CA1223455A - Coincidence correction in particle analysis - Google Patents

Abstract

ABSTRACT

Flat beam optical sensing performed transverse of a flow aperture, of the particles passing through the aperture, directly indicates the presence of individual particles in the aperture. The indication can be used to eliminate or otherwise modulate the coincidence errors resulting in particle measurements taken through the length of the aperture.

Description

~2~45X

This invention rel~tes generally to electronic particle counting and analyzing ~pparatu6 utilizing an aperture and, in particular, relates to correcting errors in counting and analyzing resulting from the coincidence of a plurality of particles in the aper~ure.
Particle analysis apparatus usmg an aperture is well-kncwn. 5ee U.S. Patent 2,656,508. me aperture of such apparatus provides a minute scanning aperture, ambit, or sensing zone relative to or through which pass and are detected, counted, and analyzed, single particles at a rate often well in excess of one thousand per ~econd. Coincidence of two particles in the scanning ambit occurs quite often due to the physical parameters of the scanning aperture and par,icle concentration. The effect i6 that one particle is believed tG be detected, counted and analyzed while two or more particles are actually located ~imultaneously in the sensing zone.
Correction for counting errors caused by such coincidence has been performed in several ways. One way is for an operator to refer to a coincidence correction chart which presents the proper error corrected count for a very large selection of counts produced by the devlce. This provides an accurate result but is time consuming and prohibits fully automatic recording and processing of error corrected counts.
Other way~ have been developed which electrically manipulate the actual count or the manner of obtaining the actual count to provide an error corrected count. U.S. Patent 3,626,164 (U.S. Class 235/151.3) discloses circuitry which adds counts to the detected count to yield a corrected count which closely approximates the true particle count. U.S. Patent 3,936,740 (U.S. Class 324/71 CP) discloses circuitry which digitally delays producing the pulses reçeived from the Coulter aperture.
U.S. Patent 3,949,197 (U.S. Cla5~; 235~g2 PC~ discl~8e~ circuitry which provides a statistical correction to a detectedtrain of particle derived count pulses ~o that the effective random coincidence loss or gain of the count doe6 not induce ultimate counting error. And, U.S. Patent 4,009,443 (U.S. Cla6s 328/11~
discloses circuitry which alters the time period in which particle pulses are counted. Other examples of coincidence correction in a ~oulter aperture environment exist, but the ~tated examples are believed to be indicative of the cited U.S. cla~sifications.
Thus, coincidence correction of a count of pa;-ticles obtained in an aperture environment has been by operation on the electrical signals obtained from the aperture based upon some statistical theory. No attempt has been made directly to determine when this error causing coincidence exists.
In addition to counting errors, coincidence causes errors in analyzing other parameters, such as particle volume.
When a particle passes through an aperture, its volume may be analyzed by the amount of change in electrical current flow through the aperture. Coincidence of two particles in the aperture causes a change in the flow of electrical current different from the change effected by either particle individually. This causes errors in particle volume determination which must be corrected to determine the true particle volume. Again, no attempt previously has been made directly to determine when this error causing coincidence exists.
It would be highly advantageous to a method and apparatus for directly determining when a coincidence of particles in an aperture exists. The results of this direct determination may be used as desired, such as by correcting ~s~

data containing coincidence errors, determining when valid data exists, or otherwise.
Accordingly, the invention provides a method of correcting coincidence error occurring in parametric data from particles, the correction being effected substantially at the time that the coincidence error occurs in a parametric datum of said data, the parametric datum representing at least one particle analysis parametex and the error being introduced into the datum at the time of measurement and resulting from coincidence of at least two particles in the length of a measurement aperture as said particles pass through the aperture, the method characterized by the steps of producing sai.d parametric datum in response to a measurement made through the length of said aperture as at least one : 15 particle passes through the length of the aperture (as known per se), said producing said parametric datum being incapable of distinguishing between coincidence and noncoincidence of particles in the aperture, detecting the presence of individual particles in said aperture other than through thelength of said .20 aperture, producing a detection signal in response to detecting the presence of an individual particle in said aperture and modulating said parametric datum in response to said detection signal after the production of said parametric datum and said detection signal to obtain corrected parametric data free of said coincidence error.
Further, the invention provides apparatus for correcting coincidence error occurring in parametric data obtained from a particle analysis system producing parametric data from particles the correction being effected substantially at the time that - 3a -the coincidence error occurs in a parametric datum of said data, the parametric datum representing at least one particle analysis parameter and the error being introduced into the datum at the time of measurement and resulting from coincidence of at least two particles in the length of a measurement aperture as said particles pass through the aperture, the apparatus characterized by measurement means producing said parametric datum in response to a measurement made through the length of said aperture as at least one particle passes through the length of the aperture, (as known per se), said measurement means being incapable of distinguishing between coincidence and noncoincidence of particles in the aperture, detection means producing a detection signal in response to sensing the presence of an individual particle in said aperture, the detection means sensing the presence of individual particles other than through the length of said aperture and correction means for modulating said parametric datum in response to said detection signal after the production of said parametric datum and said detection-signal to obtain corrected parametric data free of said coincidence error.

- 3b -Accordingly, a flat beam of radiant energy is passed through an aperture transverse of the direction of particle flow therethrough. Individual particles passing through the flat beam change the distribution of radiant energy exiting the flow chamber, ~rhich forms the aperture, sufficientl~ 50 that electrical detection signals may be produced in response thereto. ,he flat beam is dimensioned in the apçrture so that the beam senses the entire cross-section of the aperture and so that the lo beam senses the particles on a one-by-one basis.`
Thereafter, the detection signals are used as desired to correct for coincidence errors in data obtained from the aperture by means other than the beam of radiant energy, such as in accordance with conventional aperture sensing principles. For example, a single detection signal during an electrical volume signal indicates no coincidence of particles in the aperture and a valid volume signal. More than one detection signal during a volume signal indicates coinci~ence of particles in the aperture and an erroneous volume signal.
In essence, the invention involves the optical sensing of a small domain, the cross-section of the aperture, to indicate the validity of data obtained from a larger domain, the length of the aperture.

~4'SS

Fiqure 1 is a ~chematic block diagram of a particle detection and analysi ~ystem utilizing an aperture, according to the invention;
Figure 2 i~ a ~ide elevational view of a flow chamber in section along a median plane, including an aperture on an increased scale, illu~trating a beam of radiant energy pas6ing through 6aid aperture transverse of the flow of particles therethrough;
Figure 3 is a top view of :the flow chamber;
Figure 4 i6 a circuit diagram illustrating a circuit which may be used with the invention to correct data for coincidence errors; and Figure 5 is a graph illustrating the time relationship of detection signals and a volume signal produced in response to two particles passing through the aperture in coincidence.

. ~5S

Turning now to the drawing, in Figure lan aperture particle analy is syc~em i8 indicated generally by the reference character 10, This system, as is well-known, include~ a flow chamber 12 providing an aperture 14 between an inlet chamber 16 and an outlet chamber 18. Particles to be analyzed are pas~ed through the flow-chamb~r 12 and aperture 14 from a particle source 20 to particle sink 22. A ~heath fluid source 24 and a sheath fluid sink 26 provide a ~heath fluid also passing through the aperture 14 which aids in maintaining the particles from source 20 at the axial center of the aperture 14.
The sourcing and sinking of particles and sheath fluid to the flow chamber 12 may be by any means desired such as by tubing or other conduit. Thus, lead 28 indicates the means of carrying the particles from ~ource 20 to the flow chamber 12. Lead 30 indicates the means carrying the sheath fluid from the source 24 to the flow chamber 12, lead 32 indicates the means carrying the particles from the flow chamber 12 to the particle sink 22 and lead 34 indicates the means carrying the sheath fluid from the flow chamber 12 to the 6ink 26.
The particle analysis system further includes a pair of electrodes 36 and 38 respectively located in the inlet chamber and outlet chamber of the flow chamber 12. The pair of electrodes are connected to a volume sense circuit 40 over leads 42 and 44 respectively. The volume sense circuit 40 provides a floW of electrical current through the ~ngth caperture 14 by way of leads 42 and 44 and electrodes 36 and 38. As is well-known in a aperture particle analysis system, particles passing through the aperture 14 change the current flow through the aperture and thi6 change in current can be measured in the volume sense circuit 40 to obtain an electrical signal indicative of the ._~2~3455 volume or other parameter of ~che part$cle~ passing through the aperture, The signal6 which are ~ ndicative of the volume of particles p~6~ng through the aperture are output on lead 43. The volu~e signal output on lead 4~, however, includes coincidence error~ which previously have been corrected for by various meanE a6 has been described hereinbefore.
In accordance with the invention, these coincidence errors are corrected by passing a flat beam of radiant energy through the optically transparent walls of the flow-chamber 12 and, in particular, through the aperture 14, transverse of th~ direction of flow of particles therethrough. This beam of radiant energy is dimensioned so as to extend at least from wall to wall of the aperture and has a height in the direction of flow of particles which is about equal to the diameter of particles flowing through the aperture. When there are no particles passing through the beam of light in the aperture 14, th~
beam of radiant energy passes through the opposite wall of the flow chamber and exists therefrom to strike a beam stop. Radiant energy from the beam which is dispersed or scattered such as by being deflected or defracted therefrom due to imperfections in the flow-chamber walls or sheath fluid, also exists from the flow chamber body, i8 angled beyond the extent of the beam stop and strikes the face of an optical sensor~ The optical sensor, in turn, provides a detection signal indicative of the amount of radiant energy striking its face.
When no particles are passing through the aperture 14 and the flat beam of radiant energy, the detection signal has a DC value, i.e., there is no change in its value. When a particle passes through the aperture 14 and the flat beam of radiant energy, it changes the distribution of radiant energy striking the face of the optical sensor due to the particle defracting 1~2~4SIS

~nd deflecting l$ght frcm the ~lat beam~ Thi6 change ln di~tribution of radiant energy striking the ~ace o~ the 3ensor ~au~e~ a ch~nge in the value of the detection fiignal ~uch that the detection signal produces a pulse or an AC value.
The pu7se of the detection 6ignal iB used to indicate when individual particles are present at the location of the flat beam in the a~erture 14. Because of the dimen6ions of the flat beam in the aperture 14, each pul~e of the detection signal indicates the presence of a single particle in the aperture. Thus, multiple pulses of the detection signal occurring during a single volume signal on lead 43 indi~ates an erroneous volume value due to coincidence. Thereafter, the erroneous v~lume ~ignal may be used as desired such as being disregarded, to avoid coincidence errors in the summation of particle vQlu~e signals obtained.
Turning again to Figure 1, a radiant energy source ~0 such a~ a laser provides a beam 52 of coherent radiant energy such as light~ Thereafter, the beam 52 is passed through beam shaping optics 54 which shapes the ~eam 52 into a flat beam 56 having the desired dimensions as discussed. Therafter, the flat beam 56 passes through the optically transparent walls 58 and 60 of flow chamber 12 and aperture 14. The radiant energy exiting the flow chamber 12 is shown in Figs. 2 and 3 as being comprised of two portions, a first order beam which compri~es light dispersed or scattered such as by defraction or deflection from flat beam 56,and the remainder ~f the radiant energy from flat beam 56 which forms a zero order beam 65. This zero order beam, of cour~e, is formed of the radiant energy of flat beam 56, which is not dispersed or scattered therefrom. The radiant energy exiting the flow chamber 12 is directed onto a light sensor 66 (Fig. 1), which, as shown in Fig. 2, includes a zero order beam stop 68 and a face 70. The zero order beam is directed :~L22345$

onto the be~m 6top 68 and i8 completely absorbed there~y. The first order beam ~ubstantially is directed onto the ~ace 70 of the light ~ensor 66 and it is thi~ energy which i8 used to provide the detection 6ignal on lead 72, which i~ pa6sed to a coincidence correction circuit 74. The output of the ~oincidence correction circuit on lead 76 thereafter is provided to a particle analyzer 78.
In Fig. 2 there is illustrated a diagrammatic representation of the flow chamber 12. Hatching of the walls 58 and 60 of the flow chamber 12 is omitted for clarity of the drawing. A source tube 80 provides particles such as 82, 84, 86 and 88 to the inlet chamber 16, aperture 14 and outlet chamber 18 and then through the tube 90~in a direction indicated by arrow 92. A sheath fluid from ~ource 24 is also provided into inlet chamber 16, which passes through aperture 14 and into outlet chamber 1~ and then to sink 26. Thus, inlet chamber 16 is in fluid communication with outlet chamber 18 through aperture 14, with the sheath fluid aiding in maintaining the particles in the axial center of aperture 14 to obtain a better volume signal therefrom.
For both mechanical and operationai reasons, the aperture i~ many times longer than the diameter of the particles to be measured. Thus, there is a potential for multiple particles to be present in the aperture 14 at any one time and this is known as coincidence. An example of coincidence is indicated by the particles 84 and 86 being within the aperture 14 ~imultaneously.
As is illust-ated in Fig. 2, the flat beam 56 has a thickness along the direction of the flow of the particles indicated by arrow 92, which is approximately e~ual to the diameter of the particles.
In Fig. ~, it is ~hown that the beam 56 has a width which is substantially equal to the width of the aperture 14, i~e., the beam 56 extends substantially from wall to wall of the ~;Z234SS

aperture 14. This is so that no particles in aperture 14 will escape detection.
In Fig. 3 a square aperture 14 is illustrated.
It will be understood that the present invention is applicable also to an aperture of a round cross-section as will be discussed hereinafter.
Because the flat beam 56 is dimensioned to have a height approximately equal to the diameter of an individual particle, the individual particles passing through the aperture 14, are sensed on a one-by-one basi~, even if the particles are closely spaced one from another. Thus, the flat beam 56 and light sensor 66 provide means by which the particles passing through the aperture 14 may ~e ~ensed on a one-by-one basiE,separate from the determina-tion of their uolumeand other than through the length of aperture 14.
In ~ig. 5, the top graph, wave form 94 illustrates the volume sïgnal obtained from circuit 40. The lower graph indi-cates the pul~es of the detection signal output by the light sensor 66. The first pulse indicated by wave form 96 corresponds to particle 86 of Fig. 2 passing through the light beam 56, while the pulse represented by wave form 98 represents the pulse later produced by particle 84 passing through beam 56. The relative values of the wave forms 94, 96 and 98 are not intended to be represented accurately in Fig. 5, only the timing relationships between the occurrence of these signals. Thus, the occurrence of two pu~ses of the detection signal during one occurrence of the volume signal may be used to indicate a coincidence of particles in the aperture 14, while an occurrence of only one detection signal Euch as is represented by a wave form 96 indicates the presence of a signal particle in the aperture 14. This latter case would occur if particle 84 of Fig. 2 were not in aperture 14 in coincidence with particle 86, and therefore, wave form 98 would not be produced during the occurrence of volume-signal wave form 94. Da~i~-line wave form 99 illustrates the extension of the volume signal when p ~ icles 84 an~ 86 are in coincidence in the aperture.

~lL2234S~ii In Fig. 4, there i6 illu~trated an embodiment of ~n electrical circuit u~ed to modulate the coincidence including raw data from the volume sense circuit 40 o o~tain corrected data free of said coincidence errors. Effectively, this circuit uses the pulses of the detection circuit to gate the passing of valid volume data to the analyzer 78, The leads 42 and 44 from electrodes 46 and 48 are diagramma-tically illustrated as bein input to volume amplifier 100. The output of volume amplifier 100 is essentially the output of volume circuit 40 on lead 43. This is a smooth wave form, substantially as illustrated by wave form 94 in Fig. 5. This signal i8 provided in coincidence correction circuit 74 to both a peak sense and hold circuit 102 and an input of a ~xrator 104 configured as a noise discriminator. The other input of the comparator 104 is connected to a variable resistance VRl providing a noise threshold level voltage.
When the signal on lead 43 exceeds the noise threshold value selected by the variable resistor~comparatOr 104 outputs a corresponding signal on lead 106 which, hereafter will be known as CONVERT, is applied to two D-type flip-flops 108 and 110 and analog to digital converter 112. The output of analog to digital csnverter 112 appears on lead 76 and analog to digital converter 112 is~connected to peak sense and hold circuit 102 by leads 114 and 116. ~ead 114 provides a signal known as STRETCHED PULSE
to the AD converter 112 while lead 116 provides a CLEAR signal to the peak sense and hold circuit 102.
Also input to coincidence correction circuit 74 is a smooth wave signal from the sensor 66 on lead 72. This is amplified in amplifier 118 and is passed along on lead 120 to comparator 122 alBo oonfigured as a noise discriminat~r. The other 3~55 input of comparator 122 i~ connected to a variable re~istor VR2 which is u~ed to provide a noise threshold level~ol~age.
~hen the signal on lead 120 is above this noi e threshold level comparatorl22 provides a corresponding signal on its output at lead 124. The s~ls on lead 124 correspond to the wave forms illustrated in the detection graph of Fig. 5. These signals or pulses are provided to the clock inputs of flip-flops 108 and 110.
The Q output of flip-flop 110 is provided on lead 126 to both the analog to digital converter 112 and to a coincidence rate meter 128.
In operation, the amplifiers 100 and 118 are used to provide logic ~ignals having useful levels. Both of the volume and detection ~ignals from amplifiers 100 and 118 respectively, are compared to threshold levels to discriminate against noise. The outputs of the discriminators, respresented by comparators 104 and 122, are squared wave forms whose durations are the length of the pulses applied thereto. The output of tbe volume noise comparator 104 is used to enable two D-type flip-flops 108 and 110. Both are cleared when no pulse is present out of the volume discriminator. Therefore, the Q outputs of both flip-flops are at the logic zero "0" state. During a volume signal, a detection pulse from the amplifier 122 clocks the tw~ flip-~lops one time. When this occurs, the Q output of flip-flop 108 goes to a logic one ~1" state, and the Q output of flip-flop 110 remains at the logic zero "0" state. If a second pulse occurs in the detection signal during the volume signal, then the Q output of flip-flop 110 on lead 126 also goes to a logic one ~1" state.
Simultaneous to the operation of the flip-flops,the volume signal has been peak sensed and held to obtain the volume of the particle. The trailing edge of the volume discriminator signal CONVERT, indicates to the analog to digital converter 112 to convert the stretched pulse from the peak sense and hold circuit 102 to a digital value. If the signal CONVERT INHIBIT on lead 126 is high or ~z~ s a logic one ~1" state, when ~he trailing edge of the signal CONVERT occur~, then the analog to digital converter 112 does not digitally convert the value and, in turn, the converter 112 produces the CLEAR ~ignal on lead 116 to clear the signal held in peak ~ense and hold circuit 102. If the signal on lead 126 is low or a logic zero "0" s~ate, when the trailing edge ~f CONVERT occur~, then the converter 112 converts the sensed and held value to a digital value, outputs the same and then provides the CLEAR signal on lead 116. The signal on lead 126 can also be applied to a coincidence rate meter 128 to obtain a ~ummation of the number of coincidence occurrences.
Thus, the coincidence correction circuit 74 may be thought of as gating the volume signal to the analog to digital converter 112 only when one detection pulse occurs during its duration.
In one particular embodiment of the inven~ion, the particles to be analyzed have a diameter of about 1 to 20 micro~eters. The length of the aperture has a length along the direction of particle flow of about 76 micrometers, while the flat beam 56 has a height along the direction of flow of the particles of about 5 micrometers.
As has been stated, the sensor 66 includes a zero order beam ~top and a ~ensor for the first order dispersion of light.
Such a sensor may be the sensor disclosed in U.S. Patent 4,038,556 to Auer. Alternatively, the sensor may sense the change in the energy of the zero order beam caused by a particle passing through the flat beam 56 while ignoring the dispersed light of the first order beam, to provide a detection signal.
In Fig. 3, a square aperture 14 is illustrated and has been indicated that a round aperture will also work.
This is because the electrical detection signal provided in response to the particle passing through the flat beam 56 is a result of the change in distribution of energy exiting the flow chamber 12 and detected by the photosensor and is not a function 9~S5 of the ab~olute guantity ~f l$ght ~tr~king the sen~or. In effect, the pul6es of the detection Eignal are a re~ult of the change of di~tribution of light ~triking the sensor and, thus,steady state characterictics of the ~y~tem such a~ the index of refraction of the 6heath fluid, ~he optical clarity of the wall6 of the fluid chamber and the cross-6ectional configuration of the aperture areessentially irrelevant.

Claims (25)

The embodiment of the invention in which an exclusive property or privilege is claimed is defined as follows:

1. A method of correcting coincidence error occurring in parametric data obtained from a particle analysis system of the type which produces parametric data from particles, the correction being effected substantially at the time that the coincidence error occurs in a parametric datum of said data, the parametric datum representing at least one particle analysis parameter and the error being introduced into the datum at the time of measurement and resulting from coincidence of at least two particles in the length of a measurement aperture as said particles pass through the aperture, the method comprising the steps of A. producing said parametric datum in response to a measurement made through the length of said aperture as at least one particle passes through the length of the aperture, the producing of said parametric datum being incapable of distinguishing between coincidence and noncoincidence of particles in the aperture;
B. detecting the presence of individual particles in said aperture other than through the length of said aperture;
C. producing a detection signal in response to detecting the presence of an individual particle in said aperture; and D. modulating said parametric datum in response to said detection signal after the production of said parametric datum and said detection signal to obtain corrected parametric data free of said coincidence error.

2. The method as defined in claim 1 wherein the said particles pass through said aperture in a first direction axial of said aperture and the step of detecting said particles includes passing a beam of radiant energy through said aperture transverse to said first direction.

3. The method as defined in claims 1 or 2 and the step of dimensioning the beam of radiant energy to cause said beam to be flat so that all of said particles passing through said aperture pass through said beam.

4. The method as defined in claims 1 or 2 and the step of dimensioning the beam of radiant energy to cause said beam to be flat, so that all of said particles passing through said aperture pass through said beam, the aperture having certain width and the particles having at least about one diameter and said beam is dimensioned to provide it with a height in said first direction of about said at least one diameter and a width equal to about said certain width.

5. The method as defined in claim 1 wherein the step of detecting said particles includes optically sensing the radiant energy received from said beam of radiant energy passing through said aperture, said optically sensing includes producing said detection signal in response to a change in the distribution of radiant energy so received effected by said particles passing through said beam of radiant energy.

6. The method as defined in claim 5 wherein the particles passing through said beam effect a first order beam comprising radiant energy dispersed from said beam and a zero order beam comprising the remainder of the radiant energy of said beam and the step of optically sensing includes providing a beam stop receiving substantially all of said zero order beam and a face receiving substantially all of said first order beam.

7. The method as defined in claim 1 wherein the step of detecting said particles includes optically sensing the radiant energy received from said beam of radiant energy passing through said aperture, said optically sensing includes producing said detection signal in response to a change in the distribution of radiant energy so received effected by said particles passing through said beam of radiant energy, the step of producing said detection signal including producing pulses in response to particles passing through said beam of radiant energy.

8. The method as defined in claims 1 or 2 wherein the step of modulating said parametric data includes the step of gating each parametric datum in response to said detection signal to pass a correct parametric datum free of said coincidence errors.

9. The method as defined in claims 1 or 2 wherein the step of modulating said parametric data includes the step of gating each parametric datum in response to said detection signal to pass a correct parametric datum free of said coincidence errors, said detection signal including pulses representing individual sensed particles, and the step of modulating said parametric data includes the added steps of sensing and holding the value of each parametric datum and counting the number of detection signal pulses occurring during the production of each parametric datum, said gating step including gating each sensed and held parametric datum in response to the number of detection signal pulses which are counted during the production of that parametric datum.

10. The method as defined in claims 1 or 2 in which the parametric datum is modulated in response to said detection signal immediately after the production of said parametric datum and detection signal.

11. A method of correcting coincidence errors occurring in parametric data representing at least one particle analysis parameter of a plurality of particles, and obtained from a particle analysis system, the errors being effected by coincidence of the particles in an aperture as said particles pass through the length thereof, the method comprising:

A. producing said parametric data in response to measurements taken through the length of said aperture as particles pass therethrough, there being one parametric datum produced for at least one particle passing through said aperture;
B. detecting, other than through the length of said aperture, the presence of individual particles in said aperture;
C. producing a detection signal for each particle so detected; and D. modulating said parametric data in response to said detection signals, said modulating including gating each parametric datum in response to said detection signal to pass a correct parametric datum free of said coincidence errors.

12. The method as defined in claim 11 in which said detection signal includes pulses representing individual sensed particles, and said modulating said parametric data includes sensing and holding the value of each parametric datum, and counting the number of detection signal pulses occurring during the production of each parametric datum, said gating including gating each sensed and held parametric datum in response to the number of detection signal pulses which are counted during the production of that parametric datum.

13. Apparatus for correcting coincidence error occurring in parametric data obtained from a particle analysis system producing parametric data from particles the correction being effected substantially at the time that the coincidence error occurs in a parametric datum of said data, the parametric datum representing at least one particle analysis parameter and the error being introduced into the datum at the time of measurement and resulting from coincidence of at least two particles in the length of a measurement aperture as said particles pass through the aperture, the apparatus comprising:
A. measurement means producing said parametric datum in response to a measurement made through the length of said aperture as at least one particle passes through the length of the aperture, said measurement means being incapable of distinguishing between coincidence and noncoincidence of particles in the aperture;
B. detection means producing a detection signal in response to sensing the presence of an individual particle in said aperture, the detection means sensing the presence of individual particles other than through the length of said aperture; and C. correction means for modulating said parametric datum in response to said detection signal after the production of said parametric datum and said detection signal to obtain corrected parametric data free of said coincidence error.

14. The apparatus as defined in claim 13 in which said particles pass through said aperture in a first direction axial of said aperture and said detection means include a beam of radiant energy passing through said aperture transverse to said first direction.

15. The apparatus as defined in claim 14 in which said beam is flat and further, is dimensioned so that all of said particles passing through said aperture must pass through said flat beam.

16. The apparatus as defined in claim 14 in which said beam is flat and further is dimensioned so that all of said particles passing through said aperture must pass through said beam, said aperture having a certain width, said particles having at least about one diameter and said beam having a height in said first direction of about said at least about one diameter and a width equal to about said certain width.

17. The apparatus as defined in claims 13 or 14 in which said detection means include optical sensor means receiving the radiant energy from said beam of radiant energy passing through said aperture, said optical sensor means for producing said detection signal in response to a change in the distribution of radiant energy so received effected by said particles passing through said beam of radiant energy.

18. The apparatus as defined in claims 13 or 14 in which said detection means include optical sensor means receiving the radiant energy from said beam of radiant energy passing through said aperture, said optical sensor means for producing said detection signal in response to a change in the distribution of radiant energy so received effected by said particles passing through said beam of radiant energy, said particles passing through said beam effecting a first order beam comprising radiant energy dispersed from said beam and a zero order beam comprising the remainder of the radiant energy of said beam, said optical sensor means including a beam stop receiving substantially all of said zero order beam and a face receiving substantially all of said first order beam.

19. The apparatus as defined in claims 13 or 14 in which said detection means include optical sensor means receiving the radiant energy from said beam of radiant energy passing through said aperture, said optical sensor means for producing said detection signal in response to a change in the distribution of radiant energy so received effected by said particles passing through said beam of radiant energy, said detection signal including pulses produced in response to particles passing through said beam of radiant energy.

20. The apparatus as defined in claims 13 or 14 in which said correction means include gating means for gating each datum of said parametric data in response to said detection signal to pass a corrected parametric datum free of said coincidence errors.

21. The apparatus as defined in claims 13 or 14 wherein said correction means include gating means for gating each datum of said parametric data in response to said detection signal to pass a corrected parametric datum free of said coincidence errors, said detection signal including pulses representing individual sensed particles, said correction means include sense and hold means for sensing and holding the value of each parametric datum, and counting means for counting the number of detection signal pulses occurring during each parametric datum, said gating means for gating each parametric datum from said sense and hold means in response to the number of detection signal pulses which are counted by said counting means during the production of that parametric datum.

22. The apparatus as defined in claims 13 or 14 wherein said correction means include gating means for gating each datum of said parametric data in response to said detection signal to pass a corrected parametric datum free of said coincidence errors, said detection signal including pulses representing individual sensed particles, said correction means include sense and hold means for sensing and holding the value of each parametric datum, and counting means for counting the number of detection signal pulses occurring during each parametric datum, said gating means for gating each parametric datum from said sense and hold means in response to the number of detection signal pulses which are counted by said counting means during the production of that parametric datum, said gating means pass each parametric datum from said sense and hold means in response to one detection signal pulse being counted during the production of that parametric datum.

23. The apparatus as defined in claims 13 or 14 in which said correction means is capable of modulating said parametric datum in response to said detection signal immediately after said parametric datum and said detection signal is produced.

24. Apparatus for correcting coincidence errors occurring in parametric data representing at least one particle analysis parameter of a plurality of particles, and obtained from a particle analysis system, the errors being effected by coincidence of the particles in an aperture as said particles pass through the length thereof, the apparatus comprising:
A. measurement means for producing said parametric data in response to measurements taken through the length of said aperture as particles pass therethrough, there being one parametric datum produced for at least one particle passing through said aperture;

B. detection means producing a detection signal in response to the detection, other than through the length of said aperture, of the presence of individual particles in said aperture; and C. correction circuit means for modulating said parametric data in response to said detection signals, said correction circuit means including gating means for gating each datum of said parametric data in response to said detection signal to pass a corrected parametric datum free of said coincidence errors.

25. The apparatus as defined in claim 24 in which said detection signal includes pulses representing individual sensed particles, and said correction circuit means include sense and hold means for sensing and holding the value of each parametric datum, and counting means for counting the number of detection signal pulses occurring during each parametric datum, said gating means for gating each parametic datum from said sense and hold means in response to the number of detection signal pulses which are counted by said counting means during the production of that parametric datum.