JP2011232090A - Differentiation type electric mobility measurement apparatus, measuring method using differentiation type electric mobility measurement apparatus, program used for differentiation type electric mobility measurement apparatus and computer-readable recording medium recording the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make it possible to notice the change of particle diameter of charged particle of an object to be measured even with a sole DMA.SOLUTION: Particle diameter distribution measuring means changes classification voltage by means of a voltage generation apparatus to measure detection signals of a particle measurement apparatus, thereby measuring the particle diameter distribution of the charged particle in sample gas. Sheath gas flow rate control means changes the flow rate of sheath gas supplied from a sheath gas supply part in at least two ways and judges whether or not the change of particle diameter occurs during the passing of the charged particle through a DMA based on the comparison of particle distributions measured for different sheath gas flow rate.

Description

  The present invention relates to a differential electric mobility measuring device (hereinafter referred to as “DMA”), and more specifically, DMA itself, a measuring method using DMA, a program used for DMA, and a computer recording the program. The present invention relates to a readable recording medium.

  DMA is widely used as a device for measuring the particle size of particles contained in aerosols (see Patent Document 1 and Non-Patent Document 1) for measuring aerosols in the environment and industrially manufactured particles. Yes. The aerosol is in a state where solid or liquid fine particles are present in a relatively stable floating state in the gas, and is contained in the exhaust gas of an automobile, the exhaust gas from a factory, or the like.

  In the particle size measurement by DMA, it is known that the particle size is not correctly measured when the particle is volatile. Therefore, in the commercially available DMA, only the non-volatile (non-volatile) particles are the measurement object.

  As a method of measuring particle size reduction using DMA, a method using two DMAs and a heating device is known (see Patent Document 2 and Non-Patent Document 2). This method is called a tandem DMA method. First, particles having a specific particle size are selected and introduced into a heating apparatus by the first DMA. A gas containing particles is heated by a heating device (it is possible not to heat) to desorb volatile components, and then a particle size distribution is measured by a second DMA. By comparing the transmission particle size set by the first DMA with the particle size measured by the second DMA, the particle size reduction can be measured. However, in this method, two DMAs are required, and the apparatus becomes large. Also, the time required for particles to pass through the pipe connecting the two DMAs is the classifying part of the DMA (the inlet slit that serves as a charged particle introduction port to the space between the pair of electrodes to which the classification voltage is applied and the classified charge. Distinguishing whether the particle size has decreased in the DMA or in the pipe because it is very long compared to the time required for the particle to pass through the space (the space between the outlet slits serving as the classification particle discharge port for discharging particles from the space) Difficult to do. Therefore, when measured by the tandem DMA method, it is highly likely that the particle size cannot be measured by the DMA itself, although the particle size is correctly measured.

Japanese Patent No. 3487756 Japanese Patent No. 4066989

Jpn. J. Appl. Phys., 41, 922-924 (2002) Aerosol Sci. Technol., 41, 898-906 (2007)

  In the commercially available DMA, only the non-volatile (non-volatile) particles are measured. However, when the composition of the target particles is not clear, it is unknown whether it is non-volatile or not, and it is not easy to determine whether it can be a measurement target. Especially when the DMA is operating under certain conditions, this cannot be known.

  An object of the present invention is to make it possible to know a change in the particle size of a charged particle to be measured even with a single DMA.

  The DMA includes a pair of electrodes, a voltage generator that applies a voltage between the pair of electrodes, a sheath gas supply unit that introduces a sheath gas from one end of the space between the pair of electrodes to the space, and a sheath gas supply unit An inlet slit provided on the downstream side of one of the pair of electrodes and serving as a charged particle inlet for supplying a sample gas containing charged particles in the sheath gas flow, and the inlet slit for the sheath gas flow An outlet slit provided downstream of the pair of electrodes and discharging charged particles classified by electrostatic force generated by the voltage, and charged particles discharged from the outlet slit are counted. A particle measuring instrument.

DMA directly measures the electric mobility of charged particles in a sample gas. There is a relationship of the following equation between the electric mobility Zp and the particle size Dp.
Zp = qeCc / (3πμDp) (Formula 1)
Here, q is the charge amount, e is the elementary charge, Cc is the Cunningham correction coefficient, and μ is the gas viscosity coefficient. In addition, in the cylindrical DMA as shown in FIG. 2 as an embodiment of the present invention, only the charged particles having the electric mobility Zp that are classified and satisfy the condition of the following equation pass through the exit slit, and the particle measuring instrument Can be reached.
Zp = (Qs + Qa) ln (R2 / R1) / (2πVL) (Formula 2)
Here, Qs is a sheath gas flow rate, Qa is a sample gas flow rate, ln is a natural logarithm, R2 is an inner radius of the outer cylinder electrode, R1 is an outer radius of the inner cylinder electrode, and V is a potential difference between the outer cylinder electrode and the inner cylinder electrode. That is, the classification voltage, L is the vertical distance between the entrance slit and the exit slit. From this relationship, when the classification voltage is changed, the electric mobility Zp of the charged particles detected under the classification voltage is obtained, and then the particle diameter Dp is obtained from the electric mobility Zp.

  FIG. 8A shows a schematic view of the outer cylindrical electrode and the vicinity of the inner cylindrical electrode when nonvolatile particles are classified under the measurement conditions of the sheath gas flow rate Qs and the classification voltage Vs in the cylindrical DMA shown in FIG. When the classification voltage Vs and the sheath gas flow rate Qs, the particle A having the particle diameter Dps obtained from the equations 1 and 2 reaches the exit slit. On the other hand, FIG. 8B shows a schematic view of the outer cylinder electrode and the vicinity of the inner cylinder electrode when volatile particles are classified under the same conditions in the DMA. In the case of volatile particles, after entering the space between the outer cylinder electrode and the inner cylinder electrode from the entrance slit, the particle size decreases while passing through the space. The decrease in the particle size is a decrease in L as can be seen from Equations 1 and 2, that is, the particle A having the particle size Dp does not reach the exit slit. At the same time, particles that reach the exit slit reach particle B having a particle size larger than Dps. As a result, under the condition for measuring the number of particles A having a particle diameter Dps, the number of particles B is measured, and the particle diameter B is measured as a particle having a particle diameter Dps smaller than the actual particle diameter. Not measured. For convenience, FIG. 8B shows only particles B that reach the exit slit as particles contained in the aerosol.

  Therefore, in order to know whether charged particles are not volatilized in the DMA, the present invention measures the particle size distribution at several points, at least two points, by changing the time for the charged particles to pass through the DMA. . The time for passing through the DMA is changed by adjusting the sheath gas flow rate. Therefore, in the present invention, as also shown in FIGS. 1 and 3 showing an embodiment, the computer system 6 changes the voltage by the voltage generator 4 and outputs the detection signal of the particle measuring instrument 3. Particle size distribution measuring means 12 for taking in and measuring the particle size distribution of charged particles in the sample gas, sheath gas flow rate control means 14 for changing the flow rate of the sheath gas supplied from the sheath gas supply unit to at least two types, and different sheath gas flow rates Particle size change for determining whether or not there is a change in particle size while charged particles pass between the entrance slit and the exit slit in the space between the pair of electrodes based on a comparison of the particle size distribution measured originally Determination means 16.

  The particle size change determining means 16 obtains, for example, a difference in number density for each particle size of each particle size distribution measured at different sheath gas flow rates, and a difference between the maximum value and the minimum value of the difference is preset. When it is larger than the threshold value, it is determined that the particle size has changed. In that case, the particle size change determination means 16 can also normalize the particle size distributions measured at different sheath gas flow rates and determine whether there is a change in particle size based on the difference. An example of normalization is to divide the difference between the maximum value and the minimum value of the difference by the maximum value of the number density of one particle size distribution.

  The DMA of the present invention can further include a display unit 18. When the particle size change determining means 16 determines that the particle size has changed, it can output to the display section 18 that the sample gas containing the charged particles is not suitable for measurement.

  In a preferred embodiment, the computer system 6 further includes a particle size estimation unit 20 that calculates a particle size when there is no change in the particle size when the particle size change determination unit 16 determines that the particle size has changed. Can do. The particle size estimation means 20 is configured to determine a particle size distribution at a peak position of each particle size distribution measured under a plurality of types of sheath gas flow rates and a time required for the charged particles to pass between the entrance slit and the exit slit. t is determined, and the amount of change in particle size is expressed as a function of time t, so that the particle size when the passing time t is extrapolated to zero is set as the particle size at the peak position of the distribution before the particle size change. is there. That is, the original particle size is estimated by an algorithm from the change in particle size when the passage time t is changed.

The time t during which the charged particles pass through the classification region includes the space H between the electrodes, the volume H of the region surrounded by the positions of the entrance slit and the exit slit, the sheath gas flow rate Qs and the sample gas flow rate Qa flowing through the region. From
t = H / (Qs + Qa)
As required.

As the pair of electrodes, if an outer cylinder electrode and an inner cylinder electrode arranged concentrically as shown in FIG. 2 are used,
H = L (R2 ² −R1 ² ) π
Therefore, the passage time t can be calculated by the following equation.
t = L (R2 ² −R1 ² ) π / (Qs + Qa)
Here, L is the vertical distance between the inlet slit and the outlet slit, R2 is the inner radius of the outer cylinder electrode, R1 is the outer radius of the inner cylinder electrode, Qs is the sheath gas flow rate, and Qa is the sample gas flow rate.

  According to this aspect, it is possible to estimate the particle diameter of volatile particles that are not to be measured in the normal usage of DMA. This is a judgment material for selecting an apparatus when using another measuring apparatus. That is, if it is determined that the particles are volatile particles, it is not suitable for measurement by DMA, and thus measurement by other means is necessary. In this case, according to this aspect, an approximate particle size can be known. Therefore, the particle size is a material for determining what kind of measuring device should be used for the sample. For example, if the estimated particle size according to this embodiment is larger than 100 nm, it can be determined that the sample is suitable for measurement by the laser scattering method. If the estimated particle size is smaller than 100 nm, the sample has a laser. Since measurement by the scattering method is not appropriate, it can be determined that another measurement method must be selected.

  The computer system 6 may further include a measurement stopping unit 22 that stops the measurement operation of the sample gas being measured when the particle size change determining unit 16 determines that the particle size has changed.

  The differential electric mobility measurement method of the present invention uses DMA, changes the flow rate of the sheath gas supplied from the sheath gas supply unit into at least two types, and the particle size distribution of charged particles in the sample gas under each sheath gas flow rate. The particle size distribution measuring step for measuring the particle size and the particle size change determining step for determining whether there is a change in the particle size while the charged particles pass through the DMA from the comparison of the particle size distribution measured under different sheath gas flow rates And.

  The program of the present invention is a program used in DMA, and is a program for causing a computer to function as the particle size distribution measuring means 12, the sheath gas flow rate control means 14, and the particle size change determining means 16.

  When the DMA further includes a display unit 18, if the particle size change determining means 16 of this program determines that there has been a change in the particle size, the sample gas containing the charged particles is suitable for measurement. It can be output to the display unit 18.

  This program can further include the above-mentioned particle size estimation means 20.

  This program may further include the measurement stopping means 22 described above.

  The computer-readable recording medium of the present invention records the above program.

  According to the present invention, a DMA user can know whether or not charged particles in a sample gas to be measured can be a DMA measurement target even when only one DMA is used. This improves the reliability of the particle size distribution measured by DMA.

It is a block diagram which shows one Example. It is a schematic sectional drawing which shows the DMA part in the Example. It is a block diagram which shows the control part in the Example. It is a flowchart which shows operation | movement of the Example. It is a graph which shows the simulation result of the particle size change of a non-volatile particle and a volatile particle. It is a graph which shows the simulation result which shows the influence of the sheath gas flow volume with respect to the particle size distribution of a non-volatile particle. It is a graph which shows the same simulation result as a normalized difference. It is a graph which shows the simulation result which shows the influence of the sheath gas flow volume with respect to the particle size distribution of a volatile particle. It is a graph which shows the same simulation result as a normalized difference. It is the graph which showed the particle size distribution of the measurement result using the same Example by the number density. It is the graph which showed the particle size distribution of the measurement result using the same Example by the normalized difference. It is a flowchart which shows the further operation | movement of the Example. FIG. 3 is a schematic view of the outer cylindrical electrode and the vicinity of the inner cylindrical electrode when nonvolatile particles are classified in the cylindrical DMA shown in FIG. 2. FIG. 3 is a schematic view of the outer cylinder electrode and the vicinity of the inner cylinder electrode when volatile particles are classified in the cylindrical DMA shown in FIG. 2.

  One embodiment is shown in FIGS. An example of DMA2 is shown in FIG. 2, but the present invention can be applied to any DMA. The DMA 2 can be variously modified with respect to the shape of the electrode, the arrangement direction, the voltage application method, the flow direction of the sheath gas, and the like, and there are actually various types of commercially available products. FIG. 2 only schematically shows the parts necessary for the description.

  An inner cylinder electrode 103 is provided inside the housing 101 of the DMA 2 so as to coincide with the central axis of the housing 101. In this example, the casing 101 has a cylindrical shape and the inner cylinder electrode 103 has a columnar shape, but may have other shapes. The casing 101 is made of a conductive material, and the inner surface is an outer cylinder electrode 104. The inner cylinder radius of the outer cylinder electrode 104 is R2, and the outer diameter radius of the inner cylinder electrode 103 is R1. The housing 101 is disposed on an insulating base 102. The inner cylinder electrode 103 is disposed on the insulating base 119, and the inner cylinder electrode 103 is insulated from the housing 101 by the base 119 and the base 102. A rotating body-like space is formed between the electrodes 103 and 104. The inner cylinder electrode 103 and the outer cylinder electrode 104 constitute a counter electrode, and can generate a classification voltage for classifying charged fine particles according to electric mobility. The electrode 104 is grounded, the electrode 103 is connected to the voltage generator 4, and the voltage generator 4 is connected to the controller 100. The control unit 100 includes the computer system 6 and the interface 5 shown in FIG. The voltage applied between the electrodes 103 and 104 is controlled by the voltage generator 4 from the control unit 100.

  A sheath gas supply unit 107 is provided on the top of the housing 101. An uncharged gas is supplied to the sheath gas supply unit 107 at a constant flow rate via the flow rate control device 1, and the uncharged gas is introduced into the casing 101 from the sheath gas supply unit 107 as a sheath gas. A commutator 109 for laminating the sheath gas is provided at the upper end of the space between the electrodes 103 and 104, and the sheath gas that has passed through the commutator 109 is supplied into the space as a laminar flow.

  An annular inlet slit 111 surrounding the inner cylindrical electrode 103 is provided as a charged aerosol introduction port on the outer cylindrical electrode 104 side in the space between the electrodes 103 and 104, and the charged aerosol is introduced into the sheath gas flow from the inlet slit 111. It is supplied at a constant flow rate. In order to supply charged aerosol to the entrance slit 111, a charging device (not shown) is provided outside the classification device 2. Charged aerosol charged by the charging device is supplied to the entrance slit 111.

  The inner cylinder electrode 103 is formed with an annular outlet slit 120 for discharging the classified fine particles at a position below the inlet slit 111. The exit slit 120 is connected to the particle measuring device 3 that detects the number density of charged particles through the classified particle discharge port 122. The particle measuring instrument 3 is a Faraday cup or a condensed nucleus counter.

  The distance in the vertical direction from the inlet slit 111 to the outlet slit 120 of the charged aerosol is L, and the space between the electrodes 103 and 104 is a classification region 105 between the inlet slit 111 and the outlet slit 120.

  The casing 101 is supplied with sheath gas and charged aerosol at a constant flow rate. Some of those gases supplied to the casing 101 are discharged together with the classified charged particles from the outlet slit 120 through the classified particle discharge port 122 and guided to the sub-counter 3, and the remaining gas is discharged. The flow rate is controlled at a constant flow rate by the flow rate control device 9 from a discharge port 124 provided in the lower part of the body 101 and discharged.

  The charged aerosol charged in the DMA 2 by the charging device is supplied as a sample gas to the classification region 105 through the inlet slit 111, moves downward in the axial direction together with the sheath gas supplied from the sheath gas supply unit 107, and is formed in the classification region 105. Under the influence of the electric field, the particles are attracted in the direction of the central axis at a speed corresponding to the electric mobility of fine particles of individual particle sizes in the charged aerosol. As a result, only the charged particles 112 that reach the exit slit 120 while drawing a predetermined locus corresponding to the electric field at that time are guided to the particle measuring instrument 3 from the classified particle discharge port 122, and the number of the charged particles 112 is the electric quantity. As counted.

  The voltage applied between the voltage generator 4 and the electrodes 103 and 104 is changed by the control unit 100, and the number of charged particles having a particle size corresponding to the voltage is counted, whereby the particle size distribution is measured.

  As shown in FIG. 1, a signal from the computer system 6 is converted by the interface 5 to control the flow control device 1, the voltage generator 4, and the flow control device 9. Further, the signal from the particle measuring instrument 3 is converted by the interface 5 and taken into the computer system 6. The computer system 6 and the interface 5 constitute the control unit 100 shown in FIGS.

  As shown in FIG. 3, the control unit 100 includes a particle size distribution measuring unit 12, a sheath gas flow rate controlling unit 14, a particle size change determining unit 16, a particle size estimating unit 20, and a measurement stopping unit 22. Yes.

  The particle size distribution measuring means 12 measures the particle size distribution of the charged particles in the charged aerosol supplied as the sample gas by changing the classification voltage by the voltage generator 4 and measuring the detection signal of the particle measuring instrument 3.

  The sheath gas flow rate control means 14 changes the flow rate of the sheath gas supplied from the sheath gas supply unit 107 via the flow rate control devices 1 and 9 into at least two types.

  The particle size change determining means 16 determines whether or not there is a change in particle size while charged particles pass through the DMA 2 from comparison of particle size distributions measured under different sheath gas flow rates.

  A display unit 18 such as a liquid crystal display is connected to the control unit 100. When the particle size change determining means 16 determines that the particle size has changed, the display unit 18 can display that the sample gas containing the charged particles is not suitable for measurement.

The particle size estimation means 20 estimates the particle size when it is assumed that there is no change in the particle size when the particle size change determination means 16 determines that the particle size has changed. An example of a method for estimating the particle size is to determine the particle size at the peak position of the distribution and the time t during which the charged particles pass through the classification region 105 for each of the particle size distributions measured under multiple types of sheath gas flow rates, The particle size when the passage time t is extrapolated to zero is estimated as the particle size at the peak position of the distribution before the particle size change. The time t during which charged particles pass through the classification region 105 is the case of the DMA in FIG.
t = L (R2 ² −R1 ² ) π / (Qs + Qa) (Formula 3)
Can be calculated. L is the distance between the inlet slit 111 and the outlet slit 120, R2 is the inner radius of the outer cylinder electrode 104, R1 is the outer radius of the inner cylinder electrode 103, Qs is the sheath gas flow rate, and Qa is the sample gas flow rate.

  When the classified charged particles are volatile particles, the particle size changes from the exit slit 120 to the particle measuring instrument 3, but after entering the exit slit 120, the particle size changes. There is no influence on the count value by the particle measuring instrument 3.

  The measurement stopping unit 22 stops the measurement operation of the sample gas being measured when the particle size change determining unit 16 determines that the particle size has changed.

  Referring back to FIG. 1, the DMA 2 is connected with a temperature measuring device 7 that measures the temperature in the housing 101 and a pressure measuring device 8 that measures the pressure. The measurement signals of the temperature measuring device 7 and the pressure measuring device 8 are taken into the computer system 6 through the interface 5. The measured values of temperature and pressure taken into the computer system 6 are displayed or recorded together with the measurement result of DMA2.

  An embodiment of a measurement method using the apparatus of this embodiment will be described with reference to the flowchart of FIG. The measurement is performed according to the following procedure. The particle size distribution is measured at the sheath gas flow rate A (step S101). For example, the flow rate A is set to the maximum flow rate at which the target particle size range can be normally measured by DMA. The particle size distribution measurement is the same as the normal measurement except that it is performed at the sheath gas flow rate A. Normal measurement is as follows. The computer system 6 sends a signal to the flow rate control devices 1 and 9 so that the sheath gas flow rate becomes the flow rate A, sends a signal to the voltage generator 4 and applies a classification voltage to the DMA. The classification voltage is a voltage applied between the inner cylinder electrode 103 and the outer cylinder electrode 104. This voltage is set to be negative or positive depending on the polarity of the charged particles. The computer system 6 waits for a sufficient time for the particles classified by DMA by the applied voltage to reach the particle measuring instrument 3, and then receives a signal corresponding to the number of particles from the particle measuring instrument 3, and integrates it for a certain period of time. Record. The number of particles is recorded by changing the applied voltage one after another. The voltage to be applied may be changed from the low voltage side to the high voltage side, or vice versa, or the voltage increase and decrease may be appropriately combined. A temperature signal and a pressure signal are received and recorded from the temperature measuring device 7 and the pressure measuring device 8, respectively. Calculate the particle size distribution from the recorded results. For the vertical axis of the particle size distribution, the integrated value of the number of particles at each recorded classification voltage may be used, and the integrated value of the number of particles is used as a constant flow pump (not shown) downstream of the particle measuring instrument 3. A value obtained by dividing by the integral value of the flow rate, such as, may be used. The value obtained by dividing the integral value of the number of particles by the integral value of the flow rate is the number density, and the number / cc (number per cubic centimeter) is generally used as the unit. Regarding the horizontal axis, if the shape, temperature, pressure, and sheath gas flow rate of the apparatus do not change, the applied voltage V and the particle size Dp are in a one-to-one correspondence from the relationship of Equations 1 and 2. Since the detected temperature value and the detected pressure value are recorded, the reliability of the measurement data can be ensured if the recorded temperature and pressure are constant.

  Next, the particle size distribution is measured at the sheath gas flow rate B (step S102). For example, the flow rate B is set to the minimum flow rate at which the particle size range measured at the flow rate A can be normally measured. Processing similar to that in step S101 is performed to obtain a particle size distribution at the flow rate B.

  It is determined whether there is a change in particle size between the flow rate A and the flow rate B (step S103). The change is determined by a method such as taking a difference between particle size distributions, or obtaining and comparing the center particle size by peak detection in each particle size distribution. If it is determined that the particle size distribution has changed, the display ends indicating that a sample not suitable for measurement is being measured (step S104).

  The simulation result about the influence which the particle size reduction in DMA has on the measurement is shown in FIGS. 5A to 5E. FIG. 5A shows the change over time of particle size reduction in a gas not containing the vapor of the component of the particles. 201 is a non-volatile particle | grain, 202 is a time change of a volatile particle | grain. The dotted line 203 uses a certain DMA (Wyckoff standard type, standard state), the sheath gas flow rate is 19.0 SLM (standard liter per minute), the aerosol gas flow rate is 1.0 SLM, and the sum of the sheath gas flow rate and the aerosol gas flow rate (below) Represents the time required for the particles to pass through the DMA when the total gas flow rate is 20 SLM, and the dotted line 204 shows the sheath gas flow rate while keeping the aerosol gas flow rate constant at 1.0 SLM. The time required for the particles to pass through the DMA when using the 9.0 SLM (total gas flow is 10 SLM) is shown. The particle size of the non-volatile particles does not change with time, but the particle size of the volatile particles decreases with time.

  Next, simulation results of graphs obtained by measuring the particle size distribution are shown in FIGS. 5B to 5E. As the particle size distribution, a lognormal distribution assumed to be exhibited by a general aerosol was assumed.

A graph 205 in FIG. 5B shows a distribution obtained when the particle size distribution of nonvolatile particles is measured with a total gas flow rate of 20 SLM, and a graph 206 shows a distribution when the total gas flow rate is 10 SLM. A graph 207 in FIG. 5C represents the result of the normalized difference calculated by the following equation.
I _d (D _p ) = (I ₂₀ (D _p ) −I ₁₀ (D _p )) / I ₂₀ max (Formula 4)
Here, I ₂₀ (D _p ) is the number density at the total gas flow rate 20 SLM at the particle size Dp, I ₁₀ (D _p ) is the number density at the total gas flow rate 10 SLM, and I ₂₀ max is the total gas flow rate ₂₀ SLM. The maximum number density of the particle size distribution is shown.

  A graph 208 in FIG. 5D shows a distribution obtained when the particle size distribution of volatile particles is measured with a total gas flow rate of 20 SLM, and a graph 209 shows a distribution when the total gas flow rate is 10 SLM. Graph 209 in FIG. 5E represents the normalized difference result calculated by Equation 4.

  Next, an example of a change determination method will be described. The determination is made by setting a threshold value for the difference between the maximum value and the minimum value of the normalized differences. As shown in the graph 207 of FIG. 5C, there is no difference in the nonvolatile particles. For volatile particles, there is a difference of 0.8 as shown in graph 210 of FIG. 5E. If the difference threshold is set to 0.1, it is determined that there is a difference between the graphs 208 and 209 and a message indicating that they are not suitable for measurement is displayed. The threshold can be arbitrarily set.

  Moreover, the method of determining the presence or absence of a particle size change may be other methods. For example, the particle size center may be obtained by peak detection and compared.

  The results obtained in the DMA measurement experiment are shown in FIG. 6A. FIG. 6A shows the result (301) of measuring particles containing volatile substances at a total gas flow rate of 20 SLM and the result of measurement (302) at a total gas flow rate of 10 SLM. The peak appearing at the particle size of 18 nm is that of the non-volatile particles serving as the nucleus, and does not change even when the total gas flow rate is changed.

  On the other hand, the broad peak appearing in the vicinity of the particle size of 100 nm in the graph 301 as a result of measurement with the total gas flow rate of 20 SLM is due to particles having volatile substances attached to the nonvolatile particles. This peak near a particle size of 100 nm at a total gas flow rate of 20 SLM is a total gas flow rate of 10 SLM, that is, a measurement result 302 when the passage time in the DMA is twice that of the total gas flow rate of 20 SLM. You can see that it has moved to. In order to make this difference easy to see, the result of calculation using Equation 4 is shown in the graph 303 of FIG. 6B. The difference between the minimum value and the maximum value of the plot of the graph 303 is 0.17. If the above-mentioned standard (threshold is set to 0.1) is temporarily applied, it is determined that this measurement is measuring a sample that is not suitable for measurement, and a message indicating that a sample that is not suitable for measurement is being measured is displayed. .

  Another embodiment of the measuring method using the apparatus of this embodiment will be described with reference to the flowchart of FIG. In this case as well, the process up to the determination of suitability for measurement (steps S101 to S104) is the same as in the embodiment of FIG. In this embodiment, an attempt is made to estimate the particle size before entering DMA for volatile particles determined to be inappropriate.

  The particle size distribution is measured at a sheath gas flow rate A1 different from steps S101 and S102 (step S401). This flow rate A1 is set to an average value of the flow rates A and B, for example. As a particle diameter at each of the flow rates A, B, and A1, a particle diameter center value is obtained by peak detection or the like. Further, the DMA passage time t of each particle of the flow rates A, B, and A1 is calculated by Equation 3 (step S402). These three particle size center values are plotted as shown in FIG. 5A, with the particle size as the vertical axis and the time t as the horizontal axis. By applying curve fitting to the result, the particle size (initial particle size) at t = 0 is obtained (step S403).

  It is determined whether or not the error of the initial particle size is below the reference (step S404). If the error is above the reference, the sheath gas flow rate A2 is set to a flow rate different from A, B, A1, and the particle size distribution measurement Is performed (step S401). This operation is repeated until the standard is satisfied. The initial particle diameter estimated when the value is below the reference is displayed and the process ends (step S405).

1 Flow control device (for sheath gas)
2 DMA
3 particle measuring instrument 4 voltage generator 5 interface 6 computer system 7 temperature measuring instrument 8 pressure measuring instrument 9 flow control device (for surplus gas)
DESCRIPTION OF SYMBOLS 12 Particle size distribution measurement means 14 Sheath gas flow control means 16 Particle size change judgment means 18 Display part 20 Particle size estimation means 103 Inner cylinder electrode 104 Outer cylinder electrode 105 Classification area | region 107 Sheath gas supply part 111 Charged aerosol inlet slit 120 Outlet slit

Claims (12)

A pair of electrodes;
A voltage generator for applying a voltage between the pair of electrodes;
A sheath gas supply section for introducing sheath gas into the space from one end of the space between the pair of electrodes;
An inlet slit provided on one electrode side of the pair of electrodes downstream of the sheath gas supply unit and serving as a charged particle introduction port for supplying a sample gas containing charged particles in the flow of the sheath gas;
An outlet slit that is provided on the other electrode side of the pair of electrodes downstream of the inlet slit with respect to the sheath gas flow and discharges charged particles classified by electrostatic force generated by the voltage;
A particle counter for counting charged particles discharged from the exit slit;
Particle size distribution measuring means for measuring the particle size distribution of charged particles in the sample gas by changing the voltage by the voltage generator and taking in the detection signal of the particle measuring instrument;
Sheath gas flow rate control means for changing the flow rate of the sheath gas supplied from the sheath gas supply unit into at least two types;
From the comparison of particle size distributions measured under different sheath gas flow rates, it is determined whether or not there is a change in particle size while the charged particles pass between the entrance slit and the exit slit in the space between the pair of electrodes. A differential type electric mobility measuring device comprising a particle size change determining means.   The particle size change determination means obtains a difference in number density for each particle size of each particle size distribution measured at different sheath gas flow rates, and the difference between the maximum value and the minimum value of the difference is determined based on a preset threshold value. The differential electric mobility measuring apparatus according to claim 1, wherein it is determined that the particle size has changed when the particle size is large.   The differential electric mobility measurement according to claim 2, wherein the particle size change determining means normalizes each particle size distribution measured at different sheath gas flow rates and determines whether there is a change in particle size based on the difference. apparatus. With a display,
4. The method according to claim 1, wherein when the particle size change determination unit determines that there is a change in particle size, the display unit outputs that the sample gas containing the charged particles is not suitable for measurement. The differential electric mobility measuring device described. When the particle size change determining means determines that there is a change in particle size, the particle size change determining means further comprises a particle size estimating means for calculating the particle size when there is no change in particle size,
The particle size estimation means includes a particle size at a peak position of each particle size distribution measured under a plurality of types of sheath gas flow rates and a time required for the charged particles to pass from the entrance slit to the exit slit. t is determined, and the amount of change in particle size is expressed as a function of time t, so that the particle size when the passing time t is extrapolated to zero is set as the particle size at the peak position of the distribution before the particle size change. The differential electric mobility measuring device according to any one of claims 1 to 3.
Here, the passage time t is determined from the space H between the electrodes, the volume H of the region surrounded by the positions of the inlet slit and the outlet slit, and the sheath gas flow rate Qs and the sample gas flow rate Qa flowing through the region.
t = H / (Qs + Qa)
As required.   5. The differential electric transfer according to claim 1, further comprising a measurement stop unit that stops the measurement operation of the sample gas being measured when the particle size change determination unit determines that the particle size has changed. Degree measuring device. A pair of electrodes;
A voltage generator for applying a voltage between the pair of electrodes;
A sheath gas supply section for introducing sheath gas into the space from one end of the space between the pair of electrodes;
An inlet slit that is provided on one electrode side of the pair of electrodes downstream of the sheath gas supply unit and serves as a charged particle introduction port for supplying a sample gas containing charged particles in the flow of the sheath gas;
An outlet slit that is provided on the other electrode side of the pair of electrodes at a position downstream of the inlet slit with respect to the sheath gas flow, and discharges charged particles classified by electrostatic force generated by the voltage;
A particle counter for counting charged particles discharged from the exit slit;
Particle size distribution measuring means for measuring the particle size distribution of charged particles in the sample gas by taking in the detection signal of the particle measuring instrument by changing the voltage by the voltage generator;
Using a differential electric mobility measuring device with
A particle size distribution measuring step of changing the flow rate of the sheath gas supplied from the sheath gas supply unit into at least two types, and measuring the particle size distribution of charged particles in the sample gas under each sheath gas flow rate;
From the comparison of the particle size distribution measured under different sheath gas flow rates, the change in the particle size while the charged particles pass through the classification region between the entrance slit and the exit slit in the space between the pair of electrodes. A particle size change determination step of determining presence or absence;
A differential electric mobility measurement method comprising: A pair of electrodes;
A voltage generator for applying a voltage between the pair of electrodes;
A sheath gas supply section for introducing sheath gas into the space from one end of the space between the pair of electrodes;
An inlet slit that is provided on one electrode side of the pair of electrodes downstream of the sheath gas supply unit and serves as a charged particle introduction port for supplying a sample gas containing charged particles in the flow of the sheath gas;
An outlet slit that is provided on the other electrode side of the pair of electrodes at a position downstream of the inlet slit with respect to the sheath gas flow, and discharges charged particles classified by electrostatic force generated by the voltage;
A particle counter for counting charged particles discharged from the exit slit;
A sheath gas flow rate control device capable of adjusting the sheath gas flow rate by controlling the operation of the voltage generator and the sheath gas supply unit, and means for measuring the particle size distribution of charged particles in the sample gas by taking the detection signal of the particle measuring instrument In a program used in a differential electric mobility measuring device comprising:
A program for causing a computer to function as the particle size distribution measuring unit, the sheath gas flow rate control unit, and the particle size change determining unit according to any one of claims 1 to 3. The differential electric mobility measuring device further includes a display unit,
9. The program according to claim 8, wherein when the particle size change determining means determines that there is a change in particle size, the display unit displays an indication that the sample gas containing the charged particles is not suitable for measurement. . The program further includes a particle size estimation unit that estimates a particle size when it is assumed that there is no change in the particle size when the particle size change determination unit determines that the particle size has changed.
The particle size estimation means includes a particle size at a peak position of each particle size distribution measured under a plurality of types of sheath gas flow rates and a time required for the charged particles to pass from the entrance slit to the exit slit. t is determined, and the amount of change in particle size is expressed as a function of time t, so that the particle size when the passing time t is extrapolated to zero is set as the particle size at the peak position of the distribution before the particle size change. The program according to claim 8 or 9.
Here, the passage time t is determined from the space H between the electrodes, the volume H of the region surrounded by the positions of the inlet slit and the outlet slit, and the sheath gas flow rate Qs and the sample gas flow rate Qa flowing through the region.
t = H / (Qs + Qa)
As required.   10. The program according to claim 8, further comprising a measurement stopping unit that stops the measurement operation of the sample gas being measured when the particle size change determining unit determines that the particle size has changed. .   The computer-readable recording medium which recorded the program as described in any one of Claims 8-11.

Images