Method and apparatus for measuring particles in a fluid

• US 4,830,494 A
• Filed: 07/09/1987
• Issued: 05/16/1989
• Est. Priority Date: 07/10/1986
• Status: Expired due to Term

• Current Assignee: KOWA Company Limited
• Original Assignee: KOWA Company Limited
• Inventors: Akiyama, Kouichi, Ito, Eiichi, Ishikawa, Muneharu, Fujita, Akihiro, Kawamura, Masunori
• Primary Examiner(s): Willis, Davis L.
• Assistant Examiner(s): Koren, Matthew W.
• Application Number:
  US07/072,228
• Time in Patent Office: 677 Days
• Field of Search: 356/336, 356/339, 356/246, 250/564, 250/574, 250/576
• US Class Current: 356/336
• CPC Class Codes: G01N 15/1459 the analysis being performed on a sample stream
• CPC Class Codes: G01N 2015/0222 from dynamic light scattering, e.g. photon correlation spectroscopy
• CPC Class Codes: G01N 2015/0244 with cutting-out molecular scatter
• CPC Class Codes: G01N 2015/1447 Spatial selection
• CPC Class Codes: G01N 2021/4707 Forward scatter; Low angle scatter
• CPC Class Codes: G01N 21/53 within a flowing fluid, e.g. smoke

Abstract

Disclosed is a method and apparatus for measuring particles in a fluid by irradiating the fluid containing the particle with a laser beam and analyzing the laser light scattered by the particle to determine the characteristics of the particle. An elliptical laser beam is projected into a particle detection area in which the particles to be measured are caused to flow. The laser light scattered by the particle is received for photoelectric conversion into a time-series photoelectric signal in a direction along which the particle flows. The photoelectric signal is subjected to a moving average process to determine a time width during which the signal exceeds a predetermined level to cause the change in intensity of the scattered light. This change is recognized as a change in intensity caused by the passage of the particle through the particle detection area when the time width falls within a certain range.

Claims

1. A method for measuring a particle in a fluid by irradiating the fluid containing the particle with a laser beam and analyzing the laser light scattered by the particle to determine the characteristics of the particle, comprising the steps of:

forming in said fluid a particle detection area in which said particle to be measured is caused to flow;

projecting said laser beam into said particle detection area with its section elliptical in form in said particle detection area; and

receiving the laser light scattered by said particle in a direction along which said particle flows, and analyzing the same to determine the characteristics of said particle.

2. A method as set forth in claim 1, wherein said particle is caused to flow through said particle detection area substantially perpendicularly to the direction of projection of said laser beam.

3. A method as set forth in claim 1, wherein said laser beam is projected so that its longer axis of the elliptical section lies perpendicularly to the direction of flow of said particle in said particle detection area.

4. An apparatus for measuring particles in a fluid by irradiating the fluid containing the particle with a laser beam and analyzing the laser light scattered by the particles to determine the characteristics of the particles, comprising:

a measuring cell in which a sample liquid containing particles to be measured is received;

means for generating a laser beam;

means for projecting said laser beam into a selected area in said measuring cell in which said particles are to be measured with its section elliptical in form in said selected area;

means for generating in said selected area a flow of particles which passes in a direction substantially perpendicular to the direction of said laser beam;

a photoelectric detector disposed in the direction of said flow of particles for receiving the laser light scattered by the particles; and

means for processing a signal derived from said photoelectric detector to determine the characteristics of said particles.

5. An apparatus as set forth in claim 4, wherein said means for generating a flow includes means for effecting a circular flow of particles in said selected area of said measuring cell.

6. An apparatus for measuring particles in a fluid by irradiating the fluid containing the particles with a laser beam and analysing the laser light scattered by the particles to determine the characteristics of the particles, comprising:

a measuring cell in which a sample liquid containing particle to be measured is received;

means for generating a laser beam;

means for projecting said laser beam into a selected area in said measuring cell in which said particles are to be measured.

means for generating in said selected area a flow of particles which passes in a direction substantially perpendicular to the direction of said laser beam;

a photoelectric detector for receiving the laser light scattered by the particles;

a mask with a slit disposed in the front of said photoelectric detector for limiting the scattered laser light impinging thereon;

an actuator for driving said mask in a direction perpendicular to the direction along which said slit extends;

means for processing a signal derived from said photoelectric detector to determine the characteristics of said particles;

means for storing the position of said mask and the intensity of background light in the scattered laser light at the position of said mask; and

means for effecting the successive driving of said mask until the mask reaches a position in which said intensity of background light is at a maximum.

7. A method for measuring particles in a fluid by irradiating the fluid containing the particle with a laser beam and analyzing the laser light scattered by the particle to determine the characteristics of the particle, comprising the steps of:

forming in said fluid a particle detection area in which said particle to be measured is caused to flow;

projecting said laser beam into said particle detection area; and

receiving the laser light scattered by said particle for photoelectric conversion into a time-series photoelectric signal;

determining a time width during which a change in intensity of the scattered laser light occurs in which said time-series photoelectric signal exceeds a predetermined level; and

recognizing the change in intensity of the scattered light as a change in intensity caused by the passage of said particle through said particle detection area when said time width falls within a certain range, and processing the photoelectric signal to determine the characteristics of said particle.

8. A method as set forth in claim 7, wherein said time-series photoelectric signal is subjected to a moving average process before said time width is determined.

9. A method as set forth in claim 7, wherein said predetermined level is set so as to remove the background light from the scattered light.

10. A method as set forth in claim 7, wherein the recognition whether the time width falls within the certain level is conducted by comparing the time width with the time during which said particle passes through the particle detection area.

11. A method as set forth in claim 7, wherein an elliptical laser beam is used as said laser beam.

12. A method as set forth in claim 7, wherein said laser light scattered by said particle is received in a direction along which said particle passes.

13. A method as set forth in claim 7, wherein said particle is caused to flow in said particle detection area in the form of a laminar stream.

14. An apparatus for measuring particles in a fluid by irradiating the fluid containing the particle with a laser beam and analyzing the laser light scattered by the particle to determine the characteristics of the particle, comprising:

a measuring cell in which a sample liquid containing particles to be measured is received;

means for generating a laser beam;

means for projecting said laser beam into a selected area in said measuring cell in which said particles are to be measured;

means for generating in said selected area a flow of particles which passes in a direction substantially perpendicular to the direction of said laser beam;

a photoelectric detector for receiving the laser light scattered by the particle for photoelectric conversion into a time-series photoelectric signal;

storage means for storing said time-series signal from said photoelectric detector;

means for comparing said photoelectric signal stored in said storage means with a predetermined level to obtain a time width during which the photoelectric signal exceeds said predetermined level to cause a change in intensity of the scattered light; and

means for processing said time-series photoelectric signal to determine the characteristics of said particle;

wherein said change in intensity of the scattered light is recognized as a change in intensity caused by the passage of said particle through said particle detection area when

said time width falls within a certain range.

15. A method for measuring a particle in a fluid by irradiating the fluid containing the particle with a laser beam and analyzing the laser light scattered by the particle to determine the characteristics of the particle, comprising the steps of:

forming in said fluid a particle detection area in which said particle to be measured is caused to flow;

focussing a laser beam having a beam waist into the center of said particle detection area;

receiving laser light scattered by a particle passing through said particle detection area with a lens and imaging the scattered light on a rectangular aperture disposed at an imaging point of the center of said particle detection area along the optical axis of said lens; and

providing one side of said rectangular aperture shorter than the radius of the beam waist of said focused laser beam such that the intensity of said laser beam within an optically conjugate region of said rectangular aperture is more than one half of the maximum intensity at the focus point of said laser beam.

16. A method as set forth in claim 15, wherein said laser beam is focused to an elliptical cross-section in said particle detection area, with the major axis of said elliptical cross-section perpendicular to the direction of flow of said particle.

17. A method as set forth in claim 15, further comprising driving said aperture by an actuator in a direction perpendicular to a plane determined by both optical axes of said laser beam focused in said particle detection area and said scattered laser light received by said lens until the aperture reaches a position in which the intensity of light impinging on the aperture due to the fluid within said particle detection area is at a maximum.

18. A method for measuring a particle in a fluid by irradiating the fluid containing the particle with a laser beam and analyzing the laser light scattered by the particle to determine the characteristics of the particle, comprising the steps of:

forming in said fluid a particle detection area in which said particle to be measured is caused to flow;

projecting a laser beam into said particle detection area;

receiving laser light scattered by said particle and converting said scattered light into a time series of photoelectric pulses by photon counting;

determining a time width during which a change in intensity of the scattered laser light occurs in which said time series of photoelectric signal exceeds a predetermined level;

recognizing the change in intensity of the scattered light as the passage of said particle through said particle detection area when said time width falls within a certain range; and

processing the photoelectric pulses to determine the characteristics of said particle.

19. A method as set forth in claim 18, wherein said time-series photoelectric signal is subjected to a moving average process before said time width is determined.

20. A method as set forth in claim 18, wherein said predetermined level is selected to remove background light due to said fluid within said particle detection area from the scattered light.

21. A method as set forth in claim 18, wherein the step of recognizing whether the time width falls within the certain level comprises comparing the time width with the time during which said particle passes through the particle detection area.

22. A method as set forth in claim 18, wherein an elliptical laser beam is used as said laser beam.

23. A method as set forth in claim 18, wherein the step of receiving said laser light scattered by said particle comprises receiving the light through a rectangular aperture set on an imaging point of a receiving lens.

24. A method as set forth in claim 18, wherein said particle is caused to flow in said particle detection area in a laminar stream.

25. A method for measuring particles in a fluid by irradiating the fluid containing the particles with a laser beam and analyzing the laser light scattered by a particle to determine the size distribution of the particles, comprising the steps of:

forming a particle detection area at a middle point of a wall and the center of a measuring cell having a cylindrical flow region;

introducing a sample fluid at an inflow rate through an inlet pipe, having a smaller diameter than the radius and the height of said cylindrical flow region, into said cylindrical flow region tangentially along an interior wall of said measuring cell;

mixing said sample fluid with fluid within said flow region to distribute said sample fluid into elements over the cross-section of said cylindrical flow region;

forming a swirling stream of mixture around said center of said cylindrical flow region;

stabilizing said swirling stream as a laminar flow by a stirrer rotating at said center of said cylindrical flow region;

detecting the particles contained in said elements of said sample fluid passing through said particle detection area at a constant rate in a uniform direction; and

discharging part of said mixture flowing in said cylindrical flow region from an outlet pipe connected tangentially with the flow region and at a flow rate equal to the sample inflow rate.

26. An apparatus for measuring particles in a fluid by irradiating the fluid containing the particle with a laser beam and analyzing the laser light scattered by the particle to determine the characteristics of the particle, comprising:

a measuring cell comprising a cylindrical vessel, an inlet pipe and an outlet pipe both having the same inner diameter which is smaller than the radius or the height of said cylindrical vessel and both connected tangentially with an interior wall of the vessel, and windows formed in said interior wall;

means for introducing a sample fluid into said measuring cell and means for discharging said sample fluid from said measuring cell;

means for stabilizing a flow in said cylindrical vessel in a swirling laminar stream, comprising a rotatable stirrer located at the center of said cylindrical vessel;

means for generating a laser beam;

means for focussing said laser beam through one of the windows into a selected area located at the middle point of said interior wall and the center of said cylindrical vessel in which said particles are to be measured;

means for receiving the laser light scattered by a particle passing through said selected area, comprising a lens for collecting said scattered light and a rectangular aperture set at an imaging point of said lens to define a particle detection area within the region of said focused laser beam at said selected area; and

photoelectric detecting means for measuring the light power received from said aperture by photon counting.

27. An apparatus as set forth in claim 26;

further comprising an actuator for driving said aperture in a direction perpendicular to a plane determined by both optical axes of said laser beam focused in said particle detection area and said collecting lens, and means for stopping the driving of said aperture when the aperture reaches a position in which the intensity of light impinging on said aperture due to said fluid is at a maximum.

28. An apparatus as set forth in claim 26;

wherein said means for focussing said laser beam includes means for projecting the beam with an elliptical cross-section in said selected area.

29. An apparatus for measuring particles in a fluid by irradiating the fluid containing the particle with a laser beam and analyzing the laser light scattered by the particle to determine the characteristics of the particle, comprising:

a measuring cell in which a sample fluid containing particles to be measured is maintained;

means for generating a laser beam;

means for projecting said laser beam into a selected area in said measuring cell;

photoelectric detecting means for receiving the laser light scattered by the particle and for converting said laser light into time-series photoelectric pulses by photon counting;

storage means for storing values associated with said time-series pulses from said photoelectric detecting means;

means for comparing said stored values in said storage means with a predetermined level to obtain a time width during which the photoelectric pulse exceeds said predetermined level; and

means for processing said time-series photoelectric signal to determine the characteristics of said particle, including means for determining that a change in intensity of the scattered light is caused by the passage of said particle through said selected area when said time width falls within a certain range.