A method for improving the detection accuracy of a portable β-ray particulate matter monitor

Abstract

The invention relates to the technical field of particle monitors, and specifically discloses a method for improving the detection accuracy of a portable beta-ray particle monitor. The method comprises the following steps: at a specific time before and after the start of a vacuum pump sampling process, by detecting and counting paper tape points between a beta radiation source and a beta ray detector, a concentration compensation value caused by changes such as temperature during a sampling period can be calculated by a concentration calculation formula; after an effective judgment is made on the calculated concentration compensation value, the sampling concentration is finally compensated, thereby reducing the influence of temperature factors on the measured value of the particle concentration after sampling; before formally starting the sampling, the vacuum pump is turned on for air extraction operation, so that the paper tape undergoes a certain deformation, thereby reducing the deviation between the measured value of the particle concentration after sampling and its true value; and a DHS system adopts PID dynamic adjustment to prevent overcharging due to heating, thereby reducing the influence of unreasonable heating methods on the measured value of the particle concentration after sampling.

Description

Technical Field

[0001] The invention belongs to the technical field of particle monitors, and in particular relates to a method for improving the detection accuracy of a portable beta-ray particle monitor. Background Art

[0002] At present, the application of β-ray particle monitoring instruments is mainly divided into online and portable, and the environments in which the two are used are obviously different. Online instruments are mainly used in indoor constant temperature and humidity environments, and the entire measurement system is relatively stable. Portable instruments are mainly used for outdoor point monitoring and are greatly affected by seasonal weather and other factors. For portable β-ray particle monitoring instruments, while ensuring accurate mechanical precision, the measurement process is still affected by external factors such as temperature changes inside the instrument, air density between the radiation source and the detector, and filter membrane deformation, making it difficult to ensure monitoring accuracy.

[0003] In addition, my country has a vast territory, and the geographical and climatic environmental conditions vary greatly between the north and south, and between the east and west. In particular, the high temperature and high humidity in the south and the high wind speed and high altitude in the west can easily lead to moisture in the measuring unit of portable instruments. Due to the constraints of the measurement principle of portable instruments, if moisture is mixed into the measuring unit of the instrument, it will greatly interfere with the measurement results. In order to minimize the impact of this problem, the solution of existing portable instruments is usually to heat the sampling tube. However, when faced with complex situations such as high temperature and humidity and drastic changes in temperature and humidity, it is necessary to remove moisture from the particulate matter and avoid the loss of volatile substances caused by high-temperature heating. In addition, the dehumidification and heating process of the dynamic heating system (DHS) will cause part of the heat to be transferred into the instrument through the connector, so a reasonable heating control method needs to be adopted.

[0004] The portable β-ray particulate monitoring instrument is affected by outdoor sunlight, weather changes, heat conduction of the DHS heating system, heating of internal components of the instrument, etc. The temperature change during the measurement cycle will cause a significant change in the air density between the radiation source and the detector, and the sampling process of the sampling pump will cause a slight deformation of the filter membrane, resulting in changes in the count value before and after sampling. The temperature change cannot make the portable instrument and the online instrument in a stable environment to compensate through the background value within the cycle. In addition, the unreasonable DHS heating and dehumidification control method cannot well balance the retention of moisture and volatile substances in the air, which will further affect the accuracy of the particle concentration. Summary of the invention

[0005] The purpose of the present invention is to provide a method for improving the detection accuracy of a portable beta-ray particle monitor. The method provided by the present invention can reduce the influence of factors such as temperature, filter membrane deformation, and DHS dynamic heating system on the particle concentration measurement results.

[0006] To achieve the above object, the present invention provides the following technical solution: A method for improving the detection accuracy of a portable β-ray particulate matter monitor, the method being:

[0007] First, calculate the temperature compensation value T 补 = T1 - T2, and the temperature change value T before and after sampling = T0 - T x , where T1 is the temperature between the β-ray detector and the β-ray source where the second tape is located at the start of the first tape sampling; T2 is the temperature between the β-ray detector and the β-ray source where the second tape is located before the completion of the first tape sampling; T0 is the temperature between the β-ray detector and the β-ray source where the first tape is located before sampling; T x is the temperature between the β-ray detector and the β-ray source where the first tape is located after sampling;

[0008] Then, when T ≥ 1°C, calculate the compensation value m of the concentration through the formula I2 = I1exp(-λm 补 ), where I1 is the intensity of the second tape irradiated by the β-ray at the start of the first tape sampling; I2 is the intensity of the second tape irradiated by the β-ray before the completion of the first tape sampling; λ is the absorption coefficient per unit area of the tape; 补

[0009] Finally, when the values of T 补 , m 补 are all positive, the compensation value m of the concentration is effective, and the compensated sampled particulate matter concentration is m + m 补 ; when the values of T 补 , m 补 are all negative, the compensation value m of the concentration is also effective, and the compensated sampled particulate matter concentration is m - m 补 补 . 补

[0010] Preferably, in order to reduce the concentration measurement deviation caused by the deformation of the first tape before and after sampling, before sampling starts, a pumping operation is performed on the first tape to cause a certain deformation of the first tape.

[0011] Preferably, in order to reduce the concentration measurement deviation caused by an unreasonable heating control method, the method further includes detecting the temperature and humidity of the ambient air, denoted as T 环 , H 环 , detecting the temperature and humidity of the air entering the portable β-ray particulate matter monitor, denoted as T 仪 , H 仪 , and judging that when H 仪 < H 设 , it indicates that the moisture in the current monitor internal air will not have a great impact on the measurement of particulate matter, and DHS is not started; when H 仪 > H设 When it is time, the DHS starts to heat up and dynamically adjusts the humidity to H through PID 设 around, H 设 is the set humidity.

[0012] Preferably, after the DHS starts to heat up, calculate T 仪 -T 环 >Δt, control to reduce the heating power of the DHS or stop heating, where Δt is the defined temperature of the portable β-ray particulate matter monitor.

[0013] Preferably, after the DHS starts to heat up, during the process of heating and dehumidifying, if the heating temperature is too high and exceeds the upper limit of the DHS temperature, the temperature switch of the DHS will disconnect and stop heating; when the temperature exceeds the protection temperature set by the system, the system will disconnect the power supply of the DHS and stop heating.

[0014] Preferably, during the interval between the end of one sampling period and the start of the second sampling period, the DHS maintains the heating power at the end of the first sampling period unchanged.

[0015] Advantages of the present invention:

[0016] Before the formal sampling starts, the paper tape sampling point is moved to directly below the sampling nozzle through the lead screw motion mechanism, and the vacuum pump is turned on for air extraction operation, causing a certain deformation of the paper tape. The advantage of this operation is that during the formal sampling, the change in the measured thickness of the paper tape is reduced, and thus the deviation between the measured value of the particulate matter concentration after sampling and its true value is reduced;

[0017] At specific times before and after the start of the vacuum pump sampling process, by detecting and counting the paper tape points between the β radiation source and the β-ray detector, the compensation value of the concentration caused by changes in temperature, etc. during the sampling period can be calculated through the concentration calculation formula; after effectively judging the calculated concentration compensation value, finally, the sampling concentration is compensated, thereby reducing the influence of temperature factors on the measured value of the particulate matter concentration after sampling;

[0018] The DHS system adopts PID dynamic regulation to prevent overheating. The temperature difference between the heated gas and the ambient air is controlled within a certain range, reducing the influence of unreasonable heating methods on the measured value of the particulate matter concentration after sampling. Description of the Drawings

[0019] Figure 1 is a schematic structural diagram of the portable β-ray particulate matter monitor in Embodiment 1;

[0020] Figure 2 is a schematic diagram of the sampling process of the portable β-ray particulate matter monitor in Embodiment 1;

[0021] Figure 3 Schematic diagram of the sampling process of the portable β-ray particulate matter monitor in Embodiment 1;

[0022] Figure 4 Schematic diagram of the sampling process of the portable β-ray particulate matter monitor in Embodiment 1;

[0023] Figure 5 Schematic diagram of the sampling process of the portable β-ray particulate matter monitor in Embodiment 1;

[0024] Figure 6 Schematic diagram of the structure of the portable β-ray particulate matter monitor in Embodiment 2;

[0025] Figure 7 For Figure 6 Schematic diagram of the structure of the dynamic heating system in

[0026] Annotations in the figure:

[0027] Particulate matter cutter 1, dynamic heating tube 2, sampling nozzle 3, paper tape 4, air extraction port 5, flow regulating valve 6, vacuum pump 7, β-ray detector 8, β-ray source 9, dynamic heating system 10, dynamic heating tube 101, silica gel heating plate 102, temperature switch 103, temperature sensor 104, temperature control system 105. Detailed implementation manners

[0028] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the invention. Obviously, the described embodiments are only a part of the embodiments of the invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0029] Given the formula I = I0exp(-λm), where: I is the ray intensity after the β-ray penetrates the diaphragm, I0 is the ray intensity when there is no diaphragm blocking the β-ray, λ is the absorption coefficient per unit area of the diaphragm, and m is the weight per unit area of the diaphragm. It can be seen from this formula that the particulate matter concentration is mainly related to the attenuation change of the β-ray intensity at the same sampling point before and after sampling.

[0030] The analysis of the influence of temperature and filter membrane deformation is as follows:

[0031] The change in the measured thickness of the filter membrane after sampling will cause a change in the ray intensity passing through the filter membrane, and further cause a deviation between the measured value and the true value of the mass of the filter membrane after sampling.

[0032] Air density = 1.293 * (actual pressure / standard physical atmospheric pressure) × (273.15 / actual absolute temperature)... Formula (a)

[0033] Absolute temperature = Celsius temperature + 273.15... Formula (b)

[0034] As can be seen from Formula (a) and Formula (b), the change in temperature will cause the change in air density. The change in air density, that is, the change in the mass of air per unit volume, will directly affect the number of photons that the β-ray source irradiates on the β-ray detector through the paper tape.

[0035] Example 1

[0036] This example provides a method for improving the detection accuracy of a portable β-ray particulate matter monitor, which can reduce the influence of filter membrane deformation and temperature on the particulate matter measurement results. First, introduce the basic structure of the portable β-ray particulate matter monitor in this example, including a particulate matter cutter 1, a dynamic heating tube 2, a sampling nozzle 3, a paper tape 4, an air extraction port 5, a flow regulating valve 6, a vacuum pump 7, a β-ray detector 8, a β-ray source 9, and a lead screw motion mechanism (not shown in the figure). The above structures are all the structures of the portable β-ray particulate matter monitor in the prior art, and the connection relationship will not be elaborated. In this example, the positions ① of 1 section of the paper tape and ② of 2 sections of the paper tape are marked on the paper tape 4. At the initial position, as Figure 1 shown, position ① is located between the β-ray detector 8 and the β-ray source 9, and position ② is located on the right side of position ①. The left and right in this example are based on the positions shown in the drawings of this example.

[0037] When the measurement period (such as 1 hour) starts, the paper tape 4 moves from right to left along with the lead screw motion mechanism in the direction of the arrow. The paper tape 4 moves from position ① to Figure 2 the position shown, that is, directly below the sampling nozzle 3, and position ② moves to Figure 2 the position shown, that is, between the β-ray detector 8 and the β-ray source 9. After the lead screw motion mechanism sends the paper tape 4 to the above position and stabilizes it, the sampling nozzle 3 descends to press the paper tape 4 tightly, and the vacuum pump 7 is started to extract air for a specific time (such as 4 minutes). The purpose of such an operation is to ensure to a certain extent that before the formal air extraction and sampling, the paper tape 4 generates a certain deformation, and the change in the measured thickness of the paper tape 4 after the formal sampling is reduced, so that the deviation between the measured value of the particulate matter mass on the paper tape after sampling and its true value is reduced.

[0038] After the above air extraction operation is completed, the sampling nozzle 3 rises. As Figure 2 shown, the paper tape 4 moves from left to right along with the lead screw motion mechanism in the direction of the arrow. The position ① of the paper tape 4 moves to Figure 3 the position, that is, between the β-ray detector 8 and the β-ray source 9, and position ② moves to Figure 3The initial state position of the measurement shown. After the lead screw motion mechanism transports the 4-point of the paper tape to the above position and stabilizes, the β-ray detector 8 is turned on for a specific time (such as 4 minutes) to detect the optical signal of the β radiation source 9 irradiating the β-ray detector 8 through the 1-segment paper tape at position ①, and the counting unit counts it as I0, and records the temperature between the β-ray detector 8 and the β-ray source 9 at this time as T0.

[0039] After the above detection is completed, as Figure 3 shown, the paper tape 4 moves from right to left along with the lead screw motion mechanism in the direction of the arrow. The position ① of the paper tape 4 moves to Figure 4 the position, that is, directly below the sampling nozzle 3, and the position ② moves to Figure 4 the position shown, that is, between the β-ray detector 8 and the β-ray source 9. After the lead screw motion mechanism transports the 4-point of the paper tape to the above position and stabilizes, at this time the sampling nozzle 3 descends to press the paper tape 4 tightly, the vacuum pump 7 is started, and air is pumped for a specific time (such as 45 minutes) to start the formal sampling. During the sampling time period, simultaneously with the start of the vacuum pump 7, the β-ray detector 8 is turned on for a specific time (such as 4 minutes) to detect the optical signal of the β radiation source 9 irradiating the β-ray detector 8 through the 2-segment paper tape at position ②, and the counting unit counts it as I1, and records the temperature between the β-ray detector 8 and the β-ray source 9 at this time as T1. Before the specific time of air pumping is completed (such as 4 minutes), the β-ray detector 8 is turned on again to detect the optical signal of the β radiation source 9 irradiating the β-ray detector 8 through the paper tape at position ②, and the counting unit counts it as I2, and records the temperature between the β-ray detector 8 and the β radiation source 9 at this time as T2.

[0040] When the specific time of sampling air pumping (such as 45 minutes) is completed, the vacuum pump 7 stops, and the sampling nozzle 3 rises. As Figure 4 shown, the paper tape 4 moves from left to right along with the lead screw motion mechanism in the direction of the arrow. The position ① of the paper tape 4 moves to Figure 5 the position, that is, between the β-ray detector 8 and the β-ray source 9, and the position ② moves to Figure 5 the initial state position of the measurement shown. After the lead screw motion mechanism transports the 4-point of the paper tape to the above position and stabilizes, the β-ray detector 8 is turned on for a specific time (such as 4 minutes) to detect the optical signal of the β radiation source 9 irradiating the β-ray detector 8 through the paper tape at position ① (with sampling dust spots), and the counting unit counts it as I x , and records the temperature between the β-ray detector 8 and the β-ray source at this time as T x .

[0041] After the above pre-sampling air pumping process and sampling process, we can calculate the temperature compensation value T 补 = T1 - T2 (1), and the temperature change value before and after sampling T = T0 - T x (2).

[0042] Due to the inherent uncertainty (about 3‰) of the portable β-ray particulate matter monitor, especially when the temperature change before and after the sampling period is not obvious (<1℃), the uncertainty will cause deviation in compensation. Therefore, the temperature drift can be judged according to the above formula (2).

[0043] When T≥1℃, the compensation value m of the concentration is calculated by the formula I2 = I1exp(-λm 补 )(3), where I1 is the intensity of the β-ray irradiation on the second tape at the start of the sampling of the first tape; I2 is the intensity of the β-ray irradiation on the second tape before the completion of the sampling of the first tape; and λ is the absorption coefficient per unit area of the tape. 补

[0044] The validity of the compensation value m 补 can be judged by formula (1). When T 补 and m 补 are both positive, the compensation value m of the concentration is valid, and the compensated sampling particulate matter concentration is m + m 补 ; when T 补 and m 补 are both negative, the compensation value m of the concentration is valid, and the compensated sampling particulate matter concentration is m - m 补 . 补 补

[0045] Embodiment 2

[0046] This embodiment provides a method for improving the detection accuracy of a portable β-ray particulate matter monitor. By the method of this embodiment, the influence caused by the unreasonable heating method of the dynamic heating system on the measurement result of the particulate matter concentration can be reduced. On the basis of Embodiment 1, the portable β-ray particulate matter monitor of this embodiment further includes a dynamic heating system 10 (DHS), which includes a dynamic heating tube 101, a silica gel heating plate 102, a temperature switch 103, a temperature sensor 104, and a temperature control system 105. Further, the particulate matter monitor also includes a temperature and humidity module 11 for detecting the temperature and humidity of the air entering the interior of the monitor.

[0047] When the sampling period starts, the vacuum pump 7 is started and adjusted to a stable flow rate through the flow control valve 6. The ambient air passes through the particulate matter cutter 1 to cut the particle size of the particulate matter in the ambient air. After removing the moisture in the particulate matter through the dynamic heating system 10 first, it passes through the sampling nozzle 3 and the paper tape 4 for the collection of the particulate matter.

[0048] Due to the limitation of the working principle of the portable β-ray particulate matter monitor, if moisture enters the measurement unit of the instrument, it will cause great interference to the measurement result. To solve this problem, a reasonable heating control method needs to be adopted.​​​

[0049] This embodiment is implemented through the following steps:

[0050] First, detect the temperature and humidity of the ambient air, denoted as T 环 , H 环 , and preliminarily judge the current ambient conditions based on the temperature and humidity of the ambient air.

[0051] Then, when the sampling period starts, measure the temperature and humidity of the air entering the particulate matter monitoring through the temperature and humidity module 11, denoted as T 仪 , H 仪 .

[0052] When H 仪 <H 设 , it indicates that the moisture in the air inside the current particulate matter monitor will not have a great impact on the measurement of particulate matter, and DHS does not start; when H 仪 >H 设 , DHS starts the silica gel heating plate 102 for heating and dynamically adjusts the humidity to about H 设 , where H 设 is the humidity set by the system. During the heating and dehumidification process, if the heating temperature is too high, when the temperature exceeds the upper temperature limit defined by the temperature switch 103, the temperature switch 103 will disconnect and stop the power supply heating of the silica gel heating plate 102; when the temperature exceeds the protection temperature set by the system, the system will stop the dynamic adjustment, that is, stop the power supply heating of the silica gel heating plate 102.

[0053] Due to the heating and dehumidification of the DHS system, the temperature of the passing ambient air will increase. When the incoming air temperature T 仪 - T 环 >Δt, where Δt is the temperature limit set by the system, such as 10 °C, the system automatically reduces the heating power or stops heating.

[0054] When waiting for the interval period of the second sampling cycle after one sampling cycle ends, the system maintains the DHS heating power at the end of the first sampling cycle unchanged.

[0055] Although the embodiments of the invention have been shown and described, for those of ordinary skill in the art, it can be understood that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the invention. The scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A method for improving the detection accuracy of a portable β-ray particulate matter monitor, characterized in that, The method is as follows: First, calculate the temperature compensation value T 补 = T1 - T2, and the temperature change value before and after sampling T = T0 - T x , where T1 is the temperature between the β-ray detector and the β-ray source where the second tape is located at the start of sampling of the first tape; T2 is the temperature between the β-ray detector and the β-ray source where the second tape is located before the completion of sampling of the first tape; T0 is the temperature between the β-ray detector and the β-ray source where the first tape is located before sampling; T x is the temperature between the β-ray detector and the β-ray source where the first tape is located after sampling; Then, when T ≥ 1°C, the compensation value m of the concentration is calculated through the formula I2 = I1exp(-λm 补 ) 补 , where I1 is the intensity of the β-ray irradiation on the second tape at the start of the sampling of the first tape; I2 is the intensity of the β-ray irradiation on the second tape before the completion of the sampling of the first tape; λ is the absorption coefficient per unit area of the tape; Finally, when T 补 , m 补 are both positive, the concentration compensation value m 补 is valid, and the sampled particulate matter concentration after compensation is m + m 补 ; when T 补 , m 补 are both negative, the concentration compensation value m 补 is also valid, and the sampled particulate matter concentration after compensation is m - m 补 .

2. The method for improving the detection accuracy of a portable β-ray particulate matter monitor according to claim 1, wherein: To reduce the concentration measurement deviation caused by deformation before and after sampling of the first section of the paper tape, before the sampling starts, an air extraction operation is performed on the first section of the paper tape to cause a certain deformation of the first section of the paper tape.

3. The method for improving the detection accuracy of a portable β-ray particulate matter monitor according to claim 1, wherein To reduce the concentration measurement deviation caused by unreasonable heating control methods, the method further includes detecting the temperature and humidity of the ambient air, denoted as T 环 , H 环 , detecting the temperature and humidity of the air entering the portable β-ray particulate matter monitor, denoted as T 仪 , H 仪 , and judging that when H 仪 <H 设 , it indicates that the moisture in the current monitor's internal air will not have a great impact on the measurement of particulate matter, and DHS does not start; when H 仪 >H 设 , DHS starts heating and dynamically adjusts the humidity to around H 设 , where H 设 is the set humidity.

4. The method for improving the detection accuracy of a portable β-ray particulate matter monitor according to claim 3, characterized in that: After the DHS starts heating, calculate T 仪 -T 环 > Δt, control to reduce the heating power of the DHS or stop heating, where Δt is the defined temperature of the portable β-ray particulate matter monitor.

5. The method for improving the detection accuracy of a portable beta-ray particulate matter monitor according to claim 3, wherein: When the DHS starts to heat, during the heating and dehumidification process, if the heating temperature is too high and exceeds the temperature upper limit of the DHS, the temperature switch of the DHS will disconnect and stop heating; when the temperature exceeds the protection temperature set by the system, the system will disconnect the power supply of the DHS and stop heating.

6. The method for improving the detection accuracy of a portable β-ray particulate matter monitor according to claim 3, wherein: During the interval when one sampling cycle ends and waits for the start of the second sampling cycle, the DHS maintains the heating power at the end of the first sampling cycle unchanged.

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