Abstract:
An improvement is described for use in a system that identifies particles in a fluid such as water by passing the fluid through a passage in a transparent carrier and detecting light from a laser beam that is scattered by particles, followed by comparing the scatter pattern to those of known particles, which increases the rate at which particles are detected. A plurality of transparent carriers with through passages are provided, and a narrow beam is directed through each carrier to scatter light from particles at a detect zone in each carrier passage. In one arrangement ( 60 ), the carriers ( 62, 64, 66 ) are connected in series, so a limited amount of water passes through detect zones ( 24 A,  24 B.  24 C) to generate a high rate of particle detection. In another arrangement ( 130 ), the carrier passages are connected in parallel, so when a larger sample of water is available different parts of the water sample pass through different carrier passages, to again increase the rate of particle detection.

Description:
CROSS-REFERENCE 
   Applicant claims priority from U.S. provisional application Ser. No. 60/373,221 filed Apr. 16, 2002. 

   BACKGROUND OF THE INVENTION 
   There is a need to detect and/or identify unknown microscopic particles (e.g. up to about 50 microns diameter) such as pathogenic microorganisms in fluid such as water or air. Applicant&#39;s earlier U.S. Pat. No. 6,519,033 describes a system for detecting and identifying such particles. A laser beam is directed through the water, with a small region of the water being designated to be a detect zone. Photodetectors are aimed precisely at the detect zone. When a particle passes through the detect zone, it scatters laser light, and the scattered light is detected by the photodetectors. This can be referred to as an interrogation of the particle. The outputs of the photodetectors are delivered to a computer which compares the light scatter pattern (eventvector) of the particle to light scatter patterns of particles of each of a plurality of known species of particles, such as species of pathogens. The computer can indicate whether the unknown particle that was just detected, is of one of the plurality of species of particles whose scatter patterns are recorded in the computer&#39;s memory. 
   Since the filing date of the above application, applicant has developed carriers each consisting of a glass sphere with a passage bored through it. Water to be tested is flowed through the passage. In one example, the passage has a diameter of 9 mm and the detect zone from which scattered light is detected has a width and length of 1.5 mm and a thickness of 0.1 mm. Water at a velocity such as 8 cm per second can be flowed in laminar flow through the passage. With such a velocity, it takes 1.5 milliseconds for a particle to move through the beam of a thickness of 0.1 mm. If one assumes that the liquid contains 500 particles per milliliter, the fluid passes at a velocity of 8 cm per second, and the detect zone has the above-described dimensions, one would expect about 100 particles per second to pass through the detect zone. Each particle takes about 1.5 milliseconds to pass through the beam. If the water has very few particles, such as five particles per milliliter, then one might expect to detect only one particle per second. 
   A large number of particles such as thousands, typically must be interrogated in order to determine the condition of the water. Many particles will be algae of different known species. Occasionally, a particle may be one of the pathogens that passes through a water treatment plant, and is one of the known species programmed into the computer. A danger generally does not arise from a few pathogens, but only from a considerable density of pathogens in the water. A large number of particles may have to be interrogated to determine the density of particles in the water, so as to determine whether the water is acceptable or not. If the apparatus detects only about one particle per second, then it may take a few thousand seconds to detect a few thousand particles so as to obtain a reliable reading on the quality of the water. It may take an hour to interrogate a few thousand particles, and such a period of time may be unacceptable for several reasons, including where a researcher has to wait around for the data, or where the delay can result in considerable quantities of unhealthy water being pumped through a municipal water system before the problem is caught. Apparatus that increases the rate of particle detection would be of value. 
   SUMMARY OF THE INVENTION 
   In accordance with one embodiment of the present invention, a system is provided for detecting and/or identifying particles in a fluid such as water, which enables the more rapid detection of particles. The system includes a plurality of carriers that each comprises transparent material through which a light beam passes and which has a passage through which fluid can flow, so a particle passing through a detect zone lying along the light beam can produce light scatter patterns. To increase the rate at which particles are detected, applicant provides a plurality of carriers, and a source for a plurality of light beams that each passes through one of the carriers to produce a scatter pattern that is detected and analyzed. The plurality of carriers can be connected in series or in parallel. A connection in series enables the detection of a high percent of particles in a water sample that has a limited sample volume. A connection in parallel is especially useful where there is plenty of water available to be interrogated. 
   The novel features of the invention are set forth with particularity in the appended claims. The invention will be best understood from the following description when read in conjunction with the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is an isometric view of a portion of a particle identifying system of the present invention, showing a transparent carrier, a laser light source, and photodetectors. 
       FIG. 2  is an isometric view of a system of the invention, wherein a plurality of carriers of the type illustrated in  FIG. 1 , are connected in series, and each has a light source and photodetectors. 
       FIG. 3  is a sectional side view of only the carriers and conduits that connect them in series, of  FIG. 2 . 
       FIG. 3A  is an enlarged sectional view of an end portion of one of the carriers of  FIG. 3 . 
       FIG. 4  is an isometric representation of the detect zone and passage of the carrier of  FIG. 1 . 
       FIG. 5  is a plan view of the detect zone and passage of  FIG. 4 , showing one possibility for increasing detection rate, which is fraught with problems. 
       FIG. 6  is an isometric view of a fluid distributer of a type that can lie between carriers in  FIG. 3 . 
       FIG. 7  is a sectional view of a group of carriers of the type illustrated in  FIG. 1 , but connected in parallel. 
       FIG. 8  is an isometric view of a group of carriers similar to that of  FIG. 2 , but with a different detection arrangement. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1  illustrates part of a particle identifying system  10  which includes a carrier element or carrier  12  with a passage  14 . Fluid such as water containing microscopic particles to be detected, flows through the passage. A light source in the form of a laser  16  generates a laser light beam  20  that passes through the carrier  12 , with most of the laser beam energy absorbed by a dump  22 . The laser beam extends primarily perpendicular to the passage, and preferably extends perpendicular to the passage. In one example, the laser beam is red light of a wavelength of 0.6 microns, and is used to detect particles having a diameter on the order of three microns (0.3 to 30 microns). 
   The laser beam  20  passes through a detect zone  24  lying along the axis  26  of the passage. When a particle in the fluid passes through the detect zone, the particle scatters light in multiple directions. A plurality of photodetectors  30  spaced around the carrier, detect light scattered in multiple directions. The intensity of light scattered in each of multiple directions is a pattern that can be used to identify the species of the unknown particle that has just passed through the detect zone  24 . This is accomplished by comparing light scattered in the different directions by an unknown particle, to light scattered by particles of known species when they were passed through the system. U.S. Pat. No. 6,519,033 describes a method for comparing the scatter patterns. 
   It is noted that in some cases it is desired to determine only the presence of a particle. For example, there may be a need to determine the density of microscopic particles (e.g. from 0.3 to 30 microns) in a fluid. In that case, only a single photodetector may be required. 
   In  FIG. 1 , the laser beam  20  is assumed to move in a forward F direction. The carrier is formed of glass having an index of refraction of 1.55. If the carrier has cylindrical outer walls, then light scattered from the detect zone  24  at an angle A of up to 410 above or below the laser beam path  34  would pass through the interface of the glass and surrounding air and reach the photodetectors  30 . However, if the scatter angle A above or below the beam path  34  is more than 410, then such light would be internally reflected by a cylindrical surface. To avoid this, applicant constructs the front of the carrier  12  with a spherical outer surface  32  having a sphere center lying in the carrier passage (or constructs the carrier front surface with conical upper and lower surfaces). 
   In one example, the passage has a diameter D of 9 mm and the carrier has a spherical outside diameter of 64 mm. As indicated in  FIG. 4 , the laser beam at the detect zone  24 , has a width W of 1.5 mm and a thickness T of 0.1 mm. The detect zone has a width W of 1.5 mm and a length L of 1.5 mm. If the concentration of microscopic particles in the fluid is 500 particles per cm 3  and the fluid is moving downward at a velocity of 8 cm per second, then one might expect to have a particle pass through the detect zone at an average of once per 10 milliseconds. We might expect there to be two particles passing simultaneously through the detect zone  24  once in every ten particle detections. The detection of two particles simultaneously in the detect zone is not used by applicant, so such detections are useless and are preferably scarce. The small thickness T of the laser beam is desirable to minimize the number of occurrences of two particles lying simultaneously in the detect zone. 
     FIG. 5  shows that the area occupied by the detect zone  24 , as viewed along the axis  26  of the passage, is about 2.25 mm 2 . With a passage diameter D of 9 mm, and a passage area of 64 mm 2 , the detect zone  24  occupies only about 3.5% of the cross-sectional area of the passage. As a result, about 96.5% of the particles in the fluid are not detected. For accurate identification of pathogens in a fluid that may contain primarily other microscopic particles, it is desirable that a very large number of detections take place for a sample of given volume, and during a moderate period of time of perhaps one minute. It might be thought that the diameter D of the passage could be reduced to slightly over 1.5 mm and the fluid could be moved rapidly through the passage. However, as the diameter of the passage decreases, capillary effects occur, where surface tension of the fluid resists rapid fluid movement, and where rapid fluid movement can result in turbulence and consequent generation of microscopic bubbles. Microscopic bubbles reflect original laser light and scattered light, and can prevent accurate operation of the system. 
   It would be possible to direct a few laser beams such as  50  and  52  in  FIG. 5 , in addition to the original laser beam  20 . Then, it would be possible to provide additional groups of photodetectors that are each directed at a corresponding one of the detect zones such as  54 ,  56 , in addition to the original detect zone  24  lying along laser beam  20 . This has the disadvantage that a photodetector  30 A oriented at certain angles and directed at one detect zone  24 , might pick up light from another detect zone. Also, there is a greater possibility of a photodetector picking up light reflected from walls of the passage. 
   In accordance with one embodiment of the present invention, applicant provides a system  60  shown in  FIG. 2 , which includes a plurality of carriers  62 ,  64 ,  66  with passages  14 A,  14 B,  14 C. The passages are all connected to the same fluid source  68  so fluid  69  from the source can flow simultaneously through all of the carriers  62 – 66 . In  FIG. 2 , the carriers are connected in series, so the same fluid that passes through a passage  14 A of the first carrier  62 , subsequently passes through passages  14 B,  14 C of the other carriers. Three corresponding lasers  72 ,  74 ,  76  direct separate light beams through each of the carriers, and through corresponding detect zones  24 A,  24 B and  24 C. (A single laser beam can be split into three beams). Three sets of photodetectors  80 ,  82 ,  84  are connected to a computer  88  which compares the pattern of light scatter from each of the detect zones  24 A,  24 B,  24 C to patterns previously recorded for known species of particles, such as pathogenic bacteria. The computer  88  has a memory  130  which stores numerous scatter patterns for particles that are all of one species, such as thousands of scatter patterns for particles of a particular species that were positioned in different orientations when they passed through the detect zone, and that vary somewhat in shape and size. The memory preferably holds multiple scatter patterns for each of several species. The memory also stores the scatter pattern for the unknown particle. A comparer  132  which is a stored program that directs a central processing unit  134  to make computations, compares the pattern of the unknown particle to the patterns for the known species of particles to look for a match. 
   There is a slight possibility that a particle detected at one detect zone such as  24 A, would be detected at one of the other detect zones  24 B or  24 C. However, the possibility is low, such as about 7% in the above example for the size of the detect zone and the diameter of the passage when three carriers are used. However, even if such double detection of a particle occurs, it can be useful because it is not only the species of the particle, but the particular orientation of the particle that is detected and that is used to determine whether the particle is one of a known group of species of particles. 
     FIG. 3  shows the manner in which the carriers  62 – 66  are connected in series, with  FIG. 3A  showing greater details. Each carrier has a recess  90  at each of its ends. A coupling  92 ,  93  projects into the recess and has surfaces that press against O-rings  94 ,  96 . The passage  100 ,  102  in each coupling is of the same size as the passage such as  24 B in the carrier  64 , and they are aligned, to avoid turbulence and consequent generation of microscopic bubbles. A fluid distributer  110 ,  112  is shown lying between pairs of carriers to move full with lying at the middle of one carrier passage toward the periphery of a next passage. One example of such distributer is shown in  FIG. 6 , in which an aerodynamically-shaped part  114  diverts fluid away from the middle of the passage, while minimizing turbulence. 
   In  FIG. 2 , a large container forms the source  68  that holds a fluid  69  such as water that has just been taken from a reservoir at a water treatment plant. The water flows through the carriers by gravity, with tests indicating a flow rate of about 8 cm per second for a single carrier of the type described above. 
     FIG. 7  illustrates another system  130  in which the carriers  62 ,  64 ,  66  are connected in parallel rather than in series. This is especially useful where the size of the sample is virtually unlimited, as where some water in a reservoir of a water treatment plant is pumped through a pipe  140  to couplings  142 ,  144 ,  146 . The couplings connect to the passages of the carriers. The outputs of the carriers are delivered through a coupling  150  back to the reservoir. A connection in series has the advantage that no particle will pass through two or three detect zones and produce a plurality of scatter patterns to be analyzed. However, the parallel connection of  FIG. 7  requires a greater through flow of water than a series connected system. A valve can be positioned along each conduit  142 – 146 , so all but one of the valves can be closed, if the sample volume is limited. 
     FIG. 8  illustrates another system  150  which includes the three carriers  62 ,  64 ,  66  connected in parallel or in series. A light source comprising three lasers  151 – 153  produce laser beams  20 A,  20 B,  20 C that pass through a detect zone in each carrier, and the scattered light must be detected by photodetectors. However, instead of using three separate sets of photodetectors, applicant uses a single row  160  of CCD&#39;s (charge coupled detectors). Also, applicant uses three plate-shaped holograms  162 ,  164 ,  166 . Each hologram directs light scattered from each corresponding detect zone  172 ,  174 ,  176  to corresponding CCD photodetectors of the row  160 . If there are a large number of particles per volume of water, so there is often an occurrence where two particles (in one or more detect zones) are detected simultaneously, then the laser beams can be derived from three different lasers that are each operated to generate short duration (e.g. 300 microseconds) pulses in sequence. Otherwise, a single laser beam can be broken up into the three beams  20 A,  20 B,  20 C. 
   Thus, the invention provides a system for detecting and/or identifying particles in a fluid, by detecting scattering of light as a particle passes through a detect zone of a carrier, which increases the detection rate of particles. A plurality of carriers are provided, that are connected so at least portions of the sample fluid such as water passes through all of the carriers. The carriers can be connected in series, or in parallel, and when a large number of carriers are used they can be connected in both series and parallel. Conduits that connect to carriers, can have the same internal cross-section as the carrier passages, such as the same diameter for cylindrical passages in the carrier and conduit, with the end of each passage being enlarged to receive a conduit end and an O-ring. 
   Although particular embodiments of the invention have been described and illustrated herein, it is recognized that modifications and variations may readily occur to those skilled in the art, and consequently, it is intended that the claims be interpreted to cover such modifications and equivalents.