WO2002073165A2 - Photodetector for particle counting - Google Patents

Photodetector for particle counting Download PDF

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Publication number
WO2002073165A2
WO2002073165A2 PCT/GB2002/001062 GB0201062W WO02073165A2 WO 2002073165 A2 WO2002073165 A2 WO 2002073165A2 GB 0201062 W GB0201062 W GB 0201062W WO 02073165 A2 WO02073165 A2 WO 02073165A2
Authority
WO
WIPO (PCT)
Prior art keywords
flow
fluid
light
photodetector
scattered
Prior art date
Application number
PCT/GB2002/001062
Other languages
French (fr)
Other versions
WO2002073165A3 (en
Inventor
Barrington James Hill
Original Assignee
Facility Monitoring Systems Limited
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Facility Monitoring Systems Limited filed Critical Facility Monitoring Systems Limited
Priority to AU2002236079A priority Critical patent/AU2002236079A1/en
Publication of WO2002073165A2 publication Critical patent/WO2002073165A2/en
Publication of WO2002073165A3 publication Critical patent/WO2002073165A3/en

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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N1/00—Sampling; Preparing specimens for investigation
    • G01N1/02—Devices for withdrawing samples
    • G01N1/22—Devices for withdrawing samples in the gaseous state
    • G01N1/2202—Devices for withdrawing samples in the gaseous state involving separation of sample components during sampling
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N15/00—Investigating characteristics of particles; Investigating permeability, pore-volume or surface-area of porous materials
    • G01N15/02—Investigating particle size or size distribution
    • G01N15/0205—Investigating particle size or size distribution by optical means
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N1/00—Sampling; Preparing specimens for investigation
    • G01N1/02—Devices for withdrawing samples
    • G01N1/22—Devices for withdrawing samples in the gaseous state
    • G01N1/24—Suction devices
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N1/00—Sampling; Preparing specimens for investigation
    • G01N1/02—Devices for withdrawing samples
    • G01N1/22—Devices for withdrawing samples in the gaseous state
    • G01N1/2202—Devices for withdrawing samples in the gaseous state involving separation of sample components during sampling
    • G01N2001/222—Other features
    • G01N2001/2223—Other features aerosol sampling devices

Definitions

  • This invention relates to a detector for particle counting. More particular, but not exclusively, this invention relates to a non-imaging detector for use in particle counting apparatus, and to apparatus having such a detector.
  • apparatus for monitoring particles comprised in a fluid the apparatus including:
  • a light source operable so as to generate a beam of light which intersects the flow, the light striking particles present in the flow of fluid and being scattered thereby;
  • the detector means including a photodetector which extends in a direction along at least a portion of the fluid flow, the photodetector being spaced laterally from the flow;
  • the photodetector is formed so as to be concave about the fluid flow and disposed around at least a portion of the flow.
  • the means for generating a flow of the fluid may include an inlet nozzle and an outlet nozzle for the fluid.
  • a pump may be provided to draw the fluid through the inlet nozzle and the outlet nozzle.
  • the light source may comprise a source of laser light.
  • a light stop may be provided to absorb light from the source which has not been scattered.
  • the photodetector consists of photodiodes .
  • the photodetector consists of a number of diodes physically and electrically connected together so as to provide a single unbroken surface.
  • the detector is in the form of a rectilinear trough.
  • the rectilinear trough may have a base and two opposed sides.
  • the detector is in the form of a curved trough.
  • the detector may be concave so as to surround at least a part of the flow of fluid.
  • two detectors may be provided, one either side of the fluid flow.
  • the fluid is air.
  • the fluid is gas.
  • measurement of the scattered light gives a measure of the number of particles present.
  • measurement of the scattered light also gives a measure of the size of particles present.
  • Figure 1 is a diagram of one embodiment of the invention
  • Figure 2 shows the apparatus of Figure 1 viewed from the line A - A' in Figure 1 and in the direction of the arrows;
  • Figure 3 is a corresponding view of a second embodiment of the invention.
  • Figure 4 is a corresponding view of a third embodiment
  • FIG 5 is a corresponding view of a fourth embodiment .
  • the apparatus includes a housing 1.
  • An air inlet pipe 2 draws sample air into the housing for example by means of a pump (not shown) .
  • the sampled air flows through an inlet nozzle 3, which in this example is tapered and approximately rectilinear in cross section, as shown in Figures 1, 2 and 5, although the inlet nozzle may be round as shown in Figures 3 and 4 or of any suitable alternative configuration such as rectangular.
  • the air is drawn from the inlet nozzle 3 to an outlet nozzle 4, again by a pump (not shown), and thence is expelled out of the housing.
  • the outlet nozzle 4 may equally be of any suitable configuration.
  • a light source in the form of a laser 5 is attached to the housing and is configured so as to send a beam 6 of laser light through a light passage 7 in the housing (which may contain suitable laser optics 8) to intersect the flow of air passing from the inlet nozzle 3 to the outlet nozzle 4.
  • a light stop 10 is also provided to absorb light which has not been scattered.
  • the photodetector 9 is connected to control and monitoring circuitry (not shown) .
  • a display (not shown) is also provided to provide an operator with readings of measured particle number and/or size.
  • a vacuum pump may be provided, attached to the outlet, to draw air into the apparatus through the inlet, across the sampling volume and out of the outlet nozzle.
  • the photodetector 9 is shown in more detail in Figure 2.
  • the photodetector is in the form of a rectilinear trough, having a base 11 and two opposed sides 12, 13.
  • the rectilinear trough extends along a substantial segment of the flow path from the inlet nozzle 3 to the outlet nozzle 4 and is concave so as to surround at least a part of the flow.
  • the detector 9 therefore reduces the effects of recirculation of particles by virtue of the sides of the trough masking the light scattered by recirculating particles from reaching the detector.
  • the detector may also act as a guide, helping to entrain the flow in the direction from the inlet to the outlet nozzle and so minimise recirculation of particles in and out of the laser beam.
  • the detector sides 12, 13 serve to reduce flow in the direction of the laser beam.
  • the photodetector is preferably composed of many small photodiodes which are joined together physically and electrically so as to form a single unbroken detecting surface, the active surface of which faces the air flow so as to detect scattered light.
  • Figure 3 shows a photodetector 14 in the form of a curved trough. In Figure 3 this is shown in conjunction with a circular inlet nozzle 15 - it may be advantageous to match the shape and dimensions of the photodetector to the shape and dimensions of the inlet nozzle, so that the detector is roughly parallel to the flow.
  • Figure 3 also shows an additional photodetector 16 placed opposite the first photodetector 9. It may also be possible to join the two photodetectors 14, 16 together, leaving apertures for the entry and egress of the laser beam (this embodiment is not shown) .
  • a second photodetector may be provided with any of the detector configurations shown herein. (The laser beam 6 is not shown in any of Figures 3 - 5.)
  • Figure 4 shows a photodetector 17 having a V-shaped cross- section and Figure 5 shows a photodetector 18 having a trapezoidal cross-section.

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  • Chemical & Material Sciences (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Health & Medical Sciences (AREA)
  • General Health & Medical Sciences (AREA)
  • Physics & Mathematics (AREA)
  • Analytical Chemistry (AREA)
  • Biochemistry (AREA)
  • General Physics & Mathematics (AREA)
  • Immunology (AREA)
  • Pathology (AREA)
  • Molecular Biology (AREA)
  • Biomedical Technology (AREA)
  • Engineering & Computer Science (AREA)
  • Dispersion Chemistry (AREA)
  • Investigating Or Analysing Materials By Optical Means (AREA)

Abstract

An apparatus is provided for monitoring particles comprised in a fluid. The apparatus includes means (2, 3, 4, 15) for generating a flow of the fluid. A light source (5) is operable so as to generate a beam (6) of light which intersects the flow, the light striking particles present in the flow of fluid and being scattered thereby. Detector means (9, 14, 16, 17, 18) is provided for detecting the scattered light, the detector means including a photodetector which extends in a direction along at least a portion of the fluid flow, the photodetector being spaced laterally from the flow. The photodetector (9, 14, 16, 17, 18) is formed so as to be concave about the fluid flow and disposed around at least a portion of the flow.

Description

DETECTOR FOR PARTICLE COUNTING.
This invention relates to a detector for particle counting. More particular, but not exclusively, this invention relates to a non-imaging detector for use in particle counting apparatus, and to apparatus having such a detector.
There are many applications in which it is important to monitor the amount of airborne contamination. An example is the fabrication of semiconductor devices, where airborne contaminants may give rise to expensive manufacturing defects. Many techniques have therefore been developed to monitor particulate contamination. An example of such a technique is given in United States Patent No. 5 085 500, which shows a non-imaging laser particle counter. This device consists of a light source, such as a laser, which is directed so as to intersect a flow of fluid sample. Light from the laser is scattered by contaminant particles in the fluid, and the scattered light is detected. By monitoring the amount of detected light, it is possible to determine the number and size of contaminant particles present in the fluid, since light is scattered roughly in proportion to the square of the particle's radius. It is therefore possible to calibrate the equipment so as to enable the determination of particle size from the amount of detected scattered light.
The diverging configuration of the detectors shown in United States Patent No. 5 085 500 is intended to minimise the effects of stray light within the apparatus. However, this design does not solve the problem fully. For example, some of the particles entrained in the fluid sample recirculate in and out of the laser beam, scattering a great deal of light and appearing to the observer like many large particles. This will result in the apparatus reporting a greater number of contaminant particles than are actually present.
There is therefore a requirement for improved detector apparatus that avoids the above problem. In particular, there is a requirement for apparatus that can accurately monitor contaminant particles present in a fluid.
It is an object of the present invention to provide such apparatus.
According to one aspect of the present invention there is provided apparatus for monitoring particles comprised in a fluid the apparatus including:
a) means for generating a flow of the said fluid;
b) a light source operable so as to generate a beam of light which intersects the flow, the light striking particles present in the flow of fluid and being scattered thereby; and
c) means for detecting the scattered light, the detector means including a photodetector which extends in a direction along at least a portion of the fluid flow, the photodetector being spaced laterally from the flow;
whereby the photodetector is formed so as to be concave about the fluid flow and disposed around at least a portion of the flow.
The means for generating a flow of the fluid may include an inlet nozzle and an outlet nozzle for the fluid. A pump may be provided to draw the fluid through the inlet nozzle and the outlet nozzle.
The light source may comprise a source of laser light.
A light stop may be provided to absorb light from the source which has not been scattered.
Preferably, the photodetector consists of photodiodes . Advantageously, the photodetector consists of a number of diodes physically and electrically connected together so as to provide a single unbroken surface.
According to one aspect, the detector is in the form of a rectilinear trough. The rectilinear trough may have a base and two opposed sides. According to another aspect, the detector is in the form of a curved trough. The detector may be concave so as to surround at least a part of the flow of fluid. According to another aspect of the present invention, two detectors may be provided, one either side of the fluid flow.
Preferably, the fluid is air. Advantageously, the fluid is gas. Further preferably, measurement of the scattered light gives a measure of the number of particles present. Advantageously, measurement of the scattered light also gives a measure of the size of particles present.
For a better understanding of the present invention and to show more clearly how it may be carried into effect reference will now be made, by way of example, to the accompanying drawings which show schematically various embodiments of the present invention. The figures are not to scale.
Figure 1 is a diagram of one embodiment of the invention;
Figure 2 shows the apparatus of Figure 1 viewed from the line A - A' in Figure 1 and in the direction of the arrows;
Figure 3 is a corresponding view of a second embodiment of the invention;
Figure 4 is a corresponding view of a third embodiment; and
Figure 5 is a corresponding view of a fourth embodiment . In Figure 1 the apparatus includes a housing 1. An air inlet pipe 2 draws sample air into the housing for example by means of a pump (not shown) . The sampled air flows through an inlet nozzle 3, which in this example is tapered and approximately rectilinear in cross section, as shown in Figures 1, 2 and 5, although the inlet nozzle may be round as shown in Figures 3 and 4 or of any suitable alternative configuration such as rectangular. The air is drawn from the inlet nozzle 3 to an outlet nozzle 4, again by a pump (not shown), and thence is expelled out of the housing. The outlet nozzle 4 may equally be of any suitable configuration. A light source in the form of a laser 5 is attached to the housing and is configured so as to send a beam 6 of laser light through a light passage 7 in the housing (which may contain suitable laser optics 8) to intersect the flow of air passing from the inlet nozzle 3 to the outlet nozzle 4.
Light striking particles which are present in the air flow is scattered, some of the light being detected by a photodetector 9. A light stop 10 is also provided to absorb light which has not been scattered. The photodetector 9 is connected to control and monitoring circuitry (not shown) . A display (not shown) is also provided to provide an operator with readings of measured particle number and/or size.
A vacuum pump may be provided, attached to the outlet, to draw air into the apparatus through the inlet, across the sampling volume and out of the outlet nozzle. The photodetector 9 is shown in more detail in Figure 2. In this embodiment, the photodetector is in the form of a rectilinear trough, having a base 11 and two opposed sides 12, 13. The rectilinear trough extends along a substantial segment of the flow path from the inlet nozzle 3 to the outlet nozzle 4 and is concave so as to surround at least a part of the flow. The detector 9 therefore reduces the effects of recirculation of particles by virtue of the sides of the trough masking the light scattered by recirculating particles from reaching the detector. The detector may also act as a guide, helping to entrain the flow in the direction from the inlet to the outlet nozzle and so minimise recirculation of particles in and out of the laser beam. The detector sides 12, 13 serve to reduce flow in the direction of the laser beam. The photodetector is preferably composed of many small photodiodes which are joined together physically and electrically so as to form a single unbroken detecting surface, the active surface of which faces the air flow so as to detect scattered light.
Although for ease of manufacture it may be easier to construct the photodetector from a number of flat photodetector plates joined together, there are many possible configurations of the photodetector. Figure 3 shows a photodetector 14 in the form of a curved trough. In Figure 3 this is shown in conjunction with a circular inlet nozzle 15 - it may be advantageous to match the shape and dimensions of the photodetector to the shape and dimensions of the inlet nozzle, so that the detector is roughly parallel to the flow. Figure 3 also shows an additional photodetector 16 placed opposite the first photodetector 9. It may also be possible to join the two photodetectors 14, 16 together, leaving apertures for the entry and egress of the laser beam (this embodiment is not shown) . A second photodetector may be provided with any of the detector configurations shown herein. (The laser beam 6 is not shown in any of Figures 3 - 5.)
Figure 4 shows a photodetector 17 having a V-shaped cross- section and Figure 5 shows a photodetector 18 having a trapezoidal cross-section. As previously stated, there are many possible configurations apparent to the person skilled in the art without departing from the present invention.

Claims

1. An apparatus for monitoring particles comprised in a fluid the apparatus including:
a) means (2, 3, 4, 15) for generating a flow of the said fluid;
b) a light source (5) operable so as to generate a beam (6) of light which intersects the flow, the light striking particles present in the flow of fluid and being scattered thereby; and
c) means (9, 14, 16, 17, 18) for detecting the scattered light, the detector means including a photodetector which extends in a direction along at least a portion of the fluid flow, the photodetector being spaced laterally from the flow;
whereby the photodetector (9, 14, 16, 17, 18) is formed so as to be concave about the fluid flow and disposed around at least a portion of the flow.
2. An apparatus as claimed in claim 1, characterised in that the means for generating a flow of the fluid includes an inlet nozzle (3, 15) and an outlet nozzle (4) for the fluid.
3. An apparatus as claimed in claim 2, characterised in that a pump is provided to draw the fluid through the inlet nozzle (3, 15) and the outlet nozzle (4) .
4. An apparatus as claimed in any preceding claim, characterised in that the light source (5) comprises a source of laser light.
5. An apparatus as claimed in any preceding claim, characterised in that a light stop (10) is provided to absorb light from the source (5) which has not been scattered.
6. An apparatus as claimed in any preceding claim, characterised in that the photodetector (9, 14, 16, 17, 18) consists of photodiodes.
7. An apparatus as claimed in claim 6, characterised in that the photodetector (9, 14, 16, 17, 18) consists of a number of diodes physically and electrically connected together so as to provide a single unbroken surface.
8. An apparatus as claimed in any preceding claim, characterised in that the detector (9) is in the form of a rectilinear trough.
9. An apparatus as claimed in claim 8, characterised in that the rectilinear trough has a base (11) and two opposed sides (12, 13) .
10. An apparatus as claimed in any one of claims 1 to 7, characterised in that the detector (14) is in the form of a curved trough.
11. An apparatus as claimed in claim 8, 9 or 10, characterised in that the detector (9, 14, 16, 17, 18) is concave so as to surround at least a part of the flow of fluid.
12. An apparatus as claimed in any preceding claim, characterised in that two detectors (9, 14, 16, 17, 18) are provided, one either side of the fluid flow.
13. An apparatus as claimed in any preceding claim, characterised in that measurement of the scattered light gives a measure of the number of particles present.
14. An apparatus as claimed in claim 13, characterised in that measurement of the scattered light also gives a measure of the size of particles present.
PCT/GB2002/001062 2001-03-14 2002-03-08 Photodetector for particle counting WO2002073165A2 (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AU2002236079A AU2002236079A1 (en) 2001-03-14 2002-03-08 Photodetector for particle counting

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GB0106349A GB0106349D0 (en) 2001-03-14 2001-03-14 Detector for particle counting
GB0106349.4 2001-03-14

Publications (2)

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WO2002073165A2 true WO2002073165A2 (en) 2002-09-19
WO2002073165A3 WO2002073165A3 (en) 2003-01-09

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GB (1) GB0106349D0 (en)
WO (1) WO2002073165A2 (en)

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4804853A (en) * 1987-04-23 1989-02-14 High Yield Technology Compact particle flux monitor
EP0350768A2 (en) * 1988-07-11 1990-01-17 Pacific Scientific Company Particle size measuring instrument with direct scattered light detection
EP0421406A2 (en) * 1989-10-04 1991-04-10 Canon Kabushiki Kaisha Apparatus and method for separating or measuring particles to be examined in a sample fluid
US5085500A (en) * 1989-11-28 1992-02-04 Tsi Incorporated Non-imaging laser particle counter
EP0898161A2 (en) * 1997-08-20 1999-02-24 Ngk Insulators, Ltd. Method for detection of solid particles in fluid and particle sensor used in said method

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4804853A (en) * 1987-04-23 1989-02-14 High Yield Technology Compact particle flux monitor
EP0350768A2 (en) * 1988-07-11 1990-01-17 Pacific Scientific Company Particle size measuring instrument with direct scattered light detection
EP0421406A2 (en) * 1989-10-04 1991-04-10 Canon Kabushiki Kaisha Apparatus and method for separating or measuring particles to be examined in a sample fluid
US5085500A (en) * 1989-11-28 1992-02-04 Tsi Incorporated Non-imaging laser particle counter
EP0898161A2 (en) * 1997-08-20 1999-02-24 Ngk Insulators, Ltd. Method for detection of solid particles in fluid and particle sensor used in said method

Also Published As

Publication number Publication date
AU2002236079A1 (en) 2002-09-24
WO2002073165A3 (en) 2003-01-09
GB0106349D0 (en) 2001-05-02

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