Measurement of statistical parameters of a distribution of suspended particles

• US 4,052,600 A
• Filed: 01/06/1975
• Issued: 10/04/1977
• Est. Priority Date: 01/06/1975
• Status: Expired due to Term

• Current Assignee: Leeds & Northrup Co.
• Original Assignee: Leeds & Northrup Co.
• Inventors: Wertheimer, Alan L.
• Primary Examiner(s): Wise, Edward J.
• Application Number:
  US05/538,382
• Time in Patent Office: 1,002 Days
• Field of Search: 235/151.3, 235/92 PC, 356/103, 356/102, 350/162 R, 350/162 SF
• US Class Current: 702/179
• CPC Class Codes: G01N 15/0205 by optical means
• CPC Class Codes: G01N 2021/4716 Using a ring of sensors, or a combination of diaphragm and sensors; Annular sensor

Abstract

A rotating mask having three spatial filters is placed in the light path after a laser beam is passed through a sample having a collection of particles. The mask sequentially filters the light scattered by each particle to produce at a detector receiving the filtered light a response which is in accordance with the second, third and fourth power of the particle diameter. The detector integrates the response to all particles in the laser beam and the signal resulting from the integration of the response due to the individual filters is used to calculate statistical parameters. The mean of the area distribution is calculated as the third power response divided by the second power response. The mean of the volume distribution is calculated as the fourth power response divided by the third power response and the standard deviation of the area distribution as the square root of the product of the mean of the area distribution and the difference between the mean of the volume distribution and the mean of the area distribution.

Claims

1. Apparatus for measuring the mean of the area distribution, the mean of the volume distribution, and the standard deviation of the area distribution of a collection of particles comprising:

means for passing a light beam through said collection of particles,

means for filtering the light diffracted from said beam through a first filter which transmits light flux diffracted from each particle proportional to the second power of its radius,

means for filtering the light diffracted from said beam through a second filter which transmits light flux diffracted from each particle proportional to the third power of its radius,

means for filtering the light diffracted from said beam through a third filter which transmits light flux diffracted from each particle proportional to the fourth power of its radius,

means for producing a first, second and third signal (X₂, X₃ and X₄, respectively) in response to the integral of the light flux detected passing through the respective first, second and third filters due to all of the particles of said collection,

means for calculating the mean of the area distribution (M_A) of the particles in said collection as a number proportional to the ratio X₃ /X₂,

means for calculating the mean of the volume distribution (M_v) of the particles in said collection as a number proportional to the ratio X₄ /X₃, and

means for calculating the standard deviation of the area distribution of the particles in said collection as the square root of the product M_A (M_v - M_A).

2. Apparatus for measuring the mean of the area distribution of a collection of particles comprising:

means for passing a light beam through said collection of particles,

means for filtering the light diffracted from said beam through a first filter which transmits light flux diffracted from each particle proportional to the second power of its radius,

means for filtering the light diffracted from said beam through a second filter which transmits light flux diffracted from each particle proportional to the third power of its radius,

means for producing a first and second signal (X₂ and X₃, respectively) in response to the integral of the light flux detected passing through the respective first and second filters due to all of the particles of said collection,

means for calculating the mean of the area distribution (M_A) of the particles in said collection as a number proportional to the ratio X₃ /X₂.

3. Apparatus for measuring the mean of the volume distribution of a collection of particles comprising:

means for passing a light beam through said collection of particles,

means for filtering the light diffracted from said beam through a first filter which transmits light flux diffracted from each particle proportional to the third power of its radius,

means for filtering the light diffracted from said beam through a third spatial filter which transmits light flux diffracted from each particle proportional to the fourth power of its radius,

means for producing a first and second signal (X₃ and X₄, respectively) in response to the integral of the light flux detected passing through the respective first and second filters due to all of the particles of said collection,

means for calculating the mean of the volume distribution (M_v) of the particles in said collection as a number proportional to the ratio X₄ /X₃.

4. Apparatus for continuously measuring the mean of the area distribution, the mean of the volume distribution, and the standard deviation of the area distribution of a flowing sample of fluid suspended particles comprising:

means for directing a light beam through said sample;

means for sequentially filtering the light diffracted by said particles said means including a rotating mask having spaced thereon radially oriented spatial filters including

a first spatial filter which transmits light flux diffracted from each particle proportional to the second power of its radius,

a second spatial filter which transmits light flux diffracted from each particle proportional to the third power of its radius,

a third spatial filter which transmits light flux diffracted from each particle proportional to the fourth power of its radius, and

a stationary chopping blade operable to block the diffracted light in sectors other than that occupied by that one of the spatial filters as sequentially selected;

means for producing a first, second and third signal (X₂, X₃ and X₄, respectively) in response to the integral of the light flux detected passing through the respective first, second and third spatial filters due to all of the particles of said sample and summed over a predetermined time, and

computer means for

calculating the mean of the area distribution (M_A) of the particles in said sample as a number proportional to the ratio X₃ /X₂,

calculating the mean of the volume distribution (M_v) of the particles in said sample as a number proportional to the ratio X₄ /X₃, and

calculating the standard deviation of the area distribution of the particles in said sample as the square root of the product M_A (M_v -M_A).

5. Apparatus for continuously measuring the mean of the area distribution of a flowing sample of fluid suspended particles comprising:

means for directing a light beam through said sample;

means for sequentially filtering the light diffracted by said particles said means including a rotating mask having spaced thereon radially oriented spatial filters including

a first spatial filter which transmits light flux diffracted from each particle proportional to the second power of its radius,

a second spatial filter which transmits light flux diffracted from each particle proportional to the third power of its radius, and

a stationary chopping blade operable to block the diffracted light in sectors other than that occupied by that one of the spatial filters as sequentially selected;

means for producing a first and second signal (X₂ and X₃, respectively) in response to the integral of the light flux detected passing through the respective first and second spatial filters due to all of the particles of said sample and summed over a predetermined time, and

computer means for calculating the mean of the area distribution (M_A) of the particles in said sample as a number proportional to the average value of ratio X₃ /X₂ over a predetermined period of time.