JP2004301689A - Wide-range particle counter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To measure aerosol with high accuracy and with high reliability over a wide particle size range. <P>SOLUTION: This wide-range particle counter 10 has partitions for separately detecting bulky particles and minute particles in the aerosol. Bulky particles are counted by an optical particle counter to determine their sizes. Minute particles are classified by a differential mobility analyzer to determine their sizes, then passed through an evaporator and a condenser, and counted. The use of the different partitions makes it possible to count and measure the wide ranging particle sizes with high accuracy and with high reliability in a single device. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method and apparatus for measuring aerosol particle distribution over a wide range of particle sizes. In particular, the invention relates to the measurement of particles suspended in a gas called an aerosol. The most common carrier gas is air, but other gases such as nitrogen, helium, argon, CO ₂ And other gases and the like may be a medium for particle suspension. The particles can be solids, liquids or mixtures thereof.
[0002]
[Prior art]
In the surrounding atmosphere, particles can be present in a size range from about 2 nanometers (nm) to over 50,000 nm in diameter. Particles in the range from 10 nm to 10,000 nm are most important from a health and safety point of view. At present, there is no single device capable of measuring particles over this range. The wide range of particle counters (WPCs) described herein make this possible.
[0003]
Currently, commercially available particle counters have a limited working range size, and several different particle counters are required to properly analyze aerosols.
[0004]
Aerosols occur in both natural and man-made environments. They are important in scientific research and technical applications. Aerosol particles in the atmosphere can scatter light and affect the visibility of the atmosphere. Suspended particles, when inhaled, accumulate in the lungs and can affect human health. It is often necessary to measure aerosol particles so that the source of the particles can be controlled or, if the source cannot be controlled, advance precautions can be taken.
[0005]
Aerosols can be generated intentionally for scientific and technical applications. In experimental studies, for example, aerosols with a controlled size distribution are needed to test filters and other particle collectors to determine their efficiency. In medical applications, drug mixtures are often generated in aerosol form for distribution to the lungs for treatment of disease. At this time, the particle size distribution is important. Because the particle size determines the specific area of the lung where the inhaled particles will accumulate, and determines the effectiveness and effectiveness of the inhaled drug. In all cases in this specification, a gas containing suspended particles is referred to as an aerosol, and there is no limitation as to the chemistry of the particles, the chemistry of the gas, and the physical state of each of them.
[0006]
Currently, one of the most widely used aerosol measuring instruments is the Optical Particle Counter (OPC) first described in US Pat. No. 2,732,753 (O'Consky). In OPC, an aerosol is passed through a beam of light to cause optical scattering. Next, the light signal scattered from each particle is detected and correlated to the particle size. OPC can detect particles down to lower size limits of about 100 nm in diameter. At this time, some special OPCs were designed to detect particles of about 60 nm in diameter or characteristic size.
[0007]
Another particle measurement instrument is a condensation nucleus counter (CNC), which is also referred to as a condensation particle counter. The most widely used CNC is that based on U.S. Pat. No. 4,790,650. In this CNC, the aerosol is initially saturated with the working fluid vapor at an elevated temperature. A typical working fluid is butyl alcohol and a typical saturator temperature is 35 ° C. The vapor-deposited aerosol then passes through a condenser, typically maintained at 5 ° C., to cool the gas and condense the vapor onto the particles to form droplets. Droplets are counted by optical scattering as in conventional OPC. The CNC can detect particles even smaller than the lower size limit of OPC. The droplets formed by vapor condensation are much larger than the particles themselves, thus making them easier to detect by light scattering.
[0008]
Since the CNC can only count particles and cannot measure the particle size, to determine both size and particle count, the CNC requires a size analyzer, such as a mobility analyzer. Must be combined with A differential mobility analyzer (DMA) is typically used for sizing. The DMA method of size classification is based on the electrical mobility of a single charged particle, ie, a particle that carries a single electron charge unit. Riu and Puy (1974 degrees), and Natson and Phytoby (1975) were developers of DMAs for this application. A publication describing this DMA method was published in April 1974 in the Journal of Colloids and Surface Chemistry, Vol. 47, No. 1 in Benjamin Y. H. Liu, David Y. H. See, "Submicron Aerosol Standard and Major Absolute Calibration of Condensation Nuclei Counters", described by Puy, and in the 1975 Journal of the Aerosol Science, pages 443-451. O. Natson and K.S. T. "Aerosol Classification by Electrical Mobility: Devices, Theory and Applications" described by Fitzby.
[0009]
Recent improvements in DMA can be found in Darrenchen, David Y., published in the Aerosol Science Journal Vol. 30, No. 8, pages 983-999, published by Chen et al. H. Puy, George W. An article by Murholand and Marco Fernandez, "Design and Testing of Aerosol / Sheet Entrance for High-Resolution Measurements Using DMA" (1995). The development of nano-DMA for particle measurements below 50 nm in particle diameter is disclosed by Puy et al. In US Pat. No. 6,230,572 B1. These recent developments have further improved the accuracy and range of DMA devices.
[0010]
The DMA method of size classification relies on the fact that the electrical mobility of a single charged particle is inversely related to particle size. Polydisperse aerosols over a certain size, including single charged particles, can be classified according to size in an electric field and can generate almost monodisperse aerosols within a narrow range of electrical mobilities. it can. The aerosol thus generated contains particles of approximately the same size. DMA is generally limited to particles smaller than about 500 nm in diameter.
[0011]
All aerosol measuring instruments do have their own size limitations. In the case of DMA, the limitation is due to the low electrical mobility of the large particles. As the particle size increases, the voltage required to sort the particles by electrical mobility also increases. At normal flow rates used in differential mobility analysis, voltages on the order of 10,000 volts may be required to classify particles with a diameter of 500 nm. For this reason, mobility analysis is rarely used above the upper limit size of about 500 nm.
[0012]
On the other hand, OPC is limited to the particle size at which it can be detected satisfactorily due to the scattered light signal from the particle which generally decreases with decreasing particle size. Below about 100 nm, the scattered light signal starts to shift to the so-called Rayleigh scattering region. In this region, the signal fluctuates approximately at the sixth power of the particle size. Thus, a reduction factor of 2 in particle size results in a 64-fold reduction in the scattered light signal. Detecting small particles smaller than 100 nm becomes increasingly difficult, even when using high power lasers, optics with high numerical apertures, and sensitive photodetectors as light sources. Light particle counters have been designed to detect particles of about 60 nm in diameter, but the equipment required is generally large and expensive. For this reason, high sensitivity optical particle counters are not widespread.
[0013]
In principle, the optical particle counter can be further improved to detect particles smaller than 60 nm. With further advances, even smaller particles may be detectable. However, advances in optical particle counting technology have made it less useful for aerosol measurements over a wide size range. Optical particle counter designers have not recognized the problems associated with a wide range of particle counts and the special requirements that must be met to measure particles over a wide range of sizes. The request will be described using the following example.
[0014]
In the surrounding atmosphere, the aerosol size distribution generally follows Jung's law. This law stipulates that the concentration of aerosol particles larger than a certain size is inversely proportional to the cube of the particle size. If the concentration of atmospheric particles greater than 50 nm is, for example, 30,000 particles per cc, the concentration of particles greater than 500 nm will be a factor below 1,000, ie on the order of 30 particles per cc. For particles larger than 5,000 nm, the concentration is reduced by a factor of one million, ie, on the order of 0.03 particles per cc.
[0015]
The sharply falling concentration of large particles in the atmosphere means that even if a single detector has been developed that can detect particles over a wide size range, for example from 50 nm to 10,000 nm in diameter, Shows that when operated at a particular sample flow rate, it will produce a very high particle count rate for small particle ranges and a very low count rate for large particle ranges.
[0016]
For example, a sample flow rate of 1 liter per minute (lpm) or 1,000 cc per minute would result in 30,000,000 particles per minute in the 50 nm to 500 nm diameter range, which would be counted. You need to do it. Such count rates will generally be too high and exceed the count rate limits of current optical counter technology. On the other hand, particles sampled over 5,000 nm will only give 30 counts per minute when sampled by the detector. Such particle counts are usually too low for purposes such as statistical accuracy.
[0017]
At a more reasonable rate, to count fine particles in the atmosphere in the range of 50 nm to 500 nm, the detector flow rate only needs to count 3,000,000 particles per minute. For example, it can be reduced to 0.1 (lpm). At such a sampling flow rate, the detector will only count three particles per minute in the range greater than 5,000 nm, thus degrading the statistical accuracy of large particle counting. On the other hand, in order to improve the statistical counting accuracy for large particles, if the sampling flow rate is increased, for example to 10 (lpm), so that 300 particles per minute in the range greater than 5,000 nm can be counted It is necessary to count 300,000,000 particles in the range of 50 nm to 500 nm, thus exacerbating the counting rate requirement of the counter for fine particles.
[0018]
This example illustrates why OPC cannot measure aerosols over a wide size range, and why conventional OPCs themselves do so accurately over the entire particle size range of interest in aerosols. It shows whether it is essentially impossible to make any measurements.
[0019]
[Means for Solving the Problems]
The present invention provides multiple flow rates by forming suitable flow rates for detecting and measuring aerosol particles over a wide size range, typically 10 nm to 10,000 nm in diameter, and more broadly 2 nm to 50,000 nm. A single measurement device built on a common chassis or single platform using sensors. Devices that measure particle sizes from 10 nm to 10,000 nm are referred to as wide-range particle counters (WPCs), and devices that range from 2 nm to 50,000 nm are referred to as ultra-wide-range particle counters (UWPCs). You. These devices make it possible to perform measurements that are not possible with currently available device configurations.
[0020]
The WPC described herein is based on a novel combination of multiple sensors or detectors that combines electrical mobility analysis and optical detection to form a single device covering a wide range of particle sizes. ing. Each sensor is optimized in terms of particle measurement range, aerosol flow rate, reduction of particle loss in the sampling line, optical and electrical design.
[0021]
The measurement device of the present invention is single in design, but can still perform automatic measurements over a wide size range.
The lower limit is preferably between 2 nm and 20 nm, and the upper limit may be anywhere between 5,000 nm and 50,000 nm.
[0022]
The device is provided with control means for controlling operating parameters to ensure reliable device operation, measurement accuracy and ease of use.
The number of sensors, flow meters, pumps and other components is minimized so that complex devices such as WPCs can be manufactured at a simplified and reasonable cost.
[0023]
The resulting device described herein is estimated to weigh less than about 35 pounds, making the device compact and convenient to use.
[0024]
BEST MODE FOR CARRYING OUT THE INVENTION
In FIG. 1, a typical wide-range particle counter 10 is shown. The components shown in FIGS. 1 and 2 are provided on a chassis or platform 11 that accommodates the components. The chassis or platform forms the support structure for the component. The controller described below can receive an operator input from the control or function button 11A. The display screen 11B is provided for displaying a message or read data from an internal processor or a computer forming the controller.
[0025]
An inlet nozzle or tube 11C is also shown, which leads to internal lines and counters.
FIG. 1A is a schematic diagram of a wide-range particle counter 10 according to the first preferred embodiment. The particle counter 10 is provided on the chassis or housing 11 shown in FIG. This includes two light scattering particle sensors 12 and 14, a differential mobility analyzer 16, a saturator 18, a condenser 20, an ionizer 22, and pumps 24, 26, 28 associated therewith. , Flow meters 30, 32 and 33 and a particle filter 34. The saturator 18, condenser 20 and light scattering particle counter 14 can be made as a sub-assembly, as indicated by the dashed lines.
[0026]
The first particle sensor 12 is a light scattering particle counter (LPC) for detecting coarse particles of a certain size, typically larger than 300 nm in diameter. The aerosol is pumped by the pump or flow generator 24 from the inlet line 11C through line 38 and through the LPC 12 at a flow rate of Q / min. ₁ Pulled in liters (lpm). To measure the aerosol flow, the aerosol air flow also passes through a flow meter 30. The output signal from the flow meter 30, which indicates the flow rate, passes through the light scattering ₁ Used in conjunction with the controller 40 to change the speed of the pump 24 to maintain
[0027]
At the same time, the second air flow rate Q ₂ Is formed in line 42 by branching into line 38, so that the same aerosol source is formed in both tributaries. The flow in the line 42 carries particles according to the method of the present invention to detect particles below a certain restricted size, typically 300 nm in diameter. This flow is established by the pump 26. Flow Q ₂ Flows through the ionizer 22 and the line 42 is connected to the differential mobility analyzer (DMA) 16. The output line from DMA 16 is connected to a saturator 18, a condenser 20, and a light scattering particle sensor 14 used as a light scattering droplet counter (LDC). The output of the flow meter 32 is Q ₂ Is used in conjunction with the electronic controller 40 to change the speed of the pump 26 to maintain the desired value. The electronic controller 40 may be part of an overall system 39 having power, signal and data capable output and control electronics. System 39 is mounted on the chassis.
[0028]
A third pump 28 connected to the sheath flow outlet of DMA 16 provides a constant air flow Q in line 50 to DMA to provide the required clean sheath gas flow for DMA. ₃ To maintain. The flow sensor and the controllers required to maintain this flow at a constant value are not shown for brevity and clarity. The sheath flow is drawn from an annular space 49 surrounding the high voltage electrode 53. Flow Q ₃ A high efficiency particle filter 34 is used in line 50 to remove unwanted particulate contaminants in the flow before the flow is introduced back into the DMA 16 in the sheath flow inlet chamber 51. After passing through DMA, sheath flow Q ₃ Passes through flow meter 33 before the flow goes to the inlet of pump 28 to complete the flow loop. The flow signal output from the flow meter 33 has a constant sheath flow Q ₃ Used in conjunction with the electronic controller 40 to change the speed of the pump 28 to maintain
[0029]
Flow Q in line 38 for coarse particle detector or counter 12 ₁ Is generally the flow rate Q for a fine particle detector or DMA 16 ₂ Must be higher. For atmospheric measurements, a 10 to 1 Q ₁ / Q ₂ Is reasonably and completely achievable. For other applications, a flow ratio of 2: 1 or even 1: 1 may be sufficient.
[0030]
Due to Jung's law of the atmospheric size distribution, the flow ratio less than 1 to 1, ie Q ₁ <Q ₂ Would not be very useful for aerosol size distribution analysis using the multiple sensor approach described herein. In the preferred embodiment shown in FIG. 1, a typical value for the flow rate is Q ₁ = 3 (lpm), Q ₂ = 0.3 (lpm). A typical clean sheath flow rate for DMA 16 is typically and preferably Q ₃ = 3 (lpm).
[0031]
There is an intermediate range of particle sizes that can be accurately measured by both fine and coarse particle detectors. This intermediate size range can be from 90 nm to 600 nm. Thereby, for a coarse particle detector having a nominal lower limit of 200 nm, the coarse detector will be operating in this intermediate range. Fine particle detectors with an upper limit of 300 nm also operate within this intermediate range.
[0032]
In addition to the embodiment of FIG. 1A, other embodiments can be used. FIG. 2 is mounted on a chassis 11 as shown in FIG. 1 for aerosol measurement over a particle diameter range of 10 nm to 10,000 nm. In this embodiment, two light scattering particle counters 60 and 62 are used to cover a diameter range of 1,000 nm to 10,000 nm and a diameter range of 100 nm to 1,000 nm, respectively. A fine particle counter composed of a CNC, shown as a light scattering droplet counter 64, receives the flow from DMA 66 through line 78. This stream passes through a saturator 68 and a condenser 70 connected in series by line 72. A fine particle counter 64 is used to cover the diameter range from 10 nm to 100 nm. Again, the two counter assemblies, both the fine and coarse particle counters, overlap in the mid-size range.
[0033]
The inlet flow to the system 59 passes through line 76 from source 77 to the entrance of light scattering particle ₁ Transport. Line 76 can be connected to inlet tube 11C of FIG. The output portion is connected to a line 78 via a flow meter 80, and further connected to the inlet side of a pump 82. The flow signal from the flow meter 80 is provided to the controller 84, which signals the appropriate flow rate Q ₁ Is used to control the pump 82 so that is established at line 76. The pump 82 discharges a flow returning to the atmosphere away from the inlet of the line 76. The controller 84 can be part of an overall control system 85 based on a computer to control the required functions.
[0034]
Line 86 is connected to line 76 and provides a flow rate Q provided to counter 60. ₁ Lower flow rate Q ₂ To carry the particles. Flow Q ₂ Is provided to the second light scattering particle counter 62. The output flow from the light scattering counter 62 is connected to the inlet of a pump 90 via a flow meter 88. A flow meter 88 is also connected to provide a flow signal to a controller 84, which controls the appropriate flow rate Q on line 86. ₂ Adjust pump 90 to establish The output of the pump 90 is discharged to the atmosphere again at a distance from the inlet line 76.
[0035]
The line 94 is connected to a line 85 on the input side of the light scattering particle counter 62, and is connected to a differential mobility analyzer 66 via an ionizer 96 to obtain a flow rate Q. ₃ Transport. Flow Q ₃ Is established by the pump 98 at the output of the counter 64. The pump provides a flow rate Q to pump 98 via line 72, output line 100 from counter 64, and flow meter 102. ₃ Transport. Condenser 70 condenses the vapor generated by saturator 68A onto the particle nuclei to form droplets counted by light scattering counter 64.
[0036]
Flow meter 102 provides a signal to controller 84 to control pump 98 to provide the desired level of flow through lines 72 and 94. The flow from the pump 98 is discharged into the atmosphere.
[0037]
In FIG. 2, three separate pumps 82, 90 and 98 are shown and the gas flow Q ₁ , Q ₂ And Q ₃ To maintain their respective constant values, individual flow sensors and controllers are used. Another way to maintain a constant gas flow is to use a critical orifice connected to a common vacuum source maintained by a single vacuum pump. When sampling the gas from atmospheric pressure, when the vacuum is at about half the pressure of the atmosphere, the flow becomes blocked and reaches a constant value. By selecting an appropriate orifice size, the flow rate Q ₁ , Q ₂ And Q ₃ Can be maintained at a constant value without a separate sensor and variable speed pump.
[0038]
The required sheath flow for the differential mobility analyzer is provided along line 104 and the flow rate Q ₄ Is represented by Sheath flow enters the DMA chamber 103 and is directed through the annular sheath flow passage 107 and flows down the central high voltage electrode 105.
[0039]
The flow line 104 comes from the output of a pump 106 having an input line 108 leading from a sheath flow annular passage 107 of the differential mobility analyzer through a flow meter 110. The high efficiency filter 112 has a flow rate Q ₄ Is provided in the line 104 on the output side of the pump 106 so that the flow of the air is kept very clean. Flow meter 110 also provides a signal to controller 84 to control pump 106 to establish an appropriate flow rate.
[0040]
The respective particle delivery flow rate for the three sensor combination 59 is Q ₁ , Q ₂ And Q ₃ These flows are represented by Q ₁ > Q ₂ > Q ₃ It has the relationship This particular embodiment of the invention has the advantage of further improving the statistical counting accuracy over the entire size range. At the same time, the configuration of the embodiment shown in FIG. 2 reduces the size range of particles that must be classified by the DMA 66 and, as described below, the required high voltage for the central electrode 105 of the DMA. , And further reduces the physical size and weight of DMA66.
[0041]
In yet another embodiment of a particle counter assembled in the same schematic diagram as FIG. 2, two light scattering particle counters 60 and 62 are provided with a diameter range of 5,000 nm to 50,000 nm and a diameter range of 500 nm to 5,000 nm. It can be used to measure particles in the diameter range. The DMA-CNC combination for fine particles can then be used to measure particles in the diameter range from 10 nm to 500 nm. The size range of the modified ultra-wide-range particle counter (UWPC) is between 10 nm and 50,000 nm, and thus can even be much wider than the size range of the wide-range particle counter shown in the specific example of FIG. The possible flow rates for the ultra wide range alternative to the particle counter of FIG. ₁ = 30 liters per minute (lpm), Q ₂ = 3 (lpm) and Q ₃ = 0.3 (lpm). Sheath flow Q ₄ Remains virtually the same as in the particular embodiment of FIG.
[0042]
In addition to the above, other coarse and fine particle sensors can be used in combination to overcome the fundamental limitations of individual sensors when applied to aerosol measurements. This aerosol measurement is, in some cases, almost 50 times, ie, particle size diameter spans a span of 2-100 nm, and more than 10 times concentration, ie, less than 0.001 particles per cc. From 10 per cc ⁷ Over the span up to the state exceeding. A single measurement assembly with a particle count sensor as described herein allows for such a measurement.
[0043]
The combination, including the type and number of sensors used in the combination, can be used to provide wide-range particle counting techniques for different purposes and / or different applications without substantially departing from the basic principles and approaches of the present invention. It will be apparent to one skilled in the art of particle counting technology that other modifications may be made to achieve the purpose of
[0044]
For certain optical particle counters that can be used in wide-range particle counters, FIGS. 3, 4 and 5 show two possible designs. In FIG. 3, the optical sensor is used as a light scattering droplet counter (LDC) for the CNC, such as that shown at 14 in FIG. 1A and at 64 in FIG. LDC uses forward scattering optics and a solid state diode laser 120 as the light source. The laser 120 has a suitable projection lens (not shown) to project an almost parallel beam of collimated light through a condenser lens 122 mounted on the wall of a housing 124. The lens 122 is a cylindrical lens that focuses the laser beam represented by 126 on the axis 125 between the aerosol inlet nozzle 128 and the aerosol outlet tube 130. Beam 126 expands after passing through its focal point at axis 125 and is projected onto lens 132 having opaque light absorbing surface portion 134. This opaque light absorbing surface portion 134 absorbs the laser beam and thus acts as a beam stop at the center of the lens.
[0045]
The aerosol is passed through nozzle 128 and into LDC housing 124. The nozzle is tapered so that it tapers toward its tip, and when the aerosol reaches the tip of the nozzle, the flow cross-section increases over a major portion of the line so that the aerosol is accelerated to high velocities. Have been very small. This high velocity aerosol is a gas containing the particles to be detected, passes across the focused laser beam 126 and flows out of the light scattering particle counter housing 124 through an outlet tube 130. As each particle passes through the focused laser beam at region 127, it scatters light in all directions. The condenser lens 132 focuses the scattered light within the angular range of the scattered light stretched by the lens 132 onto the photodiode detector 136. Although a single lens 132 is shown as a focusing lens for scattered light, more than one lens, i.e., multiple element lenses, may be used as a focusing means to improve performance.
[0046]
4 and 5, an optical particle sensor 150 using a 90 ° scattering optical system is shown. Optical particle sensor 150 is used as a light scattering particle counter, such as those shown at 12, 60 and 62 in FIGS. 1A and 2 to measure the size of the particles by detecting the scattered light signal. . Mounted on the housing 152 of the sensor 150 is a cylindrical lens 154 that focuses the laser beam 156 in the housing along the axis of the beam generated by the diode laser 158. The collecting lens 160 is mounted in a collar or tube provided on the side wall of the housing 152 and collects light scattered from particles passing across the laser beam focus 164. The aerosol is conveyed into the housing 152 through an inlet nozzle 162 that narrows the aerosol to a narrow flow as it passes across the focused area or focus 164 of the laser beam 156. The gas flow exits through tube 166. The common axis of the inlet nozzle 162 and the tube 166 is at 90 ° to the axis of the condenser lens 160.
[0047]
Light scattered from the particles provides an optical signal in a direction approximately 90 ° from the laser beam as the particles pass through the focused laser beam. These scattered light signals are collected by the condenser lens 160 and detected by the photodiode detector 168. A conical cavity 169 in the far end wall of the housing is open for receiving the laser light beam 156 and functions as an optical trap for absorbing the laser light. As each particle traverses the focused region 164 of the laser beam 156, the light signal scattered from the particle is detected by a photodiode detector 168. Note that the lens 160 is focused so that light scattered from particles that have passed through the focal point of the laser beam is directed to reach the detection surface of the photodiode detector 168.
[0048]
An optical particle sensor with both the forward scattering optics shown in FIG. 3 and the 90 ° scattering optical sensors of FIGS. 4 and 5 can be used to detect light scattered from the particles. However, due to particle size adjustment, light scattered within a certain narrow angle in the forward direction from the optical axis of the laser beam, that is, traveling in the same direction as the laser beam or the traveling direction of the laser beam It is generally preferred to use light scattering optics that reject scattered light that deviates only a small angle from the light.
[0049]
Light scattering particle sensors with forward scattering optics that maximize the collection of light signals scattered in the forward direction are more sensitive, but cause a scattering signal that is not a unit price function of particle size. This phenomenon, known as Mie scattering, can cause ambiguity in the measured particle size. For this reason, light scattering particle sensors with 90 ° scattering optics (FIGS. 4 and 5) or light from a focusing lens arranged at finite angles, for example 30 °, 45 °, 60 °, etc. A light scattering particle sensor with an axis is preferred. If the collection optics is designed to reject light signals scattered near the forward direction of the light beam, a light scattering particle sensor using a mirror instead of a lens can also be used.
[0050]
1A, the flow rate Q established by the pump 26 ₂ Passes through the ionizer 22, the DMA 16, the saturator 18, the condenser 22 and the light scattering droplet counter 14. The ionizer 22 typically includes a small, low level radioactive source such as, for example, radioactive krypton 85 or polonium 210. The α-rays, β-rays, or γ-rays emitted from the ionization source ionize air (gas) molecules. The ionized gas molecules then collide with the aerosol particles to cause a low level of charge to appear on the particles.
[0051]
When a charged particle reaches a state of charge equilibrium with ions, called the Boltzmann equilibrium, the charged particle becomes a certain amount of particles (charged and uncharged) in the gas. Have a relationship. In Boltzmann equilibrium, particles of a particular size and carrying, for example, a single charge occupy a fixed ratio to the total number of particles of that size in the gas. Since this ratio is known from theory, by measuring a single charged particle of that size, the total number of particles of that size in the gas can be determined.
[0052]
Different designs exist for differential mobility analyzers for aerosol classification by electrical mobility. The basic principles of operation of DMA are well known. A schematic of the preferred design for DMA is shown at 180 in FIG. It should be understood that the DMA shown in FIG. 6 is a preferred form of DMAs 16 and 66 in FIGS. 1A and 2. In this design, the central metal cylinder 182 forming the electrode is concentric with the outer tubular main cylinder 184 and its nested shorter outer cylinder 186. The inner and outer cylinders 182, 184 and 186 are each formed with a different electrical potential selected to establish a radial electric field in the annular space 200 between the inner cylinder 182 and the outer cylinders 184 and 186. The inner metal electrode cylinder 182 has a high voltage V ₁ And the outer cylinders 184 and 186 into which they are nested are installed. Outer cylinders 184 and 186 have the same inner diameter such that their inner surfaces form a single cylinder surface of uniform inner diameter. The inner cylinder 182 is supported by the upper insulating support 181 and the lower insulating support 183. Thus, the central high voltage electrode is insulated from the outer metal cylinder.
[0053]
A polydisperse aerosol source 188 carrying particles at Boltzmann charge balance is introduced into aerosol inlet 190 at the top of DMA 180. The aerosol inlet is separate from the sheath flow inlet. This polydisperse aerosol flows radially outward within the horizontal gap space 192, forming a passage between the end walls of the outer cylinders 184 and 186. The aerosol then passes through a short upper annular space 194 between the short outer cylinder 186 and the upper portion of the main outer cylinder 184 to form a lower end of the cylinder 186 and the interior of the main outer cylinder 184. Appears through the gap or space 196 between the shoulder 198 and the shoulder 198. The aerosol flows into the annular space 200 between the inner surface 202 of the cylinder 184 and the outer surface 204 of the inner high voltage electrode cylinder 182. A radial electric field is established between surfaces 202 and 204 and is used for mobility classification.
[0054]
As described above, the clean sheath gas flow required for mobility classification is introduced from the source 206 into the DMA through the clean sheath flow inlet tube 208 in the top wall 210 of the main outer cylinder 184. You. Tube 208 carries a sheath gas flow across chamber 192. The sheath gas flow passes through a fine mesh screen 212, which distributes the flow evenly across the cross-sectional area of the annular space 200, establishing a laminar flow below the screen 212. When this laminar sheath gas flow merges with the polydisperse aerosol flow emerging through slit 196, the flows combine to form a single laminar flow, and a high voltage central electrode cylinder 182 and a grounded cylinder It flows down the annular space 200 between 184 and 186.
[0055]
A portion of the flow in the annular space 200 can exit through a slit or passage 220 in the central electrode 182. This passage 220 is connected to an outlet bore 222 in the central electrode that opens through the insulating support 182 and leads to the particle counter. In addition, there are several spaced outlet holes 224 in the flange 226 of the support 183. Flange 226 functions to block annular passage 200 except for hole 224. Next, the flow exits through the opening 228 in the end wall 230 formed by the insulating support 183.
[0056]
Particles from a polydisperse source 188 with a charge having an electrical polarity opposite to the high voltage polarity of the inner cylinder 182 are drawn into the cylinder. When the center electrode has a positive polarity, the charged particles attracted to the outer surface 204 of the inner high voltage electrode cylinder 182 are negatively charged. As charged particles from the source 188 move and pass across laminar flow in the space 200 between the cylinder surfaces 202 and 204, they are classified, ie, separated according to electrical mobility. Small particles with high electrical mobility move through the laminar sheath flow more quickly than larger particles, and the small particles are deposited on the outer surface 204 of the cylinder 182 above the exit slit 220. Particles larger than the selected size that have a lower mobility and move at a lower speed do not reach the outer surface 204 of the cylinder 198. These larger particles (greater than the design cutoff size) are transported in excess flow through flow distribution holes 224 in the flange 226 of the lower insulating support 183 to the flow plenum 227 and the openings 228. Is discharged through.
[0057]
There is a small aerosol gas flow drawn through the outlet slit 220. This flow is generated by the flow generating means, pumps 26 and 98, respectively, as shown in FIGS. 1A and 2. Particles within the narrow range of electrical mobilities, and thus within the narrow size range, are deflected near the slit 220 and are conveyed as a monodisperse aerosol to the outlet passage 222 by the generated small airflow.
[0058]
For aerosol size distribution analysis, the high voltage on inner electrode 182 is adjusted through a series of voltage values using voltage controller 234. At each high voltage setting, the monodisperse particles at the outlet are counted by the CNC, as shown in FIGS. 1A and 2, with a saturator, condenser and light scattering droplet counter. The results can then be analyzed to give the size distribution of the aerosol.
[0059]
Saturators, such as saturators 18 and 68 in the CNC, are made from a porous material saturated with a working fluid, usually butyl alcohol in liquid form, and are shown as being taken from source 240 ( 1A and 2). The porous material is maintained at a suitably high temperature using a heater 242, typically 35 degrees. The passages in the porous material, such as passages 18A and 68A of FIGS. 1 and 2, allow the aerosol passing therethrough to be heated and saturated with the working fluid vapor as it passes.
[0060]
The condensers 20 and 70 consist of one or more flow passages in a solid metal block maintained at a low temperature, typically 5 ° C., using a cooler 244. As the heated vaporized aerosol passes through the condenser 20 or 70, the gas cools and supersaturates the vapor or gas. The supersaturated vapor condenses on the particles in the aerosol to form droplets, which are detected by respective light scattering droplet counters 114 and 64. The droplets formed are larger than the particles and are more easily counted.
[0061]
Since the purpose of wide-range particle analysis using WPC is to characterize the aerosol over most of its overall particle size range, the sample withdrawn by WPC for size distribution analysis is analyzed. It is important that this is a representative sample of the atmosphere to be obtained. For atmospheric aerosol measurements, the combined flow of the aerosol sample was drawn through the same common inlet and this total flow was analyzed for size distribution analysis by the respective coarse and fine particle detectors shown in FIG. 1A. Two subparts, Q ₁ And Q ₂ Is usually preferred. If the atmosphere to be analyzed is the interior space of a room with uniformly distributed airborne particles, the sample flow Q through separate sampling inlets for analysis by two separate particle counters ₁ And Q ₂ Can be pulled in. This is because the atmosphere is substantially uniform throughout the room.
[0062]
Sample flow Q of FIG. 1A for detection of coarse particles ₁ Transports coarse particles up to 10,000 nm in diameter for analysis, it is preferred that the flow path between the sampling inlet and the particle detection area in the coarse particle counter be relatively short. In addition, to avoid particle accumulation in the sampling line due to particle inertia that can occur when the flow direction changes, flow paths such as line 38, for example, should be provided so that the sample flow is hardly changed in the flow direction. It is important that the design be relatively straight.
[0063]
On the other hand, with a typical upper particle size of 200 nm, the air flow Q carrying the particles for detection by a fine particle detector Q ₂ For, there is less concern for particle loss during sampling and transport. Q ₂ Can be relatively long and can include one, two, or more 90 ° bends. The schematic flow diagram of FIG. 1, which shows a preferred embodiment, shows how this can be achieved. Coarse particle flow Q ₁ Is shown entering the coarse particle detector directly along line 38 without substantial change in flow direction. On the other hand, fine particle flow Q ₂ Is sampled from the entrance at line 42 and undergoes two 90 ° bends before entering the entrance of the fine particle detector, including DMA16.
[0064]
Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be routinely made in detail without departing from the spirit and scope of the invention.
[Brief description of the drawings]
FIG. 1 is a schematic diagram depicting a wide-range particle counter device showing a chassis or housing.
FIG. 1A is a schematic diagram of one embodiment of the present invention.
FIG. 2 is a schematic diagram of a second embodiment of the present invention using a different sensor configuration.
FIG. 3 is a cross-sectional view of one embodiment of a light-scattering droplet counter used in the particle counter of the present invention.
FIG. 4 is a cross-sectional view of an optical particle sensor used in the present invention using a focusing adapter at 90 ° to the laser beam.
FIG. 5 is a top cross-sectional view of the optical particle counter of FIG. 4, taken along line 5-5 of FIG.
FIG. 6 is a cross-sectional view of a differential mobility analyzer used in the present invention.
[Explanation of symbols]
10 Wide range particle counter
11 Chassis or platform
11A control or function button
11B display screen
11C Inlet nozzle or inlet pipe
12,14 Light scattering particle sensor
16 Differential mobility analyzer
18, 18A Saturator
20 condenser
22 ionizer
24, 26, 28 pump
30, 32, 33 flow meters
34 Particle Filter
38 lines
39 Overall System with Power, Signal and Data Processable Output and Control Electronics
40 Controller
42 lines
49 annular space
50 lines
51 Sheath flow inlet chamber
53 High voltage electrode
59 system
60, 62 light scattering particle counter
64 light scattering droplet counter
66 DMA
68, 68A Saturator
70 condenser
72 lines
76 lines
77 aerosol source
78 lines
80 flow meter
82 pump
84 Controller
85 Overall Control System
86 lines
88 flow meter
90 pump
94 lines
96 ionizer
98 pump
100 output lines
102 flow meter
103 chamber
104 lines
105 Central high voltage electrode
106 pump
107 Annular sheath flow passage
108 input line
110 flow meter
112 High efficiency filter
114 Light Scattering Droplet Counter
120 solid state diode laser
122 Condensing lens
124 housing
125 axis
126 laser beam
127 areas
128 Aerosol inlet nozzle
130 Aerosol outlet pipe
132 condenser lens
134 Opaque light absorbing surface
136 Photodiode detector
150 Optical Particle Sensor
152 housing
154 cylindrical lens
156 laser beam
158 diode laser
160 condenser lens
162 inlet nozzle
164 laser beam focusing
166 tubes
168 Photodiode detector
169 Conical cavity
180 DMA
181 Upper insulating support
182 Central metal cylinder
183 Lower insulating support
184 outer tubular main cylinder
186 outer cylinder
188 Polydisperse aerosol source
190 aerosol entrance
192 horizontal gap space
194 Upper annular space
196 gap / slit
198 shoulder
200 annular space
202 inside surface
204 outer surface
206 Clean sheath flow source
208 Clean sheath flow inlet tube
210 Top Wall
212 mesh screen
220 Passage / Exit slit
222 bore / exit passage
224 exit hole
226 flange
227 Flow filling room
228 opening
230 End Wall
234 Voltage Controller
240 liquid source
242 heater
244 cooler

Claims (8)

An apparatus for detecting particles in a gas over a wide range of particle sizes,
The broad particle size range includes upper and lower limits, and intermediate particle sizes between the upper and lower limits,
The device comprises:
Detecting a coarse particle in the coarse particle range between the upper limit and the intermediate particle size, a coarse particle detector,
Detecting a fine particle in the fine particle range between the lower limit and the intermediate particle size, a fine particle detector,
Signal processing means for processing an electrical signal from the coarse particle detector and the fine particle detector,
With
The apparatus, wherein the coarse particle detector and the fine particle detector, and the signal processing means are mounted on a common chassis. The device of claim 1, wherein the lower limit is in a particle size range from 2 nanometers to 20 nanometers. The device of claim 1, wherein the upper limit is in a particle size range between 5,000 nanometers and 50,000 nanometers. A gas flow generator that provides a gas flow containing particles to be detected by the coarse particle detector, and a gas flow containing particles to be detected by the fine particle detector,
The apparatus of claim 1, wherein a volume fraction of gas flow for the coarse particle detector is at least as large as a volume fraction of gas flow for the fine particle detector. 5. The apparatus of claim 4, wherein the volume fraction of gas flow for the coarse particle detector is at least twice the volume fraction of gas flow for the fine particle detector. An apparatus for measuring a polydisperse aerosol over a wide range of sizes in an aerosol flow,
A first optical detector for detecting particles in the aerosol having the particles and producing an output indicative of the particle size;
A classifier that receives at least a portion of the aerosol and produces an aerosol output modified to have particles having substantially uniform electrical mobility;
A condenser for receiving a working fluid and condensing a vapor of the working fluid on the particles classified by the classifier to form droplets in the modified aerosol;
A second optical detector for receiving and detecting droplets in the modified aerosol from the condenser;
An apparatus comprising: An apparatus for detecting particles in a gas,
With the chassis,
A coarse particle detector,
A fine particle detector,
Signal processing means for processing an electrical signal from the coarse particle detector and the fine particle detector,
With
The coarse particle detector and the fine particle detector, and the signal processing means are mounted on the same chassis,
The coarse particle detector and the fine particle detector so that the volume ratio of the gas flow passing through the coarse particle detector is at least as large as the volume ratio of the gas flow passing through the fine particle detector. The device further comprising means for maintaining gas flow through the device. A first pump for maintaining a flow rate of the gas flow passing through the coarse particle detector at a desired value;
A second pump for maintaining the flow rate of the gas flow passing through the fine particle detector at a desired value;
A sensor for detecting a flow rate of a gas flow passing through the fine particle detector and the coarse particle detector,
Means for adjusting the speed of the pump to maintain the flow rate of the gas flow at a respective desired value;
The apparatus of claim 7, further comprising:

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