JP2018151381A - Particulate count detector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To precisely detect a particulate count even when a voltage applied between an electric field generation electrode and a collection electrode is low.SOLUTION: A particulate count detector 10 comprises a charge generation element 20, a collection device 50, a count measuring device 56, and a gas discharge part 60. The charge generation element 20 adds charge 18 to particulates 16 in a gas to generate charged particulates P. The collection device 50 is applied with a voltage Vp between the electric field generation electrode 52 and collection electrode 54 to collect the charged particulates P at the collection electrode 54. The count measuring device 56 detects the number of charged particulates P, having been collected at the collection electrode 54, based upon a current varying with the number of the charged particulates P. The gas discharge part 60 is provided downstream from the collection electrode 54. Charged particulates P having been accumulated in a charge storage part 66 push charged particulates, which are not collected at the collection electrode 54, back toward the collection electrode with Coulomb repulsive force.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a particle number detector.

  As the particle number detector, ions are generated by a corona discharge in a charge generation element, the particles in the gas to be measured are charged by the ions, the charged particles are collected by a collecting electrode, and the collected particles are collected. One that measures the number of fine particles based on the amount of charge is known (see, for example, Patent Document 1).

International Publication No. 2015/146456 Pamphlet

  However, in Patent Document 1, when the electric field strength applied to the collecting electrode is low, charged fine particles that cannot be collected by the collecting electrode are generated and discharged out of the vent pipe. There was a problem of lowering. In order to avoid this problem, it was necessary to increase the electric field strength applied to the collecting electrode.

  The present invention has been made to solve such a problem, and has as its main object to accurately detect the number of fine particles even when the electric field strength applied to the collecting electrode is low.

The particle number detector of the present invention is
A charge generating unit that adds charged charges to the fine particles in the gas introduced into the vent pipe to form charged fine particles;
A charged particulate collection unit that generates an electric field downstream of the gas flow from the charge generation unit and collects the charged particulates by a collection electrode disposed in the electric field;
A number detection unit that detects the number of the charged fine particles based on a physical quantity that varies according to the number of the charged fine particles collected by the collection electrode;
A gas discharge part provided on the downstream side of the gas flow from the collecting electrode;
With
The gas discharge unit includes a charge accumulation unit that accumulates the charged fine particles not collected by the collection electrode, and the charged fine particles accumulated in the charge accumulation unit are collected by the collection electrode. The charged fine particles that did not exist are pushed back to the collecting electrode side by Coulomb repulsion,
Is.

  In this fine particle number detector, the charge generated in the charge generation unit is added to the fine particles in the gas introduced into the vent tube to form charged fine particles. The charged fine particles are collected by a collection electrode provided on the downstream side of the gas flow with respect to the charge generation unit. Then, the number of fine particles in the gas is detected based on a physical quantity that changes according to the number of charged fine particles collected by the collecting electrode. Here, the gas discharge part provided in the downstream of the gas flow rather than the collection electrode is provided with the charge storage part which accumulate | stores the charged fine particle which was not collected by the collection electrode. The charged fine particles accumulated in the charge accumulation unit push the charged fine particles not collected by the collection electrode back to the collection electrode side by Coulomb repulsion. For this reason, even if charged fine particles that flow to the gas discharge part without being collected by the collecting electrode are generated because the electric field strength where the collecting electrode is disposed is low, they are captured by the charged fine particles accumulated in the charge accumulating part. It is pushed back to the collector electrode side and finally collected by the collector electrode. Therefore, even if the intensity of the electric field applied to the collection device is low, the number of fine particles can be detected with high accuracy.

  In this specification, “charge” includes ions in addition to positive charges and negative charges. “Detecting the number of fine particles” determines whether or not the number of fine particles falls within a predetermined numerical range (for example, whether or not a predetermined threshold value is exceeded) in addition to measuring the number of fine particles. Including cases. The “physical quantity” may be a parameter that changes based on the number of charged fine particles (charge quantity), and examples thereof include current.

  In the particle number detector of the present invention, the gas discharge part has a gas passage hole having a smaller gas flow path area than the part provided with the collecting electrode, and the charge storage part is formed on the inner wall of the gas passage hole. It may be provided. This increases the electrostatic capacity of the charge storage unit and increases the amount of charged fine particles stored in the charge storage unit, making it easier to push charged fine particles that have not been collected by the collection electrode back to the collection electrode side. Become. In this case, the gas discharge part has an insulating support plate provided in a direction intersecting the axial direction of the vent pipe, and the support plate is a rod that generates an electric field with the collecting electrode. The gas field generation electrode may penetrate and the said gas passage hole may be provided so that the said support plate may be penetrated. In this case, the support plate provided with the gas passage hole also plays a role of supporting the electric field generating electrode, so that it is not necessary to separately provide a member for supporting the electric field generating electrode, and the structure is simplified. The vent pipe has a circular cross section, the support plate is a disc, and the electric field generating electrode passes through the center, and the gas passage hole is on a circumference concentric with the support plate. A plurality may be provided at equal intervals. In this way, since the gas flow field is rotationally symmetric with respect to the central axis of the vent pipe, the distance to diffuse and form a uniform flow field can be shortened, resulting in a compact device. Can be

  In the fine particle number detector of the present invention, the charge storage section may include a dielectric material that is dielectrically polarized. A positive or negative charge appears on the surface of the dielectric material. Therefore, charged fine particles having a polarity opposite to the polarity of the charge are attracted to the surface of the dielectric. In this case, the dielectric may be dielectrically polarized using the electric field of the charged particulate collection unit. In this way, it is not necessary to separately provide a device for generating an electric field for dielectric polarization. In addition, the charge storage portion may have a structure in which a covering member having a higher dielectric constant than that of the base member is provided on the surface of the insulating base member. Since the covering member has a relative dielectric constant higher than that of the base member, more charged fine particles can be accumulated. Therefore, it becomes easy to push back the charged fine particles flowing to the gas discharge part to the collecting electrode side.

  In the particle number detector of the present invention, the charge storage unit may use the other electrode plate of a capacitor in which one electrode plate is connected to the ground. Even in this case, charged fine particles can be stored in the charge storage section.

  Although the particle number detector of the present invention is not particularly limited, it is used in, for example, atmospheric environment investigation, indoor environment investigation, pollution investigation, combustion particle measurement of automobiles, particle generation environment monitoring, particle synthesis environment monitoring, etc. .

FIG. 3 is a cross-sectional view illustrating a schematic configuration of the particle number detector 10. AA sectional drawing of FIG. Sectional drawing of the periphery of the charge storage part 66 (enlarged view in the circle of FIG. 1). FIG. 6 is a cross-sectional view of the periphery of the charge storage unit 166. FIG. 6 is a cross-sectional view of the periphery of a charge storage unit 266. FIG. 6 is a cross-sectional view of the periphery of a charge storage unit 366. FIG. 6 is a cross-sectional view of the periphery of a charge storage unit 466. FIG. 6 is an explanatory diagram of the charge generation element 120. Explanatory drawing of the gas ventilation hole 164. FIG.

  Preferred embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a cross-sectional view showing a schematic configuration of the particle number detector 10, FIG. 2 is a cross-sectional view taken along line AA in FIG. 1, and FIG. 3 is an enlarged view in a circle in FIG.

  The fine particle number detector 10 detects the number of fine particles contained in gas (for example, automobile exhaust gas). The particle number detector 10 includes a charge generation element 20, a surplus charge removing device 40, a collecting device 50, and a gas discharging unit 60 along the gas flow direction in the vent pipe 12. Further, the collection device 50 includes a number measuring device 56.

  The vent pipe 12 is a pipe-like member having a circular cross section extending along the gas flow direction, and includes electrically insulating ceramic portions 12a, 12c, and 12e and conductive metal portions 12b, 12d, and 12f. The gas is introduced into the vent pipe 12 from one end of the vent pipe 12 (left end in FIG. 1), then passes through the vent pipe 12 and is discharged to the outside through the gas exhaust section 60 (right end in FIG. 1). . An outer pipe 14 made of metal and having a step is disposed outside the metal portion 12f forming the downstream end portion of the vent pipe 12 and the exhaust pipe 70 having the same diameter as the metal portion 12f.

  The charge generation element 20 is provided on the gas inlet side of the vent pipe 12. The charge generation element 20 applies a voltage between the needle-like electrode 22 having a sharp tip, the counter electrode 24 disposed to face the tip of the needle-like electrode 22, and the needle-like electrode 22 and the counter electrode 24. And a discharge power source 26. A portion other than the tip of the needle electrode 22 is surrounded by a ceramic portion 12 a of the vent pipe 12. The counter electrode 24 is integrated with the metal portion 12 b of the vent pipe 12. When a predetermined voltage is applied between the needle electrode 22 and the counter electrode 24, corona discharge is generated between the electrodes 22 and 24. As the gas passes through the corona discharge, a charge 18 (for example, a positive charge) is added to the fine particles 16 in the gas. The fine particles 16 to which the charge 18 is added are referred to as charged fine particles P. The needle-like electrode 22 may be formed by printing it on the inner surface of the vent pipe 12 in a flat shape.

  The surplus charge removing device 40 is a device that removes the charge 18 that has not been added to the fine particles 16, and is provided between the charge generating element 20 and the collecting device 50. The surplus charge removing device 40 includes a rod-shaped electric field generating electrode 42 disposed on the central axis of the vent pipe 12 and a removing electrode 44 surrounding the electric field generating electrode 42. The removal electrode 44 is the metal portion 12 d of the vent pipe 12. Since the ceramic portion 12c exists between the removal electrode 44 and the counter electrode 24, both are electrically insulated. Between the electric field generating electrode 42 and the removal electrode 44, a voltage Vi that is one digit or more smaller than the voltage applied between the electric field generating electrode 52 and the collecting electrode 54 of the collecting device 50 described later is applied. . As a result, a weak electric field is generated between the electric field generating electrode 42 and the removal electrode 44 of the surplus charge removing device 40. Therefore, of the charges 18 generated by the charge generation element 20, the surplus charges 18 that have not been added to the fine particles 16 are attracted to the removal electrode 44 by this weak electric field. As a result, a current Ii corresponding to the amount of surplus charge 18 flows through the ammeter 46 connected to the removal electrode 44. The current Ii is measured when the surplus charge amount is examined, but is not particularly necessary for detecting the number of fine particles.

  The collection device 50 is a device that collects the charged fine particles P. The collecting device 50 includes a rod-shaped electric field generating electrode 52 disposed on the central axis of the vent pipe 12 and a collecting electrode 54 surrounding the electric field generating electrode 52. The collecting electrode 54 is the metal portion 12 f of the vent pipe 12. Since the ceramic portion 12e exists between the collection electrode 54 and the removal electrode 44, both are electrically insulated. When a voltage Vp of an electric field generating power source (not shown) is applied between the electric field generating electrode 52 and the collecting electrode 54, an electric field is generated between the electric field generating electrode 52 and the collecting electrode 54. The charged fine particles P that have flown into the portion of the ventilation pipe 12 where the collection device 50 is provided are attracted to the collection electrode 54 by this electric field and collected on the collection electrode 54. The collecting electrode 54 is connected to the number measuring device 56.

  The number measuring device 56 is a device that measures the number of the fine particles 16 based on the charge amount of the charged fine particles P collected by the collecting electrode 54. Between the number measuring device 56 and the collecting electrode 54, a capacitor 55a, a resistor 55b, and a switch 55c (for example, a semiconductor switch) are connected in series from the collecting electrode 54 side. When the switch 55c is turned on, a current based on the electric charge 18 of the charged fine particles P collected by the collecting electrode 54 is passed to the number measuring device 56 as a transient response through a series circuit including a capacitor 55a and a resistor 55b. Communicated. The number measuring device 56 measures an electric current value using an ammeter, and calculates the number of fine particles 16 based on the electric current value.

  The gas discharge unit 60 includes a ceramic support plate 62 provided on the downstream side of the collecting electrode 54, a gas passage hole 64 provided in the support plate 62, and a charge storage unit 66 capable of storing charged fine particles P. I have. The support plate 62 has a disk shape, and is disposed inside the outer pipe 14 so as to be orthogonal to the gas flow direction. The outer pipe 14 is grounded and has an effect of suppressing noise by electrostatically shielding the collecting electrode 54. The electric field generating electrode 52 of the collection device 50 passes through the center of the support plate 62. Further, the downstream end of the collecting electrode 54 (the metal portion 12f of the vent pipe 12) is inserted into the support plate 62 in a non-penetrating state. As shown in FIG. 2, a ring-shaped gas passage hole 64 is provided between the electric field generating electrode 52 and the collecting electrode 54 in the support plate 62 as viewed from the direction of gas flow. The charge storage section 66 is an inner wall of the gas passage hole 64 and is made of ceramic, that is, a dielectric. Therefore, when the voltage Vp is applied between the electric field generating electrode 52 and the collecting electrode 54, an electric field is generated between the electric field generating electrode 52 and the collecting electrode 54, and the gas passing through the charge accumulation unit 66 is passed. The dielectric on the inner wall of the hole 64 is dielectrically polarized. Even if the collecting electrode 54 is not inserted into the support plate 62, dielectric polarization occurs due to the electric field generated between the electric field generating electrode 52 and the outer pipe 14. The relative dielectric constant of the support plate 62 is not particularly limited, but is preferably 7 or more, and more preferably 9 or more.

  Further, the gas passage hole 64 has a smaller gas flow path area than the portion where the collecting electrode 54 is provided. That is, the cross-sectional area when the gas passage hole 64 is cut so as to be perpendicular to the gas flow direction is smaller than the cross-sectional area when the gas passage on the upstream side of the gas flow with respect to the support plate 62 is similarly cut. It has become. The ratio d2 / d1 between the inner diameter d1 and the outer diameter d2 of the ring-shaped gas passage hole 64 shown in FIG. 2 is a parameter that affects the amount of charge stored in the charge storage section 66. The smaller d2 / d1, the higher the capacitance of the charge accumulating portion 66 and the greater the amount of accumulated charge compared to a circular gas passage hole having a diameter d2, which is preferable. For example, if d2 / d1 is 2 or less, the amount of accumulated charges can be increased by a factor of about 2 compared to a circular gas passage hole having a diameter d2. Further, the difference Δd (= d2−d1) between the outer diameter d2 and the inner diameter d1 corresponds to the channel width. However, when the channel width is constant, the larger the inner diameter d1, the smaller d2 / d1 is preferable.

  Next, a usage example of the particle number detector 10 will be described. When measuring particulates contained in the exhaust gas of an automobile, the particulate number detector 10 is attached in the exhaust pipe of the engine. At this time, the particle number detector 10 is attached so that the exhaust gas is introduced into the vent pipe 12 from the inlet (left end in FIG. 1) of the particle number detector 10 and discharged from the outlet (right end in FIG. 1). The fine particles 16 contained in the exhaust gas of the automobile are charged with the charges 18 when passing through the charge generating element 20 to become charged fine particles P. The charged fine particles P pass through the surplus charge removing device 40 whose electric field is weak and the length of the removing electrode 44 is short, and reaches the collecting device 50. Further, of the electric charges 18 generated by the electric charge generating element 20, the excessive electric charges 18 that have not been added to the fine particles 16 are attracted to the removal electrode 44 of the excessive electric charge removing device 40 even if the electric field is weak, and are discarded to the GND. Thereby, surplus charges 18 that have not been added to the fine particles 16 hardly reach the collection device 50. When the charged fine particles P reach the collection device 50, they are attracted to the collection electrode 54 and collected. A current based on the charge 18 of the charged fine particles P attached to the collecting electrode 54 is transmitted to the number measuring device 56 as a transient response through a series circuit including a capacitor 55a and a resistor 55b.

  The relationship between the current I and the charge amount q is I = dq / (dt), q = ∫Idt. Accordingly, the number measuring device 56 integrates (accumulates) the current value over a period during which the switch 55c is on (switch-on period) to obtain an integrated value (accumulated charge amount) of the current value. After the switch-on period, the accumulated charge amount is divided by the elementary charge to obtain the total number of charges (collected charge number), and the collected charge number is divided by the average value of the number of charges added to one fine particle 16. By doing so, the number of the fine particles 16 attached to the collecting electrode 54 over a certain time (for example, 5 to 15 seconds) can be obtained. The number measuring device 56 repeats and accumulates calculations for calculating the number of the fine particles 16 in a predetermined time over a predetermined period (for example, 1 to 5 minutes), so that the fine particles attached to the collecting electrode 54 over the predetermined period. The number of 16 can be calculated. Further, by using the transient response by the capacitor 55a and the resistor 55b, it becomes possible to measure even with a small current, and the number of particles 16 can be detected with high accuracy. For a minute current at a pA (picoampere) level or an nA (nanoampere) level, for example, a minute current can be measured by increasing the time constant using the resistor 55b having a large resistance value.

  Here, when the voltage Vp applied between the electric field generating electrode 52 and the collecting electrode 54 is high, since the intensity of the electric field generated in the collecting device 50 is high, the charged fine particles P that pass through the collecting device 50 are almost all. The whole amount is collected by the collecting electrode 54. On the other hand, when the voltage Vp is low (for example, when it is one digit smaller than the above-described high voltage), since the intensity of the electric field generated in the collection device 50 is low, a part of the charged fine particles P passing through the collection device 50 In some cases, the gas is not collected by the collection electrode 4 and reaches the gas passage hole 64 of the gas discharge unit 60. At this time, the dielectric constituting the inner wall of the gas passage hole 64 (that is, the charge storage portion 66) is in a state of being dielectrically polarized by the electric field generated between the electric field generating electrode 52 and the collecting electrode 54. When the charged fine particles P pass through the charge storage portion 66 in the initial state (the state where the charged fine particles P are not stored), the charged fine particles P are attracted to and stored in the charge storage portion 66 by a dielectrically polarized dielectric. However, when a new charged fine particle P passes through the charge accumulation unit 66 after the charged fine particle P is accumulated, the charged fine particle P accumulated in the charge accumulation unit 66 collects the new charged fine particle P by Coulomb repulsion. Push back to the electrode 54 side. The situation at this time is indicated by a dotted arrow in FIG. The charged fine particles P pushed back are finally collected by the collecting electrode 54. Therefore, even when the voltage Vp is low, the number of charged fine particles P that are not collected by the collecting electrode 54 and discharged to the outside of the vent pipe 12 can be suppressed.

  A portion of the collection electrode 54 exposed to the internal space of the vent pipe 12 is a portion that substantially collects the charged fine particles P.

  In the fine particle number detector 10 described in detail above, the number measuring device 56 can accurately detect the fine particle number even when the electric field of the collecting device 50 is high as well as low.

  Further, the gas discharge part 60 has a gas passage hole 64 having a gas passage area smaller than the part where the collecting electrode 54 is provided, and the charge storage part 66 is provided on the inner wall of the gas passage hole 64. As a result, the electrostatic capacity of the charge accumulating unit 66 increases, and the amount of charged fine particles P accumulated in the charge accumulating unit 66 increases, so that the charged fine particles P that have not been collected by the collecting electrode 54 are collected on the collecting electrode side. It becomes easier to push back.

  Further, since the charge accumulating portion 66 is a dielectrically polarized dielectric and positive or negative charges appear on the surface, the charged fine particles P having a polarity opposite to the polarity of the charges are attracted and accumulated on the surface of the dielectric. Can do.

  Furthermore, since the dielectric constituting the charge storage section 66 is dielectrically polarized using the electric field generated in the collection device 50, there is no need to separately provide a device for generating an electric field for dielectric polarization.

  In addition, since the support plate 62 plays a role of supporting the electric field generating electrode 52, it is not necessary to provide a member for separately supporting the electric field generating electrode 52, and the structure is simplified.

  The present invention is not limited to the above-described first embodiment, and it goes without saying that the present invention can be implemented in various modes as long as it belongs to the technical scope of the present invention.

  For example, in the above-described embodiment, the inner wall of the gas passage hole 64 provided in the support plate 62 is used as it is as the charge accumulation unit 66, but the charge accumulation units 166, 266, and 366 shown in FIGS. Good. In FIG. 4, the inner wall of the gas passage hole 64 is covered with a covering member 163 having a relative dielectric constant higher than that of the support plate 62, and the surface of the covering member 163 is used as the charge storage portion 166. In FIG. 5, the peripheral portion 62 a of the gas passage hole 64 in the end surface on the gas upstream side of the support plate 62 is covered with a covering member 263 having a higher relative dielectric constant than the support plate 62, and the surface of the covering member 263 is charged. The storage unit 266 is used. In FIG. 6, the inner wall of the gas passage hole 64 and the peripheral portion 62 a of the gas passage hole 64 are covered with a covering member 363 having a relative dielectric constant higher than that of the support plate 62, and the surface of the covering member 363 is used as the charge storage portion 366. Yes. The charge storage units 166, 266, and 366 shown in FIGS. 4 to 6 have more charge than the above-described embodiment because the relative dielectric constant of the covering members 163, 263, and 363 is higher than that of the support plate 62 (base member). Fine particles P can be accumulated. Therefore, it becomes easy to push back the charged fine particles P that have flowed to the gas discharge unit 60 toward the collecting electrode. The relative dielectric constant of main ceramics is shown in Table 1 below.

  Or you may employ | adopt the electric charge storage part 466 shown in FIG. In FIG. 7, a metal electrode 463 is provided on the inner wall of the gas passage hole 64 provided in the support plate 62, one electrode plate of the external capacitor 464 is connected to the metal electrode 463, and the other electrode plate is grounded (GND). Connected to. In this case, the surface of the metal electrode 463 becomes the charge storage portion 466. The charge accumulating unit 466 can also accumulate charged fine particles P as in the above-described embodiment, and the accumulated charged fine particles P push the new charged fine particles P back to the collecting electrode 54 side by Coulomb repulsion. Therefore, the same effect as the above-described embodiment can be obtained.

  In the above-described embodiment, the acicular electrode 22 and the counter electrode 24 are used as the charge generation element 20, but the present invention is not particularly limited thereto. For example, as shown in FIG. 8, a discharge electrode 122 exposed on the inner surface of the vent pipe 12 and an induction electrode 124 that is opposed to the discharge electrode 122 and embedded in the inner wall of the vent pipe 12 may be used. In this case, the inner wall of the vent pipe 12 sandwiched between the electrodes 122 and 124 functions as a dielectric layer. The discharge electrode 122 preferably has a plurality of protrusions on the outer periphery. Even if a voltage is applied between the discharge electrode 122 and the induction electrode 124, electric charges are generated by air discharge.

  In the embodiment described above, the gas passage hole 64 is a ring-shaped hole as shown in FIG. 2, but is not particularly limited to the ring shape, and may be a rectangular hole, for example. Further, the AA sectional view of FIG. 1 may be FIG. 9 instead of FIG. In FIG. 9, a plurality of small-diameter gas passage holes 164 are provided between the electric field generating electrode 52 and the collecting electrode 54 in the support plate 62. The electric field storage unit 166 serves as an inner wall portion of the gas passage hole 164. Even if it does in this way, the effect similar to embodiment mentioned above is acquired. The plurality of gas passage holes 164 are preferably provided at equal intervals on the same circumference. In this way, since the gas flow field is rotationally symmetric with respect to the central axis of the vent pipe 12, the distance until diffusion and formation of a uniform flow field can be shortened. Can be made compact. Although FIG. 9 shows an example in which six gas passage holes 164 are provided, the number of gas passage holes 164 may be any number as long as it is two or more.

  In the embodiment described above, the surplus charge removing device 40 is provided, but the surplus charge removing device 40 may not be provided.

  In the embodiment described above, the case of measuring the number of positively charged fine particles P has been described, but the number of negatively charged fine particles P may be measured.

10 Particle number detector, 12 Vent pipe, 12a, 12c, 12e Ceramic portion, 12b, 12d, 12f Metal portion, 14 Outer pipe, 16 Particle, 18 Charge, 20 Charge generating element, 22 Needle electrode, 24 Counter electrode, 26 Power source for discharge, 40 Surplus charge removal device, 42 Electric field generation electrode, 44 Removal electrode, 46 Ammeter, 50 Collection device, 52 Electric field generation electrode, 54 Collection electrode, 55a Capacitor, 55b Resistor, 55c Switch, 56 Measuring device, 60 gas discharge part, 62 support plate, 62a peripheral part, 64,164 gas passage hole, 66,166,266,366,466 charge storage part, 70 exhaust pipe, 120 charge generation element, 122 discharge electrode, 124 Induction electrode, 163, 263, 363 Cover member, 463 Metal electrode, 464 Part capacitor, P charged fine particles.

Claims (8)

A charge generating unit that adds charged charges to the fine particles in the gas introduced into the vent pipe to form charged fine particles;
A charged particulate collection unit that generates an electric field downstream of the gas flow from the charge generation unit and collects the charged particulates by a collection electrode disposed in the electric field;
A number detection unit that detects the number of the charged fine particles based on a physical quantity that varies according to the number of the charged fine particles collected by the collection electrode;
A gas discharge part provided on the downstream side of the gas flow from the collecting electrode;
With
The gas discharge unit includes a charge accumulation unit that accumulates the charged fine particles not collected by the collection electrode, and the charged fine particles accumulated in the charge accumulation unit are collected by the collection electrode. The charged fine particles that did not exist are pushed back to the collecting electrode side by Coulomb repulsion,
Particle number detector. The gas discharge part has a gas passage hole having a smaller gas flow path area than the part where the collecting electrode is provided, and the charge storage part is provided on the inner wall of the gas passage hole.
The fine particle number detector according to claim 1. The gas discharge portion has an insulating support plate provided in a direction intersecting the axial direction of the vent pipe, and the support plate generates a rod-shaped electric field that generates an electric field with the collecting electrode. The generation electrode is penetrated, and the gas passage hole is provided so as to penetrate the support plate.
The fine particle number detector according to claim 2. The vent pipe has a circular cross section,
The support plate is a disc and the electric field generating electrode passes through the center,
A plurality of the gas passage holes are provided at equal intervals on a circumference concentric with the support plate,
The fine particle number detector according to claim 3. The charge storage unit includes a dielectric material having a dielectric polarization,
The particle number detector according to any one of claims 1 to 4. The charge accumulating part is obtained by dielectric polarization of the dielectric using the electric field of the charged particulate collection part.
The fine particle number detector according to claim 5. The charge storage portion has a structure in which a covering member having a higher dielectric constant than that of the base member is provided on the surface of the insulating base member.
The particle number detector according to claim 5 or 6. The charge storage unit utilizes the other electrode plate of the capacitor in which one electrode plate is connected to the ground.
The particle number detector according to any one of claims 1 to 4.

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