US 2732753 A
Description (OCR text may contain errors)
Jan. 31, 1956 c, o' o s 2,732,753
MEANS FOR CIRCULATING A PARTICLE CARRYING STREAM THROUGH AN ILLUMINATION ZONE Original Filed April 16, .1948
INVEN TOR. 01155751? r. O'KONSK/ BY W POW A T TOfiA/EYS United States Patent ING STREAM THROUGH AN ILLUMINATION ZONE Chester T. OKonski, Berkeley, Calif,
Continuation of abandoned application Serial'No. 21,326, i
This application August '29, 1952,
April 16, 1948. Serial No. 307,081
Claims. cl; 88-14) This invention relates to a new and improved means for circulating a fluid stream containing particles to be illuminated through an illumination zone located within a closed chamber such as may be incorporated within a colloidal particle counter or generally similar or related device. The present application is a continuation of co-pending application, Serial No. 21,326 filed April 16, 1948, now abandoned.
It is contemplated that the practice of the present invention will have particular utility in connection with various means and methods particularly devised for metering the number of particles contained within a fluid body or stream and/ or for determining sizes of particles contained Within such fluid streams or bodies. As examples of the foregoing, it has been found that the particular apparatus iliustrated in the drawings and hereinafter described, in conjunction with suitable known electronic means hereinafter briefly mentioned, can bev successfully utilized to count the number of colloidal particles contained within an aerosol stream, as for example, smoke, dust, smog or like aerosol streams.
As a practical example of the foregoing it is contemplated that the practice of the present invention will have utility in testing the efliciency of gas mask filters which are specifically designed to filter toxic or obnoxious particles, such as harmful bacteria, from the surrounding air prior to inhalation. A principal object of the present invention is to disclose and provide for a novel and useful means for, and a method of, circulating a stream of particle carrying fluid into a closed chamber through a restricted focus area or illumination zone located in said chamber and thence outwardly from said chamber in such way as to insure that each particle passes through said focus area or illumination zone at least once and only once in its travel through said chamber.
Another object of the invention is to provide means for, and to disclose a method of, sheathing a fluid particle carrying stream within the core of a larger surrounding tubular stream of substantially particle free fluid which functions to circulate said particle carrying stream into a closed chamber through a relatively restricted focus area or illumination zone and outwardly of said chamber, in such way as to constantly maintain said particle carrying fluid within the core of said surrounding tubular particlefree fluid. i
Numerous other objects and advantages of the present invention will become apparent upon reading the following specification and referring to the accompanying drawings in which similar characters of reference represent corresponding parts in each of the several views.
In the drawings:
Fig. l is a vertical longitudinal cross-sectional view taken on the center line of the lens system in a preferred example of the particle counter.
Fig. 2 is a sectional view taken on line 22 of Fig. 1.
Fig. 3 is a block diagram of a known electronic system which may be employed in association with the present invention for counting particles contained in an aerosol stream.
The device embodying the present invention as shown in Figs. 1 and 2 in the drawings comprises apparatus specifically developed for counting smoke particles contained in an aerosol stream.
The device illustrated comprises optical apparatus including a lens housing 1 in which is mounted two aspheric condensing lenses 2 and 3. The optical system further comprises a light source 4 which may consist of a conventional 6 volt 50 candlepower automobile headlight bulb preferably mounted for adjustable vertical and horizontal movement relative to lenses 2 and 3.
More specifically lamp 4 is preferably mounted in a split brass block 5, one side of which is screwed to an annular plate 6. This allows the lamp to be adjustably clamped in a horizontal plane. The plate is shown as being fastened to the shoulder of cylinder piece 8 by means of two machine screws 7 passing through short slots out along a vertical diameter of the plate, thus allowing vertical adjustment of the lamp. The cylinder is machined to a sliding fit over the end of the lens housing 1 and may be screwedin place by means of a set screw extending through a slot in the top of the cylinder which allows the lamp to be moved relatively toward and away from the lenses for accurate focusing.
Mounted adjacent lens 3 is a transparent glass plate 18 to the face of which is cemented a masking disc 19 of opaque material such as black paper which is adapted to produce coaxial hollow cones of light 21 and 22. As illustrated in Fig. 1 the lenses 2 and 3 bring to focus the light beam emitted from light source 4 at focus area 23. To simplify the drawing the focus area is shown as a point source producing a point image, although actually the focused image of the filament of the electric lamp will have a determinable and measurable width. For example, if the aforesaid 6 volt 50 candle-power automobile headlight buib is employed the image of the filament at the focus area 23 will be about 4 mm. wide. The shadow cast by the paper disc 19 consists of two similar coaxial cones 25 and 26 with their apices near the focus area.
As will appear more fully hereinafter smoke or other particle carrying fluid entering the inlet tube 37 is caused to be circulated into closed chamber 28, sometimes hereinafter referred as the smoke cell, through the well defined limits of the focus area 23 and outwardly from said chamber. Light scattered from the smoke or other particles will activate light sensitive phototube or photocell such as indicated at 29, which in turn may be electrically connected to various types of electronic mechanisms and circuits hereinafter briefly mentioned for electronically counting the number of particles passing through the focus area and/or for determining size of the particles passing through the focus area.
As heretofore mentioned the smoke cell compiises a closed chamber having normally closed vents 31 and 32 which may be employed to flush the smoke cell 28 with a clear particle free-fluid, such as filtered air, before using the device in its intended manner. Vents 31 and 32 may be kept closed in any suitable manner as for example by pinched rubber hoses connected to them (not shown) or by other suitable means.
A diaphragm 33 having a central aperture 33a is mounted in the smoke cell to the light source side of the inlet and exhaust tubes hereinafter described, and serves to shield the photosensitive cell from stray light.
A tubular shield 30, disposed between lens 30a and the photosensitive cell, also protects the latter from stray light. Preferably the interior surfaces of the smoke cell and tubular shield 30 are painted with dull optical black lacquer.
. The means shown for circulating the fluid particle carryin 'str'ea'iifintochahiber 28 and through the focus area 23-comprises two concentric tubes37 and 38-and an exhaust tube 39 axially-- aligned with tubes 37 and 38 and having. substantiallythe same diameter as. outer concentric tube38. More specifically the' outer concentric tube 38 is adapted for connection as at 41 ton source of substantially "clear' particle 'free circulating fluid, such as filtered air. In this connection the outer end of tube 38 may be connected with a supplyline in which is disposed a suitable filterlnot shown) for filtering a'ir prior to its flow into tube 38, The filtered air supply source is "also'preferably provided with a conventional flow'pump 40 or like means for pumping filtered air through tube '38 at a predet'erm'ined rate-of flow. 'In' this regard the'fil t'ered air 'supplydineis also preferably provided with a suitab'le conventional figvv meter (not shown) to"indicate the'rat of new of air being pumpedinto said't'ube 38. The inner end portion ofthe outer tube 38 extends into the interior of the'cliamber '28 alon g an axis disposed perpendicular to the axis the light beam from source 13. The inner end extremity of tube 38 terminates' interiorly of chamber'2 8 adjacent focusarea 23 and said tube is disposed in axial alignment \vith th c center point of said focus area. I I I I Inner concentric tube 37 of: substantially smaller diameter than 'outer tube 38 thereby establishing an air passage between the exterior surfaces of inner tube 37 and the interior surface of tube 38. The outer end of tube 37 is adapted to be connected to the source of particle carrying fluid to be illuminated, such as a smoke stream. For example, if it is desired to count the pain ticles suspended in the atmosphere in a given locality the outer end of tube 37 would simply be maintained in open flow communication with the atmosphere. It is important that the interior cross-sectional area of inner tube 37 be substantially less'than the well defined limits or width of the focusarea'through which the particle carrying fluid stream is adapted to pass through. In short, it is considered essential to thepractical operativeness of the device that allof the particles carried in the smoke or other particle carrying stream which is introduced into chamber 28 via tub'e 37 pass through and be illuminated "within the focus'area atle'ast once and, of course, only once. v v
Exhaust tube 39 preferably projects into chamber 28 fromthe side thereof .opposite inlet tubes 37'and. 38. The inner portion of the exhaust tube 39 p rojects into the chamber in coaxial alignment withsaid inlet tubes 37 and 38 andl th'e jinneren'd extremity of said exhaust tubeterminatesjadjacent'thefoc 'siarea on the sijdethereof opposite the endfextremities ,of inlet tubes 3.7" and 38. The outer end "of exhaust rune 39, is adapted. for
connection to asuitabie liowjmet fi(not shown) and a conventional vacumnpumpns 1p; Iikeimea'n's whichfis provided to induce outwardjexhaustfflow .of thfeffiui ds entering the chamberviainle'f ti1bes137 and 38.
The above described arrangement of elements comprising tubes 37, 38 and39]and associated pumps 40 and 45, are adapted to operate so as to continuously forward the stream 'of particle" carrying fluid, such as smoke, through the focusjfaiea Whileflsheathedprencased within theihollow' ,eore ofi epntinuOusIy .flow; ing'tubul'ar s'treambf particle-free circulating fluid such as filtered air. More specifically, the flow pump cennected with tube 38 isoperated at a speedto pu'mp filtered 'airthrough tube '38 at a pre-d etermined rate of flow. The rate offfiow through tube 38 may be deter mined and maintained by use of a suitable flow meter (notshown) connected to tube 381 Vacuum pump 45 associated with exhaust tube 39 m ay be simultaneously operated to withdraw at a'measured ratethe' fluid intro; duced into chamber ZS'via inlet tubes 37rand-3s at a-pred'etermined rate br'ssw substantially higher than the rate;of
flow of filtered air being pumped through line 38 by (ill its associated flow pump 40 Thus flow pump 40 may -be-operated-to circulatefiltered air through tube 38 at predetermined rate of flow of four liters per minute. In
view of the fact that the flow rate on the exhaust sidc of the smoke ch-'amb'erds greater than the flow rate of filtered air being introduced into the chamber. through inlet tube 38 the pressure within the smoke cell 28 is reduced, thereby-inducing an inwardflow of particle carrying fluid through the inlet tube 37 which builds up to: a steady state in'which the sum of the flow rates in tubes 37 and '38 equalstlie-exhaust flow rate' in tube 39.
Moreover, it is believed evident that the fiow rate of the particle carryingst'ream :thr'ough tube 37 is equal to the difference between the known flow rates through tubes 38 and 39. In the example given above, the flow rate thr'ouglitube 37 can bereadily determined simply by subtractingthe knownflow rate of three liters per minthe through tube" 38' from the known flow rate of 4 liters per minute through exhaust tube 29 which gives assumes-"1 liteniiefiminiite' flow rate through tube 37. It"s'h'oi1Id"be pa'rtieul arly 'noted that this arrangementfor measuring "the flow rate does not require any constrictions, such as are employed in conventional flow meters; inthe' s'moke:"inlef'tube 37 or the smoke flow line'leadiiig to this tu'beQ' It is well known that constricdons-off this sorr'w 'ma disturb the fiow pattern in the smoke stream and causeremoval of some of the smoke arad s-j thereby limi ting the usefulness of such convenuenaifiowjmewnng -arrangements. The improved system; described hereiri," is I generally superior because it minimizes deposition of the smoke particles. ""It isalsoimpor'tant that the smoke stream remains completely sheathed within vthe stream of particle free air and accordingly no practic al possibility exists for the 'particles in the s'tnoke'stream to escape through said sheath into the smoke cell with consequent danger of recirculation back through'the focus area, in spite of the unavoidable mixing of the outer layers of the filtered air stream'with air contained in the smoke cell. I
The s'heathfof' filtered a'ir,'ent'ering through the outer concentric tube 38 is maintained at about the same linear rate'offlow as the smoke stream flowing through tube 37.- "Morespecifieallyj in the preferred embodiment, the ratio betweenthefiow rate of the filtered air stream in tube 38I'and thatof the; smokestream through inlet tube 37-is adjustedfto beequal to the ratio between the cross-sectional' areafof the stream in 38 and the cross sectional-area of the stream37. Thi s insures that the linear rate offlo'w of the 'smoke'strearn through the focus ype commercially available pho otoeell's, .such as. heretofore indicated at 29 .'rn ay .b'e 'used.aecordingito specific requirements of instruments present invention, it has been found that the-, cgmtnercially available RCA type 931A electron multiplier tube and the photoconductive thallous sulfide ccll willgive detectable responses to scattered light from individual smoke particles passing through -the .foeus area of the smoke cell.
Theiesponse of, the photocell to particles at the focus area in. the presentembodimentresults in the production ofp ulses of photocurrent when the particles. traverse the focus area of theinstrument. Assuming thatthe device is to be employed primarily to count individually the pulses,ofiphotocugrent; and to determine the time rate of production fiznulses; which,. when related to the flow rate, gives immediately the. Yolumeconcentration of detectable; particles in. the rsmoke :stream passing through the/focu'sarea of-the smoke-cell; the apparatus with which such counting may be effected is diagramatically illusphotocell 29. The electrical signals from the photocell are fed to a conventional electronic amplifier 50, in which the steady component of the signal is blocked out and the pulses are amplified. The amplified pulses are fed to a conventional discriminator and trigger circuit 51, such as the type illustrated by Dunning in Review of Scientific Instruments, volume 5, page 387 (i934), for exampie. The discriminator is adjusted to a predetermined level to reject pulses below a certain amplitude, and the trigger circuit is activated by pulses above that level. The output of the trigger circuit is fed to the mechanical register 52, from which readings may be taken in conventional ways to establish the rate of production of electrical signals which exceed the predetermined level. An oscilloscope 53 is connected across the output of the amplifier 59, to aid in adjusting the instrument and in interpreting the source of the pulses. Thus, large pulses arising from dust particles can often be distinguished from the pulses produced by the smoke particles, and an indication of the sizes of the individual smoke particles can be obtained from the sizes of the pulses.
In the embodiment shown in Fig. l, the photosensitive cell 29 and the first vacuum tube of the amplifier system, mounted in the socket 33b, may be maintained at a low humidity within the sealed enclosure 34 by means of a desiccant shown at 35, and electrical connections carried out through the pins 36. Such an arrangement eliminates any undesirable effects of moisture upon the operation of the photosensitive cell and the first vacuum tube in the conventional amplifier as indicated diagrammatically in Fig. 3.
It is understood that the above electronic system does not constitute a part of the present invention per se, such circuits being well known and understood in the art, and it is evident that other well-known electronic circuits may be employed successfully in connection with metering a particle carrying stream.
It is also well known that the output of any amplifier contains spurious and random pulses which interfere with the detection of small electrical signals such as those obtained from sub-micron particles in the embodiment herein described, and that the interference from such signals can be reduced by employing various types of filter circuits which reduce the band-width of the response system. This employment of filter circuits, to
improve the ratio of signal to spurious noise pulses, leads to the production of signals which depend in size upon the time interval during which the particle is in the focus area of the optical system. A further factor, which may make the signal depend upon the time interval in this way, is the frequency response of the photosensitive device itself. It has been found, in the case of the thallous sulfide cell, that this effect was quite large, even when filter circuits were not employed. Since it is highly desirable that the signal produced be representative of the particle, and substantially independent of its line of flight within the cross-sectional area of the smoke inlet tube 37, the particular arrangement of the smoke stream within a flowing sheath of air, in which all-of the smoke particles traverse the focus area at substantially the same velocity, is one which is to be preferred to all existing systems taught by prior art, in applications involving counting of individual particles.
1. In combination with a light source and optical means for illuminating, at a relatively small focus area, particles carried in a fluid medium through said focus area, the combination of elements comprising: means forming a closed chamber surrounding said focus area a first inlet tube adapted for connection to a source of substantially clear particle-free circulating fluid located exteriorly of said chamber; the inner end of said first inlet tube extending into the interior of said chamber from a first side thereof along an axis disposed perpendicular to the beam of light brought to focus at said focus area; the end extremities of said inner end portion of said first inlet tube terminating adjacent said focus area at the first side thereof and in axial alignment with the central point of said focus area; a second inlet tube adapated to be connected to a source of particle-carrying fluid to be illuminated in said focus area; the inner end portion of said second inlet tube being of substantially smaller diameter than said first inlet tube and disposed concentrically within said first inlet tube defining an annular fluid passage between the exterior surfaces of said second tube and the interior surfaces of said first inlet tube; the inner end of said second inlet tube terminating adjacent the inner end of said first inlet tube adjacent said focus area at the first side thereof; and an exhaust port formed in said chamber spaced from the inner end extremities of said first and second inlet tubes and located at the second side of said focus area opposite said first side, the space between the inner ends of said first and second tubes and said exhaust port being occupied solely by the atmosphere of said chamber.
2. The combination according to claim 1 and wherein said exhaust port is formed in the second side of said chamber directly opposite and in axial alignment with the inner ends of said first and second inlet tubes.
3. In combination with a light source and optical means for illuminating, at a relatively small focus area, particles carried in a fluid medium through said focus area, the combination of elements comprising: means forming a closed chamber surrounding said focus area a first inlet tube adapted for connection to a source of substantially clear particle-free circulating fluid located exteriorly of said chamber; the inner end of said first inlet tube extending into the interior of said chamber from a first side thereof along an axis disposed perpendicular to the beam of light brought to focus at said focus area; the end extremities of said inner end portion of said first inlet tube terminating adjacent said focus area at the first side thereof and in axial alignment with the central point of said focus area; a second inlet tube adapted to be connected to a source of particlecarrying fluid to be illuminated in said focus area; the inner end portion of said second inlet tube being of substantially smaller diameter than said first inlet tube and disposed concentrically within said first inlet tube defining an annular fluid passage between the exterior surfaces of said second tube and the interior surfaces of said first inlet tube; the inner end of said second inlet tube terminating adjacent the inner end of said first inlet tube adjacent said focus area at the first side thereof; an exhaust tube leading from the interior to the exterior of said chamber; the inner end of said exhaust tube projecting inwardly into said chamber from a second side thereof and terminating adjacent said focus area at the second side thereof in spaced relation from and directly opposite and in axial alignment with the inner ends of said first and second inlet tubes; and means associated with said first inlet tube and said exhaust tube for circulating fluid streams through said first and said second inlet tubes into said chamber through said focus area and outwardly from said chamber through said exhaust tube; the space between the inner ends of said first and second tubes and the inner end of said exhaust tube being occupied solely by the atmosphere of the chamber.
4. The combination according to claim 3 and wherein said last named means comprises: first means including pump means connected to said first inlet tube for circulating substantially particle-free fluid through said first inlet tube into said chamber at a predetermined flow rate; and second means including pump means connected to said exhaust tube for withdrawing fluid from said chamber through said exhaust tube at a predetermined flow '7 rate greater than the flow rate of said particle-free fluid being circulated, through'said first inlet tube into said chamber through said first inlet tube.
5. In combination witha light source and optical means for illuminating at a relatively smallfocus area, particles carried. in a fluid medium-through said focus area, the combination of elements comprising: -means forming a closed chamber surrounding said focus area a first inlet tube extending into the interior of said chamber from a first side thereof along an axisdisposed perpendicular to the beam of light brought to focus at said focus area; a second inlet tube disposed concentrically within said first inlet tube defining an annular passage between the exterior of said second tube and the interior of said first tube; the inner end extremities of said first and second tubes terminating adjacent said focus area at the first side thereof and in axial alignment with the central point of said focus area; an exhaust poit formed in the second side of said chamber spaced from the inner end extremities of said first and second tubes and located at the second side of said focus area opposite said first side; an annular stream of substantially clear particle free fluid circulating from a source located exteriorly of said cham- References Cited th e'file of this patent UNITED STATES PATENTS 1,724,870 Belt ;ac: Aug. 13, 1929 1,911,130 Hannigan May 23, 1933 2,042,095 Grant n May 26, 1936 2,333,791 3 r V n Nov. 9, 1943 FOREIGN PATENTS 417,116 'Great Britain".. Sept. 28, 1934