WO2018163704A1

WO2018163704A1 - Microparticle number detector

Info

Publication number: WO2018163704A1
Application number: PCT/JP2018/004386
Authority: WO
Inventors: 京一菅野; 和幸水野; 英正奥村
Original assignee: 日本碍子株式会社
Priority date: 2017-03-10
Filing date: 2018-02-08
Publication date: 2018-09-13

Abstract

This microparticle number detector 10 is provided with an electric charge generating element 20, a collecting device 40, a number detecting device 56, and a shielding body 60. The electric charge generating element 20 adds electric charges generated by electrical discharge to microparticles 16 in a gas to thereby convert the microparticles into charged microparticles P. The collecting device 40 collects the charged microparticles P in a collecting electrode 46 when a voltage is applied between an applying electrode 42 and a ground electrode 44. The number measuring device 56 detects the number of the charged microparticles P on the basis of a current varying according to the number of charged microparticles P collected by the collecting electrode 46. The shielding body 60 is provided between the electric charge generating element 20 and the number measuring device 56. Even when noise due to electrical discharge is generated from the electric charge generating element 20, the noise is shielded by the shielding body 60, and it is thus difficult for the noise to affect the number measuring device 56.

Description

Particle count detector

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 in which the number measuring device measures the number of fine particles based on the amount of electric charge is known (for example, see Patent Document 1).

International Publication No. 2015/146456 Pamphlet

However, there is a possibility that noise generated by corona discharge in the charge generation element may leak and reduce the measurement accuracy of the number measuring device.

The present invention has been made to solve such a problem, and has as its main object to suppress the influence of noise generated by discharge in the charge generation section on measurement accuracy.

The particle number detector of the present invention is
A charge generation unit that adds charged charges generated by discharge to the fine particles in the gas introduced into the vent pipe to form charged fine particles;
Provided on the downstream side of the gas flow with respect to the charge generation unit, a collection electrode is disposed between the pair of collection electric field generation electrodes, and a collection voltage is applied between the pair of collection electric field generation electrodes A charged particulate collection unit that collects the charged particulates on the collection electrode;
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 shielding part provided at least between the charge generation part and the number detection part;
It is equipped with.

In this particle number detector, the charge generated by the discharge is added to the particles in the gas introduced into the vent tube to form charged 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 detection unit detects the number of fine particles in the gas based on a physical quantity that changes according to the number of charged fine particles collected by the collection electrode. Here, a shielding part is provided between the charge generation part and the number detection part. Even if noise (for example, noise caused by electromagnetic induction or noise caused by electrostatic induction) is generated by electric discharge in the charge generation unit, the noise is shielded by the shielding unit and thus hardly affects the number detection unit. Therefore, it is possible to suppress the influence of noise generated by the discharge on the measurement accuracy.

In this specification, “charge” includes positive charges and negative charges as well as ions. “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 shielding part may be integrated with a grounded electrode of the pair of collecting electric field generating electrodes. In this case, the number of components can be reduced as compared with the case where the shielding portion is provided separately from the pair of collection electric field generation electrodes.

In the particle number detector of the present invention, the charge generation unit includes a discharge electrode and a counter electrode that is opposed to the discharge electrode and grounded, and the shielding unit is integrated with the counter electrode. Also good. In this case, the number of parts can be reduced as compared with the case where the shielding portion is provided separately from the counter electrode.

In the particle number detector of the present invention, the shielding part may surround at least the entire periphery of the charge generation part. By doing so, the effects of electromagnetic shielding and electrostatic shielding are further enhanced.

The particle number detector of the present invention is provided between the charge generation unit and the charged particle collection unit, a removal electrode is disposed between a pair of removal electric field generation electrodes, and the pair of removal electric field generation electrodes When a removal voltage lower than the collection voltage is applied between them, an excess charge that has not been added to the fine particles is collected by the removal electrode, and the shielding unit includes the pair of The removal electric field generation electrode may be integrated with a grounded electrode. In this way, in the fine particle number detector provided with the surplus charge removing unit, the number of parts can be reduced as compared with the case where the shielding unit is provided separately from the pair of removed electric field generating electrodes.

In the particle number detector according to the present invention, an upstream end of the gas flow in the shielding portion protrudes from the ventilation pipe to form a protrusion, and is connected to an exhaust pipe that discharges the gas by the protrusion. It may be possible. In this way, it is not necessary to separately provide an attachment portion for attaching the particle number detector to the exhaust pipe.

The fine particle number detector of the present invention is used in, for example, atmospheric environment surveys, indoor environment surveys, pollution surveys, combustion particle measurement of automobiles, particle generation environment monitoring, particle synthesis environment monitoring, and the like.

FIG. 3 is a cross-sectional view illustrating a schematic configuration of the particle number detector 10. FIG. 2 is a cross-sectional view taken along the line AA in FIG. FIG. 3 is a cross-sectional view illustrating a schematic configuration of a particle number detector 110. FIG. 3 is a cross-sectional view illustrating a schematic configuration of a particle number detector 210. FIG. 3 is a cross-sectional view illustrating a schematic configuration of a particle number detector 310. FIG. 4 is a cross-sectional view illustrating a schematic configuration of a particle number detector 410. FIG. 6 is a cross-sectional view of a modified example of the particle number detector 10. FIG. 6 is an explanatory diagram of the charge generation element 120.

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, and FIG.

The fine particle number detector 10 measures the number of fine particles contained in a gas (for example, exhaust gas from an automobile). As shown in FIG. 1, the fine particle number detector 10 includes a charge generating element 20, a collecting device 40, a detector main body 50, and a shield 60 in a ceramic vent pipe 12. The vent pipe 12 has a gas inlet 12a for introducing gas into the vent pipe 12 and a gas outlet 12b for discharging the gas that has passed through the vent pipe 12.

The charge generation element 20 includes a needle electrode 22 and a counter electrode 24 provided so as to be exposed on a wall facing the needle electrode 22, provided on the side of the vent pipe 12 close to the gas inlet 12 a. is doing. The counter electrode 24 forms part of the shield 60. The needle electrode 22 and the counter electrode 24 are connected to a discharge power source 26 that applies a voltage Vp (for example, a pulse voltage). The charge generating element 20 generates an air discharge due to a potential difference between the two electrodes when a voltage Vp is applied between the needle-like electrode 22 and the counter electrode 24. As the gas passes through the air discharge, the fine particles 16 in the gas are added with charges 18 (here, negative charges) to become charged fine particles P.

The collection device 40 is a device that collects the charged fine particles P, and is provided in the hollow portion 12 c in the vent pipe 12. The collection device 40 has a pair of collection electric field generation electrodes (application electrode 42 and ground electrode 44) and a collection electrode 46. The application electrode 42 and the ground electrode 44 are embedded at positions facing each other on the wall of the vent pipe 12. The application electrode 42 is an electrode having a negative potential −V1. The level of the negative potential −V1 is from the −mV order to −several tens of volts. The ground electrode 44 is an electrode connected to the ground. The ground electrode 44 forms part of the shield 60. The collection electrode 46 is disposed between the application electrode 42 and the ground electrode 44, and is exposed on the wall of the hollow portion 12 c in which the ground electrode 44 is embedded. As a result, an electric field from the ground electrode 44 toward the application electrode 42 is generated inside the hollow portion 12c. Therefore, the charged fine particles P (negatively charged) that have entered the hollow portion 12c are attracted to the ground electrode 44 by the generated electric field and collected by the collecting electrode 46 installed in the middle thereof.

The detector main body 50 includes a series circuit unit 52 and a number measuring device 56. The series circuit unit 52 is provided between the collecting electrode 46 and the number measuring device 56. A capacitor 53, a resistor 54, and a switch (preferably a semiconductor switch) 55 are connected in series to the series circuit portion 52 from the collecting electrode 46 side. 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 46. When the switch 55 is turned on, a current based on the charge 18 of the charged fine particles P collected by the collecting electrode 46 is transmitted to the number measuring device 56 as a transient response through a series circuit including the capacitor 53 and the resistor 54. Is done. 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 shield 60 is made of a conductive material (for example, a metal such as copper, aluminum, or an aluminum alloy). The shield 60 is formed in a cylindrical shape having a rectangular cross section including the first shield plate 61 and the second shield plate 62 (see FIG. 2), and is grounded to the ground. The first shielding plate 61 is disposed in the wall of the vent pipe 12 so as to partition the charge generating element 20 and the detector main body 50. The first shielding plate 61 is formed so as to cover the entire detector main body 50 by extending the ground electrode 44 of the collection device 40 to the downstream side in the gas flow direction, and the counter electrode 24 of the charge generation element 20. It is formed so as to be integrated. On the other hand, the second shielding plate 62 is embedded on the side of the wall of the vent pipe 12 close to the outer surface so as to cover the needle electrode 22 of the charge generation element 20 and the application electrode 42 of the collection device 40. The cylindrical shield 60 surrounds the entire periphery of the charge generation element 20 and the collection electrode 46.

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 particulate matter detector 10 is attached so that the exhaust gas is introduced into the vent pipe 12 from the gas inlet 12a of the particulate detector 10 and discharged from the gas outlet 12b.

The fine particles 16 contained in the exhaust gas introduced into the vent pipe 12 from the gas introduction port 12a are charged with the charge 18 (negative charge in this case) generated by the discharge of the charge generation element 20, and then become the charged fine particles P. Enter 12c. At this time, even if noise is generated by discharge, the shield 60 prevents the noise from leaking to the detector body 50 side. When the charged fine particles P entering the hollow portion 12c reach the collection device 40, they are attracted to the ground electrode 44 and collected by the collection electrode 46 installed in the middle thereof. A current based on the charge 18 of the charged fine particles P attached to the collecting electrode 46 is transmitted to the number measuring device 56 as a transient response through a series circuit including a capacitor 53 and a resistor 54.

The relationship between the current I and the charge amount q is I = dq / (dt), q = ∫Idt. Therefore, the number measuring device 56 integrates (accumulates) the current value over a period during which the switch 55 is turned 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. Thus, the number of fine particles 16 attached to the collecting electrode 46 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 46 over the predetermined period. The number of 16 can be calculated. Further, by using the transient response by the capacitor 53 and the resistor 54, it is possible to measure even with a small current, and the number of the fine particles 16 can be detected with high accuracy. In the case of 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 54 having a large resistance value.

Here, the correspondence between the components of the present embodiment and the components of the present invention will be clarified. The charge generation element 20 of this embodiment corresponds to a charge generation unit of the present invention, the collection device 40 corresponds to a charged particle collection unit, the detector main body 50 corresponds to a number detection unit, and the shield 60 shields. It corresponds to the part.

According to the fine particle number detector 10 of the present embodiment described in detail above, since the shielding body 60 is provided, even if noise is generated by discharge in the charge generation element 20, the noise is shielded by the shielding body 60. The Therefore, it is possible to suppress the influence of noise generated by the discharge on the measurement accuracy. Particularly, since the shield 60 is cylindrical and surrounds the entire periphery of the charge generation element 20 and the collection electrode 46, the effect of electromagnetic shielding and electrostatic shielding is further enhanced.

Further, the shield 60 is integrated with the counter electrode 24 of the charge generation element 20 and the ground electrode 44 of the collection device 40. Therefore, the number of parts can be reduced as compared with the case where the shield 60 is provided separately from the counter electrode 24 and the ground electrode 44.

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 shield 60 integrated with the counter electrode 24 of the charge generation element 20 and the ground electrode 44 of the collection device 40 is used. However, like the particle number detector 110 shown in FIG. Instead of the shield 60, a shield 160 may be employed. In FIG. 3, the same components as those in the above-described embodiment are denoted by the same reference numerals. The shield 160 is formed in a cylindrical shape including the first shield plate 161 and the second shield plate 62. The first shielding plate 161 is integrated with the ground electrode 44 of the collection device 40, but is formed separately from the counter electrode 24 of the charge generation element 20. Even in this case, since the shield 160 is arranged so as to partition the charge generating element 20 and the detector main body 50, the influence on the measurement accuracy of noise generated by the discharge in the charge generating element 20 can be suppressed. it can. Further, since the shield 160 is integrated with the ground electrode 44 of the collection device 40, the number of parts can be reduced as compared with the case where the shield 160 is provided separately from the ground electrode 44.

Alternatively, a shield 260 may be employed instead of the shield 60 as in the particle number detector 210 shown in FIG. In FIG. 4, the same components as those in the above-described embodiment are denoted by the same reference numerals. The shield 260 is formed in a cylindrical shape including the first shield plate 261 and the second shield plate 62. The first shielding plate 261 is integrated with the counter electrode 24 of the charge generation element 20, but is formed separately from the ground electrode 44 of the collection device 40. Even in this case, since the shield 260 is disposed so as to partition the charge generation element 20 and the detector main body 50, the influence on the measurement accuracy of noise generated by the discharge in the charge generation element 20 can be suppressed. it can. Further, since the shield 260 is integrated with the counter electrode 24 of the charge generation element 20, the number of components can be reduced as compared with the case where the shield 260 is provided separately from the counter electrode 24.

In the above-described embodiment, the surplus charges 18 that have not been added to the fine particles 16 out of the charges 18 generated by the charge generation element 20 are not removed, but such surplus charges 18 may be removed. The particle number detector 310 of FIG. 5 is an example in which the surplus charge removing device 30 is provided between the charge generating element 20 and the collecting device 40. In FIG. 5, the same components as those in the above-described embodiment are denoted by the same reference numerals. The surplus charge removing device 30 has a pair of removing electric field generating electrodes (applying electrode 32 and ground electrode 34) and a removing electrode 36. The application electrode 32 and the ground electrode 34 are embedded in positions facing each other on the wall of the vent pipe 12. The application electrode 32 is an electrode having a negative potential −V2. The absolute value of the negative potential −V2 is one digit or more smaller than the absolute value of the negative potential −V1 of the collection device 40. The ground electrode 34 is an electrode connected to the ground. The removal electrode 36 is disposed between the application electrode 32 and the ground electrode 34, and is exposed on the wall of the hollow portion 12 c in which the ground electrode 34 is embedded. As a result, a weak electric field is generated between the application electrode 32 and the ground electrode 34 of the surplus charge removing device 30. Therefore, 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 ground electrode 34 by this weak electric field, captured by the removal electrode 36, and then discarded to the ground. . Therefore, surplus charges 18 are not collected by the collection electrode 46 of the collection device 40 and counted as the number of charged fine particles P. The shield 360 is formed in a cylindrical shape including the first shield plate 361 and the second shield plate 62. The 1st shielding board 361 is arrange | positioned so that the detector main body 50 and other apparatuses (the charge generation element 20, the surplus charge removal apparatus 30, and the collection apparatus 40) may be partitioned off. The detector body 50 is isolated from other devices by a shield 360. Therefore, it is possible to suppress the influence of noise generated by the discharge in the charge generation element 20 on the measurement accuracy.

The shield 360 in FIG. 5 is provided separately from each of the counter electrode 24 of the charge generation element 20, the ground electrode 34 of the surplus charge removing device 30, and the ground electrode 44 of the collection device 40. However, the shield 360 is integrated with at least one of these. May be used. The particle number detector 410 in FIG. 6 is an example in which the first shielding plate 461 constituting the shielding body 460 is integrated with the counter electrode 24, the ground electrode 34, and the ground electrode 44. In FIG. 6, the same components as those in the above-described embodiment are denoted by the same reference numerals. In this way, the number of parts can be reduced as compared with the shield 360 of FIG.

In the particle number detector 10 of the above-described embodiment, as shown in FIG. 7, the protruding portion 60 a is formed by protruding the upstream end portion of the gas flow in the cylindrical shield 60 from the vent pipe 12. It may be formed. This protrusion 60a can be connected to an exhaust pipe 70 for discharging gas. In this way, it is not necessary to separately provide an attachment portion for attaching the particle number detector 10 to the exhaust pipe 70. 3 to 6 may be similar to this.

In the above-described embodiment, the needle-like electrode 22 is provided so that the tip protrudes into the hollow portion 12c. However, the present invention is not particularly limited to this. For example, a flat needle electrode may be provided by printing on the inner wall surface of the vent pipe 12 at a position facing the counter electrode 24.

In the embodiment described above, the acicular electrode 22 and the counter electrode 24 are used as the charge generating element 20, but the present invention is not particularly limited thereto. For example, as shown in FIG. 8, a charge generating element 120 in which an induction electrode 124, a dielectric layer 123, and a discharge electrode 122 are laminated in this order on the inner surface of the vent pipe 12 may be used. The discharge electrode 122 preferably includes a plurality of protrusions 122a on the outer periphery. The induction electrode 124 is integrated with the first shielding plate 61. Even when the voltage of the discharge power supply 26 is applied between the discharge electrode 122 and the induction electrode 124, electric charges are generated by air discharge. Even if noise is generated during the discharge, the noise is shielded by the shield 60 and thus hardly affects the detector body 50 (see FIG. 1). Therefore, it is possible to suppress the influence of noise generated by the discharge in the charge generation element 20 on the measurement accuracy.

In the above-described embodiment, the cylindrical shielding body 60 including the first shielding plate 61 and the second shielding plate 62 is adopted, but the lower first shielding plate 61 and the upper second shielding plate 62 are connected. It may be provided separately, or only the lower first shielding plate 61 may be provided. The same applies to FIGS.

In the above-described embodiment, a pipe having a rectangular cross section is used as the vent pipe 12, but a pipe having a circular cross section may be used. In that case, the shield 60 is also formed in a cylindrical shape having a circular cross section.

In the above-described embodiment, the case of measuring the number of negatively charged fine particles P has been described, but the number of fine particles 16 can be similarly measured even for positively charged fine particles P. When measuring the number of positively charged charged fine particles P, for example, a positive voltage may be applied to the applying electrode 42 to collect the charged fine particles P on the collecting electrode 46.

This application is based on Japanese Patent Application No. 2017-45634 filed on Mar. 10, 2017, and the entire contents of which are incorporated herein by reference.

The present invention can be used to detect the number of fine particles in exhaust gas from a power machine such as an automobile.

10 particle number detector, 12 vent tube, 12a gas inlet, 12b gas outlet, 12c hollow part, 16 particles, 18 charge, 20 charge generation element, 22 needle electrode, 24 counter electrode, 26 discharge power supply, 30 Surplus charge removal device, 32 application electrode, 34 ground electrode, 36 removal electrode, 40 collection device, 42 application electrode, 44 ground electrode, 46 collection electrode, 50 detector body, 52 series circuit section, 53 capacitor, 54 resistance , 55 switch, 56 count measuring device, 60 shield, 60a protrusion, 61 first shield plate, 62 second shield plate, 70 exhaust pipe, 110, 210, 310, 410 fine particle number detector, 120 charge generation element , 122 discharge electrode, 122a protrusion, 123 dielectric layer, 124 induction electrode, 160, 260, 3 0,460 shields, 161,261,361,461 first shielding plate, P charged fine particles.

Claims

A charge generation unit that adds charged charges generated by discharge to the fine particles in the gas introduced into the vent pipe to form charged fine particles;
Provided on the downstream side of the gas flow with respect to the charge generation unit, a collection electrode is disposed between the pair of collection electric field generation electrodes, and a collection voltage is applied between the pair of collection electric field generation electrodes A charged particulate collection unit that collects the charged particulates on the collection electrode;
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 shielding part provided at least between the charge generation part and the number detection part;
Particle number detector equipped with.
The shield is integrated with the grounded electrode of the pair of collected electric field generating electrodes.
The fine particle number detector according to claim 1.
The charge generation unit includes a discharge electrode and a counter electrode that is opposed to the discharge electrode and grounded
The shielding part is integrated with the counter electrode.
The fine particle number detector according to claim 1 or 2.
The shielding portion surrounds at least the entire periphery of the charge generation portion;
The fine particle number detector according to any one of claims 1 to 3.
The fine particle number detector according to any one of claims 1 to 4,
Provided between the charge generation unit and the charged particulate collection unit, a removal electrode is disposed between the pair of removal electric field generation electrodes, and is lower than the collection voltage between the pair of removal electric field generation electrodes A surplus charge removing unit that collects surplus charges not added to the fine particles when the removal voltage is applied to the removal electrode;
The shield is integrated with the grounded electrode of the pair of removed electric field generating electrodes.
Particle number detector.
The upstream end portion of the gas flow in the shielding portion protrudes from the ventilation pipe to form a protrusion, and can be connected to an exhaust pipe that discharges the gas by the protrusion.
The fine particle number detector according to any one of claims 1 to 5.