A PID sensor automatic calibration device and method

Abstract

This invention discloses an automatic calibration device and method for a PID sensor. The device includes a sealed container, a first pipe, a second pipe, and a gas path switching unit. The sealed container includes a source chamber, an adsorption medium, and a saturated VOC buffer chamber. The first pipe has a first diffusion channel, and the second pipe has a second diffusion channel, which are respectively connected to the saturated VOC buffer chamber. The gas path switching unit is connected to the first pipe, the second pipe, and the PID sensor to be calibrated, and is used to selectively connect the first pipe or the second pipe to the PID sensor to be calibrated. This invention can obtain a stable concentration ratio without high-precision temperature control of the chamber, and can eliminate the influence of zero drift and gain attenuation caused by UV lamp aging on the measurement results. It realizes automatic on-site calibration and gain compensation of the PID sensor, significantly improving the long-term accuracy and reliability of the PID sensor.

Description

Technical Field

[0001] This invention relates to the field of sensor technology, and in particular to an automatic calibration device and method for a PID sensor. Background Technology

[0002] A photoionization detector (PID) is a highly sensitive sensor widely used for detecting volatile organic compounds (VOCs). Its working principle involves using photons emitted from a high-energy ultraviolet lamp to ionize the molecules of the target gas, and calculating the gas concentration by measuring the generated ion current. The core component of the PID sensor, the ultraviolet lamp, gradually ages over time, leading to a decrease in photon output energy and causing a drift in the sensor's sensitivity (i.e., gain). Therefore, to ensure the accuracy and reliability of measurement data, PID sensors need to be calibrated periodically using standard gases of known concentrations.

[0003] Currently, calibration methods for photoionization detectors (PIDs) mainly include the standard substance gas cylinder method, the permeation tube system method, and miniaturized automatic calibration devices based on the molecular diffusion principle. While automatic calibration devices based on the molecular diffusion principle can reduce reliance on external standard gas cylinders to some extent, they typically use a single VOC substance stored in a closed cavity, with a known concentration diffused into the gas path via a capillary tube based on Fick's first law. However, the saturated vapor pressure of VOCs is extremely sensitive to temperature, causing the diffused concentration to change drastically with temperature. To ensure calibration accuracy, precise temperature control and measurement of the cavity storing the VOCs are required, typically requiring a temperature measurement accuracy better than ±0.05℃. This results in a large and complex temperature control and measurement system, increasing the manufacturing cost and integration difficulty of the entire automatic calibration device. Furthermore, the core component of the PID sensor, the ultraviolet lamp, ages over time, leading to a decrease in photon output energy, i.e., a reduction in sensor gain. However, there is a lack of online monitoring and adaptive compensation mechanisms for gain attenuation, usually requiring the sensor to be returned to the factory for recalibration, resulting in short maintenance cycles and high operating costs. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the prior art and provide an automatic calibration device and method for PID sensors.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: On one hand, the present invention provides an automatic calibration device for a PID sensor, comprising: A sealed container includes a source cavity, an adsorption medium, and a saturated VOC buffer cavity. The source cavity is used to contain liquid VOCs. The adsorption medium is filled inside the source cavity to adsorb and store the liquid VOCs and provide a stable volatilization interface. The saturated VOC buffer cavity is used to temporarily store saturated VOC vapors. A first pipe and a second pipe, the first pipe having a first diffusion channel and the second pipe having a second diffusion channel, the first diffusion channel and the second diffusion channel being respectively connected to the saturated VOC buffer cavity, the first diffusion channel and the second diffusion channel having different diffusion resistance, so as to generate VOC gas of a first concentration and VOC gas of a second concentration respectively. The gas path switching unit is connected to the first pipeline, the second pipeline, and the PID sensor to be calibrated, respectively, and is used to selectively connect the first pipeline or the second pipeline to the PID sensor to be calibrated.

[0006] Furthermore, the first diffusion channel and the second diffusion channel are disposed within the saturated VOC buffer cavity, and the first diffusion channel and the second diffusion channel are two capillaries of the same length but different inner diameters.

[0007] Furthermore, the gas path switching unit includes a first solenoid valve, a second solenoid valve, a third solenoid valve, a fourth solenoid valve, a fifth solenoid valve, and a sixth solenoid valve. The air inlet of the PID sensor is connected to an external sampling gas source via the first solenoid valve and to a zero filter via the second solenoid valve. The first pipeline is connected upstream of the air inlet of the PID sensor via the third solenoid valve and the fifth solenoid valve in sequence. The second pipeline is connected upstream of the air inlet of the PID sensor via the fourth solenoid valve and the sixth solenoid valve in sequence. The input end of the fifth solenoid valve is also connected in parallel with the input end of the sixth solenoid valve to the upstream of the air inlet of the PID sensor.

[0008] Furthermore, a microporous sintered sheet is provided at the outlet of the source cavity. The microporous sintered sheet is used to prevent the adsorption medium from blocking the diffusion channel, while allowing the volatilized VOC vapor to pass through and reach the saturated VOC buffer cavity.

[0009] Furthermore, the adsorption medium is a plurality of zeolite spheres, which adsorb and store liquid VOCs inside the zeolite spheres, and the zeolite spheres are packed together to fill the source cavity.

[0010] On the other hand, the present invention also provides an automatic calibration method based on the above-mentioned PID sensor automatic calibration device, comprising: A stable VOC vapor is provided through a VOC generation source, and the vapor is then introduced into a saturated VOC buffer chamber. The VOC vapor in the saturated VOC buffer chamber is controlled to flow through the first diffusion channel and the second diffusion channel respectively, thereby generating VOC gas of the first concentration and VOC gas of the second concentration respectively. The gas path switching unit selectively introduces either a first concentration of VOC gas or a second concentration of VOC gas into the PID sensor to be calibrated. The first measurement value of the PID sensor for the first concentration of VOC gas and the second measurement value of the second concentration of VOC gas are obtained sequentially. The current calibration coefficient is calculated based on the ratio of the first measurement value to the second measurement value, and the subsequent measurement output of the PID sensor is compensated based on the comparison result between the current calibration coefficient and the pre-stored initial calibration coefficient.

[0011] Furthermore, the selective introduction of a first concentration of VOC gas or a second concentration of VOC gas into the PID sensor to be calibrated via the gas path switching unit includes: Close the first, second, fourth, and sixth solenoid valves, and open the third and fifth solenoid valves to introduce VOC gas of the first concentration for the first measurement. Close the first, second, third, and fifth solenoid valves, and open the fourth and sixth solenoid valves to introduce VOC gas of a second concentration for a second measurement. Close the second, third, fourth, fifth, and sixth solenoid valves, and open the first solenoid valve to resume normal gas sampling.

[0012] Further, the calculation of the current calibration coefficient based on the ratio of the first measured value to the second measured value, and the compensation of the subsequent measurement output of the PID sensor based on the comparison result of the current calibration coefficient and the pre-stored initial calibration coefficient, includes: Calculate the ratio of the second measurement to the first measurement as the current calibration coefficient; Read the initial calibration coefficients pre-stored at the factory from the PID sensor; Divide the current calibration coefficient by the initial calibration coefficient to obtain the compensation factor; Divide the real-time measurement value of the PID sensor in normal operating mode by the compensation factor to obtain the calibrated final output value.

[0013] Furthermore, before closing the first, second, fourth, and sixth solenoid valves and opening the third and fifth solenoid valves to introduce VOC gas of the first concentration for the first measurement, the procedure further includes: Close the first, third, fourth, fifth, and sixth solenoid valves, and open the second solenoid valve to introduce clean air through the zero filter for zero-point measurement.

[0014] Furthermore, it also includes: The current calibration coefficient is compared with a preset threshold. When the current calibration coefficient is determined to deviate from the normal range defined by the preset threshold, an alarm signal is issued to prompt that the PID sensor needs maintenance or replacement.

[0015] The advantages of this invention compared to existing technologies are as follows: By setting up a source cavity, adsorption medium, and saturated VOC buffer cavity within a sealed container, and cooperating with two diffusion channels with different diffusion resistances, two VOC gases with a known concentration ratio can be generated sequentially under the same temperature conditions. Utilizing the characteristic that this ratio remains essentially constant at the same temperature, a stable concentration ratio can be obtained without high-precision temperature control of the cavity. By alternately measuring the sensor output values ​​at the two concentrations, the current calibration coefficient is calculated and compared with the factory initial coefficient to obtain the compensation factor. This simultaneously eliminates the influence of zero-point drift and gain attenuation caused by UV lamp aging on the measurement results. The device has a simple structure and can realize on-site automatic calibration and gain compensation of the PID sensor, significantly improving the long-term accuracy and reliability of the PID sensor.

[0016] 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

[0017] 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.

[0018] Figure 1 A schematic diagram of the structure of an automatic calibration device for a PID sensor provided in a specific embodiment of the present invention; Figure 2 A cross-sectional view of an automatic calibration device for a PID sensor provided in a specific embodiment of the present invention; Figure 3 A schematic diagram of an automatic calibration device for a PID sensor provided in a specific embodiment of the present invention; Figure 4 This is a flowchart illustrating an automatic calibration method for an automatic calibration device for a PID sensor, provided as a specific embodiment of the present invention.

[0019] Figure Labels 1. Sealed container; 11. Source cavity; 12. Saturated VOC buffer cavity; 121. Adsorption medium; 13. Microporous sintered sheet; 2. First pipe; 21. First diffusion channel; 3. Second pipe; 31. Second diffusion channel; 4. First solenoid valve; 5. Second solenoid valve; 6. Third solenoid valve; 7. Fourth solenoid valve; 8. Fifth solenoid valve; 9. Sixth solenoid valve; 100. PID sensor; 200. Zero filter. Detailed Implementation

[0020] 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.

[0021] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0022] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0023] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components, unless otherwise explicitly limited. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0024] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can mean that the first feature is in direct contact with the second feature, or that the first feature is in indirect contact with the second feature through an intermediate medium. Furthermore, "above," "over," and "on top" of the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0025] It should be noted that when an element is referred to as being "fixed to" or "set on" another element, it can be directly on the other element or there may be an intervening element. When an element is considered to be "connected to" another element, it can be directly connected to the other element or there may be an intervening element. The terms "vertical," "horizontal," "upper," "lower," "left," "right," and similar expressions used herein are for illustrative purposes only and do not represent the only possible implementation.

[0026] like Figures 1 to 3As shown in the figure, an automatic calibration device for a PID sensor provided in this embodiment of the invention includes a sealed container 1, which is made of corrosion-resistant stainless steel. The container is internally divided into a source cavity 11 and a saturated VOC buffer cavity 12. The source cavity 11 is used to contain liquid VOCs, such as ethanol or isobutylene. To prevent direct leakage of liquid VOCs and ensure a stable evaporation rate, the source cavity 11 is filled with an adsorption medium 121, which can be porous ceramic, molecular sieve, or high specific surface area metal fiber. The adsorption medium 121 stores the liquid VOCs by adsorption and provides a stable gas-liquid evaporation interface. The upper space of the source cavity 11 is connected to the saturated VOC buffer cavity 12, which has a larger volume than the source cavity 11 and acts as a buffer and pressure equalizer, allowing the VOC vapors evaporating from the surface of the adsorption medium 121 to be fully mixed and at a uniform temperature before entering the diffusion channel, forming saturated vapor. The sealed container 1 also has a first pipe 2 and a second pipe 3, which are respectively made of stainless steel capillary tubes or polytetrafluoroethylene tubes. The first pipe 2 has a first diffusion channel 21 inside, and the second pipe 3 has a second diffusion channel 31 inside. The inlets of both diffusion channels are connected to the saturated VOC buffer chamber 12. Because the two diffusion channels have different geometric dimensions (such as inner diameter, length, or curvature), their diffusion resistance to VOC vapor is different. According to Fick's first law, under the same temperature and pressure conditions, the VOC gas concentrations output through the two diffusion channels are stable at a first concentration and a second concentration, respectively, and the ratio of the two concentrations depends only on the size ratio of the diffusion channels and is almost unaffected by fluctuations in the external ambient temperature. The gas path switching unit consists of multiple miniature solenoid valves. The inlets of these solenoid valves are connected to the outlets of the first pipe 2 and the second pipe 3, respectively, and their outlets are all connected to the inlet of the PID sensor 100 to be calibrated. The control unit (such as a microcontroller) can selectively connect either the first pipe 2 or the second pipe 3 to the PID sensor 100 by controlling the on / off state of the solenoid valves, thereby achieving the switching of the calibration gas concentration. The above structure eliminates the need for high-precision constant temperature control of the sealed container 1 and the use of an expensive mass flow controller, greatly reducing the cost and size of the automatic calibration device.

[0027] In some embodiments, the first diffusion channel 21 and the second diffusion channel 31 are disposed inside the saturated VOC buffer chamber 12, and the first diffusion channel 21 and the second diffusion channel 31 are two capillary tubes of the same length but different inner diameters. Because of the same length but different inner diameters, their flow conductances differ, with the channel with the larger inner diameter outputting a higher VOC concentration. These two capillary tubes are directly embedded in the wall of the saturated VOC buffer chamber 12, with their inlet ends extending into the saturated VOC buffer chamber 12 and their outlet ends extending out of the saturated VOC buffer chamber 12 to connect to the gas path switching unit. This integrated design reduces connecting pipes and connectors, lowering the risk of leakage.

[0028] exist Figure 3 In the illustrated embodiment, the gas path switching unit employs a valve group consisting of six solenoid valves to achieve switching between multiple airflow modes. Specifically, the gas path switching unit includes a first solenoid valve 4, a second solenoid valve 5, a third solenoid valve 6, a fourth solenoid valve 7, a fifth solenoid valve 8, and a sixth solenoid valve 9. The inlet of the first solenoid valve 4 is connected to an external sampling gas source (i.e., the ambient air to be monitored), and its outlet is connected to the air inlet of the PID sensor 100. The inlet of the second solenoid valve 5 is connected to a zero filter 200 (i.e., a clean air source, such as a filter element containing activated carbon and a high-efficiency filter), and its outlet is also connected to the air inlet of the PID sensor 100. The inlets of the third solenoid valve 6, the fourth solenoid valve 7, and the second solenoid valve 5 are directly connected to the outlet of the zero filter 200. The outlet of the third solenoid valve 6 is connected to the inlet of the first pipe 2, the outlet of the first pipe 2 is connected to the inlet of the fifth solenoid valve 8, and the outlet of the fifth solenoid valve 8 is connected upstream of the air inlet of the PID sensor 100. Similarly, the outlet of the fourth solenoid valve 7 is connected to the inlet of the second pipe 3, the outlet of the second pipe 3 is connected to the inlet of the sixth solenoid valve 9, and the outlet of the sixth solenoid valve 9 is also connected in parallel to the upstream of the air inlet of the PID sensor 100. The outlets of the fifth solenoid valve 8, the sixth solenoid valve 9, the first solenoid valve 4, and the second solenoid valve 5 are directly connected, so the first and second pipes are connected in parallel. By controlling the switching combination of the six solenoid valves, four working modes can be achieved: normal sampling mode (first solenoid valve 4 is open, the others are closed), zero-point calibration mode (second solenoid valve 5 is open, the others are closed), low concentration calibration mode (third and fifth solenoid valves 8 are open, the others are closed), and high concentration calibration mode (fourth and sixth solenoid valves 9 are open, the others are closed). This design can utilize two solenoid valves in series (such as the third and fifth) to ensure that the second diffusion path is completely cut off during the first concentration measurement, avoiding cross-interference.

[0029] exist Figure 3 In the illustrated embodiment, a microporous sintered sheet 13 is disposed at the outlet of the source cavity 11, i.e., at the connection point between the source cavity 11 and the saturated VOC buffer cavity 12. The microporous sintered sheet can be made of sintered stainless steel, sintered ceramic, or microporous polyethylene, with an average pore size controlled between 10 and 50 micrometers. The microporous sintered sheet serves to prevent the adsorption medium 121 from clogging the diffusion channels while allowing VOC vapors to pass freely. During assembly, zeolite balls or other adsorption media 121 are first inserted into the source cavity 11, then the microporous sintered sheet is placed inside the outlet end cap of the source cavity 11, and the end cap is then sealed and secured using threads or clamps.

[0030] To achieve optimal adsorption and volatilization characteristics, the adsorption medium 121 is preferably composed of multiple zeolite spheres. Zeolite possesses a uniform microporous structure, high specific surface area, and good thermal stability. In specific implementation, zeolite spheres with a diameter of approximately 2-3 mm are selected. First, they undergo high-temperature activation treatment, and then are immersed in liquid VOCs (such as isobutylene or ethanol) to allow the zeolite spheres to fully adsorb the liquid VOCs to saturation, with an adsorption volume ratio of approximately 2:1 (the volume of liquid VOCs occupies about 2 / 3 of the zeolite sphere packing volume). Then, the saturated zeolite spheres are naturally packed to fill the entire source cavity 11. This structure ensures that the liquid VOCs are firmly locked inside the zeolite, preventing leakage even when the device is inverted. Simultaneously, the pores between and within the zeolite spheres form stable volatilization channels, enabling long-term, uniform release of VOC vapors and resulting in a long service life.

[0031] like Figures 1 to 4 As shown, this embodiment of the invention also provides an automatic calibration method based on the above-mentioned device, the method comprising the following steps: S10-S50.

[0032] S10. Provide stable VOC vapor through the VOC generation source and allow the vapor to enter the saturated VOC buffer chamber 12.

[0033] Specifically, the liquid VOC stored in the adsorption medium 121 in the source cavity 11 evaporates naturally at room temperature, and the generated vapor passes through the microporous sintered sheet 13 and enters the saturated VOC buffer cavity 12, where it stays briefly and reaches saturation.

[0034] S20, the VOC vapor in the saturated VOC buffer chamber 12 is controlled to flow through the first diffusion channel 21 and the second diffusion channel 31 respectively, thereby generating VOC gas of the first concentration and VOC gas of the second concentration respectively.

[0035] S30. Selectively introduce either a first concentration of VOC gas or a second concentration of VOC gas into the PID sensor 100 to be calibrated via the gas path switching unit.

[0036] S40. Sequentially measure and obtain the first measurement value of the PID sensor 100 for the first concentration of VOC gas and the second measurement value of the second concentration of VOC gas.

[0037] For steps S20-S40, the control unit issues a command to the gas path switching unit to first connect the first diffusion channel 21 to the PID sensor 100, allowing saturated vapor to flow through the PID sensor 100 at a first concentration, and recording the first measurement value; subsequently, the gas path switching unit connects the second diffusion channel 31, allowing saturated vapor to flow through the PID sensor 100 at a second concentration, and recording the second measurement value. Since the two measurements are completed alternately within a very short time (e.g., a few seconds), the ambient temperature during the measurements can be considered to be the same, therefore the ratio of the two concentrations is constant.

[0038] In some embodiments, step S30 specifically includes the following steps: S301-S303.

[0039] S301. Close the first solenoid valve 4, the second solenoid valve 5, the fourth solenoid valve 7 and the sixth solenoid valve 9, and open the third and fifth solenoid valves 8 to introduce VOC gas of the first concentration for the first measurement.

[0040] S302. Close the first solenoid valve 4, the second solenoid valve 5, the third solenoid valve 6 and the fifth solenoid valve 8, and open the fourth and sixth solenoid valves 9 to introduce VOC gas of the second concentration for the second measurement.

[0041] S303. Close the second solenoid valve 5, the third solenoid valve 6, the fourth solenoid valve 7, the fifth solenoid valve 8 and the sixth solenoid valve 9, and open the first solenoid valve 4 to resume normal gas sampling.

[0042] For steps S301-S303, during low-concentration VOC measurement, the control unit performs the following operations: closes the first solenoid valve 4 (cuts off the external sampling gas source), closes the second solenoid valve 5 (cuts off clean air), closes the fourth solenoid valve 7 and the sixth solenoid valve 9 (cuts off the second diffusion channel 31), and simultaneously opens the third solenoid valve 6 and the fifth solenoid valve 8. At this time, the low-concentration VOC gas output from the first diffusion channel 21 passes through the third solenoid valve 6 and the fifth solenoid valve 8 sequentially before entering the PID sensor 100, achieving the measurement of the first concentration. During high-concentration VOC measurement, the control unit closes the first solenoid valve 4, the second solenoid valve 5, the third solenoid valve 6, and the fifth solenoid valve 8, and simultaneously opens the fourth solenoid valve 7 and the sixth solenoid valve 9, allowing the high-concentration VOC gas output from the second diffusion channel 31 to enter the PID sensor 100. After completing all calibrations, the control unit closes the second solenoid valve 5, the third solenoid valve 6, the fourth solenoid valve 7, the fifth solenoid valve 8, and the sixth solenoid valve 9, opening only the first solenoid valve 4, restoring the device to normal gas sampling and monitoring status.

[0043] In some embodiments, to improve calibration accuracy, a zero-point calibration step is performed before low-concentration and high-concentration measurements. Specifically, the control unit closes the first solenoid valve 4, the third solenoid valve 6, the fourth solenoid valve 7, the fifth solenoid valve 8, and the sixth solenoid valve 9, opening only the second solenoid valve 5. At this time, clean air (VOC-free) generated by the zero filter 200 is introduced into the PID sensor 100, and the measured sensor output value is the current zero-point offset. The control unit records this zero-point offset value and automatically subtracts it when subsequently calculating the first and second measured values, thereby eliminating errors caused by changes in ambient temperature or baseline drift of the sensor itself.

[0044] S50. Calculate the current calibration coefficient based on the ratio of the first measured value to the second measured value, and compensate the subsequent measurement output of the PID sensor 100 according to the comparison result between the current calibration coefficient and the pre-stored initial calibration coefficient.

[0045] In some embodiments, step S50 specifically includes the following steps: S501-S504.

[0046] S501. Calculate the ratio of the second measurement value to the first measurement value as the current calibration coefficient.

[0047] S502: Read the initial calibration coefficients pre-stored at the factory from the PID sensor 100.

[0048] S503. Divide the current calibration coefficient by the initial calibration coefficient to obtain the compensation factor.

[0049] S504. Divide the real-time measurement value of the PID sensor 100 in normal operating mode by the compensation factor to obtain the final calibrated output value.

[0050] For steps S501-S504, firstly, the second measured value (corresponding to the high concentration) is divided by the first measured value (corresponding to the low concentration) to obtain the current calibration coefficient Kcal. For example, assuming the measured low concentration is 0.182 ppm and the high concentration is 0.256 ppm, then Kcal is approximately 1.407. Next, the initial calibration coefficient Kinit, measured under standard conditions at the time of manufacture, is read from the memory chip built into the PID sensor 100; for example, it is 1.561. Then, the compensation factor factor is calculated, which is Kcal divided by Kinit; in this example, it is approximately 0.901. This factor reflects the degree of gain attenuation relative to the factory value; a value less than 1 indicates a decrease in sensitivity. Finally, when the sensor is operating normally, the real-time measured concentration value Cact needs to be divided by this compensation factor to obtain the calibrated final output value Cfinal. Thus, even if the gain changes due to aging or contamination of the UV lamp, the sensor output can still accurately reflect the actual VOC concentration.

[0051] In some embodiments, the automatic calibration method of the PID sensor automatic calibration device further includes the following step: S60.

[0052] S60. Compare the current calibration coefficient with the preset threshold. When it is determined that the current calibration coefficient deviates from the normal range defined by the preset threshold, issue an alarm signal to prompt the PID sensor 100 to need maintenance or replacement.

[0053] Specifically, the control unit compares the calculated current calibration coefficient Kcal with a preset threshold range. This threshold range is set at the factory based on the gain variation range of the sensor during normal operation; for example, the first threshold is 0.7 and the second threshold is 1.3. If Kcal is lower than the first threshold (e.g., 0.7), it indicates that the sensor gain has been severely attenuated, possibly due to the UV lamp running out of life or severe contamination. If Kcal is higher than the second threshold (e.g., 1.3), it may indicate that the sensor has suffered unforeseen contamination or circuit failure. In either case, the control unit sends an alarm signal to the host computer via audible and visual alarms, LCD display, or communication interface, prompting the operator to clean the PID sensor 100, replace the UV lamp, or return it for factory repair. Simultaneously, although the concentration value output by the sensor continues to be compensated, the alarm message reminds the user that the reliability of the measurement result has decreased.

[0054] In summary: By setting up the source chamber 11, adsorption medium 121, and saturated VOC buffer chamber 12 within the sealed container 1, and cooperating with two diffusion channels with different diffusion resistances, two VOC gases with a known concentration ratio can be generated successively under the same temperature conditions. Utilizing the characteristic that this ratio is basically constant at the same temperature, a stable concentration ratio can be obtained without high-precision temperature control of the chamber. By alternately measuring the sensor output values ​​at the two concentrations, the current calibration coefficient is calculated and compared with the factory initial coefficient to obtain the compensation factor. This simultaneously eliminates the influence of zero-point drift and gain attenuation caused by UV lamp aging on the measurement results. The device has a simple structure and can realize on-site automatic calibration and gain compensation of the PID sensor 100, significantly improving the long-term accuracy and reliability of the PID sensor 100.

[0055] 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. An automatic calibration device for a PID sensor, characterized in that, include: A sealed container includes a source cavity, an adsorption medium, and a saturated VOC buffer cavity. The source cavity is used to contain liquid VOCs. The adsorption medium is filled inside the source cavity to adsorb and store the liquid VOCs and provide a stable volatilization interface. The saturated VOC buffer cavity is used to temporarily store saturated VOC vapors. A first pipe and a second pipe, the first pipe having a first diffusion channel and the second pipe having a second diffusion channel, the first diffusion channel and the second diffusion channel being respectively connected to the saturated VOC buffer cavity, the first diffusion channel and the second diffusion channel having different diffusion resistance, so as to generate VOC gas of a first concentration and VOC gas of a second concentration respectively. The gas path switching unit is connected to the first pipeline, the second pipeline, and the PID sensor to be calibrated, respectively, and is used to selectively connect the first pipeline or the second pipeline to the PID sensor to be calibrated.

2. The automatic calibration device for a PID sensor according to claim 1, characterized in that, The first diffusion channel and the second diffusion channel are disposed in the saturated VOC buffer cavity, and the first diffusion channel and the second diffusion channel are two capillaries of the same length but different inner diameters.

3. The automatic calibration device for a PID sensor according to claim 1, characterized in that, The gas path switching unit includes a first solenoid valve, a second solenoid valve, a third solenoid valve, a fourth solenoid valve, a fifth solenoid valve, and a sixth solenoid valve. The air inlet of the PID sensor is connected to an external sampling gas source via the first solenoid valve and to a zero filter via the second solenoid valve. The first pipeline is connected upstream of the air inlet of the PID sensor via the third solenoid valve and the fifth solenoid valve in sequence. The second pipeline is connected upstream of the air inlet of the PID sensor via the fourth solenoid valve and the sixth solenoid valve in sequence. The input end of the fifth solenoid valve is also connected in parallel with the input end of the sixth solenoid valve to the upstream of the air inlet of the PID sensor.

4. The automatic calibration device for a PID sensor according to claim 1, characterized in that, A microporous sintered sheet is provided at the outlet of the source cavity. The microporous sintered sheet is used to prevent the adsorption medium from blocking the diffusion channel, while allowing the volatilized VOC vapor to pass through and reach the saturated VOC buffer cavity.

5. The automatic calibration device for a PID sensor according to claim 1, characterized in that, The adsorption medium consists of multiple zeolite spheres, which adsorb and store liquid VOCs inside the zeolite spheres, and the zeolite spheres are packed together inside the source cavity.

6. An automatic calibration method based on the PID sensor automatic calibration device according to any one of claims 3-5, characterized in that, include: A stable VOC vapor is provided through a VOC generation source, and the vapor is then introduced into a saturated VOC buffer chamber. The VOC vapor in the saturated VOC buffer chamber is controlled to flow through the first diffusion channel and the second diffusion channel respectively, thereby generating VOC gas of the first concentration and VOC gas of the second concentration respectively. The gas path switching unit selectively introduces either a first concentration of VOC gas or a second concentration of VOC gas into the PID sensor to be calibrated. The first measurement value of the PID sensor for the first concentration of VOC gas and the second measurement value of the second concentration of VOC gas are obtained sequentially. The current calibration coefficient is calculated based on the ratio of the first measurement value to the second measurement value, and the subsequent measurement output of the PID sensor is compensated based on the comparison result between the current calibration coefficient and the pre-stored initial calibration coefficient.

7. The automatic calibration method of the PID sensor automatic calibration device according to claim 6, characterized in that, The selective introduction of a first concentration of VOC gas or a second concentration of VOC gas into the PID sensor to be calibrated via the gas path switching unit includes: Close the first, second, fourth, and sixth solenoid valves, and open the third and fifth solenoid valves to introduce VOC gas of the first concentration for the first measurement. Close the first, second, third, and fifth solenoid valves, and open the fourth and sixth solenoid valves to introduce VOC gas of a second concentration for a second measurement. Close the second, third, fourth, fifth, and sixth solenoid valves, and open the first solenoid valve to resume normal gas sampling.

8. The automatic calibration method of the PID sensor automatic calibration device according to claim 6, characterized in that, The calculation of the current calibration coefficient based on the ratio of the first measured value to the second measured value, and the compensation of the subsequent measurement output of the PID sensor based on the comparison result of the current calibration coefficient and the pre-stored initial calibration coefficient, includes: Calculate the ratio of the second measurement to the first measurement as the current calibration coefficient; Read the initial calibration coefficients pre-stored at the factory from the PID sensor; Divide the current calibration coefficient by the initial calibration coefficient to obtain the compensation factor; Divide the real-time measurement value of the PID sensor in normal operating mode by the compensation factor to obtain the calibrated final output value.

9. The automatic calibration method of the PID sensor automatic calibration device according to claim 7, characterized in that, Before closing the first, second, fourth, and sixth solenoid valves and opening the third and fifth solenoid valves to introduce VOC gas of the first concentration for the first measurement, the procedure further includes: Close the first, third, fourth, fifth, and sixth solenoid valves, and open the second solenoid valve to introduce clean air through the zero filter for zero-point measurement.

10. The automatic calibration method of the PID sensor automatic calibration device according to claim 8, characterized in that, Also includes: The current calibration coefficient is compared with a preset threshold. When the current calibration coefficient is determined to deviate from the normal range defined by the preset threshold, an alarm signal is issued to prompt that the PID sensor needs maintenance or replacement.

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