JP2008145347A - Faraday cup ammeter and particle measuring apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a Faraday cup ammeter receiving no charge of charged particles which are charged on a particle collecting section. <P>SOLUTION: The perimeter of the particle collecting section 11 is covered by a conductive member 13 and fixed by a plurality of conductive pins 15. The particle collecting section 11 and the conductive member 13 are electrically insulated by an insulating material 17, and a conductive cage 19 is disposed around the insulating material 17. An ammeter 23 for detecting a charge collected by the particle collecting section 11 is disposed between the conductive cage 19 and an earth 21. A switch (charge discharging mechanism) 27 for switching on/off states of a connection is disposed in the middle of a lead wire 25. An integral current value charged on the particle collection section 11 is calculated by the ammeter 23. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an apparatus for measuring a sample gas supply amount, for example, a particle measuring apparatus for measuring the number of particles contained in an environmental gas.

Aerosol generally means a colloid in which the dispersion medium is a gas and the dispersoid is a liquid or a solid, and indicates an environmental gas such as an automobile exhaust gas.
As an apparatus for measuring the number of particles, an electromobility measuring apparatus is used that measures after charging particles in the aerosol to be measured and classifying the charged charged particles using the difference in moving speed in the electric field. Yes. Since there is a certain relationship between the electric mobility and the particle diameter, the particle diameter can be specified by specifying the electric mobility.

As the electric mobility measuring device, a differential mobility analyzer (DMA) capable of selecting fine particles having a specific electric mobility and an electric mobility in the vicinity thereof (see Patent Document 1). Then, there is an integral type electric mobility measuring device that can select fine particles having an electric mobility smaller than a certain electric mobility.
As a particle concentration coefficient device used for these, a Faraday cup ammeter as shown in FIG. 4 has been used.

In this Faraday cup ammeter, the particle collecting unit 11 is formed in a filter shape so as to collect charged particles in the gas flow. A wire net (conductive member 13) for fixing the particle collecting part 11 is placed on the upper part of the particle collecting part 11.
The particle collecting part 11 and the conductive member 13 on the upper part thereof are electrically insulated by an insulating material 17, and a conductive cage 19 is provided around the insulating material 17. Between the conductive cage 19 and the earth 21, an ammeter 23 for detecting the charge collected by the particle collecting unit 11 is provided, and the number of particles is calculated by calculating the valence of the particles to this current value. Is required.
The entire apparatus is surrounded by a cover 31 so that gas is introduced from the inlet 33 and gas is discharged from the outlet 35.

Japanese Patent No. 3449359

Conventionally, the Faraday cup ammeter shown in FIG. 4 is often used for research purposes, and the continuous measurement time is at most several hours. Combined with the low flow rate of the introduced gas, the charged particles remaining in the filter are charged. The measurement was not affected.
However, it is necessary to process a large flow rate of sample gas for automobile exhaust gas measurement applications and the like. In that case, in order to achieve a low pressure loss while flowing a large amount of gas through the filter, it was necessary to use a filter bent in a corrugated shape or a filter processed into a cylindrical shape.
Along with this, the charged particles charged in the filter are saturated, which makes measurement impossible.

  Therefore, an object of the present invention is to provide a Faraday cup ammeter that does not receive the charge of charged particles charged in a particle collecting portion.

  The Faraday cup ammeter of the present invention includes a particle collection unit that collects charged particles in a gas flow, a conductive cage that is electrically insulated from the particle collection unit and covers the entire circumference thereof, and a particle collection unit. And an ammeter that measures the amount of charge collected in the particle collection unit by measuring the amount of charge that is induced by the charged electric charge and transferred from the surroundings to the conductive cage. The particle collection unit has a charge release mechanism that discharges the charged charges to the ground.

  The periphery of the particle collecting portion is covered with a conductive member, and the charge discharging mechanism can be configured by a switch for switching the connection between the conductive member and the ground.

  The particle collecting portion and the conductive member can be fixed by, for example, a pin.

  The particle collecting portion can be formed in a filter shape or a cylindrical shape.

  The charge release mechanism discharges the electric charge charged in the particle collecting portion to the ground with a predetermined integrated current value measured by the ammeter.

  The particle measuring apparatus of the present invention includes a charging mechanism that charges charged particles, a pair of counter electrodes that are arranged to face each other in order to classify charged particles by electric mobility, from one end side of the classification region to the classification region. A sheath gas supply unit that supplies uncharged gas as a sheath gas, a sample gas supply unit that supplies sample gas from the upstream side of the classification region, and a part of the charged particles from the downstream side of the classification region are sucked at a constant flow rate in the sheath gas flow direction. A particle classification mechanism provided with a suction part that performs the above and a Faraday cup ammeter of the present invention provided downstream of the suction part.

  In order to change the charge of the supplied gas, the charging mechanism may be provided with a unipolar charging mechanism that reverses the polarity.

  In order to change the charge of the particles to be classified, the counter electrode may be provided with a power source for applying a reverse potential.

  According to the present invention, since the charged particles charged in the particle collecting portion can be discharged, the decrease in the particle collecting ability due to the repulsive force between particles and the measurement current error due to the charge charge are eliminated, and the accuracy is improved. High particle measurement can be performed.

  When the connection between the conductive member and the ground is switched by a switch, it becomes possible to discharge electric charges from the particle collecting portion when necessary.

  If the particle collecting part and the conductive member are fixed by a pin, the electric charge charged in the particle collecting part can be efficiently discharged to the outside through the conductive member.

  If the electric charge charged in the particle collecting part with a predetermined integrated current value is discharged to the ground, it is possible to prevent an excessive electric charge from being charged in the particle collecting part in advance, and more accurate. High particle measurement can be performed.

  If a particle measuring device including a charging mechanism, a particle classification mechanism, and the Faraday cup ammeter of the present invention is used, it is possible to classify charged particles and measure the number of particles.

  If the charging mechanism is provided with a unipolar charging mechanism that reverses the polarity, the particle collecting part charged to one of the polarities can be extinguished by the other polarity.

  If a power source for applying a reverse potential to the counter electrode is provided, the charge polarity of the particles can be changed, the charge charge in the particle collector can be eliminated, and more accurate particle measurement can be performed. become able to.

The present invention will be described in detail below based on examples.
FIG. 1 shows a vertical cross-sectional view of one embodiment of a Faraday cup ammeter.
The particle collecting unit 11 is formed in a filter shape so as to collect charged particles in the gas flow. The periphery of the particle collecting unit 11 is covered with a conductive member 13 and fixed by a plurality of conductive pins 15, so that the charges in the particle collecting unit 11 can be easily discharged to the outside.

A general commercially available air filter can be used as the particle collecting unit 11, and the size, shape, and material are selected according to the type and flow rate of the particle and the fluid containing the particle. It is desirable to have a 0.3 μm DOP capture efficiency of about 99.9%.
For example, ADVANTEC glass fiber filter pleats compact cartridge filter MCG, Pall Corporation glass fiber filter Type A / E, and the like can be mentioned.
Examples of the conductive member 13 include a metal material such as a wire mesh formed in a mesh shape or a honeycomb shape, a thin wire wound around, a member integrated with the conductive pin 15, and the like. In the case of using a mesh-like or honeycomb-like member for the conductive member 13, it is sufficient that the interval is sufficient (for example, 10 μm to 2 mm) to collect charges charged in the particle collecting unit 11.
Examples of the conductive pins 15 include screws and nails.

The particle collecting unit 11 and the surrounding conductive member 13 are electrically insulated by an insulating material 17, and a conductive cage 19 is provided around the insulating material 17. As a material of the insulating material 17, PTFE (polytetrafluoroethylene) or PEEK (polyetheretherketone) material can be used.
An ammeter 23 is provided between the conductive cage 19 and the earth 21 for detecting the charge collected by the particle collecting unit 11. The number of particles can be obtained by calculating the valence of the particles in the current value of the ammeter 23.

One end of a lead wire 25 that discharges charges is connected to the conductive member 13, and the other end of the lead wire 25 is connected to the ground 21. Further, a switch (charge discharge mechanism) 27 for switching connection on / off is provided in the middle of the lead wire 25.
The switch 27 provided on the lead wire 25 may be manually turned on / off, or the switch may be automatically switched when the ammeter 23 indicates a predetermined integrated current value. Also good.

  In the configuration of the Faraday cup ammeter described above, if a gap is generated around the conductive pin 15, particles are discharged without being collected from the gap, so that the periphery of the conductive pin 15 is ensured to be airtight. It is necessary to. For example, a metal pin may be press-fitted into a flexible Teflon (registered trademark) filter. In addition, during the measurement of the number of particles, it is necessary to accumulate electric charges, so that the switch 27 is normally left open. At this time, the lead wire 25 and the cage 19 are prevented from contacting each other.

  The entire Faraday cup ammeter is surrounded by a cover 31 so that gas is introduced from the inlet 33 and gas is discharged from the outlet 35.

Next, the operation of this embodiment will be described.
For example, a gas containing positively charged fine particles is introduced from the gas introducing unit 33, and the charged fine particles are collected by the particle collecting unit 11.
The electric charge of the fine particles collected in the particle collecting unit 11 is measured by the ammeter 23 by the charge charged in the particle collecting unit 11 and transferred from the surroundings to the conductive cage 19. Is required.

  The ammeter 23 measures the accumulated current value due to charging. When the integrated current value exceeds a predetermined threshold value, the integrated current is released to the ground 21 by closing the switch 27. This releasing operation may be performed artificially or automatically. Thereby, the electric charge accumulated in the particle collecting unit 11 is released to the earth 21 through the conductive pin 15, the conductive member 13, and the lead wire 25, and the charging of the particle collecting unit 11 is eliminated.

  In the above operation, the charge is released by closing the switch 27 and the charging of the particle collecting unit 11 is eliminated. However, the charging of the fine particles introduced from the gas introducing unit 33 may be controlled. Specifically, after introducing a gas containing fine particles charged positively, a gas containing fine particles charged negatively may be introduced. Thereby, the charge of the particle | grain collection part 11 is canceled by plus and minus charge, and electrification is canceled.

Next, another embodiment will be described.
FIG. 2 is a vertical sectional view of the particle measuring apparatus.
A cylindrical center electrode 43 is provided inside the cylindrical housing 41 so as to coincide with the center line 42 of the housing 41. The inner surface of the housing 41 is an outer electrode 44, and the center electrode 43 and the outer electrode 44 constitute a counter electrode. The central electrode 43 and the outer electrode 44 generate an electric field for classifying the charged particles according to the electric mobility, and the rotating space formed between the electrodes 43 and 44 is the classification region 45. The center line 42 is formed in a cylindrical shape in the cylindrical casing 41.

  A sheath gas supply unit 47 for introducing an uncharged gas as a sheath gas at a constant flow rate Qc is provided at the upper part of the casing 41, and an insulating first for laminating the sheath gas is provided upstream of the classification region 45. A rectifying mechanism 49 is provided. The first rectifying mechanism 49 is composed of a plurality of plates arranged in parallel to each other in the vertical direction. The sheath gas that has passed through the first rectifying mechanism 49 is supplied to the classification region 45 as a laminar flow.

  The discharge port 51a of the sample gas supply unit 51 is provided on the upstream side of the classification region 45 so that the discharge direction is parallel to the sheath gas flow. The tip of the discharge port 51a is the flow rate of the introduced sample gas and the flow rate of the sheath gas. The flow rates of both gases are set so that the flow rate difference is zero. The sample gas is supplied from the charging mechanism 40 at a constant flow rate Qa in parallel with the sheath gas flow. The charging mechanism 40 is provided with a monopolar charging mechanism (not shown) that reverses the polarity, and can control the charging of charged fine particles.

A suction port 57a of the suction part 57 is provided on the downstream side of the classification region 45 so that the suction direction is parallel to the sheath gas flow, and the flow rate difference between the suctioned charged particle flow rate and the sheath gas flow rate is zero. The suction speed is set so that The charged particles are sucked at a constant flow rate Qs in parallel with the sheath gas flow.
A detector 58 that detects the number of charged particles sent together with the sheath gas as an electric quantity is disposed downstream of the suction unit 57. The detector 58 is the Faraday cup ammeter shown in FIG.
A sheath gas discharge part 53 is provided outside the lower end of the classification region 45 at the lower part of the casing 41, that is, downstream of the sheath gas flow, and the gas is discharged at a constant flow rate Qe.

  The center electrode 43 is supported at the casing 41 by the first rectifying mechanism 49 whose upper end is laminarized with the insulating member 50 and the gas flow, and the lower end of the center electrode 43 is the first laminar flow of the insulating member 59 and the sheath gas. By being supported by the casing 41 by the second rectifying mechanism 56 having the same structure as the first rectifying mechanism 49, the central electrode 43 and the casing 41 serving as the external electrode are electrically insulated.

  For example, the diameter of the center electrode 43 is 50 mm, and the inner diameter of the outer electrode 44 is 66 mm. In the cylindrical portion of the center electrode 43, the distance between the center electrode 43 and the outer electrode 44 is constant at about 8 mm. A classification voltage of 1 to 1500 V is applied between the electrodes 43 and 44.

Pumps 63 and 61 are provided as suction mechanisms downstream of the suction part 57 and the sheath gas discharge part 53, respectively.
A detector 58 between the suction unit 57 and the pump 63 can detect the charge of the classified particles and calculate the number of particles.

  A power supply 67 for applying a reverse potential is provided between the counter electrodes 43 and 44 so that the potential between the counter electrodes 43 and 44 can be controlled.

Next, the operation of this embodiment will be described. When a voltage is applied between the electrodes 43 and 44, a horizontal electric field is generated in the classification region 45 to classify charged particles according to electric mobility.
For example, a gas containing fine particles charged positively is introduced from the charging mechanism 40. Of the sample gas introduced into the classification region 45 from the discharge port 51 a of the sample gas supply unit 51, classified charged particles are sucked from the suction port 57 a of the suction unit 57 and sent to the detector 58.
In the detector 58, the charged fine particles in the gas are collected by the particle collecting unit 11, and the charge and the number of particles are measured by the ammeter 23.

The ammeter 23 measures the accumulated current value due to charging. When the integrated current value exceeds a predetermined threshold value, a gas containing fine particles charged negatively from the charging mechanism 40 is introduced. Thereby, the electric charge of the particle | grain collection part 11 is canceled, and electrification is eliminated.
In addition, even when a reverse potential is applied by the power source 67, the charges in the particle collecting unit 11 are canceled out and the charging is eliminated.

Next, another embodiment of the Faraday cup ammeter will be described.
FIG. 3 is a perspective view of a filter portion of a corrugated cylindrical processed filter type Faraday cup ammeter.
The particle collecting unit 11 has a triple structure by the support media 41 and 42 and is stacked in a bellows shape.
The triple-structured particle collecting unit 11 is sandwiched between a core 47 and a protector 43 and is fixed in a cylindrical shape. In addition, an O-ring 45 is provided on the upper part of the device, and can be connected to other devices.

The circumference of the cylindrical ammeter is covered with a conductive member 13b, and the conductive member 13a can be inserted into the inside of the cylinder. The conductive member 13 a and the conductive member 13 b are connected and fixed by a conductive pin 15 that penetrates the particle collecting portion 11.
Further, the conductive member 13 b and the ground 21 are connected to the lead wire 25 via the switch 27. When the switch 27 is closed, the accumulated current charged in the conductive member 11 can be released. As a result, a decrease in particle collection ability due to the repulsive force between particles and a measurement current error due to charge charge can be eliminated, and highly accurate particle measurement can be performed.

  The present invention can be used as an apparatus for measuring the number of fine particles contained in an aerosol such as automobile exhaust gas in real time.

Fig. 3 shows a vertical cross section of a Faraday cup ammeter. It is a vertical sectional view of a particle measuring device. It is a perspective view of the filter part of a corrugated cylindrical processing filter type Faraday cup ammeter. 1 shows a vertical cross-sectional view of a conventional Faraday cup ammeter.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Particle collection part 13 Conductive member 15 Conductive pin 17 Insulation material 19 Conductive cage 21 Ground 23 Ammeter 25 Lead wire 27 Switch 31 Case

Claims (8)

A particle collector for collecting charged particles in the gas stream;
A conductive cage that is electrically insulated from the particle collector and covers the entire circumference thereof;
An ammeter that measures the amount of electric charge collected in the particle collecting unit by measuring the electric charge that is induced by the electric charge charged in the particle collecting unit and moves from the periphery to the conductive cage; ,
With
The Faraday cup ammeter characterized in that the particle collecting part has a charge release mechanism for discharging a charged charge to the ground.   2. The Faraday cup ammeter according to claim 1, wherein a periphery of the particle collecting unit is covered with a conductive member, and the charge discharging mechanism is configured by a switch that switches connection between the conductive member and ground.   The Faraday cup ammeter according to claim 1 or 2, wherein the particle collecting unit and the conductive member are fixed by a pin.   The Faraday cup ammeter according to any one of claims 1 to 3, wherein the particle collecting part is formed in a filter shape or a cylindrical shape.   The said electric charge discharge | release mechanism discharge | releases the electric charge charged to the said particle | grain collection part to earth | ground with the predetermined | prescribed integrated electric current value which the said ammeter measured. Faraday cup ammeter. A charging mechanism for charging particles to be charged;
A pair of counter electrodes arranged opposite to each other to classify charged particles by electric mobility, a sheath gas supply unit that supplies uncharged gas as a sheath gas from one end side of the classification region to the classification region, A particle classification mechanism including a sample gas supply unit that supplies a sample gas from the upstream side, and a suction unit that sucks a part of the charged particles from the downstream side of the classification region at a constant flow rate in the flow direction of the sheath gas;
The Faraday cup ammeter according to any one of claims 1 to 5, provided downstream of the suction unit;
A particle measuring apparatus.   The particle measuring apparatus according to claim 6, wherein the charging mechanism includes a unipolar charging mechanism that reverses polarity.   The particle measuring apparatus according to claim 6 or 7, wherein the counter electrode is provided with a power source for applying a reverse potential.

Images