WO2019239588A1

WO2019239588A1 - Fine particle number detector

Info

Publication number: WO2019239588A1
Application number: PCT/JP2018/022967
Authority: WO
Inventors: 英正奥村; 和幸水野
Original assignee: 日本碍子株式会社
Priority date: 2018-06-15
Filing date: 2018-06-15
Publication date: 2019-12-19
Also published as: JPWO2019239588A1

Abstract

A fine particle number detector comprises a case, a charge generating part, a collecting electrode part, a storage part, and a number detecting part. The case has a ventilation passage. The charge generating part imparts a charge, which is generated by discharging electricity, to fine particles which are in a gas introduced into the ventilation passage, and makes the fine particles into charged fine particles. The collecting electrode part is provided farther downstream a flow of the gas than the charge generating part, and collects the charged fine particles and excess charge which was not imparted to the fine particles. The storage part stores a correspondence relationship between a number concentration of the fine particles in the gas, which was found in advance, and a current which flows in the collecting electrode. The number detecting part finds the number of fine particles which are included in the gas on the basis of the correspondence relationship which is stored in the storage unit and the current which actually flows in the collecting electrode.

Description

Particle count detector

The present invention relates to a particle number detector.

As the particle number detector, ions are generated by corona discharge with a charge generation element, and the particles in the gas are charged with charged ions to form charged particles. The charged particles are collected by a measuring electrode, and the collected charged particles are collected. A device that measures the number of fine particles based on the amount of charge of the fine particles is known. For example, in Patent Document 1, based on q = ∫Idt, the amount of accumulated charge is obtained by integrating the current flowing through the measurement electrode with time, and the amount of accumulated charge is divided by the elementary charge. The number of attached fine particles is obtained. That is, it is assumed that only charged fine particles are collected on the measurement electrode. For this reason, in Patent Document 1, a removal electrode is provided between the charge generation element and the measurement electrode, and charges that have not been charged in the fine particles (excess charge) are collected by the removal electrode, thereby improving the detection accuracy of the number of fine particles. It has also been proposed to do.

International Publication No. 2015/146456 Pamphlet

However, it is theoretically possible to collect only the surplus charges with the removal electrode and only the charged fine particles with the measurement electrode, but it was not easy to realize. Therefore, a new technique for measuring the number of fine particles in the gas has been awaited.

The present invention has been made to solve such a problem, and has as its main object to easily measure the number of fine particles in a gas as compared with the prior art.

The present invention adopts the following means in order to achieve the above-mentioned main object.

The particle number detector of the present invention is
A housing having a ventilation path;
A charge generating unit that adds charged charges generated by discharge to the fine particles in the gas introduced into the air passage to form charged fine particles;
A collecting electrode provided on the downstream side of the gas flow with respect to the charge generation unit and collecting the charged fine particles and surplus charges not added to the fine particles;
A storage unit for storing a correspondence relationship between the concentration of fine particles in the gas obtained in advance and a current flowing through the collection electrode;
A number detection unit for determining the number of fine particles contained in the gas based on the correspondence and the current actually flowing through the collection electrode;
It is equipped with.

In this particle number detector, charged particles and surplus charges that have not been added to the particles are collected by a collecting electrode, and the correspondence between the concentration of the number of particles in the gas determined in advance and the current flowing through the collecting electrode are actually measured. The number of fine particles contained in the gas is determined based on the current flowing through the collection electrode. The collecting electrode does not need to collect only the charged fine particles, and collects both the charged fine particles and surplus charges. Therefore, the number of fine particles in the gas can be measured more easily than in the past. The number of fine particles in the gas can be obtained by such a method because the present inventors have captured the concentration of fine particles in the gas and both the charged fine particles and the surplus charges in the collecting electrode. This is because it has been found that there is a correspondence between the current flowing through the collecting electrode when collected.

In this specification, “charge” includes positive charges and negative charges as well as ions.

In the particle number detector of the present invention, the correspondence relationship is as follows: y = ax + b (a, a, where x is the particle number concentration of the gas and y (pA) is the current flowing through the collection electrode. b may be a constant, a> 0, b> 0). Such an expression can be obtained, for example, by the method of least squares from the relationship between the gas having a known fine particle number concentration and the current flowing through the collection electrode.

In the fine particle number detector of the present invention, the collection electrode may collect the charged fine particles and the excess charge by an electric field. In this way, both the charged fine particles and the surplus charges can be efficiently collected on the collecting electrode.

In the fine particle number detector of the present invention, the charge generation unit may include a discharge electrode, an induction electrode, and a dielectric layer sandwiched between the discharge electrode and the induction electrode. When such a charge generation part is employed, a good correspondence between the concentration of the number of fine particles in the gas and the current flowing through the collecting electrode occurs. In this case, it is preferable to apply a sinusoidal voltage as a discharge voltage to the discharge electrode. This is because the sine wave voltage is less likely to generate noise than the pulse voltage.

FIG. 3 is an explanatory diagram of the particle number detector 10. FIG. 6 is a perspective view of the particle detection element 20. FIG. 3 is a cross-sectional view taken along line AA in FIG. 2. FIG. 3 is a sectional view taken along line BB in FIG. 2. FIG. 3 is an exploded perspective view of the particle detection element 20. Explanatory drawing which shows an example of a sine wave voltage. The graph which shows an example of the correspondence of the fine particle number density | concentration in gas, and the electric current which flows through the collection electrode. The schematic block diagram of the experimental apparatus 80. FIG.

Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is an explanatory view of a particle number detector 10 according to an embodiment of the present invention, FIG. 2 is a perspective view of a particle detector 20, FIG. 3 is a cross-sectional view taken along the line AA in FIG. FIG. 5 is an exploded perspective view of the particle detecting element 20. In the present embodiment, the vertical direction, the horizontal direction, and the front-rear direction are as shown in FIGS.

As shown in FIG. 1, the fine particle number detector 10 detects the number of fine particles 26 (see FIG. 5) contained in the exhaust gas flowing through the exhaust pipe 12 of the engine. The particle number detector 10 includes a particle detection element 20 and an accessory unit 70 including

various power sources

36 and 56 and a number detection unit 60.

As shown in FIG. 1, the fine particle detection element 20 is attached to a ring-shaped pedestal 16 fixed to the exhaust pipe 12 while being inserted in a columnar support 14. The particulate detection element 20 is protected by a protective cover 18. A hole (not shown) is provided in the protective cover 18, and the exhaust gas flowing through the exhaust pipe 12 passes through the ventilation path 24 provided at the lower end of the particulate detection element 20 through the hole. As shown in FIG. 4, the particle detection element 20 includes a housing 22 including a charge generation unit 30, a collection unit 50, and a heater electrode 72.

As shown in FIG. 1, the housing 22 is a rectangular parallelepiped that is long in a direction intersecting with the axial direction of the exhaust pipe 12 (here, a direction substantially orthogonal). The housing 22 is an insulator, and is made of ceramics such as alumina. A lower end 22 a of the housing 22 is disposed inside the exhaust pipe 12, and an upper end 22 b is disposed outside the exhaust pipe 12. An air passage 24 is provided at the lower end 22 a of the housing 22. Various terminals are provided on the upper end 22 b of the housing 22.

The axial direction of the air passage 24 coincides with the axial direction of the exhaust pipe 12. As shown in FIG. 2, the air passage 24 extends from a rectangular gas inlet 24 a provided on the front surface of the housing 22 to a rectangular gas outlet 24 b provided on the rear surface of the housing 22. It is a rectangular parallelepiped space. The housing 22 includes a pair of left and

right walls

22c and 22d that constitute the air passage 24 (see FIG. 2).

The charge generator 30 is provided on each of the pair of left and

right walls

22c and 22d so that charges are generated near the gas inlet 24a in the air passage 24. Hereinafter, for convenience of explanation, the charge generation unit 30 provided on the wall 22c will be described, but the charge generation unit 30 provided on the wall 22d is the same as this. The charge generation unit 30 includes a discharge electrode 32 and two

induction electrodes

34 and 34. The discharge electrode 32 is provided along the inner surface of the wall 22c, and has a plurality of fine protrusions around a rectangle as shown in FIG. The two

induction electrodes

34 and 34 are rectangular electrodes, and are embedded so as to be parallel to the discharge electrode 32 with a space in the wall 22c. In the charge generation unit 30, a sine wave voltage is applied between the discharge electrode 32 and the two

induction electrodes

34, 34 as a high-frequency high voltage of the discharge power source 36 (one of the attached units 70), whereby both electrodes Air discharge occurs due to the potential difference between them. At this time, a portion of the housing 22 between the discharge electrode 32 and the

induction electrodes

34 and 34 serves as a dielectric layer. By this air discharge, the gas existing around the discharge electrode 32 is ionized to generate a positive charge 28. Here, the induction electrodes 34 are connected to the ground. An example of the sine wave voltage is shown in FIG. In FIG. 6, the zero volt is not a dotted line but a solid line (a line below the middle line of the sine wave (one-dot chain line)). Therefore, the absolute value of the positive peak voltage is larger than the absolute value of the negative peak voltage. A part of the electric charge generated by the positive voltage is deposited on the electrode, but if the accumulated electric charge remains, the electric charge is hardly generated at the next discharge. When the sine wave voltage of FIG. 6 is used, the deposited charge disappears in a negative voltage period. Therefore, electric charges can be generated continuously and efficiently.

As shown in FIG. 4, the fine particles 26 contained in the gas enter the air passage 24 through the gas introduction port 24 a, and the charges 28 generated by the air discharge of the charge generation unit 30 when passing through the charge generation unit 30. After being added to become charged fine particles P, they move backward. Further, among the generated charges 28, those not added to the fine particles 26 move rearward as surplus charges Q.

The collection unit 50 is provided downstream of the charge generation unit 30 in the ventilation path 24. The collection unit 50 collects charged fine particles P and surplus charges Q, and has an electric field generating electrode 52 and a collection electrode 54. The electric field generating electrode 52 is provided along the inner surface of the right wall 22 d and is exposed in the air passage 24. The collecting electrode 54 is provided along the inner surface of the left wall 22 c and is exposed in the air passage 24. The electric field generating electrode 52 and the collecting electrode 54 are disposed at positions facing each other. The electric field generating electrode 52 is an electrode to which a voltage V1 (positive potential) is applied by a collecting power source 56 (one of the attached units 70). The collection electrode 54 is an electrode connected to the ground via an ammeter 62. Thereby, a relatively strong electric field is generated between the electric field generating electrode 52 and the collecting electrode 54 of the collecting unit 50. Therefore, the charged fine particles P and surplus charges Q flowing through the air passage 24 are attracted to and collected by the collecting electrode 54 by this electric field.

Note that the size of the

electrodes

52 and 54 of the collection unit 50 and the strength of the electric field generated between the

electrodes

52 and 54 are such that both the charged fine particles P and the surplus charges Q are collected by the collection electrode 54. Is set as follows.

The number detection unit 60 is one of the attached units 70 and includes an ammeter 62, a storage unit 64, and a calculation unit 66. The ammeter 62 has one terminal connected to the collecting electrode 54 and the other terminal connected to the ground. The ammeter 62 measures a current based on both the charge 28 and the surplus charge Q of the charged fine particles P collected by the collecting electrode 54. The storage unit 64 stores a correspondence relationship between the concentration of the number of fine particles in the gas obtained in advance and the current flowing through the collection electrode 54. The calculation unit 66 obtains the particle number concentration based on the correspondence stored in the storage unit 64 and the current actually measured by the ammeter 62.

The heater electrode 72 is embedded in the housing 22. The heater electrode 72 is a belt-like heating element (see FIG. 5) drawn in a zigzag manner. The heater electrode 72 is connected to a power supply device (not shown), and generates heat when energized by the power supply device. The heater electrode 72 heats each electrode such as the housing 22 and the collecting electrode 54.

Next, the configuration of the particle detection element 20 will be further described with reference to the exploded perspective view of FIG. The fine particle detecting element 20 is composed of seven sheets S1 to S7. Each of the sheets S1 to S7 is formed of the same material as that of the housing 22. For convenience of explanation, the first sheet S1, the second sheet S2,... Are referred to from the left to the right, and the right side surface of each of the sheets S1 to S7 is referred to as the front surface, and the left side surface is referred to as the back surface. The thicknesses of the sheets S1 to S7 may be set as appropriate. For example, all the sheets S1 to S7 may be the same or different.

A heater electrode 72 is provided on the surface of the first sheet S1. One end and the other end of the heater electrode 72 are disposed above the surface of the first sheet S1, and a heater electrode terminal 75 provided above the back surface of the first sheet S1 through a through hole of the first sheet S1. , 75 are connected to each other.

The

induction electrodes

34 and 34 are provided on the surface of the second sheet S2. The

induction electrodes

34, 34 are combined into one wiring 34a. The end of the wiring 34a is disposed above the surface of the second sheet S2, and is provided above the back surface of the first sheet S1 through the through holes of the second sheet S2 and the first sheet S1. It is connected to the electrode terminal 35. On the surface of the second sheet S2, the wiring 54a of the collecting electrode 54 is provided along the vertical direction. The upper end of the wiring 54a is connected to the collecting electrode terminal 55 provided above the back surface of the first sheet S1 through the through holes of the second sheet S2 and the first sheet S1.

The discharge electrode 32 and the collection electrode 54 are provided on the surface of the third sheet S3. The collection electrode 54 is connected to the wiring 54a of the second sheet S2 through the through hole of the third sheet S3, and is further connected to the collection electrode terminal 55 through this wiring 54a.

The air passage 24, that is, a rectangular parallelepiped space is provided on the lower end side of the fourth sheet S4.

The discharge electrode 32 and the electric field generating electrode 52 are provided on the back surface of the fifth sheet S5.

The

induction electrodes

34 and 34 are provided on the back surface of the sixth sheet S6. The

induction electrodes

34, 34 are combined into one wiring 34a. The end of the wiring 34a is disposed above the back surface of the sixth sheet S6 and is connected to the wiring 34a of the induction electrode 34 of the second sheet S2 through the through holes of the third to sixth sheets S3 to S6. Has been. Therefore, the

induction electrodes

34 and 34 provided on the sixth sheet S6 are also connected to the induction electrode terminal 35 provided above the back surface of the first sheet S1.

The wiring 32a of the discharge electrode 32 and the wiring 52a of the electric field generating electrode 52 are provided on the back surface of the seventh sheet S7 in the vertical direction. The lower end of the wiring 32a is connected to the discharge electrodes 32 provided on the third and fifth sheets S3 and S5 through the through holes of the fourth to sixth sheets S4 to S6. The lower end of the wiring 52a is connected to the electric field generating electrode 52 provided on the back surface of the fifth sheet S5 through the through holes of the fifth and sixth sheets S5 and S6. The upper ends of the

wires

32a and 52a are connected to the discharge electrode terminal 33 and the electric field generating electrode terminal 53 provided above the surface of the seventh sheet S7 through the through holes of the seventh sheet S7.

Here, an example of the correspondence relationship between the concentration of the number of fine particles in the gas and the current flowing through the collecting electrode 54 is shown in FIG. The configuration of the experimental apparatus 80 used to acquire the data shown in FIG. 7 and the procedure for measuring the total detected current will be described with reference to FIG.

The experimental apparatus 80 includes a particle generator 81 (manufactured by PALAS, DNP digital 3000), a diluter 82 (manufactured by TESTO, MD19-3E), a compressor 83, a mass flow controller 84, a particle counter 86 (manufactured by TSI 3776), The particle number detector 10 was provided. Specifically, the outlet of the particle generator 81 was connected to the inlet of the diluter 82, and the outlet of the compressor 83 was connected to the inlet of the diluter 82 via the mass flow controller 84. The outlet of the diluter 82 was connected to the particle counter 86 and the particle number detector 10 via a valve 85. A mass flow controller 87 and a vacuum pump 88 were connected to the outlet of the particle number detector 10 in this order. As the particle counter 86, a built-in mass flow controller and a vacuum pump were used.

The measurement procedure for all detected currents is as follows. First, the valve 85 was set so that the outlet of the diluting device 82 and the particle counter 86 communicated and the outlet of the diluting device 82 and the particle number detector 10 were shut off. Then, nitrogen gas was supplied to the particle generator 81, and a predetermined high voltage pulse wave was applied to a pair of carbon electrodes incorporated in the particle generator 81. As a result, electric charges were generated by the discharge, and the electric charges sputtered the carbon electrode to generate a certain amount of carbon particles per unit time. The carbon particles generated in the particle generator 81 are caused to flow into the diluter 82, the air supplied from the compressor 83 to the diluter 82 via the mass flow controller 84 and the carbon particles are mixed, and the gas containing the carbon particles is mixed. Generated. Such gas is introduced from the diluting device 82 into the particle counter 86, and the particle counter 86 measures the number of particles. The flow rate was adjusted. After the gas particle number concentration reaches the desired concentration, the valve 85 is set so that the outlet of the diluter 82 and the particle number detector 10 communicate with each other and the outlet of the diluter 82 and the particle counter 86 are blocked. The current was measured by the ammeter 62 of the particle number detector 10. The flow rates of the gas passing through the particle counter 86 and the particle number detector 10 were adjusted so as to be constant during the measurement. This adjustment was performed by a mass flow controller and a vacuum pump built in the particle counter 86, and a mass flow controller 87 and a vacuum pump 88 connected to the particle number detector 10.

The graph shown in FIG. 7 measures the total detected current y (pA) flowing through the collecting electrode 54 when a gas having a known particle number concentration x (number / cc) is passed through the air passage 24. It is a plot of measured data. The regression line equation y = ax + b (a and b are constants, a> 0, b> 0) shown in FIG. 7 was obtained by the least square method using those measured data. Although a and b are constants, these numerical values vary depending on measurement conditions (for example, gas flow rate). The storage unit 64 stores this expression as a correspondence relationship. A map or table may be stored instead of the formula. The collecting electrode 54 collects not only the charged fine particles P but also the surplus charge Q. The present inventor has a good correlation between the current y flowing through the collecting electrode 54 and the particle number concentration x. It became clear for the first time by these experiments. Although the collecting electrode 54 collects not only the charged fine particles P but also the surplus charges Q, it is not clear why a good correlation is obtained between the current y and the particle number concentration x. This is presumably because the concentration of the surplus charge Q in the gas is constant regardless of the concentration of the charged fine particles P for some reason.

Next, a manufacturing example of the fine particle number detector 10 will be described. The fine particle detection element 20 can be manufactured using a plurality of ceramic green sheets. Specifically, each of the plurality of ceramic green sheets is provided with notches, through-holes, grooves or screen printing of electrodes and wiring patterns as necessary, and then laminated and fired. Note that the notches, the through holes, and the grooves may be filled with a material (for example, an organic material) that is burned off during firing. In this way, the fine particle detection element 20 is obtained. Subsequently, the discharge electrode terminal 33 and the electric field generating electrode terminal 53 of the particulate detection element 20 are connected to the discharge power source 36 and the collection power source 56 of the attached unit 70, respectively. In addition, the induction electrode terminal 35 of the particle detection element 20 is connected to the ground, and the collection electrode terminal 55 is connected to the number detection unit 60 via the ammeter 62. Further, the

heater electrode terminals

75 and 75 are connected to a power supply device (not shown). By doing so, the particle number detector 10 can be manufactured.

Next, a usage example of the particle number detector 10 will be described. When measuring the particulates 26 contained in the exhaust gas of the automobile, the particulate detection element 20 is attached to the exhaust pipe 12 of the engine as described above (see FIG. 1). As shown in FIG. 4, the fine particles 26 contained in the exhaust gas introduced into the casing 22 from the gas inlet 24a are charged with fine particles 28 (positive charge in this case) generated by the discharge of the charge generator 30. Become P. The charged fine particles P move along the gas flow and reach the collection unit 50. On the other hand, the surplus charge Q that has not been added to the fine particles 26 also moves along the gas flow and reaches the collection unit 50. The charged fine particles P and the surplus charge Q that have reached the collection unit 50 are collected by the collection electrode 54 by the collection electric field generated by the electric field generation electrode 52. Then, the current based on the charge 28 and the surplus charge Q of the charged fine particles P collected by the collecting electrode 54 is measured by the ammeter 62, and the calculation unit 66 calculates the number of the fine particles 26 based on the current. Based on the correspondence stored in the storage unit 64 and the current actually measured by the ammeter 62, the calculation unit 66 obtains the particle number concentration corresponding to the current.

When a large number of charged fine particles P are deposited on the collecting electrode 54 with the use of the fine particle detecting element 20, new charged fine particles P may not be collected on the collecting electrode 54. For this reason, the collection electrode 54 is heated by the heater electrode 72 periodically or at the timing when the deposition amount reaches a predetermined amount, whereby the deposit on the collection electrode 54 is heated and incinerated. Refresh the electrode surface. In addition, the fine particles 26 attached to the inner peripheral surface of the housing 22 can be incinerated by the heater electrode 72.

In the fine particle number detector 10 described above, the charged fine particle P and the surplus charge Q are collected by the collecting electrode 54, and the correspondence relationship between the particle number concentration in the gas determined in advance and the current flowing through the collecting electrode 54 is as follows. The number of particles (particle number concentration) contained in the gas is determined based on the current actually flowing through the collecting electrode 54. The collection electrode 54 does not need to collect only the charged fine particles P, but collects both the charged fine particles P and the surplus charges Q. Therefore, the number of fine particles in the gas can be measured more easily than in the past.

Moreover, since the collection electrode 54 collects the charged fine particles P and the surplus charges Q by an electric field, these can be collected efficiently.

Further, the charge generation unit 30 includes a discharge electrode 32,

induction electrodes

34 and 34, and a dielectric layer (a part of the casing 22) sandwiched between the discharge electrode 32 and the

induction electrodes

34 and 34. Therefore, a good correspondence tends to occur between the concentration of fine particles in the gas and the current flowing through the collecting electrode 54. Further, since a sinusoidal voltage is applied to the discharge electrode 32 as a discharge voltage, it does not contain a high frequency component compared to the pulse voltage, and noise is less likely to occur.

It should be noted that the present invention is not limited to the above-described 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 collector 50 including the electric field generating electrode 52 and the collecting electrode 54 is used. However, the electric field generating electrode 52 is omitted, and the charged fine particles P that are in Brownian motion or surplus The charge Q may be collected by the collecting electrode 54. In this case, it is preferable to make the

walls

22c and 22d of the housing 22 approach each other. Alternatively, the electric field generating electrode 52 is omitted, and a filter that allows the passage of gas as the collecting electrode 54 but collects the charged fine particles P and surplus charges Q is adopted. You may provide so that it may cross | intersect the flow direction (for example, orthogonally crossing). In this case, the collecting electrode 54 may be mesh-shaped or honeycomb-shaped. Alternatively, the electric field generating electrode 52 is omitted, and the air passage 24 is L-shaped, that is, a shape having a first portion along the flow of exhaust gas and a second portion bent by about 90 ° from the first portion and changed in direction. The collecting electrode 54 may be provided in a bent portion (portion where the exhaust gas collides) of the air passage 24. By doing so, the charged fine particles P and the surplus charges Q in the exhaust gas collide with the collecting electrode 54 and are collected by the inertial force of the gas flow.

In the above-described embodiment, the cross-sectional shape of the air passage 24 is a quadrangle, but it may be a polygon other than a quadrangle, or a circle or an ellipse.

In the above-described embodiment, the housing 22 is made of ceramic. However, the portion of the housing 22 where the charge generation unit 30 is provided is made of ceramic, and the portion of the housing 22 where the collection unit 50 is provided is made of metal. The entire portion may also serve as the collecting electrode 54. In this case, the electric field generating electrode 52 of the collecting unit 50 is omitted.

In the above-described embodiment, the charge generation unit 30 is configured by the discharge electrode 32 provided along the inner surface of the ventilation path 24 and the two

induction electrodes

34 and 34 embedded in the housing 22. Any structure may be used as long as it generates electric charges by the above. For example, as described in Patent Document 1, the charge generation unit may be composed of a needle electrode and a counter electrode.

In the embodiment described above, the electric field generating electrode 52 is exposed to the air passage 24, but is not limited thereto, and may be embedded in the housing 22. Further, instead of the electric field generating electrode 52, a pair of electric field generating electrodes arranged so as to sandwich the collecting electrode 54 from above and below are provided in the housing 22, and an electric field generated by a voltage applied between the pair of electric field generating electrodes. Thus, the charged fine particles P and the surplus charges Q may be moved toward the collecting electrode 54.

In the above-described embodiment, an example in which the collecting unit 50 includes the electric field generating electrode 52 and the collecting electrode 54 is illustrated, but the collecting electrode 54 may be divided into a plurality of small collecting electrodes. In that case, the calculating part 66 should just calculate the number of fine particles from the corresponding relationship memorize | stored in the memory | storage part 64 based on the total electric current which added the electric current which flows through each small collection electrode.

In the above-described embodiment, the collection unit 50 is illustrated as having a pair of electrodes (the electric field generation electrode 52 and the collection electrode 54). However, the collection unit 50 includes such a pair of electrodes. A plurality of sets may be provided, and the sets may be arranged in order from the upstream side to the downstream side in the downstream region of the charge generation unit 30. In that case, the calculating part 66 should just calculate the number of microparticles | fine-particles from the corresponding relationship memorize | stored in the memory | storage part 64 based on the total electric current which added the electric current which flows through each collection electrode.

In the above-described embodiment, the sine wave voltage is applied to the charge generation unit 30, but a pulse voltage may be used instead of the sine wave voltage. As the waveform of the pulse voltage, a rectangle may be used, but various shapes such as a trapezoid, a triangle, and a sawtooth can be adopted.

In the above-described embodiment, the case where the particle number detector 10 is attached to the exhaust pipe 12 of the engine is exemplified. However, the present invention is not limited to the exhaust pipe 12 of the engine. Any tube may be used.

In the above-described embodiment, y = ax + b (a and b are constants, a> 0, as a correspondence relationship between the number concentration x (particles / cc) of the fine particles in the gas and the current y (pA) flowing through the collecting electrode 54. Although b> 0) has been exemplified, the present invention is not particularly limited to this formula. For example, a quadratic curve may be suitable as a formula representing a correspondence relationship depending on measurement conditions and the like.

The present invention is applicable to a particle number detector that detects the number of particles in exhaust gas from a power machine such as an automobile.

10 particle number detector, 12 exhaust pipe, 14 support, 16 pedestal, 18 protective cover, 20 particle detection element, 22 housing, 22a lower end, 22b upper end, 22c, 22d wall, 24 air passage, 24a gas inlet, 24b gas discharge port, 26 fine particles, 28 charge, 30 charge generation part, 32 discharge electrode, 32a wiring, 33 discharge electrode terminal, 34 induction electrode, 34a wiring, 35 induction electrode terminal, 36 discharge power supply, 50 collecting part, 52 electric field generating electrode, 52a wiring, 53 electric field generating electrode terminal, 54 collecting electrode, 54a wiring, 55 collecting electrode terminal, 56 collecting power source, 60 number detecting unit, 62 ammeter, 64 storage unit, 66 computing unit , 70 accessory unit, 72 heater electrode, 75 heater electrode terminal, 80 experimental device, 81 particle emission Device, 82 diluter, 83 compressor, 84 mass flow controllers, 85 valves, 86 particle counter, 87 a mass flow controller, 88 a vacuum pump.

Claims

A housing having a ventilation path;
A charge generating unit that adds charged charges generated by discharge to the fine particles in the gas introduced into the air passage to form charged fine particles;
A collecting electrode provided on the downstream side of the gas flow with respect to the charge generation unit and collecting the charged fine particles and surplus charges not added to the fine particles;
A storage unit for storing a correspondence relationship between the concentration of fine particles in the gas obtained in advance and a current flowing through the collection electrode;
A number detection unit for determining the number of fine particles contained in the gas based on the correspondence and the current actually flowing through the collection electrode;
Particle number detector equipped with.
The correspondence relationship is as follows: y = ax + b (a and b are constants, a> 0, b, where x (number / cc) is the fine particle number concentration of the gas and y (pA) is the current flowing through the collecting electrode. > 0),
The fine particle number detector according to claim 1.
The collecting electrode collects the charged fine particles and the surplus charges by an electric field;
The fine particle number detector according to claim 1 or 2.
The charge generation unit includes a discharge electrode, an induction electrode, and a dielectric layer sandwiched between the discharge electrode and the induction electrode.
The fine particle number detector according to any one of claims 1 to 3.
A sinusoidal voltage is applied as a discharge voltage to the discharge electrode.
The fine particle number detector according to claim 4.