Device for calibrating a particle number measuring device, calibration program, method for determining a particle size for calibration, and method for calibrating a particle number measuring device

Abstract

A device for calibrating a particle counting measuring device, a calibration program, a method for determining a particle size for calibration, and a method for calibrating a particle counting measuring device are provided, with which it is possible to reduce the effect of a change in particle size after classification and perform more accurate calibration. The calibration device 1 comprises: a particle generation unit 10; an input unit 51; a particle classification unit 20; a particle detection unit 30;a calculation unit 52 that, based on the particle size distribution of the particles at the particle detection unit 30a or a physical size factor that causes a change in the particle size at the particle detection unit 30, obtains a degree of change by which the particle size of particles arriving at the particle detection unit 30 has changed from a target particle size, and, based on the degree of change, calculates a correction amount for the particle size extracted by the particle classification unit 20 so that the particle size arriving at the particle detection unit 30 matches the target particle size; and a correction instruction unit 53 that, based on the correction amount calculated by the calculation unit 52, informs the particle classification unit 20;

Description

Calibration equipment for particle number measurement device, calibration program, method for determining particle diameter for calibration, and method for calibrating particle number measurement device

[0001] The present disclosure relates to a calibration facility for a particle number measurement device, a calibration program, a method for determining a particle diameter for calibration, and a method for calibrating a particle number measurement device.

[0002] In recent years, in order to improve the cleanliness of automobile exhaust gases, it has become increasingly important to count the number of particles in exhaust gases that are smaller in particle size than conventional ones, so-called nanoparticle-level particles. To measure such nanoparticle-level particles, particle number measurement devices such as condensation particle counters (CPCs) are used. In order to accurately count fine particles using particle number measurement devices, the particle number measurement devices must be properly calibrated. Conventionally, particle number measurement devices have been calibrated by counting particles of a predetermined particle size using a particle generator that generates droplet particles and a particle classifier that classifies the particles generated by the particle generator.

[0003] On the other hand, Patent Document 1 describes that evaporation occurs in liquid particles, causing a change in the particle size of the liquid particles, and Patent Document 2 describes that the counting efficiency of a condensation particle counter varies depending on the particle size.

[0004] Japanese Patent Application Laid-Open No. 2008-185559 Japanese Patent Publication No. 7-104259

[0005] However, in the calibration equipment and calibration methods of conventional particle number measuring devices using particle classifiers, calibration is performed assuming that particles of a desired particle diameter are extracted by the particle classifier, and no consideration is given to the possibility that the particle diameter of the particles classified and extracted by the particle classifier may change.

[0006] An object of the present disclosure is to provide calibration equipment for a particle number measuring device, a calibration program, a method for determining a particle diameter for calibration, and a method for calibrating a particle number measuring device, which are capable of reducing the influence of changes in particle diameter after classification and performing more accurate calibration.

[0007] The present disclosure solves the above-mentioned problems by the following means: For ease of understanding, the following description will be given with reference numerals corresponding to the embodiments of the present disclosure, but the present disclosure is not limited to these.

[0008] The first disclosure is a calibration facility (1, 1B) for a particle number measurement device (31) used for calibrating the particle number measurement device (31), comprising: a particle generation unit (10) that generates particles; an input unit (51) that receives an input of a target particle diameter; a particle classification unit (20) that classifies the particles generated from the particle generation unit (10) and extracts particles that correspond to the target particle diameter received by the input unit (51); a particle detection unit (30) that detects the particles extracted by the particle classification unit (20); and a physical quantity factor that causes a change in particle diameter in the particle detection unit (30) or a particle diameter classification unit (30) that detects the particles extracted by the particle detection unit (30). a calculation unit (52) that calculates a degree of change in particle diameter of particles that have reached the particle detection unit (30) from the target particle diameter based on a distribution, and calculates a correction amount for the particle diameter extracted by the particle classifying unit (20) based on the degree of change so that the particle diameter of particles that have reached the particle detection unit (30) becomes the target particle diameter; and a correction instruction unit (53) that instructs the particle classifying unit (20) to change the particle diameter of particles that have been extracted by the particle classifying unit (20) to a calibration particle diameter based on the correction amount calculated by the calculation unit (52).

[0009] The second disclosure is a calibration facility (1, 1B) for the particle number measuring device (31) described in the first disclosure, which includes a physical quantity factor detection unit (40) that detects the physical quantity factor, and the calculation unit (52) calculates the correction amount using at least the physical quantity factor obtained by the physical quantity factor detection unit (40).

[0010] The third disclosure is a calibration facility (1, 1B) for the particle number measuring device (31) described in the first disclosure, which includes a particle size distribution measuring unit (33) that is provided in the particle detection unit (30) and detects the particle size distribution of particles that reach the particle detection unit (30), and the calculation unit (52) calculates the correction amount using the particle size distribution detected by the particle size distribution measuring unit (33).

[0011] A fourth disclosure is a calibration facility (1, 1B) for a particle number measuring device (31) according to claim 1 or claim 2, wherein the physical quantity factor is at least one of temperature, humidity, pressure, flow rate, and residence time of a fluid in a flow path from the particle classification unit (20) to the particle detection unit (30).

[0012] A fifth disclosure is a calibration facility (1) for a particle number measuring device (31) described in the third disclosure, wherein the particle size distribution measuring unit (33) includes a second particle classification unit (34) that classifies particles that reach the particle size distribution measuring unit (33), and a particle number counting unit (35) that is connected downstream of the second particle classification unit (34) and counts the number of particles classified by the second particle classification unit (34).

[0013] A sixth disclosure is a calibration facility (1) for a particle number measuring device (31) according to the third or fifth disclosure, wherein the input unit (51) can receive a function of detection efficiency indicating the detection efficiency for each particle diameter of the particle number measuring device (31) to be calibrated, and the calculation unit (52) calculates the detection efficiency achieved by the particle number measuring device (31) to be calibrated at the target particle diameter using the particle diameter distribution detected by the particle size distribution measurement unit (33).

[0014] A seventh disclosure is a calibration facility (1, 1B) for a particle number measuring device (31) described in any of the first to sixth disclosures, wherein the correction instruction unit (53) instructs the particle classifying unit (20) to change a voltage applied to a classification tube provided in the particle classifying unit (20).

[0015] The eighth disclosure is a calibration equipment (1, 1B) for a particle number measuring device (31) described in any of the first to seventh disclosures, wherein the particles generated by the particle generating section (10) are mainly composed of polyalphaolefin, and the solvent for diluting the polyalphaolefin is ethanol in a weight ratio of 50% or more.

[0016] A ninth disclosure is a calibration facility (1, 1B) for a particle number measuring device (31) according to any one of the first to eighth disclosures, wherein the flow path from the particle generating unit (10) to the particle classifying unit (20) is an evaporation flow path in which evaporation of components from the surfaces of particles is carried out in advance so that a rate of reduction in particle diameter due to evaporation of components from the surfaces of particles in the flow path from the particle classifying unit (20) to the particle detecting unit (30) is less than 3%.

[0017] The tenth disclosure is a calibration program used for calibrating a particle number measuring device (31), the program including, in a computer (50), a step in which a particle generating unit (10) generates particles; a step in which an input unit (51) receives input of a target particle diameter from a user; a step in which a particle classifying unit (20) classifies the particles generated from the particle generating unit (10) and extracts particles corresponding to the target particle diameter received by the input unit (51); a step in which a particle detecting unit (30) detects the particles extracted by the particle classifying unit (20); and a calculation unit (52) calculates a physical quantity factor that causes a change in the particle diameter in the particle detecting unit (30), or is a calibration program for executing the steps of: determining a degree of change in the particle diameter of particles that have reached the particle detection unit (30) from the target particle diameter, based on the particle diameter distribution of the particles at the particle detection unit (30); and calculating a correction amount for the particle diameter extracted by the particle classification unit (20) based on the degree of change so that the particle diameter of particles that have reached the particle detection unit (30) becomes the target particle diameter; and a correction instruction unit (53) instructing the particle classification unit (20) to change the particle diameter of the particles that have been extracted by the particle classification unit (20) to a calibration particle diameter, based on the correction amount calculated by the calculation unit (52).

[0018] An eleventh disclosure is the calibration program according to the tenth disclosure, which includes a step in which a physical quantity factor detection unit (40) detects the physical quantity factor, and the calculation unit (52) calculates the correction amount using at least the physical quantity factor obtained by the physical quantity factor detection unit (40).

[0019] A twelfth disclosure is the calibration program according to the tenth disclosure, which includes a step in which a particle size distribution measuring unit (33) detects a particle size distribution of particles that reach the particle detection unit (30), and the calculation unit (52) calculates the correction amount using the particle size distribution detected by the particle size distribution measuring unit (33).

[0020] The thirteenth disclosure is a method for determining a calibration particle diameter used for calibrating a particle number measuring device (31), the method comprising: a step in which a particle generating unit (10) generates particles; a step in which an input unit (51) receives input of a target particle diameter from a user; a step in which a particle classifying unit (20) classifies the particles generated from the particle generating unit (10) and extracts particles corresponding to the target particle diameter received by the input unit (51); a step in which a particle detecting unit (30) detects the particles extracted by the particle classifying unit (20); and a calculation unit (52) calculates a physical quantity factor that causes a change in the particle diameter in the particle detecting unit (30), or The method for determining a calibration particle diameter includes the steps of: determining a degree of change in particle diameter of particles that have reached the particle detection unit (30) from the target particle diameter based on the particle diameter distribution of the particles at the particle detection unit (30); and calculating a correction amount for the particle diameter extracted by the particle classification unit (20) based on the degree of change so that the particle diameter of particles that have reached the particle detection unit (30) becomes the target particle diameter; and a step of instructing the particle classification unit (20) to change the particle diameter of the particles that have reached the particle detection unit (30) to the calibration particle diameter based on the correction amount calculated by the calculation unit (52) using a correction instruction unit (53).

[0021] A fourteenth disclosure is the method for determining a calibration particle diameter according to the thirteenth disclosure, comprising a step in which a physical quantity factor detection unit (40) detects the physical quantity factor, and the calculation unit (52) calculates the correction amount using at least the physical quantity factor obtained by the physical quantity factor detection unit (40).

[0022] The fifteenth disclosure is the method for determining a particle diameter for calibration according to the thirteenth disclosure, which includes a step in which a particle diameter distribution measuring unit (33) detects a particle diameter distribution of particles that reach the particle detection unit (30), and the calculation unit (52) calculates the correction amount using the particle diameter distribution detected by the particle diameter distribution measuring unit (33).

[0023] A sixteenth disclosure is a method for calibrating a particle number measuring device (31), in which the particle classifying unit (20) extracts particles according to a calibration particle diameter determined by the method for determining a calibration particle diameter described in any of the thirteenth to fifteenth disclosures, and the particle number measuring device (31) to be calibrated is calibrated using the particles having the calibration particle diameter extracted by the particle classifying unit (20).

[0024] According to the present disclosure, it is possible to provide calibration equipment for a particle number measuring device, a calibration program, a method for determining a particle diameter for calibration, and a method for calibrating a particle number measuring device, which are capable of reducing the influence of changes in particle diameter after classification and performing more accurate calibration.

[0025] 1 is a block diagram showing the configuration of calibration equipment 1 for a particle number measurement device according to a first embodiment. FIG. 2 is a diagram showing an example of a function of detection efficiency indicating the detection efficiency for each particle diameter of a particle number measurement device 31. FIG. 3 is a diagram summarizing the configurations of the flow path F1 before classification and the flow path F4 after classification used in an experiment to investigate the relationship between particle residence time in the flow path and particle shrinkage. FIG. 4 is a diagram plotting the effect of post-classification residence time on the particle diameter reaching the particle detection unit 30 for each pre-classification residence time. FIG. 5 is a diagram showing the effect of pre-classification residence time on shrinkage rate. FIG. 6 is a diagram showing the flow of operations when a method for determining a calibration particle diameter and a calibration method, which are mainly performed by the control unit 50. FIG. 7 is a diagram summarizing the detection efficiencies calculated for each particle diameter in each of the examples and comparative examples. FIG. 8 is a diagram plotting the results of particle diameter change ΔDp (nm) due to evaporation calculated as the difference between the classified particle diameter and the measured particle diameter for each measured particle diameter. FIG. 9 is a diagram showing the difference in detection efficiency between the comparative example and the examples at a particle diameter of 10 nm. FIG. 10 is a diagram showing the difference in detection efficiency between the comparative example and the examples at a particle diameter of 15 nm. FIG. 10 is a block diagram showing the configuration of a calibration facility 1B for a particle number measurement device according to a second embodiment.

[0026] Hereinafter, an embodiment of the present disclosure will be described with reference to the drawings.

[0027] (First embodiment) Fig. 1 is a block diagram showing the configuration of a calibration facility 1 for a particle number measurement device according to a first embodiment. Note that Fig. 1 and the other figures shown below are schematic diagrams, and the size and shape of each part are exaggerated or omitted as appropriate for ease of understanding. In addition, the following description will be given using specific numerical values, shapes, materials, etc., but these can be changed as appropriate.

[0028] The calibration equipment 1 for a particle number measurement device includes a particle generator 10, a first particle classifier 20, a particle detection unit 30, a physical quantity factor detection unit 40, and a control unit 50, and is used when calibrating a particle number measurement device 31 that is the object of calibration.

[0029] The particle generator (particle generating unit) 10 is an electrospray device that generates a large number of liquid particles. The particles generated by the particle generator 10 of this embodiment are made of a material collectively known as polyalphaolefin (PAO). In the particle generator 10 of this embodiment, this polyalphaolefin is used in a state diluted with a solvent primarily composed of ethanol. The solvent used to dilute the polyalphaolefin is an organic solvent containing a lower alcohol, preferably 50% or more ethanol by weight, more preferably 75% or more, and ideally 100% ethanol. In addition to lower alcohols, the solvent may also contain, for example, toluene. In this embodiment, the solvent used to dilute the polyalphaolefin is 100% ethanol by weight. For example, a mixture of ethanol and isopropyl alcohol can also be used as this solvent. However, because ethanol has a high polarity, increasing the proportion of ethanol can increase the number of particles generated by the particle generator 10. The electrolyte contained in the solvent may be increased to increase the number of particles generated by the particle generator 10.

[0030] The first particle classifier (particle classification unit) 20 classifies particles generated from the particle generator 10, extracts particles corresponding to a target particle size received by an input unit (described later), and releases them downstream. The first particle classifier 20 uses a differential electrostatic classifier (Differential Mobility Analyzer: DMA). The first particle classifier 20 includes a classification tube with a double cylindrical structure that functions as an electrode. Only particles with a particle size corresponding to the voltage applied to the classification tube are extracted (classified) by the first particle classifier 20. Therefore, the first particle classifier 20 can extract particles of various particle sizes by changing the voltage applied to the classification tube.

[0031] The particle detection unit 30 includes a detector that detects particles classified and extracted by the first particle classifier 20. The particle detection unit 30 is provided at a position where the particle number measurement device 31 to be calibrated can be placed. Here, "provided at a position where the particle number measurement device 31 can be placed" refers to whether the particle number measurement device 31 may be installed or not, as long as it is installable. This includes a configuration in which the particle number measurement device 31 and the particle size distribution measurement unit 33 described below are interchangeable. Note that, for ease of understanding, the particle number measurement device 31 and the particle size distribution measurement unit 33 are described here as being installed side by side, rather than being interchangeable. The particle detection unit 30 of this embodiment includes the particle number measurement device 31, a reference device 32, and the particle size distribution measurement unit 33.

[0032] The particle number measurement device 31 is a condensation particle counter (CPC) to be calibrated by the calibration facility 1 of this embodiment. The particle number measurement device 31 is used, for example, in particle measurement to confirm that harmful particles in exhaust gases are within specified values, performed in automobile manufacturing plants, inspection organizations, research institutions, etc. The particle number measurement device 31 is capable of directly or indirectly measuring exhaust gases. Calibration work is performed using the calibration facility 1 of this embodiment so that the particle number measurement device 31 can perform accurate measurements. The particle number measurement device 31 can also measure particles generated by vehicle brakes (brake dust), particles generated from tires (tire dust), particles contained in exhaust gases from factories, particles contained in the atmosphere, etc.

[0033] The reference device 32 measures the reference particle number. For example, an electrometer can be used as the reference device 32. An electrometer can measure the number of uniformly charged particles regardless of particle diameter by measuring current, and thus can obtain a reference particle number when calibrating the particle number measuring device 31. However, an electrometer is not suitable for counting particles that have not been charged, for example, particles of a target particle diameter in exhaust gas. In the calibration equipment 1 of this embodiment, the first particle classifier 20 including a charge neutralizer is provided upstream, so that only particles of a target particle diameter that have a monovalent charge can be accurately counted. Furthermore, instead of an electrometer, the reference device 32 may be, for example, a CPC with higher accuracy than the CPC to be calibrated.

[0034] The particle generator 10, first particle classifier 20, particle number measurement device 31, and reference device 32 described above are similar to conventional calibration equipment, and calibration of the particle number measurement device 31 has traditionally been performed using this configuration. However, in recent years, exhaust gas measurements have required counting the number of so-called nanoparticle-level particles, which have smaller particle diameters than conventional measurements. Research by the present applicant has revealed that changes in the particle diameter of particles classified and extracted by a particle classifier affect calibration accuracy when targeting nanoparticle-level particles. While changes in the particle diameter of particles classified and extracted by a particle classifier were not taken into account in conventional calibration procedures, their impact on calibration accuracy was previously thought to be small and negligible due to the large particle diameters of the target particles. However, when calibrating a particle number measurement device that targets very fine particles, such as particles with diameters of 15 nm or less, especially particles with diameters of 10 nm or less, it has been found that changes in the particle diameter of particles classified and extracted by a particle classifier significantly affect calibration accuracy.

[0035] The particle generator 10 has been used for calibration work in the past and is also used in this embodiment. The particle generator 10 uses electrospray to generate liquid particles, which are used for calibration. However, because the particles are liquid particles, the liquid of the liquid particles continues to evaporate immediately after generation, gradually reducing the particle diameter of the liquid particles. FIG. 2 is a diagram showing an example of a detection efficiency function indicating the detection efficiency for each particle diameter of the particle number measurement device 31. As can be seen from the relationship between particle diameter and detection efficiency shown in FIG. 2, the particle number measurement device maintains a stable detection efficiency of approximately 100% regardless of changes in particle diameter in the large particle diameter range (plateau region). In contrast, the particle number measurement device has a region (cutoff region) where the detection efficiency significantly decreases as the particle diameter decreases, and in the cutoff region, even a slight change in particle diameter significantly changes the detection efficiency. In conventional particle number measurement devices that have a cutoff region in a relatively large particle size range (a range in which particle size is greater than a predetermined value (e.g., 15 nm)), the change in particle size reduction from the particle generator to the particle number measurement device is small and has almost no effect on the measurement results. However, it has been found that in a relatively smaller particle size range than conventional devices (e.g., a range in which particle size is 15 nm or less), the change in particle size reduction from the particle generator to the particle number measurement device significantly affects the measurement results. Therefore, the calibration equipment 1 for particle number measurement devices of this embodiment includes a particle size distribution measurement unit 33 (a second particle classifier 34 and a particle number counter 35), a physical quantity factor detection unit 40, a control unit 50, and other components described below, enabling more accurate calibration of the particle number measurement device 31.

[0036] The particle size distribution measuring unit 33 detects the particle size distribution of particles that reach the particle detection unit 30. The particle size distribution measuring unit 33 in this embodiment is composed of a second particle classifier 34 and a particle number counter (particle number counter unit) 35. The second particle classifier 34 sequentially classifies particles that reach the particle size distribution measuring unit by particle size, and the classified particle sizes are sent to the particle number counter 35 located downstream for each particle size. The particle number counter 35 is connected downstream of the second particle classifier 34 and counts the number of particles classified by the second particle classifier 34. The second particle classifier 34 and the particle number counter 35 work together to sequentially change the particle size to be counted, and by counting the number of particles at each particle size, a particle size distribution indicating the distribution of particle sizes is obtained. The information obtained by the second particle classifier 34 and the particle number counter 35, or the information related to the particle size distribution, is sent to the control unit 50 (input unit 51). In this embodiment, a CPC with a smaller cutoff diameter (i.e., higher counting sensitivity for nanoparticles) than the particle number measuring device 31 to be calibrated is used as the particle number counter 35.

[0037] Flow paths F1 to F5 are formed from the particle generator 10 to the particle detection unit 30, and between the second particle classifier 34 and the particle number counter 35. Specifically, flow path F1 is a flow path connecting the particle generator 10 and the first particle classifier 20. Flow path F2 is a flow path connecting the first particle classifier 20 and the particle number measuring device 31. Flow path F3 is a flow path connecting the first particle classifier 20 and the reference device 32. Flow path F4 is a flow path connecting the first particle classifier 20 and the second particle classifier 34. Flow path F5 is a flow path connecting the second particle classifier 34 and the particle number counter 35. Flow paths F2, F3, and F4 are configured so that particle diameter changes of particles are equal. For example, the flow paths F2, F3, and F4 may be configured to have the same inner diameter and pipe length, and may be configured to have the same residence time for the flowing fluid.

[0038] The physical quantity factor detection unit 40 detects or receives input of physical quantity factors that cause a change in particle diameter, and sends the detection results to the calculation unit 52. Physical quantity factors that cause a change in particle diameter include, for example, the temperature, humidity, pressure, flow rate, and / or residence time of the fluid in the flow path from the first particle classifier 20 to the particle detection unit 30. The physical quantity factor may also be the length and / or inner diameter of the flow path from the first particle classifier 20 to the particle detection unit 30.

[0039] The control unit 50 includes an input unit 51, a calculation unit 52, and a correction instruction unit 53. The control unit 50, which is configured to include the input unit 51, the calculation unit 52, and the correction instruction unit 53, can be realized, for example, by installing and executing a calibration program (computer program) on a computer device. The control unit 50 may be a general-purpose smartphone or tablet terminal, a laptop computer, or a dedicated computer specialized for the calibration equipment 1 of particle number measurement devices. The computer device referred to in the present invention refers to an information processing device equipped with a control unit, a storage device, etc. The control unit 50 can implement a calibration method and a calibration method for determining a calibration particle diameter used for calibrating the particle number measurement device 31 by executing the calibration program.

[0040] The input unit 51 accepts input of a target particle diameter from the user P or the like. The input unit 51 can also accept a detection efficiency function indicating the detection efficiency for each particle diameter of the particle number measurement device 31 to be calibrated from the user P or the like. The function input to the input unit 51 may be, for example, a function obtained by converting the curve in FIG. 2 into a function. Alternatively, the function may be input in the form of a data group representing the curve in FIG. 2 (a function of detection efficiency with particle diameter as a variable). By accepting the function, the calculation unit 52 can estimate the detection efficiency at the target particle diameter by applying the detection efficiency measurement results without reduction correction (feedback from the particle size distribution measurement unit) to the vertical axis and the particle size data from the particle size distribution measurement unit to the horizontal axis. Furthermore, the input unit 51 can accept input of data related to the particle size distribution detected by the particle size distribution measurement unit 33. The input unit 51 may accept input, for example, from a pointing device such as a mouse, a keyboard, or a touch panel, or may accept input via communication via an external network. The information input to the input unit 51 is transmitted to the calculation unit 52.

[0041] The calculation unit 52 calculates the degree of change in the particle diameter of particles arriving at the particle detection unit 30 from the target particle diameter using the information input to the input unit 51, the information obtained from the physical quantity factor detection unit 40, and the particle diameter distribution detected by the particle diameter distribution measurement unit. In this embodiment, since liquid particles reduce in diameter due to evaporation, the degree of change is calculated as the degree of particle diameter reduction. The degree of change (reduction) calculated here may be a ratio or a difference value. Furthermore, the calculation unit 52 calculates a correction amount for the particle diameter extracted by the first particle classifier 20 based on the calculated degree of change so that the particle diameter arriving at the particle detection unit 30 becomes the target particle diameter. Note that the phrase "so that the particle diameter arriving at the particle detection unit 30 becomes the target particle diameter" does not only refer to the case where the particle diameter arriving at the particle detection unit 30 completely matches the target particle diameter. In other words, it also includes the case where a correction value is calculated so that the particle diameter arriving at the particle detection unit 30 becomes close enough to be considered the target particle diameter by approaching the target particle diameter. The correction amount calculated by the calculation unit 52 is transmitted to the correction instruction unit 53. Furthermore, the calculation unit 52 calculates the detection efficiency that the particle number measurement device 31 to be calibrated will achieve at the target particle diameter, using the particle diameter distribution detected by the particle diameter distribution measurement unit 33.

[0042] The correction instruction unit 53 instructs the first particle classifier 20 to change the particle diameter of the particles classified and extracted by the first particle classifier 20 to a calibration particle diameter based on the correction amount calculated by the calculation unit 52. This calibration particle diameter reflects the amount of change in particle diameter from the target particle diameter after classification and extraction by the first particle classifier 20 until reaching the particle detection unit 30. In other words, the calibration particle diameter is a particle diameter set in the first particle classifier 20 so that the particle diameter of particles reaching the particle detection unit 30 is the same as or close to the target particle diameter. As described above, the first particle classifier 20 extracts (classifies) only particles having a particle diameter corresponding to the voltage applied to the classification tube. Therefore, the correction instruction unit 53 instructs the first particle classifier 20 to change the voltage applied to the classification tube provided in the first particle classifier 20 to a voltage at which particles having the calibration particle diameter are extracted (classified).

[0043] In this embodiment, where particle diameters are reduced by evaporation of liquid particles, the calibration particle diameter is set to a particle diameter larger than the target particle diameter to compensate for the reduction. For example, to calibrate the particle number measurement device 31 for a particle diameter of 10 nm, assume that particles classified by the first particle classifier 20 with a target particle diameter of 10 nm have reduced in diameter to 9.8 nm by the time they reach the particle detection unit 30. In this case, a difference value of −0.2 nm or a change rate of 98% or other value is obtained as the degree of change in outer diameter. The correction instruction unit 53 compensates for this degree of change and sets the calibration particle diameter to a particle diameter that reaches the particle detection unit 30 to 10 nm or a value very close to 10 nm. In this case, the calibration particle diameter may be set to 10.2 nm, but if it is expected that the degree of reduction due to evaporation varies depending on the particle diameter, a value that takes this effect into account may also be set. The calculation unit 52 and the correction instruction unit 53 perform the above-described operations, so that the calibration equipment 1 of this embodiment can perform more accurate calibration.

[0044] Alternatively, the calibration equipment 1 may generate solid particles (such as sucrose) that do not undergo particle reduction in the particle generator 10, extract 10 nm sucrose particles in the particle classifier 20, and measure them in the particle size distribution measuring unit 33. This operation makes it possible to check and adjust the particle size measurement accuracy due to the difference in particle transport time between the second particle classifier 34 and the particle number counter 35 that constitute the particle size distribution measuring unit 33.

[0045] The above configuration of the calibration equipment 1 of this embodiment enables more accurate calibration than conventional methods. However, in addition to performing correction, it is desirable to suppress changes in particle diameter from the first particle classifier 20 to the particle detection unit 30. Particle diameter reduction due to evaporation is a phenomenon that occurs primarily in all flow paths, namely, flow paths F1, F2, F3, F4, and F5. Therefore, the time that particles spend in (passing through) flow paths F1 to F5 (hereinafter referred to as "retention time") is thought to be closely related to the particle evaporation time. Therefore, experiments were conducted to examine the relationship between particle residence time and particle reduction in these flow paths by preparing multiple inner diameters and lengths for flow path F1 before classification and flow path F4 after classification. Note that all flow paths are cylindrical.

[0046] Figure 3 shows the flow path configurations of flow path F1 before classification and flow path F4 after classification, which were used in an experiment to investigate the relationship between particle residence time in the flow path and particle shrinkage. The pre-classification residence time for flow path F1 was set to be longer than condition B0 (+0.0 sec, the reference condition), with conditions B1: +6.0 sec, B2: +9.0 sec, and B3: +10.5 sec. The actual pre-classification residence time for condition B0 (+0.0 sec) was 0.26 sec. The specific configuration of flow path F1 is shown in Figure 3. Furthermore, the post-classification residence time for flow path F4 was set to be longer than condition A0 (+0.0 sec, the reference condition), with conditions A1: +0.3 sec, A2: +0.6 sec, A3: +0.9 sec, and A4: +1.2 sec. The specific configuration of flow path F4 is shown in FIG. 3 . The actual post-classification residence time under condition A0 (+0.0 sec) was 0.22 sec. The four pre-classification flow paths F1 and the five post-classification flow paths F4 were combined, and the particle size distribution was calculated using the particle size distribution measurement unit 33 to confirm the change in particle size reaching the particle detection unit 30. The particle size of the particles classified and extracted by the first particle classifier 20 was set to 10 nm.

[0047] FIG. 4 is a graph plotting the effect of post-classification residence time on particle diameters reaching the particle detection unit 30 for each pre-classification residence time. The particle diameter on the vertical axis in FIG. 4 is GMD (Geometric Mean Diameter). As shown in FIG. 4 , particle diameters decrease as the post-classification residence time increases. It can also be determined that the shrinkage rate (slope) and shrinkage magnitude (intercept) decrease with increasing pre-classification residence time, i.e., the shrinkage is reduced. Therefore, to more clearly understand the effect of pre-classification residence time, we focused on the relationship between pre-classification residence time and shrinkage rate. FIG. 5 is a graph showing the effect of pre-classification residence time on shrinkage rate. From FIG. 5 , it can be determined that the shrinkage rate begins to converge when the pre-classification residence time exceeds +8 seconds relative to the reference (+0 seconds), and that the shrinkage rate is fairly stable at +10 seconds or more. Therefore, in this embodiment, the flow path F1 before classification is set as an evaporation flow path that promotes evaporation in advance, so that the effect of increasing the residence time before classification by about +8 seconds in Fig. 5 can be expected. By ensuring an appropriate residence time before classification in the evaporation flow path, it is possible to suppress a reduction in particle size after classification.

[0048] The effect of increasing the pre-classification residence time by approximately +8 seconds is obtained when the pre-classification residence time is increased between 6 and 9 seconds. As can be seen from FIG. 4 , this is within the region where the rate of particle diameter reduction due to evaporation of components from the particle surface in flow paths F2, F3, and F4 from the first particle classifier 20 to the particle detection unit 30 is less than 3% (particle diameter of 9.7 nm or more). That is, the flow path F1 from the particle generator 10 to the first particle classifier 20 is configured as an evaporation flow path in which evaporation of components from the particle surface occurs in advance, so that the rate of particle diameter reduction due to evaporation of components from the particle surface in flow paths F2, F3, and F4 from the first particle classifier 20 to the particle detection unit 30 is less than 3%. However, by using flow path F1 as an evaporation flow path and lengthening the pre-classification residence time, it is expected that the number of particles obtained due to particles adhering to the flow path wall surface, etc. will decrease. Therefore, in this embodiment, as described above, the solvent used to dilute the polyalphaolefin is 100% ethanol by weight, and this ethanol contains an appropriate amount of electrolyte (e.g., ammonium acetate) to increase the number of particles generated by the particle generator 10.

[0049] 4, even if sufficient component evaporation is performed in advance in the flow path F1 from the particle generator 10 to the first particle classifier 20, it is believed that particle size reduction will further progress as the post-classification residence time (increase in the post-classification residence time) increases. Therefore, it is desirable to shorten the particle residence time (post-classification residence time) as much as possible in the flow paths F2, F3, and F4 from the first particle classifier 20 to the particle detection unit 30. Furthermore, in order to accurately measure particle size at the inlet of the particle number measurement device 31 to be calibrated, it is desirable to make the particle size reduction width, i.e., residence time, in the flow paths F2, F3, and F4 uniform. For example, in order to keep the reduction width to less than 0.1 nm, it is desirable to make the residence time in the flow paths F2, F3, and F4 from the first particle classifier 20 to the particle detection unit 30 less than 1 second.

[0050] (Method of Determining Calibration Particle Diameter and Calibration Method) FIG. 6 is a diagram showing the flow of operations when the method of determining calibration particle diameter and the calibration method are carried out mainly by the control unit 50.

[0051] In step (hereinafter simply referred to as S) 11, particle generator 10 generates particles. In S12, input unit 51 accepts input of a target particle diameter from a user. In S13, first particle classifier 20 classifies the particles generated by particle generator 10 and extracts particles that correspond to the target particle diameter accepted by input unit 51.

[0052] In S14 , the particle size distribution measurement unit 33 of the particle detection unit 30 detects the particle size distribution of the particles extracted by the first particle classifier 20 and reaching the particle detection unit 30 .

[0053] In S15, the physical quantity factor detection unit 40 detects physical quantity factors that change the particle diameter, such as temperature, humidity, and atmospheric pressure.

[0054] In S16, the calculation unit 52 uses the physical quantity factors obtained by the physical quantity factor detection unit 40 and the particle size distribution obtained by the particle size distribution measurement unit 33 to determine the degree of change in the particle size of the particles that have reached the particle detection unit 30 from the target particle size.

[0055] In S17, the calculation unit 52 calculates a correction amount for the particle diameter extracted by the first particle classifier 20 based on the degree of change so that the particle diameter reaching the particle detection unit 30 becomes the target particle diameter.

[0056] In S18, the correction instruction unit 53 instructs the first particle classifier 20 to change the particle diameter of the particles extracted by the first particle classifier 20 to the calibration particle diameter based on the correction amount calculated by the calculation unit 52.

[0057] In S19, the particles extracted by the first particle classifier 20 after classification with the particle diameter changed to the calibration particle diameter are counted using the reference device 32 and the particle number measuring device 31, and the detection efficiency is calculated, i.e., calibration is performed at the target particle diameter.

[0058] By performing the above operation for each required target particle diameter, the calibration work of the particle number measuring device 31 is completed.

[0059] (Example) The calibration equipment 1 of this embodiment having the configuration described above was actually fabricated, and the results of a comparison with a conventional calibration equipment are described below. In the calibration equipment 1 of this embodiment, the pre-classification flow path F1 was configured to perform sufficient evaporation before classification under condition B0 in FIG. 3. The post-classification flow paths F2 to F4 were configured to suppress reduction in particle diameter due to evaporation after classification under condition A0 in FIG. 3. The comparative example had the same configuration as the example, except that no correction operation was performed by the control unit 50. Eight particle diameters (target particle diameters) were evaluated: 7 nm, 8 nm, 9.8 nm, 10 nm, 10.2 nm, 11 nm, 13 nm, and 15 nm.

[0060] FIG. 7 is a diagram summarizing the detection efficiencies calculated for each particle size in the Examples and Comparative Examples. The calibration process is performed by calculating the detection efficiency for each target particle size, as shown in FIG. 7. If the detection efficiency is accurately known, the actual particle number can be accurately calculated from the counting results for the corresponding particle size and the detection efficiency. As shown in FIG. 7, differences appear between the Examples and Comparative Examples when the particle size is 10 nm or less, and the conditions of the Examples in which correction is performed yielded higher detection efficiencies than the Comparative Examples in which correction is not performed. This is thought to be because the calibration process in the Comparative Examples measured the detection sensitivity at particle diameters smaller than the target particle diameter. In contrast, the measurement results in the Examples measured the detection sensitivity at the target particle diameter, so the correct detection sensitivity was measured, enabling more accurate calibration.

[0061] FIG. 8 is a plot of the particle size change due to evaporation, ΔDp (nm), calculated as the difference between the classified particle size and the measured particle size, for each measured particle size. The data in FIG. 8 is shown collectively without distinguishing between the example and comparative example data in FIG. 7 . While correction was performed in the example, the particle size change after classification is the same as in the comparative example. The particle size on the horizontal axis in FIG. 8 is the particle size input into the first particle classifier 20. Therefore, the relationship is (particle size input into the first particle classifier 20: horizontal axis) - (ΔDp: vertical axis) ≒ particle size measured by the particle size distribution measurement unit 33. From FIG. 8 , it can be seen that there is almost no change in particle size at a particle size of 15 nm (ΔDp ≒ 0), and the smaller the particle size, the greater the degree of shrinkage. It was confirmed that shrinkage is likely to occur for particles smaller than 15 nm, and that unless the degree of shrinkage is corrected, differences in the detection sensitivity measurement results will occur.

[0062] Furthermore, among the data shown in FIG. 7 above, the numerical data for 10 nm and 15 nm are summarized in tables in FIGS. 9 and 10. The measurements in FIG. 7 were performed for three days, so the respective data and average data are shown. FIG. 9 is a diagram showing the difference in detection efficiency between the Comparative Example and the Example at a particle diameter of 10 nm. FIG. 10 is a diagram showing the difference in detection efficiency between the Comparative Example and the Example at a particle diameter of 15 nm. From the numerical values ​​in FIGS. 9 and 10, it can be seen that while there is a difference in detection sensitivity of -2.82 at a particle diameter of 10 nm, there is almost no difference in detection sensitivity for a particle diameter of 15 nm even over three days.

[0063] As described above, the calibration equipment 1 of the first embodiment actually measures the degree of change in particle diameter of particles reaching the particle detection unit 30 after classification by the first particle classifier 20, and corrects the particle diameters classified and extracted by the first particle classifier 20 based on the measurement results. This compensates for the decrease in calibration accuracy due to particle diameter reduction caused by evaporation, which is particularly noticeable for very small particle diameters, such as those of approximately 10 nm, enabling more accurate calibration. Furthermore, since the flow path F1 from the particle generator 10 to the first particle classifier 20 includes an evaporation path that sufficiently evaporates components in advance, the degree of change in particle diameter of particles reaching the particle detection unit 30 after classification by the first particle classifier 20 can be reduced, thereby reducing the calibration error that occurs before correction. The calibration equipment 1 of this embodiment can address the calibration error in the detection sensitivity of 10 nm particles that arises with the introduction of a new European automotive exhaust particle detection system, thereby optimizing calibration. According to the calibration equipment 1 of this embodiment, by measuring the diameter reduction due to evaporation of PAO, which is a calibration particle component in the calibration equipment 1, the influence of this reduction on detection sensitivity calibration can be corrected, allowing for calibration with good reproducibility.

[0064] 11 is a block diagram showing the configuration of a calibration facility 1B for a particle number measurement device according to a second embodiment. The calibration facility 1B of the second embodiment differs from the calibration facility 1 of the first embodiment in that the particle detection unit 30B does not include a component corresponding to the particle size distribution measurement unit 33 in the first embodiment. Since the other points are the same as those of the calibration facility 1 of the first embodiment, parts that perform the same functions as those of the first embodiment described above are assigned the same reference numerals, and duplicated explanations will be omitted as appropriate.

[0065] The calibration equipment 1B of the second embodiment does not have a configuration equivalent to the particle size distribution measurement unit 33 of the first embodiment. Therefore, the calculation unit 52 calculates the degree of change in particle diameter of particles reaching the particle detection unit 30 from the target particle diameter based on information from the physical quantity factor detection unit 40. Here, since measurement results of particle diameters actually reaching the particle detection unit 30 are not obtained, the calculation unit 52 of the second embodiment may calculate particle residence times by inputting information about the flow paths F1, F2, and F3 of the calibration equipment 1B in advance or by inputting the information via the input unit 51. Alternatively, the particle residence times may be detected or input as physical quantity factors. Furthermore, the calculation unit 52 pre-stores data related to particle reduction shown in FIGS. 4 and 5 . Based on this information, the calculation unit 52 can calculate the degree of change in particle diameter of particles reaching the particle detection unit 30 from the target particle diameter. Subsequent operations are similar to those of the first embodiment.

[0066] According to the calibration equipment 1B of the second embodiment, highly accurate calibration can be performed with a simpler configuration. In addition, since the measurement work using the particle size distribution measurement unit 33 is not required, the calibration work can be easily performed.

[0067] (Modifications) The present disclosure is not limited to the above-described embodiment, and various modifications and variations are possible, and these are also within the scope of the present disclosure.

[0068] The first embodiment has been described as an example in which the calculation unit 52 determines the degree of change in the particle diameter of particles that have reached the particle detection unit 30 from the target particle diameter using information from both the physical quantity factor detection unit 40 and the particle size distribution measurement unit 33. However, the present invention is not limited to this, and for example, the calculation unit 52 may determine the degree of change in the particle diameter of particles that have reached the particle detection unit 30 from the target particle diameter without using a physical quantity factor. In this case, the physical quantity factor detection unit 40 may be omitted.

[0069] Also, in the first and second embodiments, it is possible to omit the physical quantity factor detection unit 40. In this case, the physical quantity factor may be input via the input unit 51, or a physical quantity factor calculated or stored in advance may be used.

[0070] In the second embodiment, instead of calculating the degree of reduction of the particle diameter from the physical quantity factor, a degree of reduction of the particle diameter calculated in advance may be used if the physical quantity factor is the same. In this case, the physical quantity factor detection unit 40 may be omitted.

[0071] Furthermore, in the first and second embodiments, if the length and / or residence time of the flow path F1 from the particle generator 10 to the first particle classifier 20 are adjusted so that sufficient evaporation of components can be performed in advance in the flow path F1, there is almost no reduction in particle diameter after passing through the first particle classifier 20. In this case, the calibration equipment 1 does not need to include some or all of the components of the control unit 50. That is, the calibration equipment may be configured to include the particle generator 10, the flow path F1 whose residence time has been adjusted in advance so that sufficient evaporation of components can be performed, the first particle classifier 20, and the particle detection unit 30 (30B).

[0072] In each embodiment, the case where the particle diameter decreases has been described as an example, but the calibration equipment of the present invention can also be used in the case where the particle diameter increases, for example.

[0073] 1, 1B Calibration equipment 10 Particle generator 20 First particle classifier 30, 30B Particle detection unit 31 Particle number measurement device 32 Standard device 33 Particle size distribution measurement unit 34 Second particle classifier 35 Particle number counter 40 Physical quantity factor detection unit 50 Control unit 51 Input unit 52 Calculation unit 53 Correction instruction unit F1 to F5 Flow path

Claims

1. Calibration equipment for a particle number measurement device used for calibrating a particle number measurement device, comprising: a particle generation unit that generates particles; an input unit that receives an input of a target particle diameter; a particle classification unit that classifies the particles generated from the particle generation unit and extracts particles that correspond to the target particle diameter received by the input unit; a particle detection unit that detects the particles extracted by the particle classification unit; a calculation unit that determines a degree of change in particle diameter of particles that reach the particle detection unit from the target particle diameter based on a physical quantity factor that causes a change in particle diameter at the particle detection unit or a particle diameter distribution of particles at the particle detection unit, and calculates a correction amount for the particle diameter extracted by the particle classifier based on the degree of change so that the particle diameter of particles reaching the particle detection unit becomes the target particle diameter; and a correction instruction unit that instructs the particle classifier to change the particle diameter of particles extracted by the particle classifier to a calibration particle diameter based on the correction amount calculated by the calculation unit.

2. Calibration equipment for a particle number measuring device according to claim 1, comprising a physical quantity factor detection unit that detects the physical quantity factor, and the calculation unit calculates the correction amount using at least the physical quantity factor obtained by the physical quantity factor detection unit.

3. Calibration equipment for a particle number measuring device according to claim 1, comprising a particle size distribution measuring unit provided in the particle detection unit and detecting the particle size distribution of particles reaching the particle detection unit, and the calculation unit calculating the correction amount using the particle size distribution detected by the particle size distribution measuring unit.

4. Calibration equipment for a particle number measuring device according to claim 1 or 2, wherein the physical quantity factor is at least one of the temperature, humidity, pressure, flow rate, and residence time of the fluid in the flow path from the particle classification unit to the particle detection unit.

5. Calibration equipment for a particle number measuring device according to claim 3, wherein the particle size distribution measuring unit comprises: a second particle classifying unit that classifies particles that reach the particle size distribution measuring unit; and a particle number counting unit that is connected downstream of the second particle classifying unit and counts the number of particles classified by the second particle classifying unit.

6. Calibration equipment for a particle number measuring device according to claim 3 or 5, wherein the input unit is capable of receiving a detection efficiency function indicating the detection efficiency for each particle diameter of the particle number measuring device to be calibrated, and the calculation unit calculates the detection efficiency achieved by the particle number measuring device to be calibrated at the target particle diameter using the particle diameter distribution detected by the particle size distribution measurement unit.

7. Calibration equipment for a particle number measuring device according to any one of claims 1 to 3, wherein the correction instruction unit instructs the particle classifying unit to change the voltage applied to a classification tube provided in the particle classifying unit.

8. Calibration equipment for a particle number measuring device according to any one of claims 1 to 3, wherein the particles generated by the particle generating unit are mainly composed of polyalphaolefin, and the solvent used to dilute the polyalphaolefin is ethanol at a weight ratio of 50% or more.

9. Calibration equipment for a particle number measuring device according to any one of claims 1 to 3, wherein the flow path from the particle generating section to the particle classifying section is an evaporation flow path in which evaporation of components from the particle surface is carried out in advance so that the rate of reduction in particle diameter due to evaporation of components from the particle surface in the flow path from the particle classifying section to the particle detecting section is less than 3%.

10. A calibration program used for calibrating a particle number measuring device, the program including: a particle generating unit generating particles; an input unit receiving an input of a target particle diameter from a user; a particle classifying unit classifying the particles generated from the particle generating unit and extracting particles corresponding to the target particle diameter received by the input unit; a particle detecting unit detecting the particles extracted by the particle classifying unit; a calculation unit determining a degree of change in particle diameter of particles arriving at the particle detecting unit from the target particle diameter based on a physical quantity factor that causes a change in particle diameter at the particle detecting unit or a particle diameter distribution of particles at the particle detecting unit, and calculating a correction amount for the particle diameter extracted by the particle classifying unit based on the degree of change so that the particle diameter of particles arriving at the particle detecting unit becomes the target particle diameter; and a correction instruction unit instructing the particle classifying unit to change the particle diameter of particles extracted by the particle classifying unit to a calibration particle diameter based on the correction amount calculated by the calculation unit. A calibration program to run.

11. A calibration program according to claim 10, comprising a step in which a physical quantity factor detection unit detects the physical quantity factors, and the calculation unit calculates the correction amount using at least the physical quantity factors obtained by the physical quantity factor detection unit.

12. A calibration program according to claim 10, comprising a step in which a particle size distribution measuring unit detects the particle size distribution of particles reaching the particle detection unit, and the calculation unit calculates the correction amount using the particle size distribution detected by the particle size distribution measuring unit.

13. A method for determining a calibration particle diameter used in calibrating a particle number measuring device, comprising: a step of generating particles by a particle generating unit; a step of receiving an input of a target particle diameter from a user by an input unit; a step of classifying particles generated from the particle generating unit and extracting particles corresponding to the target particle diameter received by the input unit; a step of detecting particles extracted by the particle classifying unit; a step of calculating a degree of change in particle diameter of particles reaching the particle detecting unit from the target particle diameter based on a physical quantity factor that causes a change in particle diameter at the particle detecting unit or a particle diameter distribution of particles at the particle detecting unit, and calculating a correction amount for the particle diameter extracted by the particle classifying unit based on the degree of change so that the particle diameter reaching the particle detecting unit becomes the target particle diameter; and a step of calculating a correction instruction unit instructing the particle classifying unit to change the particle diameter of particles extracted by the particle classifying unit to the calibration particle diameter based on the correction amount calculated by the calculation unit. A method for determining a particle size for calibration, comprising:

14. A method for determining a particle diameter for calibration according to claim 13, comprising a step in which a physical quantity factor detection unit detects the physical quantity factors, and the calculation unit calculates the correction amount using at least the physical quantity factors obtained by the physical quantity factor detection unit.

15. A method for determining a particle diameter for calibration according to claim 13, comprising a step in which a particle diameter distribution measuring unit detects the particle diameter distribution of particles reaching the particle detection unit, and the calculation unit calculates the correction amount using the particle diameter distribution detected by the particle diameter distribution measuring unit.

16. A method for calibrating a particle number measuring device, in which the particle classifying unit extracts particles based on a calibration particle diameter determined by a method for determining a calibration particle diameter as set forth in any one of claims 13 to 15, and the particle number measuring device to be calibrated is calibrated using the particles of the calibration particle diameter extracted by the particle classifying unit.

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