane is arranged close to the capillary.

[0016] Secondly, the present invention also provides an automatic calibration method for a PID sensor, comprising: Close the second air circuit valve and open the first air circuit valve; Calculate the saturated vapor concentration of the organic liquid in the storage chamber; The concentration value actually measured by the PID sensor is compared with the saturated steam concentration value to obtain the correction coefficient, and the final output value of the PID sensor is calibrated using the correction coefficient.

[0017] Further, the calculation of the saturated vapor concentration value of the organic liquid in the storage chamber includes: Calculate the saturated vapor pressure of the organic liquid; Calculate the saturated concentration of the organic liquid based on the obtained saturated vapor pressure; The diffusion flux is calculated based on the saturation concentration and diffusion coefficient of the organic liquid. Calculate molar flow rate based on diffusion flux; The concentration of organic liquid in the air flowing into the PID sensor is calculated based on the molar flow rate. Calculate the saturated vapor concentration of the organic liquid based on its concentration.

[0018] Thirdly, the present invention also provides an automatic calibration device for a PID sensor, comprising: A switch control unit is used to close the second air circuit valve and open the first air circuit valve. The calculation unit is used to calculate the saturated vapor concentration of the organic liquid in the storage chamber. The comparison unit is used to compare the concentration value actually measured by the PID sensor with the saturated steam concentration value to obtain the correction coefficient, and then use the correction coefficient to perform gain calibration on the final output value of the PID sensor.

[0019] The advantages of this invention compared to existing technologies are as follows: A PID sensor calibration system includes: a storage container with a liquid storage chamber containing an organic liquid; a capillary tube connected to the outlet of the liquid storage chamber; a gas path switching device for closing or opening the gas path between the capillary tube and the PID sensor; and a temperature control device for detecting the temperature in the liquid storage chamber and maintaining it within a constant preset temperature range. By using the organic liquid in the storage container as the VOC evaporation source for calibration, it eliminates the need for high-pressure gas cylinders, significantly reducing calibration costs, avoiding the safety hazards of cylinder handling and storage, and the inconvenience of frequent cylinder replacements. It also eliminates the complex temperature control and carrier gas flow control structure required by the permeation tube system, simplifying the overall system architecture. Furthermore, the temperature control device can detect and maintain the temperature in the liquid storage chamber within a constant preset range in real time. Combined with the precise control of the vapor diffusion rate by the capillary tube, it ensures that the organic liquid can stably evaporate to form vapor of constant concentration, providing a traceable and stable reference signal for the PID sensor and guaranteeing calibration accuracy.

[0020] The above description is merely an overview of the technical solution of the present invention. In order to better understand the technical means of the present invention, it can be implemented according to the contents of the specification. In order to make the above and other objectives, features and advantages of the present invention more obvious and understandable, preferred embodiments are described in detail below. Attached Figure Description

[0021] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the following description of the embodiments will be briefly introduced. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1 This is a schematic diagram of a PID sensor calibration system provided in a specific embodiment of the present invention.

[0023] Figure 2 This is a schematic diagram of the structure of a storage container provided in a specific embodiment of the present invention.

[0024] Figure 3 A cross-sectional view of a storage container provided in a specific embodiment of the present invention.

[0025] Figure 4This is a flowchart of an automatic calibration method for a PID sensor provided in a specific embodiment of the present invention.

[0026] Figure 5 This is a schematic block diagram of an automatic calibration device for a PID sensor provided in a specific embodiment of the present invention.

[0027] Figure Labels 1. Storage container; 11. Liquid storage chamber; 111. Breathable membrane; 112. Porous material; 2. Temperature control device; 21. Heating and cooling element; 22. Temperature sensor; 3. Gas path switching device; 31. Gas pipeline; 4. Capillary tube. Detailed Implementation

[0028] The technical solution of the present invention will be clearly and completely described below with reference to specific embodiments. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0029] It should be understood that, when used in this specification and the appended claims, the terms "comprising" and "including" indicate the presence of the described features, integrals, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, integrals, steps, operations, elements, components and / or collections thereof.

[0030] It should also be understood that the terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to limit the invention. As used in this specification and the appended claims, the singular forms “a,” “an,” and “the” are intended to include the plural forms unless the context clearly indicates otherwise.

[0031] It should also be further understood that the term "and / or" as used in this specification and the appended claims refers to any combination of one or more of the associated listed items and all possible combinations, and includes such combinations.

[0032] like Figure 1 As shown, this embodiment of the invention provides a PID sensor calibration system, including a storage container 1, a capillary tube 4, a gas path switching device 3, and a temperature control device 2.

[0033] The storage container 1 is a container with a sealed structure, which defines a liquid storage chamber 11 for containing organic liquid. The storage container 1 is made of corrosion-resistant and well-sealed metal or polymer material, such as 304 stainless steel, to avoid chemical reaction between the organic liquid and the container or leakage. The organic liquid must meet the condition that the molecular ionization potential is lower than the energy of the ultraviolet light of the PID sensor to ensure that the vapor formed by the evaporation of the organic liquid can be effectively ionized by the PID sensor, thereby providing an accurate reference signal for calibration. Ethanol, isobutylene, etc. can be selected as examples of organic liquids.

[0034] One end of the capillary tube 4 is fixedly and sealed to the outlet of the liquid storage chamber 11 through a sealing connector (such as a welded joint or a threaded sealing joint). The capillary tube 4 is made of a material with low thermal conductivity and low deformation rate, such as quartz or borosilicate glass, to reduce the influence of external temperature changes on the vapor diffusion process inside the capillary tube 4. As a key component for controlling the vapor diffusion rate, the inner diameter and length of the capillary tube 4 need to be designed according to the volatility of the organic liquid and the preset vapor diffusion rate to ensure that, at a constant temperature, the vapor emitted by the organic liquid in the liquid storage chamber 11 can be transmitted to the subsequent gas path through the capillary tube 4 at a stable rate.

[0035] In some embodiments, a microchannel structure can be used to replace the capillary 4. The microchannel structure can be fabricated on a chip using microfabrication technology. It has a smaller volume and more precise channel size, which can further improve the stability and controllability of the vapor diffusion rate, and at the same time facilitate the miniaturization and integration of the calibration system. The material of the microchannel structure can be silicon wafer, ceramic, etc., and the adsorption of vapor on the inner wall of the channel can be further reduced by surface coating (such as polytetrafluoroethylene coating), thereby reducing vapor loss.

[0036] The gas path switching device 3 is a component with a passage control function. It is installed in the gas path between the capillary tube 4 and the PID sensor. It can be a component that can be controlled by electrical or air pressure signals, such as a solenoid valve group or a pneumatic valve group. By controlling the on / off state of the gas path switching device 3, the gas path between the capillary tube 4 and the PID sensor can be closed or opened, thereby controlling whether the calibration steam enters the PID sensor. In practical applications, the gas path switching device 3 can be electrically connected to an external controller (such as a microprocessor), and the controller can send control signals to realize the automated control of gas path switching.

[0037] The temperature control device 2 is used to detect the temperature inside the liquid storage chamber 11 and maintain the temperature inside the liquid storage chamber 11 within a constant preset temperature range. The temperature control device 2 includes a heating and cooling element 21 and a temperature sensor 22. The temperature sensor 22 is used to detect the temperature inside the liquid storage chamber 11. The temperature sensor 22 can be a high-precision temperature sensor (such as a platinum resistance temperature sensor 22 or a thermocouple temperature sensor 22). It is installed on the outer wall or inside the liquid storage chamber 11 to detect the temperature inside the liquid storage chamber 11 in real time and transmit the temperature detection signal to an external controller. The heating and cooling element 21 is used to heat or cool the liquid storage chamber 11. The heating and cooling element 21 can be a combination of a semiconductor cooling chip and a heating chip, or a combination of an electric heating wire and a cooling water pipe, etc. It is connected to the liquid storage chamber 11 through heat conduction. Under the control of the controller, when the temperature sensor 22 detects that the temperature inside the liquid storage chamber 11 is higher than the preset temperature range, the heating and cooling element 21 starts the cooling function. When the temperature is lower than the preset temperature range, the heating function is started, thereby maintaining the temperature inside the liquid storage chamber 11 at a constant preset temperature range and ensuring a stable evaporation rate of the organic liquid.

[0038] By combining the storage container 1 with the organic liquid, calibration costs are reduced, avoiding the inconvenience and safety hazards of handling and storing gas cylinders. Furthermore, it eliminates the need for frequent changes in the standard gas source, improving the convenience and continuity of calibration. Compared to the permeation tube system, it eliminates the need for complex temperature control and stable carrier gas flow control, simplifying the system structure and reducing the device size, making it more suitable for scenarios with high integration requirements, such as IoT devices and portable monitoring equipment. The temperature control device 2 maintains a constant temperature in the liquid storage chamber 11, and combined with the control of the vapor diffusion rate by the capillary tube 4, it ensures a stable concentration of vapor reference signal for the PID sensor, improving the accuracy and reliability of PID sensor calibration. Simultaneously, the gas path switching device 3 enables automated control of the calibration gas path, laying the foundation for subsequent automatic calibration of the PID sensor.

[0039] In some embodiments, such as Figure 1 As shown, the liquid storage chamber 11 is filled with a porous material 112. The porous material 112 is a solid material with high specific surface area and good adsorption performance. Exemplary porous materials 112 can be zeolite, activated carbon, porous ceramics, porous polymers, etc. The porous material 112 can be filled uniformly in the liquid storage chamber 11. The filling amount must ensure that the porous material 112 can fully adsorb the organic liquid in the liquid storage chamber 11 without affecting the normal volatilization of the organic liquid. For example, when the volume of the liquid storage chamber 11 is 2 mL, 1-1.5 mL of porous material 112 can be filled so that the organic liquid can be absorbed and stored by the porous material 112 at a volume ratio of about 2:1.

[0040] The porous material 112 plays a role in the following two aspects: Firstly, the porous material 112 has a rich pore structure, which can adsorb organic liquid into the pores through physical adsorption. Even if the storage container 1 experiences slight vibration or tilting, it can effectively prevent the organic liquid from leaking, thereby improving the safety and reliability of the system. Secondly, the high specific surface area of ​​the porous material 112 provides a large number of volatilization interfaces for the organic liquid, allowing the organic liquid to volatilize uniformly on the surface of the porous material 112. This avoids situations where the local volatilization rate is too fast or too slow, achieving stable evaporation, ensuring the consistency of the steam concentration, and providing stable reference steam for PID sensor calibration.

[0041] In practical applications, porous materials 112 need to be pretreated before filling. For example, zeolite can be activated at high temperature to remove impurities and moisture in the pores and improve its adsorption performance. For activated carbon, surface modification treatment can be carried out to enhance its adsorption selectivity for specific organic liquids and avoid impurities in the organic liquid from affecting the purity of the steam after being adsorbed.

[0042] In some embodiments, the gas path switching device 3 includes a first branch connected between the capillary tube 4 and the PID sensor to form a gas path channel. This first branch can be made of a metal tube (such as a copper tube or stainless steel tube) or a polymer material tube (such as a polytetrafluoroethylene tube). The first branch is equipped with at least one on / off first gas path valve. The first gas path valve can be a solenoid valve, a manual valve, etc. In automated calibration scenarios, a solenoid valve is preferred, and this solenoid valve is electrically connected to an external controller, which sends an electrical signal to control its on / off state.

[0043] When the PID sensor needs to be calibrated, the controller sends a control signal to the first gas path valve to open it. At this time, the vapor formed by the evaporation of organic liquid in the liquid storage chamber 11 enters the first branch through the capillary tube 4, and is then transmitted to the PID sensor through the first branch to provide calibration vapor for the PID sensor. After calibration is completed, the controller sends a signal to close the first gas path valve, cutting off the gas path between the capillary tube 4 and the PID sensor, so as to prevent the continuous entry of vapor into the PID sensor and affect its normal detection operation.

[0044] like Figure 1 In the embodiment shown, SV4 is the first gas path valve, and the path with SV4 is the first branch. When SV4 is closed, the vapor formed by the evaporation of organic liquid in the liquid storage chamber 11 cannot reach the PID sensor through the first branch. Only when SV4 is open can the vapor reach the PID sensor.

[0045] In practical design, depending on the complexity and reliability requirements of the gas path, two or more first gas path valves can be set on the first branch. The multiple first gas path valves can be connected in series or in parallel. For example, when connected in series, even if one of the first gas path valves fails to seal, the other first gas path valve can still cut off the gas path, improving the reliability of gas path control. When connected in parallel, the gas path can be redundantly designed. When one first gas path valve fails, it can be switched to another first gas path valve to ensure that the calibration process is not interrupted.

[0046] By setting the first branch and the first gas path valve, precise control of the gas path between capillary tube 4 and the PID sensor is achieved. The timing of steam entering the PID sensor can be flexibly controlled according to calibration requirements, avoiding steam entering the PID sensor in the non-calibration state and ensuring that the normal detection function of the PID sensor is not interfered with.

[0047] In some embodiments, a gas pipeline 31 is further provided between the first branch and the capillary tube 4. This gas pipeline 31 is a channel with gas transmission function, and its material is consistent with that of the first branch (e.g., both are stainless steel pipes) to ensure the consistency of the gas pipeline material and reduce the adsorption differences of vapor during transmission. One end of the gas pipeline 31 is fixedly connected to the end of the capillary tube 4 away from the storage container 1 through a sealing joint (e.g., a compression fitting), and the other end is connected to the end of the first branch away from the PID sensor. All connection points are sealed to prevent vapor leakage.

[0048] The gas pipeline 31 enables a transitional connection between the capillary tube 4 and the first branch. Especially when the dimensions (such as inner and outer diameters) of the capillary tube 4 and the first branch are mismatched, the gas pipeline 31 can act as a variable diameter connector. By selecting gas pipelines 31 with different inner diameters, the capillary tube 4 and the first branch can be smoothly connected, ensuring unobstructed steam transmission. At the same time, the gas pipeline 31 can also buffer the steam flow. Since the steam transmitted by the capillary tube 4 may have flow rate fluctuations, the volume of the gas pipeline 31 can buffer the steam flow, making the steam flow rate entering the first branch more stable, thereby improving the stability of the steam concentration entering the PID sensor.

[0049] In some embodiments, the gas path switching device 3 further includes a second branch, which is a gas path channel for transmitting sampling gas. Its material is the same as that of the first branch (such as polytetrafluoroethylene tube) to ensure the consistency of gas transmission performance. One end of the second branch is connected to the sampling gas inlet (which can be connected to an external sampling pipeline to introduce the gas to be detected, such as volatile organic compounds in the air), and the other end is connected to the air inlet of the PID sensor, so that the sampling gas can enter the PID sensor for detection through the second branch. At least one second gas path valve is provided on the second branch. The second gas path valve is of the same type as the first gas path valve (such as both being solenoid valves) and is also electrically connected to an external controller, which controls its opening and closing.

[0050] In some embodiments, to ensure a smooth transition of gas within the PID sensor during gas path switching, a one-way valve can be installed on the second branch. The one-way valve is directed from the sampling gas inlet to the PID sensor to prevent calibration steam in the first branch from flowing back into the second branch through the PID sensor during gas path switching, thus avoiding contamination of the sampling gas path by calibration steam or affecting the detection results of subsequent sampling gases. In addition, a flow regulating component (such as a throttle valve) can be installed on the second branch. By adjusting the opening of the flow regulating component, the flow rate of the sampling gas entering the PID sensor can be controlled, so that the sampling gas flow rate meets the optimal detection flow rate requirements of the PID sensor, thereby improving detection accuracy.

[0051] In the appendix Figure 1 In the embodiment shown, SV1 is the first gas path valve, and the path with SV1 is the second branch. When SV1 is closed, the sampling gas cannot reach the PID sensor from the gas inlet. It can only reach the PID sensor when SV2 is open.

[0052] In some embodiments, such as Figure 3 As shown, a breathable membrane 111 is provided inside the liquid storage chamber 11. The breathable membrane 111 is a thin film material with selective air permeability. Its material can be polytetrafluoroethylene microporous membrane, polyolefin breathable membrane 111, etc. These materials have good chemical stability and can withstand the corrosion of organic liquids. At the same time, they have a uniform microporous structure, allowing the vapor formed by the evaporation of organic liquids to pass through while preventing the liquid organic liquids from passing through. The shape of the breathable membrane 111 can be designed as circular, square, etc., according to the cross-sectional shape of the liquid storage chamber 11. Its size matches the inner diameter of the liquid storage chamber 11, ensuring that the breathable membrane 111 can cover the cross-section or specific area of ​​the liquid storage chamber 11.

[0053] The permeable membrane 111 is arranged close to the capillary tube 4. The specific installation position can be set at the connection between the outlet of the liquid storage chamber 11 and the capillary tube 4. For example, the permeable membrane 111 can be fixed to the inside of the outlet of the liquid storage chamber 11, and the edge of the permeable membrane 111 can be sealed and fixed to the inner wall of the liquid storage chamber 11 by pressure ring or sealant. This ensures that the vapor formed by the evaporation of organic liquid in the liquid storage chamber 11 must pass through the permeable membrane 111 before entering the capillary tube 4. This installation method can ensure that the vapor passes through the filtration and stabilization effect of the permeable membrane 111 before entering the capillary tube 4, and at the same time prevent the liquid organic liquid from directly entering the capillary tube 4 due to shaking, tilting, etc., so as to avoid the capillary tube 4 being blocked by liquid organic liquid or affecting the vapor diffusion rate.

[0054] like Figures 2 to 4 As shown, this embodiment of the invention also provides an automatic calibration method for a PID sensor, including the following steps: S10-S30.

[0055] S10. Close the second air circuit valve and open the first air circuit valve.

[0056] When the PID sensor calibration process needs to be initiated, the external controller (such as a microprocessor) first sends control signals to the second and first gas path valves in the gas path switching device 3. The control signal switches the second gas path valve from the open to the closed state, cutting off the channel for the sampling gas to enter the PID sensor through the second branch, thus preventing the sampling gas from mixing with the subsequent calibration steam and affecting the calibration accuracy. At the same time, the control signal switches the first gas path valve from the closed to the open state, opening the gas path between the capillary tube 4 and the PID sensor, providing a path for the calibration steam to enter the PID sensor. During the valve switching process, the controller can set a short delay time (such as 1-2 seconds) to ensure that the second gas path valve is completely closed before opening the first gas path valve, further preventing the sampling gas from mixing with the calibration steam.

[0057] S20. Calculate the saturated vapor concentration of the organic liquid in the storage chamber 11.

[0058] In some embodiments, step S20 specifically includes: calculating the saturated vapor pressure of the organic liquid; calculating the saturated concentration of the organic liquid based on the obtained saturated vapor pressure; calculating the diffusion flux based on the saturated concentration of the organic liquid and the diffusion coefficient of the organic liquid; calculating the molar flow rate based on the diffusion flux; calculating the concentration of the organic liquid flowing into the air of the PID sensor based on the molar flow rate; and calculating the saturated vapor concentration value of the organic liquid based on the concentration of the organic liquid.

[0059] In this embodiment, ethanol is used as an example of an organic liquid to calculate the saturated vapor concentration value, as follows: Calculate the saturated vapor pressure: Based on the real-time temperature value (denoted as T, in °C) in the liquid storage chamber 11 transmitted by the temperature-sensing control device 2, calculate the saturated vapor pressure of ethanol according to the Antoine equation, in bar.

[0060] log10(Psat) = 5.37229 – 1670.409 / (T + 273.15 – 40.191); where T is the temperature (°C). Calculating the saturation concentration: Assuming the vapor formed by alcohol evaporation in storage chamber 11 satisfies the ideal gas law, the formula for calculating the saturation concentration (denoted as Csat) is derived based on the ideal gas law. The ideal gas law is PV=nRT, where P is the gas pressure (here, the saturated vapor pressure Psat), V is the gas volume, n is the amount of gas, and R is the ideal gas constant (the value needs to be determined according to the unit of Psat; for example, when the unit of Psat is Pa, R=8.314 Pa·m). 3 / (mol・K)), T is the thermodynamic temperature (equal to the temperature T (°C) inside the storage chamber 11 plus 273.15, in K); by transforming the formula, we can get Csat=n / V=Psat / (RT), where the unit of Csat is mol / m 3 Substituting the previously calculated Psat, the thermodynamic temperature corresponding to the real-time temperature, and the ideal gas constant R into the formula, the saturation concentration Csat of alcohol is calculated.

[0061] Calculate diffusion flux: Use the preset diffusion coefficient of ethanol in air (denoted as D, unit: m). 2 / s), the diffusion coefficient of ethanol to air is the binary diffusion coefficient D(m 2 ( / s) Referencing NIST data (D=1.29x10⁻⁵m at 25°C) 2 / s); According to Fick's first law, the expression of Fick's first law is J=-D×dC / dx. In the structure of the reservoir 11 and the capillary 4, it can be simplified to J=D×Csat / L, where L is the length of the capillary 4 (in meters). The negative sign indicates that the diffusion direction is opposite to the concentration gradient direction. In actual calculations, the negative sign can be ignored, and only the numerical value is considered. Substituting Csat, D, and L into the formula, the diffusion flux J is calculated.

[0062] Calculate the molar flow rate: The molar flow rate (denoted as n, in mol / s) is the product of the diffusion flux and the cross-sectional area of ​​capillary 4, where the cross-sectional area of ​​capillary 4 is denoted as A, in m². 2 The value is calculated based on the inner diameter of capillary tube 4 (denoted as d, in meters), using the formula A = π × (d / 2). 2 Calculate the cross-sectional area A based on the inner diameter, and then multiply the diffusion flux J by the cross-sectional area A to obtain the molar flow rate n, i.e., n = J × A.

[0063] Calculate the alcohol concentration in the air flowing into the PID sensor: Obtain the air volumetric flow rate entering the PID sensor (denoted as Q, unit: m³ / s). 3 / s), this volumetric flow rate can be detected in real time by a flow sensor installed in the gas path, or preset according to design parameters (such as preset Q as a fixed value); the alcohol concentration in the air flowing into the PID sensor (denoted as Cair, unit mol / m³) 3 Cair is the ratio of molar flow rate to air volumetric flow rate, calculated using the formula Cair = n / Q. Substituting the previously calculated n and air volumetric flow rate Q into the formula, Cair is calculated.

[0064] Calculating volume concentration: Saturated vapor concentration is usually expressed as volume concentration (e.g., ppmv, parts per million by volume). The formula for calculating volume concentration (denoted as Cppm) is derived based on the ideal gas law. The total molar concentration in air (denoted as Ctotal, unit: mol / m³) is the concentration of total substances in the air. 3 The formula is: Ctotal = Patm / (RT), where Patm is standard atmospheric pressure (in Pa, usually taken as 101325 Pa), R is the ideal gas constant, and T is the thermodynamic temperature; the volume concentration Cppm = (Cair / Ctotal) × 10 6 Substituting the expressions for Cair and Ctotal, we can simplify to obtain Cppm = (n × R × T) / (Q × Patm) × 10 6 Alternatively, by substituting the expressions for n, J, Csat, and Psat, a more direct calculation formula can be obtained; by substituting the relevant parameters into the formula, the saturated vapor concentration (volume concentration) of alcohol can be calculated, which serves as the theoretical standard concentration value for calibration.

[0065] S30. Compare the concentration value actually measured by the PID sensor with the saturated steam concentration value to obtain the correction coefficient, and use the correction coefficient to calibrate the gain of the final output value of the PID sensor.

[0066] In this embodiment, the measured concentration value of the PID sensor is compared with the saturated vapor concentration value of alcohol calculated above. A new calibration gain coefficient is calculated according to the formula, and the calibration is completed.

[0067] For example, the actual concentration value measured by the PID sensor was Cact = 0.182 ppm, while the theoretically calculated value was Ccalc = 0.214 ppm, indicating that the gain of the PID sensor decreased during use.

[0068] The correction factor is calculated as Factor = Ccalc / Ccact = 0.214 / 0.182 = 1.1758. This correction factor is saved to the PID sensor. Until the next gain calibration, the PID sensor uses this correction factor to adjust the final output value (this correction value is 1.000 in the factory default state). Thus, the final sensor output value Cfinal = Cact × Factor.

[0069] It should be understood that the sequence number of each step in the above embodiments does not imply the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present invention.

[0070] This invention also provides an automatic PID sensor calibration apparatus, which is used to perform the steps in any of the embodiments of the aforementioned automatic PID sensor calibration method. Specifically, please refer to... Figure 5 , Figure 5 A schematic block diagram of an automatic PID sensor calibration device 100 provided in an embodiment of this application is shown. The automatic PID sensor calibration device 100 specifically includes: The switch control unit 110 is used to close the second gas path valve and open the first gas path valve; the calculation unit 120 is used to calculate the saturated vapor concentration value of the organic liquid in the storage chamber 11; the comparison unit 130 is used to compare the concentration value actually measured by the PID sensor with the saturated vapor concentration value to obtain the correction coefficient, and use the correction coefficient to perform gain calibration on the final output value of the PID sensor.

[0071] In one embodiment, the calculation unit 120 is specifically used to: calculate the saturated vapor pressure of the organic liquid; calculate the saturated concentration of the organic liquid based on the obtained saturated vapor pressure; calculate the diffusion flux based on the saturated concentration of the organic liquid and the diffusion coefficient of the organic liquid; calculate the molar flow rate based on the diffusion flux; calculate the concentration of the organic liquid flowing into the air of the PID sensor based on the molar flow rate; and calculate the saturated vapor concentration value of the organic liquid based on the concentration of the organic liquid.

[0072] It should be noted that those skilled in the art can clearly understand that the specific implementation process of the above-mentioned PID sensor automatic calibration device 100 and each unit can be referred to the corresponding description in the foregoing method embodiments. For the sake of convenience and brevity, it will not be repeated here.

[0073] 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 equivalent modifications or substitutions within the technical scope disclosed in the present invention, and these modifications or substitutions should all be covered 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 PID sensor calibration system, characterized in that, include: A storage container is provided with a liquid storage chamber, the liquid storage chamber being filled with organic liquid; A capillary tube is connected to the outlet of the liquid storage chamber; An air path switching device is used to close or open the air path between the capillary and the PID sensor; A temperature-sensing control device is used to detect the temperature inside the liquid storage chamber and maintain the temperature inside the liquid storage chamber within a constant preset temperature range.

2. The PID sensor calibration system according to claim 1, characterized in that, The liquid storage chamber is filled with a porous material.

3. The PID sensor calibration system according to claim 1, characterized in that, The gas path switching device includes a first branch, which is connected between the capillary tube and the PID sensor, and at least one on / off first gas path valve is provided on the first branch.

4. The PID sensor calibration system according to claim 3, characterized in that, A gas pipeline is also provided between the first branch and the capillary tube. The end of the capillary tube away from the storage container is connected to the gas pipeline, and the first branch is connected to one end of the gas pipeline.

5. A PID sensor calibration system according to claim 3, characterized in that, The gas path switching device further includes a second branch, one end of which is connected to the sampling gas inlet and the other end of which is connected to the PID sensor. At least one second gas path valve is provided on the second branch.

6. The PID sensor calibration system according to claim 1, characterized in that, The temperature control device includes a heating and cooling element and a temperature sensor. The temperature sensor is used to detect the temperature inside the liquid storage chamber, and the heating and cooling element is used to heat or cool the liquid storage chamber.

7. The PID sensor calibration system according to claim 1, characterized in that, The liquid storage chamber is provided with a breathable membrane, which is arranged close to the capillary.

8. An automatic calibration method for a PID sensor, characterized in that, include: Close the second air circuit valve and open the first air circuit valve; Calculate the saturated vapor concentration of the organic liquid in the storage chamber; The concentration value actually measured by the PID sensor is compared with the saturated steam concentration value to obtain the correction coefficient, and the final output value of the PID sensor is calibrated using the correction coefficient.

9. The automatic calibration method for a PID sensor according to claim 8, characterized in that, The calculation of the saturated vapor concentration of the organic liquid in the storage chamber includes: Calculate the saturated vapor pressure of the organic liquid; Calculate the saturated concentration of the organic liquid based on the obtained saturated vapor pressure; The diffusion flux is calculated based on the saturation concentration and diffusion coefficient of the organic liquid. Calculate molar flow rate based on diffusion flux; The concentration of organic liquid in the air flowing into the PID sensor is calculated based on the molar flow rate. Calculate the saturated vapor concentration of the organic liquid based on its concentration.

10. An automatic calibration device for a PID sensor, characterized in that, include: A switch control unit is used to close the second air circuit valve and open the first air circuit valve. The calculation unit is used to calculate the saturated vapor concentration of the organic liquid in the storage chamber. The comparison unit is used to compare the concentration value actually measured by the PID sensor with the saturated steam concentration value to obtain the correction coefficient, and then use the correction coefficient to perform gain calibration on the final output value of the PID sensor.

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