US2948470A

US2948470A - Particle counter

Info

Publication number: US2948470A
Application number: US646397A
Authority: US
Inventors: Berkley Carl; Hyman P Mansberg; George N Thomas; Yamagami Yonehisa
Original assignee: Allen B du Mont Laboratories Inc
Current assignee: Allen B du Mont Laboratories Inc
Priority date: 1957-03-15
Filing date: 1957-03-15
Publication date: 1960-08-09
Anticipated expiration: 1977-08-09
Also published as: GB861284A

Description

Aug. 9, 196.0 c. BERKLEY Erm. 2,948,470

PARTICLE COUNTER Filed March l5, 1957 '7 Sheets-Sheet 1 Aug. 9, 1960 c. BERKLEY ErAL 2,948,470

v PARTICLE COUNTER Filed March l5, 1957 7 Sheets-Sheet 2 COUNT N0 COUNT NO COUNT Fig. 3

INVENTORS CARL BERKLEY A HYMAN P. MANSBERG BY GEORGE N. THOMAS YONEHISA YAMAGMI ATTORNEYS Ag. y9, 1960 yc. BERKLEY :TAL 2,948,470l

PARTICLE COUNTER 'I'Sheets-.Sheet 5 Filed March 15, 1957 konz.

INVENTRS Aug. 9, 1960 c. BERKLEY ErAL PARTICLE COUNTER '7 Sheets-Sheet 4 Filed March l5, 1957 umm Y A INVENTORS CARL BERKLE'Y HYMAN P. MANSBERG GEORGEMTHOMAS YONEHISA YAMAGAMI @www ATTORNEYS 'r sheets-sheet 5 Aug. 9, 1960 c. BERKLEY ETAL PARTICLE COUNTER Filed March l5, 1957 S RYGSI OE n l TMMMM @Km n mRwe@ M WENTAMA R om ILA .A ,r m E. @5mi RMNY r n meg A tm W Mmmm s EE A mozmozuli @MN viv momom 23m@ 5o@ ,MGM 5.5225100 l vo. Y JW 41| M 555mg @c+ nom oom l Nm l WN |=N mg Mw 3 A f "i i Sx Nwooo. N Q96@ @.oww 2.o. 2R10@ Q om lmnvllmk] 1 F w l l 1 K n n ooo. om-+ 8;- u o9-- 2 v .n1 3+ g @2+ E. omN+ Aug. 9, 1960 c. BERKLEY ErAL 2,948,470

PARTICLE COUNTER Filed March l5, 1957 '7 Sheets-Sheet 6v INVENTORS ATTORNEYS c, BERKLEY Erm. 2,948,470

PARTICLB COUNTER '7 Sheets-Sheet 7 Aug. 9, 1960 Filed March l5, 1957 l* rv A l A me* agrario Patented Aug. 9, 195) gaat PARTICLE COUNTER Carl Berkley, Great Notch, Hyman P. Mansherg, Fairlawn, George N. Thomas, Paterson, and Yonehisa Yamagami, Montclair, NJ., assignors to Allen B. Du Mont Laboratories, Inc., Clifton, NJ., a corporation of Delaware Filed Mar. 15, 1957, Ser. No. 646,397

Claims. (Cl. 235--92) The present invention relates to devices for scanning an area to detect particles present therein and to count the number of distinct particles in the area and more particularly to such a particle counter which requires only a single scanning beam.

'Ihere are many situations in which it is desired to count the number of objects or particles within a given area. An example of such `a situation is the situation where it is desired to count the numb-er of bacterial colonies in a dish of liquid. lIt is, of course, possible to count objects or particles by the instrumentality of a human observer, but the operation may be accomplished much more rapidly by an optical electronic scanning device. In the event that it is desired to count particles or objects having uniform size and shape, a very simple scanning device may be utilized. The present invention does not deal with such a situation however, but rather deals with a situation where it is desired to count particles of diierin-g sizes and shapes as may be encountered when it is desired to count bacterial colonies as mentioned above or in various other applications.

Previous devices for counting particles, cells or bacterial colonies, such as for instance, Patent No. 2,494,441, to J. Hillier, have utilized a ying spot scanner to scan the area in which the particles were contained', a-nd thereby generate a pulse for each intersection of the raster trace with `a particle. It was t-hen necessary however to estimate the average width of a particle in terms of raster lines, and to divide the total number of pulses by the laverage width of the particles to be counted. This system requires an operation onthe part of a human operator, namely, estimating the size of the particles. In addition, it is obviously subject to substantial error due to the operator improperly estimating the average width of the particles.

The particle counter according to' the presentV invention is not subject to the foregoing disadvantages but rather than counting individual interceptions' of the scanning line with the particle, it produces only a single counting pulse for each continuous but not re-entr'ant profile. This result is acomplished in the present invention without the necessity for using more than onescanning beam and hence the present device is relatively simple in construction and operation notwithstanding its superior accuracy and eciency.

For the sake of simplicity the present invention will be explained with reference to a particular embodiment designed to count the number of bacterial colonies in a Petri dish. It will be understood, however, that many features of the invention may be adapted to a counter for opaque particles which are scanned and detected by re'- ected as well as transmitted light. -In fact the present invention is not limited to scanning by means of light rays but may also be adaptedto systems utilizing other methods for scanning an area to sense particles.

it is accordingly an object of the present invention to provide a particle counter which will count the number of particles within a given area.

It is another object of the present invention to provide a device which will count the number of particles in a given area utilizing only a single scanning beam.

It is still `another object of the present invention to provide a particle counter which will count the number of particles in a given area where the particles diier substantially in size and shape.

It is still another object of the present invention to provide a particle scanning and counter device having a provision for eliminating any discrepancies in the particle count due to masking of the area to be counted or to the interruption due to the return of the scanning trace between lines or between frames.

lt is a further object of the present invention to provide a particle counting device which may be adapted to count` particles detected by transmitted light, by retlected light or by reflection or transmission of some m-edium other than light.

It is a still further object of the present invention to provide a particle counting device utilizing a delay line memory for line to line comparison and including automatic means for adjusting the time between scanner sweeps to compensate for temperature induced or otherwise induced variation in the ldelay time of said delay line.

Other objects Iand advantages will be apparent from a consideration of the following description in conjunction with the drawings, in which lFig. l is a block diagram ofa particle counter according to the present invention;

Fig. 2 is a schematic diagram of ian optical system suitable `for use in the particle counter of Fig. l and adaptedv to detect by transmitted light, the presence of small objects such as bacterial colonies in a translucent medium;

Fig. 3 is an illustrative representation of the scanning process, presented tov aid in the explanation of the operation of the device of Fig. 1;

Fig. 4 is a block diagram of the anti-coincidence circuit forming a part of the particle counter of Fig. 1;

Figs. 5a and 5b are schematic circuit diagrams of the signal shaping and delay circuit of the particle counter;

Fig. 6' is a schematic circuit diagram ofl the anticoincidence circuit of Fig. 4;

Fig. 7 is a block diagram of a synchronizer circuit which may be alternatively used for controlling the sweep circuit of the particle counter of Fig. l;

Fig. 8 is a schematic circuit diagram'of the synchronizer circuit of Fig. 7.

Referring now to the drawings and particularly to Fig. l, a cathode ray tube 10 provides a light source for a ying spot type scanner. Sweep and gate circuits 11 are provided tok control the deflection mechanism of the cathode ray tube 10 to produce the desired movement of the iiying spot on fthe face of the tube. It is preferredl that an ordinary linear rectangular raster be utilized which may have 1000 lines, for example. Of course the invention is not limited to the use of a rectangular raster and a helical, radial or other type scan could be used if desired.

The high voltage'supply for the cathode ray tube 10 is shown? at 12. Protection -circuits 9 are provided so that the spot will be extinguished in the event that the sweep signal is discontinuedv for any reason, and thus the cathode ray tubey is protected against burning. by a stationary spot.

The ilying spot' on the cathode ray tube 10 is directed by means of an optical system 1'3 through a Petri' dish 313 (Fig. 2) holding.v a sample containing the bacterial colonies to be counted. The optical system 13 directs the light from the cathode ray tube onto the sensitive portion of a photo tube 14.

The optical system is shown in Fig. 2. The cathode ray tube 10 produces a raster which is resolved and imaged on the plane of the culture medium of the dish 33 by means of the objective lens 31 and the mirror 32.

A condensing lens system comprising lenses 35 collects substantially all of the light passing through the dish and by means of the mirror 36 illuminates the photo sensitive surface of the photo tube 14. A mask 34 is provided to define the area of the dish 33 which is to be scanned.

The location of the photo tube 14, the condenser lenses 35 and the focal length of these condensers are chosen to produce an image of the exit pupil of objective lens 31 on the photo cathode of photo tube 14. This arrangement assures that the photo cathode will be uniformly illuminated regardless of the location of the scanning spot on the dish. The optical system therefore directs the beam from the ilying spot through the dish and bacterial colony contained therein to the photo tube 14. The photo tube 14 thus produces an electrical signal which varies with the transparency of the particular portion of the dish being scanned. ln the course of the scanning of one frame, the photo tube 14 produces an electrical signal defining the visible particles contained in the scanned dish 33.

It will be understood that the optical system of Fig. 2 is a particular embodiment designed to count minute translucent particles and that the invention is not limited to this particular scanning system but may be adapted to other systems for scanning greater areas with more or less resolution. Furthermore, an optical system adapted to utilize rellected light rather than transmitted light may equally well be used. It Will be observed that the optical system of Fig. 2 may be modified to include colored light lters to increase the sensitivity with respect to particles of a certain color or to distinguish between particles of diierent absorptions. Y

Referring again to Fig. 1 the output signal from the photo tube 14 is fed to a cathode follower 1S to avoid undue loading of the photo tube 14 by subsequent stages. The output of the cathode follower 15 is fed to the picture monitor 27 and to the optical correction circuit 16. The picture monitor 27 is not necessary to the counting function of the present invention but is desirable to provide a picture of the particles being scanned and counted.

The optical correction circuit 16 provides a self-correcting circuit in the nature of an automatic intensity control. The correction circuit 16 therefore assures that the average signal value remains substantially constant without appreciably degrading the information carried by the signal. Variations in density of the culture medium and in cathode ray tube brightness will therefore be compensated by the optical correction circuit 16. The correction circuit 16 also compensates for the reduction in illumination olf the optical axis of the system.

A Schmitt trigger circuit 17 is connected so receive the output from the optical correction circuit 16. The trigger circuit 17 assures that the signal fed to the following section is an on-off signal having two substantially discrete levels. The Schmitt trigger fires at two levels along the leading and trailing edges of a signal pulse produced by a colony of bacteria. The levels are separated by approximately three volts compared to the overall signal value of approximately 40 volts. The three volt level is not particularly critical but is sufficiently above the noise level to prevent noise pulses from operating the trigger to produce spurious trigger pulses. The trigger circuit 17 is desirable to produce pulses of uniform amplitude and uniform rise and fall times while preserving the information relative to the Width of input signals. However, various trigger type circuits may be used in place of the particular circuit described here 4 and in some cases a trigger stage may be dispensed with altogether.

The output of the trigger circuit 17 is fed to the picture monitor 27 and to an anti-coincidence circuit 24. By supplying the output of the trigger circuit 17 to the monitor 27, a picture of the area scanned is available in which the amplitude information has been removed by the trigger circuit.

The signal fed directly from the trigger 17 to the anti coincidence circuit 24 provides a signal at the anti-coincidence circuit which represents the instantaneous condition of the particular point being scanned. In addition Y to this information it is also desired to supply to the anti-coincidence circuit a signal delayed by a time equal to the time between successive lines of the raster. This will enable the anti-coincidence circuit to compare adjacent lines at the raster in a manner and for the purpose which will later be described.

The delay branch of the counter circuit is provided by the modulator 18 which modulates the signal from an oscillator 19 supplied to an RJF. amplifier 20, the modulated signal being passed through an ultrasonic delay line 21 to provide the desired signal delay. The output of the ultrasonic delay line 21 is amplified in the bandpass amplier 22 and detected by a detector amplitier 23. The detector 23 eliminates the high frequency carrier introduced by the oscillator 19. The output of the detector 23 is therefore substantially identical to the input to the modulator 18 except that it is delayed by a predetermined time substantially equal to the time between adjacent lines of the flying spot raster produced by the cathode ray tube lil. The output of the detector 23 is fed to a second input terminal of the anti-coincidence circuit 24.

T he anti-coincidence circuit 24 is designed to produce an output pulse for every complete input pulse received from the trigger circuit 17 at the No. 1 input terminal except that in the event that some portion of an input pulse is received from the detector 23 at input No. 2 of the anti-coincidence circuit 24 between the start and end of the input No. 1 pulse, no output pulse is to be produced.

The 'manner in which the anti-coincidence circuit 24 operates to accomplish this result will be explained with reference to Figs. 4 and 5 below. It will be understood, however, that while Figs. 4 and 5 show a particularly desirable anti-coincidence circuit other circuits to perform this function may be used in the present invention.

The output of the `anti-coincidence circuit 24 will represent a count of the distinct particles scanned by the scanning portion of the particle counter. This may be understood by reference to Fig. 3 in which the dish 33 being scanned is shown containing a bacterial colony 37. The area of the dish 33 to be scanned is defined by the masi; 34 shown having a circular opening. Pour raster lines in the vicinity of the bacterial colony 37 are denominated lines A, B, C and D. The signal produced by the trigger 17 during each of these scans is shown in the lower part of Fig. 3 by waveforms A', B', C' and D' respectively.

Referring to raster line A, it will be observed that the first portion of this line is blocked by the opaque mask 34 so that the Waveform A has a first portion J during which the trigger 17 is at its high output level. As the flying spot proceeds along the raster line A it reaches the edge of the mask 34 and enters the translucent area so that the output of the trigger circuit 17 then falls to the low level. Since raster line A does not intercept the bacterial colony 37, the signal remains at the low level throughout the central portion of the scan until it reaches the edge of the opaque mask 37. Near the terminal end of the scan line A the trigger circuit returns to the high level -as indicated by the area of the Waveform A indcated at H.

Special provisions are included in the circuit to prevent any count being produced due'- to the presence of the opaque mask. These provisions' will` be' discussed below. The same provisions assure that no count will be produced due to the return or ily back of the flying spot.

The ysecond line B of the raster considered in Fig. 3 is similar to the line A except that it intercepts the bacterial colony 37 so that a pulse E is produced in the central portion of the waveform B.

lt will be observed that when the waveform B is applied to the No. l or undelayed input terminal of ,the

anti-coincidence circuit 24, the waveform A is being applied to the delayed or No. 2 input terminal of the anticoincidence circuit 24. During the time when the pulse E is applied to input terminal No. 1, no pulse is applied to input terminal No. 2. This satisfies the conditions for the emission of an output pulse from the anti-coincidence circuit. Thus during the B trace of the flying spot scanner, an output pulse will be produced from the anticoincidence circuit.

Referring now to line C of the raster in Fig. 3 it will 20 be noted that a pulse F is produced during the tra'ce of line `C which starts at a point to the left of the pulse E.

When the waveform C' is applied to terminal No.1 of the anti-coincidence circuit, the waveform B will be (right) edge of the input' pulse.- Two out-puts are taken from the differentiatr 41,' a p'ositive output which is' fed to amplifier and inverter 43, and a negative output which is fed tov amplier and inverter 42. Exemplary waveforms are shown in Fig. 4' and it will be" observed that the input to amplifier and inverter 42 consists of a sharp negative pulse at the leading (left) edge of the square input portion and a sharp positive pulse at the trailing (right) edgev of the input pulse.

The input to amplifier and inverter' 42" is amplified and inverted thereby nd fedto a leading edge selector 44. The leading edge selector may be, for example, an amplifier stage' biased to substantially cut off the negative portion of the input signal. The output of the leading edge selector 44 is therefore" a positive pulseI occurring at a time co-incident with the leading edge of the input pulse to an input No'. l.

The outpu'tfrom the leading e`dge selector 44 is fed to a pulse storage device 46. The pulse storage stage 46 may consistY of a capacitor, for example, charged through a rectifier such as a thermionicvv diode. The pulse arriving at'. thev input of the pulse storage stage 46 will therefore causea constant voltage-output to be generated at the output of the pulse storage stage.

concurrently applied at terminal No. 2. Since a pulse signal E is present at terminal No. 2 during a portion of the pulse F, no output signal will be produced bythe anti-coincidence circuit. It Will be observed that the anticoincidence circuit must be precluded from' emittirig'an output pulse even though the pulse E at terminal No, Z stms after the begining of the pulse F at terminal No. l and terminates before the-termination of the pulse F.

Reference to waveforms C and D in Fig. 3 will-demonstrate that the anti-coincidence circuit will not produce an output pulse during the trace of line D. The remaining lines of the raster do notintercept the bacterial colony 37 and hence no pulse will be produced by the anti-coincidence circuit. The counter circuit is designed to produce one count for each particle scanned since Returning now to consideration of amplifier 43, the amplifier and inverter 43 provides an inversion of its input signal ina manner similar to that of the previously considered amplifier 42. The trailing edge selector 45 selects the positive trailing edge pulse and substantially eliminates the negative pulse representing the leading edge. Itwill be observed that this operation is substantially the converse of that per-formed by the leading edge selector 44.

Th'e outputl of the trailing edge selector 45 is therefore 5 a positive pulse co-incident in time with the trailing edge further counts during successive interceptions of theparti# 40 cle are blocked by the anti-coincidence circuit.`

It should be pointed out that spinulose particles will not be properly counted by the present counter but rather will be counted multiply.l Otherwise the counter is' not seriously affected by the shape of the particle; As an example, a hollow or O-shaped particle will be properly counted as will be elongated particles and substantially all other particles the size of which is within the resolution of the scanning system.

The output of the anti-coincidence circuit 24 cis fed to 50 a conventional electronic digital counter 25 and to the picture monitor 27. The counter 25 may also' be`utilized to provide Ithe pulses to synchronize the raster' sweep circuit il. The sweep may be designed to be one frame per second and i000 lines per frame for example. Of course, other sweep times and resolutions may be utilized to meet a particular situation. A register 26-may be provided to record the colony count for each frame. It will be understood that the counter 2S and vthe register 26 do not form an essential part of the invention and that other devices may be utilized to tabulate the anticoirlcidence pulses and to provide synchronizing pulses for the raster sweep circuit.

A suitable circuit arrangement for the anti-coincidence circut 24 is shown in block diagram form in Fig. 4. 65

of the' input pulse at input No. 1. The outputs of both the pulse storage stage 46 and the trailing edge selector 45 are fed to respective inputs of an and circuit 47. 'I'he and circuit 47 operates to produce an output pulse when positive signals are received from both the trailing edgel selector 4S and the pulse lstorage stage 46; When a ysignal is received from either of the foregoing stages alone,

no output is produced by the and circuit 47.

The output Vof the and circuit 47 yis fed through au amplifier I52 and a cathode follower '53? to invert and amplify the pulse output of the and circuit' 47. The amplifier 52 and the cathode follower 53 provide a signal of suitable strength and polarity to operate the counter 25 in Fig. 1. Thus amplifier 52 and cathode follower 53 may or may not be necessary depending upon the requirements of the counterv 25.

Input No. 2 which is' delayed by the delay line 21 as shown in Fig. 1 is fed to a cathode follower 49. The input signal for a scanned particle is a negative signal as indicated by the waveform at input No. 2 in Fig. 4.

The cathode follower 49 serves to isolate the input from the anti-coincidence circuit and the signal from the cathode follower' 49 is fed into a stored-pulse discharge stage 51.

The stored-pulse discharge stage 51 operates to disc harge the pulse storage stage y46 upo'n receipt of a negat1ve pulse from the cathode follower 49W. Therefore, as a pulse is received at input No. 2, the output of the pulse storage stage 46 will be returned to zero and retamed at that value at least until the end of the input pulse at input No. 2. The pulse storage stage-46 will not return to its positive value until such time as a leading edge pulse is received from the leading edge selector 44.

It will be observed that the input through input No. 2 and the vstored pulse discharge stage 51v is the dominant input to the arrangement so that when signals are present in both inputs, the input No. 2 signal will control the level of the pulse storage stage output 46. Having thus far explained the composition of the anti-coincidence circuit, it is now possible to relate this structure to the rules for operation of the anti-coincidence circuit previously set forth Without explanation. It will be recalled that the anti-coincidence circuit is required to produce an output pulse for every complete input pulse at input No. 1, except when an input pulse at input No. 2 is present at some part of the time between the initiation and the termination of the pulse at input No. 1. From the diagram of Fig. 4 it will be seen that a cdmplete pulse entering the input No. l will cause a leading edge signal and a trailing edge signal to be introduced at the respective input signals of the and circuit 47. Presence of a signal at both inputs of the and circuit 47 causes an output pulse signal to be produced by the an circuit 47. Thus in the absence of an input signal at input No. 2, the anti-coincidence circuit of Fig. 4 operates as desired.

Considering ncw the operation of the circuit when an input signal is received at input No. 2, assume that the leading edge of a pulse has been received at input No. l and that the trailing edge of this pulse has not yet been received. At this time the pulse storage stage 46 will have a constant positive output produced by the leading edge pulse. If at this time a pulse is received at input No. 2, the cathode follower 49 and storage pulse discharge device 51 will cause the pulse storage stage 46 to be discharged so that its output returns to zero. Hence when the trailing edge of the input pulse at input No. 1 arrives at the and circuit 47, no input will be present at the other input of the and circuit and hence no output signal will be produced.

It will be observed that the same result will obtain if a leading edge pulse arrives at the pulse storage stage 46 during the continuance of an input pulse from input No. 2. In this case the pul-se storage stage 46 will never have an opportunity to become charged to produce a positive output signal and thus the subsequent arrival of a trailing edge pulse at the and circuit 47 will not cause an output pulse to be generated by the anti-coincidence circuit.

An additional input, namely, input No. 3 is provided which is adapted to receive a retrace signal from the cathode ray tube sweep circuits ll. Input No. 3 is lconnected through a cathode follower 48 to an input of the stored pulse discharge stage 51 in precisely the same manner as previously explained with reference to input No. 2. Thus a signal at input No. 3 will discharge the pulse storage stage 46 in precisely the same manner as an input signal at input No. 2.

Input No. 3 will be provided with anY appropriate signal during each line retrace and each frame retrace. It will be observed from Fig. 3 that as each scan line reaches the edge of the scan it must retrace to the left edge before beginning the next scan. interception of the retracing spot by a colony or particle could cause a count in the absence of a special provision to avoid this possibility. This possibility is avoided by input No. 3 which discharges the pulse storage device between the successive forward tnaces. This same effect can be obtained by blanking the scanning spot during retrace times but this method is subject to diiculties when a manual brightness control is used for the scanning tube.

From the foregoing explanation it will be seen that the anti-coincidence circuit presented in block form in Fig. 4 satisfies the requirements previously set forth to prevent surplus counts during the successive interceptions of a particle by the scanning mechanism of Pig. l. It will be observed that the anti-coincidence circuit of Fig. 4 is such that no output pulse is generated if any pulse of the two input pulses overlap or coincide. The present circuit is therefore better adapted for use in the particle counter than those anti-coincidence circuits in which only the coincident part of overlapping pulses are blocked or gated. The latter anti-coincidence oircuits are not suitable for use in a particle counter without the inclusion of means to extend the width of the gating pulse to block the portions of the two input pulses which do not overlap.

The schematic diagram of the signal shaping and delay portion of the particle counter circuit is shown in Figs. 5a and 5b. The particular circuit shown in Figs. 5a and 5b is purely exemplary and other equivalent circuits may be utilized in various stages of the signal shaping and Idelay circuit. The video input from the photo tube ampliier is shown at 61 in Fig. 5a. An electron tube

envelope containing triodes

62 and 65 is shown at 60. The

triodes

62 and 65 together with a diode 63 and a triode 64 comprise the brightness correction stage of the shaping :and `delay circuit.

The triode 62 receives a video signal from the input terminal 61 and the biased diode 63 is connected to the cathode of the triode 62 to receive the signal therefrom and to act as a regulator. A :deviation signal is fed from the diode 63 to the triode amplier 64 and the output of the triode amplifier 64 is fed to the triode 65 which acts as la control tube. The triode 65 is also connected to the input triode 62 so that the output of the triode 65 has a wave shape generally corresponding to the video input except that the brightness or average level of the output from the triode 65 is regulated by means of the brightness correction circuit,

As previously explained, this stage serves to correct uctuations in the average signal level due to variations in the density of the culture medium, variations in cathode ray tube brightness and variations due to non-uniform characteristics of the optical system. The corrected video signal from the triode 65 is fed to the Schmitt trigger

stage comprising triodes

66, 67 and 68.

The Schmitt trigger stage operates to provide an output signal wherein the pulses due to interception of a particle are of relatively uniform amplitude and have substantially uniform rise and fall times. The invention is of course not limited to the use of the particular trigger circuit shown but rather other trigger circuits may be used or in `some cases the trigger stage might be omitted altogether.

The output of the Schmitt trigger stage is taken off vat the cathode resistor of the triode 68 and fed to the input of the cathode follower 69. The cathode follower 69 has its output connected to the channel l output terminal 7 0 leading to input No. l of the anti-coincidence circuit.

A second output is taken from the triode 65 to feed the delay section of the circuit. This output is rst fed to the modulator tube 711 which serves to modulate the 15 megacycle signal generated by the oscillator tube 72 and Iampliiied by the R.F. amplifier tube 73. The output of the R.F. amplifier tube 73 is fed to a fused quartz delay line 74.

The quartz delay line 74 has 1G00 microseconds delay. However, it will be understood that the delay will be selected in accordance with the particular application of the particle counter, the delay ordinarily being equal to the time interval between scan lines. The output of the delay line 74 is amplied by the amplifier tubes 75 (Fig. 5b) and fed to a balanced detector section including the dual triode tube 76. The semi conducto-r diodes a and Sdb serve to detect the signal from the dual triode 76 to provide a signal substantially corresponding to the signal fed into the modulator tube 7l except for the delay brought about by the delay line 74. It will be understood that the RF. modulation of the signal prior to passing it through the delay line '74 and its subsequent demodulation are particularly suitable methods for developing a signal delay by a predetermined `amount of time. However, other methods of developing a delayed signal could be substituted in the system within the scope of the invention.

The detected output from the dual triode 76 and the `diodes 80a andy 8012 isfed through amplifier 77 and cathode follower 78 to provide asuitable delayed output signal at the channel 2 output terminal 79. The signal at the channel 2 output terminal will, of course, be eonveyed yto the No. 2 input of the anti-coincidence circuit.

The signal shaping and delay circuit explained, above is designed to accept a videosignal from the photo tube. These signals are shaped to provide substantially'rectangular uniform signals retaining the pulse width information ofthe input signal. Inaddition to an undelayed output, an output delayed by a predetermined amount is also provided. The output signals are adapted to meet the requirements of the anti-coincidenee circuit. It is obvious that many different circuit arrangements may be devised which are equivalent to the circuit shown inFigs. 5a and 5b and thus the invention is not limited to that particular circuit which isshown by way of illustration only. e e e e The schematic diagram of an illustrative anti-coincidence circuit generally corresponding tothe block diagram of Fig. 4 is shown in Fig. 6r in which an input No. 1 is provided at 81. The undelayed signal from input No. l is fed to a triode 82 connected to provide a differentia/ tor stage. The triode 82 is shown as a double ytriode having its elements connectedv in parallel, but is of cou-rse, not limited to such an arrangement. The current through the triode 82 is approximately-equal to the time differential of the signal applied to its `grid due tothe differentiating action of. theRLC net-workin its plate circuit.

An output signal approximately equal tothe negative of the time differential of the No. l input signal is tapped offfrom the plate of the triode 8.2 and is fed to anampli.- fier tube 83. It will be noted that the leading edge of the input pulse at the input No. 1 is therefore marked by a sharpnegative pulse in the differentiated signalapplied to the amplifier 83, while the trailing edge of the No. l input pulse is marked by a sharp positive` pulse in the differentiated` signal applied to the amplifier tube 83.

The signal applied to the amplifier 83 is amplified and inverted by the amplifier 83 and fed to a cathode follower 84. The cathode follower 84 is provided witha negative bias such that the negative pulse arriving at'thecathode follower 84 is clipped off while the positive pulseis-transamitted and amplified. ItV will be noted that the negative pulse which is clipped is the trailingvedge signal-while the positive pulse which is passed is the lead-ingedge signal. Y.

YThe cathode follower 84 therefore acts asV aV leading edge selector and the positive signal from the cathode o-f the cathode follower 84 is fed to. one plate of atriple diode 85. The diodesection 85a which is connected to receive the signal from the cathode follower 84- has a capacitor 86 connected between its cathode and ground so that the positive signal from the cathode follower 84 charges the capacitoi 86 through the diode section 85a.v The diode section 85a acts as a rectifier to prevent the capacitor 86 from discharging back into the cathode follower circuit and thusV a pulse from. a cathode follower iseffectively stored at the charged capacitor 86.l

It is now necessary to reconsider theV signal produced by the differentiator tube 82. A second output signal from this tube is fed to the amplifier tube 87. The signal to the amplifier tube 87 is tappedio` from the cathode ofthe diferentiator 82. The signal applied to the amplifier tube 8,7v is therefore of OppQsite polarity or is inverted'relative to the polarity ofthe output signal applied to the amplifier tube 83. They amplifier tube 87 amplifies and inverts the signal received from the cathode ofthe diiferentiator tube 82, and its inverted signal is applied to the cathode follower 88.

As was the case with the cathode follower 8'4 cathode follower 88 substantially eliminates the negative pulse 10 portion of the diiferentiated'signal from the amplifier tube '87. However, it will be noted that the signal applied to the cathode follower 88 is inverted compared to the signal applied to the cathode follower 84. Therefore the cathode follower 88 substantially eliminates the leading edge pulse of the differentiated signal and amplifies and'passes the trailing edge pulse of the differentiated signal. The trailing edge pulse from the cathode follower 88 is fed to a control grid of a mixer tube 89. The potential existing at the cathode of the diode section 35a due to the capactitor 86 is applied to a second control grid of the mixer tube 89.

The plate circuit of the mixer 89 contains an inductance 90 and a diode 91 to produce a negative pulse output from this stage. 'Ihe mixer is biased so that a positive signal on either grid alone is insufficient to produce an output pulse but a positive signal on both grids will produce a negative output pulse Vfrom the mixer 89 which is fed to the triode amplifier 92 and from thence to the cathode follower 93 and the output 94. The output 94 isv connected to the counter'Y as shown in Fig. 1.

Fromv as much of `the circuit as has been thus far described it will be observed that an input pulse introduced at the No. 1 input 81 will cause a charging of the capacitor`86. by the leading edge of the :input pulse and as the trailingA edge of the pulse together with the potential from the charged capacitor 86 operates to render the mixer tubeY 89 conductive,`it will generate an output pulse which is amplified and supplied to the output 94.

The portion of the circuit which operates to prevent an output pulse upon receipt of a coincident pulse at input No: 2 will now be described. As previously explained, input No4 3 is the retrace cancelling input of the circuit and is designed to operate in the same manner as input No. '2. It will be observed that the circuit related to input No. 3 and the circuit related to input No. 2 are substantially identical but are distinct in orderV to prevent interaction' between these terminals. Input No. 2 is shown at 9S while input No. 3 is shown at 96. Each of these inputs is connected to a respective grid of a double triode having triode sections 97a and 9712. Respective D.C. restorer tubes 98a and 98b are also connected to the respective triode sections 97a and 97b. Triodes 97a and 97 b are connected as cathode followers with their cathode outputs, connected to the plates of respective diode sections 85b and 85e ofthe triple diode 85. Each of the cathodes'of the diode sections 85b and 85ek are connected to the ungrounded terminal of the capacitor 86. An input pulse at either

input

95 or 96 is'therefore transmitted by a respective cathode follower 97a or 9717 to the plate of a respective diode -section 8517 or 85C. A negative pulse applied to-either the diode section 851: or 85C allows the capacitor 86 to discharge through the diode section 851gA or 85e` thus returning the potential of the capacitor 86 and hence the second control grid of the mixertube 89 approximately to zero potential.

It will thusv be Seen that an appropriate input signal at either input No. 2 or input No. 3 will discharge the capacitor 86 and thus eliminate a necessary condition for the generation of an output pulse at the mixer tube 89. From the foregoing it will be seen that the circuit shown provides an output pulse for every input p ulse received' at input No. 1 except that in the case where some portion of an input pulse is received at input No. 2 or input No. 3 after the arrival of the leading edge ofthe pulse at input No. l and before the trailing edge of the pulse at input No. 1. no output signal will be produced.

The particular circuit shown in Fig. 6 is purely intendedvto be illustrative of one circuit capable of performing thefunction of the anti-coincidence section. The invention is not limited to the circuit shown in Fig. 6 in that different tubes and different parameter values may be. used and n fact transistors or other amplifiers may lie slbstituted in parts or in all of the circuit shown in From the foregoing explanation it is clear that in the device of Fig. l it is rather important that the flying spot scanner be synchronized so that the time interval between sweep lines is very nearly equal to the time delay produced by the delay line in `the time delay section of the device. lf this condition is not met it will be obvious that the pulses supplied to the delayed and unndelayed inputs to the anti-coincidence circuit representing successive interceptions of a signal will not arrive coincidentally. lf the discrepancy in time is sufciently great the circuit will not operate properly. Some variation in the time delay of the delay line may be expected from temperature changes and as a result of other conditions. In some cases therefore it may be desirable to provide a circuit arrangement where changes in the time constant of the delay line are automatically compensated by changing the time interval between sweep lines. It is obvious that the actual time delay between sweep lines is generally unimportant except that it is quite necessary for this time to be synchronized with the delay line time constant.

A modification to the circuit of Figs. l through 6 which provides the self-synchronizing feature explained above is shown in Figs. 7 and 8. Fig. 7 shows in block diagram form certain components of the particle counter previously explained, namely the modulator 18, RF. amplifier 20, ultrasonic delay line 21, bandpass amplifier 22 and detector and amplifier 23.

An additional modulating signal is fed to the R.F. amplifier from a blacker-than-black modulator 101. The blacker-than-black modulator provides a modulating signal which is blacker, that is to say more negative, than the black of the video signal applied from the modulator 18. The RF. amplifier therefore supplies a signal through the delay line which is modulated by the blacker-thanblack modulator signal as well as by the video signal supplied from the modulator 18. The signal to the modulator 101 is supplied by a blocking tube oscillator 102. The blocking tube oscillator 102 is a free running type oscillator synchronized by a trigger tube. The synchronizing signal for the blocking tube oscillator 102 is supplied from the sync separator 103. The sync separator 103 is connected to receive the output from the detector and amplifier Z3 and to detect the blacker-thanblack sync pulse arriving from the delay line.

The device above operates as follows. The first oscillation of the blocking tube oscillator produces an output signal to the blacker-than-black modulator which in turn e causes a blacker-than-black pulse to be impressed on the RF. carrier. The RF. amplifier therefore carries this blacker-than-black sync pulse in addition to any video information supplied by the modulator 18. The R.F. signal is delayed by the ultrasonic delay line 21 as before. The RF. signal is amplified by the bandpass amplifier 22 and detected by the detector and amplier 23, also as before.

However, the output of the detector and amplifier in addition to being transmitted to the anti-coincidence circuit is also transmitted to the sync separator 103. The sync separator 103 removes the video information retaining only the blacker-than-black synchronizing pulse.

The synchronizing pulse is transmitted by the sync separator to trigger the blocking tube oscillator 102. The normal free running period of the blocking tube oscillator 102 is adjusted to be longer than the delay time of the delay line 21. Thus the blocking tube oscillator by virtue of its free running oscillation will not pulse the blacker-than-black modulator before it is triggered by the sync separator 103.

The period of the blocking tube oscillator in operation is therefore controlled by the total transit time through the ultrasonic delay line 21 so that the output of the blocking tube oscillator 102 may be used to synchronize the scanning system. Thus a second output from the blocking tube oscillator tube 102 may be fed to the sweep circuit as a synchronizing pulse. By this means the period between lines of the ying spot scanner is synchronized with the period of the delay line in spite of changes in temperature or other varying conditions.

. The particular sync circuit is shown in Fig. 8. In Fig. 8 the blocking tube oscillator is shown as one sectionl04 of a double triode.` The second section of the double triode is the trigger tube for keying the free running oscillator tube 104. A triode 106 is connected to receive the output from the oscillator 104 and is connected to the input of the R.F. amplifier tube 73.

For simplicity the delay line and post delay amplifiers are omitted from Fig. 8. The diode 107 is utilized as a sync separator and is connected to receive the output of the amplifier tube 77. The synchronizing pulses selected by the sync separator are fed through a phase inverteramplier tube 108 to the input of the trigger tube 105. It will be seen from Fig. 8 that a signal is generated by the free running oscillator 104 which is imposed as a blacker-than-black-modulation on the RJ?. carrier and fed through the delay line and detector circuit. The detected sync pulse is separated by the separator 107 and led to the trigger tube 105, completing the cycle for initiation of a successive impulse from the oscillator 104. This arrangement is in some cases preferable to that of Fig. 1 alone in that the modification of Figs. 7 and 8 automatically compensates for differences in delay line, delay time and the time interval between lines of the flying spot scan.

From the foregoing explanation it will be seen that a particle counter is provided which will count any colony regardless of size within the resolutions of the scanning system and that the system produces only one count per particle rather than producing counts for each interception of the particle by a raster line. Furthermore, the system is arranged to avoid counts during the interception of the mask or a second interception of a particle during the scanning and during the horizontal and vertical retrace intervals.

Although a particular circuit has been described in detail it will be understood that the invention is not limited to the particular circuit shown and described but rather that many equivalent circuits may be substituted for those shown all within the scope of the invention. Accordingly the invention is not to be construed to be limited to the particular embodiment shown by way of illustration, but is rather to be limited `solely by the appended claims.

What is claimed is:

l. A particle counter for counting the number of particles in a given `area comprising scanning means for scanning said area in a succession of sweeps, sensing means for indicating the presence of a particle at the point of incidence of said scanning sweep with said particle, an automatic intensity control for regulating the output of said sensing means to maintain a relatively constant average value, a trigger circuit for producing an output of substantially rectangular waveform corresponding to the output of said sensing means', an oscillator for generating a high frequency electrical signal, a modulator connected to modulate the output of said oscillator in response to the signal from said trigger circuit, a delay line having a delay equal to the time between successive sweeps of said scanning means `and connected to receive the modulated high frequency signal from said modulator, a detector connected to receive the output from said delay line and adapted to convert said modulated high frequency signal to a rectified signal having a waveform substantially equivalent to the envelope of said modulated high yfrequency, an anti-coincidence circuit comprising a first input terminal, a second `input terminal, a third input terminal, an output terminal, diierentiator means connected to said first input terminal for generating pulses of one polarity in response to the leading edge of a pulse from said first input terminal and generating pulses of asiskiv opposite polarity in response to trailing edges of a` pulse from said first input terminal, a leading edge pulse se lector connected to receive an output signal from said dierentiator means, a trailing edge pulse selector connected to receive an output signal from .said ,difterentiator means, a signal storage element connected to receive the output from said leadingedge pulse selector for maintaining the signal -level ofl-a-signal-i-rom said leading edge pulse selector, said signal storage element also being connected to said second-and third input terminals and being adapted to be restored to -a datum level by any portion of yan input pulse from -either said second or third input terminal, an -and circuit having one input connected to said storage element and a second input connected to receive the outputof said trailing edge pulse selector, means for connecting said -first anti-coincidence circuit input terminal to receive the output of said sensing means, means for connecting said second anti-coincidence circuit input terminal to receive .the `delayed signal from said detector means, means for connecting said third input terminal to receive a signal from said scanning means during the retrace of the scanning means sweep, whereby a pulse is produced at the ouput of said anti-coincidence circuit for the first interception of a particle by said scanning means and further pulses from the same particle on successive sweeps of said scanning means during retrace of said sweep are inhibited.

2. A particle counter as claimed in claim l further including means for introducing a synchronizing signal into said delay line in synchronization with sweeps of said scanning means, and means for controlling said scanning means in response to the synchronizing signal output of said delay line to maintain the time between sweeps of said scanning means substantially equal to the delay of said delay line circuit.

3. A particle counter for counting the number of particles in a given area comprising scanning means for scanning said area in a succession of sweeps, sensing means for indicating the presence of a particle tat the point of incidence of said scanning sweep with said particle, an automatic intensity control for regulating the output of said sensing means to maintain a relatively constant average value, a trigger circuit for producing an output of substantially rectangular waveform corresponding to the output of said sensing means, an oscillator for generating a high frequency electrical signal, a modulator connected to modulate the output of said oscillator in response to the signal from said trigger circuit, a delay line having a delay equal to the time between successive sweeps of said scanning means and connected to receive the modulated high frequency signal from said modulator, a detector connected to receive the output from said delay line and adapted to convert said modulated high frequency signal to a rectified signal having a waveform substantially equivalent to the envelope of said modulated high frequency signal, an anti-coincidence circuit comprising a first input terminal, a second input terminal, a third input terminal and an output terminal, diiierentiator means connected to said first input terminal for generating pulses of one polarity in response to the leading edge of a pulse from said first input terminal and generating pulses of opposite polarity in response to trailing edges of a pulse from said first input terminal, a leading edge pulse selector connected to receive an output signal from said diiierentiator means, a trailing edge pulse selector connected to receive an output signal from said diierentiator means, a signal storage element connected to receive the output from said leading edge pulse selector for maintaining the signal level of a signal from said leading edge pulse selector, said signal storage element also being connected to said second and third input terminals and being adapted to be restored to a datum level by any portion of an input pulse from either said second or third input terminal, an and circuit having one input connected to said signal storage element and a second input connected torcccivc thc output nf( said trailing cdgc pulse selector, means for connecting Said iirst anti-coin` cidence circuit input terminal toy rcccivc the output 0f said .Sensing means, meansy for connecting said second anti-coincidence circuit input terminal to receive the delayed signal fromY said detector meansvwhereby a pulse is ,produced` atithe output of said anti-coincidence circuit for the vfirst, interception of a particle by said Scanning means and further pulses from the same particle on successive sweeps of said scanning means are inhibited.

4. A particle counter for counting the number of particles ina given area comprising scanning means for scanning said area in a succession Qi Sweeps?. .SllrSiDg means for indicating the presence of a particle, at the point of incidence of said scanning sweep with said particle, a first` oscillator for generating a high frequency elec- .trical signal, a` iirst modulator connected. to modulate the output of said first oscillator in response to the signal from said sensing means, a delay line having a delay approximatelyV equal to the time between successive sweeps of said scanning means and connected to receive the modulated high frequency signal from said first modulator, a detector connected to receive the output from said delay line and adapted to convert said modulated high frequency signal to a rectified signal having a waveform substantially equivalent to the envelope of said modulated high frequency signal, an anti-coincidence circuit having :an output terminal and two input terminals for producing an output pulse for each pulse received at a first of said input terminals which does not overlap in time with a pulse received at the second of said input terminals, means for connecting one of said input terminals to receive the output of said sensing means, and means for connecting the other of said input terminals to receive the delayed signal from said delay line, a second oscillator having a period of oscillation greater than the maximum delay time of said delay line, a blacker-thanblack modulator connected to receive the output of said second oscillator and also connected to modulate the signal from said first oscillator in a sense opposite to that of said first modulator, a synchronizing signal separator connected to separate the delayed synchronizing signal produced :at the output of said delay line, a trigger circuit driven by said synchronizing signal separator and connected to trigger said second oscillator, means for connecting the output of said second oscillator to said scanning means to synchronize the sweeps of said scanning means with the delay period of said delay line, whereby a pulse is produced at the output of said anti-coincidence circuit for one interception of a particle by said scanning means and other pulses from the same particle on consecutive sweeps of said scanning means are inhibited, and whereby the period of the sweep of said scanning means is synchronized with the delay time of said delay line.

5. A particle counter for counting the number of particles in a given area comprising scanning means for scanning said area in a succession of sweeps, sensing means for lindicating the presence of ya particle at the point of incidence of said scanning sweep with said particle, a first oscillator for generating a high frequency electrical signal, a first modulator connected to modulate the output of said rst oscillator in response to the signal from said sensing means, a delay line having a delay approximately equal to the time between successive sweeps of said scanning means and connected to receive the modulated high frequency signal from said first modulator, a detector connected to receive the output from said delay line and adapted to convert said modulated high frequency signal to a rectified signal having Aa waveform substantially equivalent to the envelope of said modulated high frequency signal, an anti-coincidence circuit having an output terminal and two input terminals for producing an output pulse for each pulse received at a first of said input terminals which does not overlap in time with a. pulse received at the second of said input terminals,

means for connecting one of said input terminals to receive the output of said sensing means, and means for connecting the other of said input terminals to receive the delayed signal from said delay line, a second oscillator having a period of oscillation greater than the maximum delay time of said delay line, a blacker-than-black modulator connected to receive the output of said second oscillator and also connected to modulate the signal from said first oscillator in a sense opposite to that of said first modulator, means for separating the blacker-than-black signal produced at the output of said delay line, a trigger circuit driven by said separated blacker-than-black signal and connected to trigger said second oscillator, means for connecting the output of said second oscillator to said scanning means to synchronize the sweeps of said scanming means with the delay period of said delay line, whereby a pulse is produced at the output of said yanticoincidence circuit for one interception of a particle by said scanning means and other pulses from the same particle on consecutive sweeps of said scanning means are 'i6 inhibited, and whereby the period of the sweep of said scanning means is synchronized with the delay time of said delay line.

References Cited in the le of this patent UNITED STATES PATENTS 2,712,065 Elehourne et al. June 28, 1955 2,731,202 Pike Jan. 17, 1956 2,731,204 Darling et al Jan. 17, 1956 2,756,627 Boychs July 31, 1956 2,789,765 Gillings Apr. 23, 1957 2,791,377 Dell etal May 7, 1957 2,791,695 Bareford et a1 May 7, 1957 2,791,697 Dell May 7, 1957 2,803,406 Nuttall Aug. 20, 1957 2,873,363 Wanlass Feb. 10, 1959 FOREIGN PATENTS Great Britain Nov. 2, 1955