CA1163294A - Aperture cleaning system - Google Patents

Abstract

ABSTRACT

A cleaning system for clearing residue left within the internal surfaces of the apertures of a particle study device in which particles In suspension are passed through one or more microscopic apertures to generate particle related signals for study of the particles in the suspension by applying thereto energy through the apertures sufficient to boil the fluid therein. The energy is applied in the form of a D.C.
current at a relatively high constant magnitude level for a relatively short continuous predetermined length of time, generally between passages of the particle suspensions. The energy applied preferably is greater than two tenths watt seconds.

Description

l 163294 The inyent,i:on rel~tes gene~lly to ~a~ticle study devices havlng one'or more'apertu~es throu~h which particles suspended ~n a ~luid are passed ~or stud~ and more particularl~ to cleani~g the resldue'left b~ the particles and ~luids on the'internal walls o~ the aperture to eliminate a bu~ldup o~ ~oreign matter in the apertures which would e~fect the accuracy o~ the signals' caused by the particles passing through the apertures.
~ particular device ~or studying partlcles of microscopic size suspended in a fluid o~ electrolyte whose electrical impedance or resistivity is su~stantiall~
different from that of the particles shown and described in U.~. ~atent No~ 3~259,842~ The ~lu~d is passed through a microscoptc apertuxe formed in an insulating wall.
Simultaneousl~, an eIectrical current is esta~lished in the aperture providing a sensing zone'wh~se impedance is changed in prop~rtion to the s~ze o~ the particle passed through the zone. The change in impedance is detected and a signal iS generated ~hose amplitude is proportional to ~o the particle size and whose durat~on is equal to the time that it required ~or t~e particle'to pass through the sensin~ zone.
The signals can be counted ~or any glven volume l of suspension passed through the zone to determine the `' 25 particle concentration or the signals can be segregated ¦ according to size and number to determine the particle ' size distribution of the suspension. The particle information derived ~rom the signals is utillzed in hospitals and laboratories and it is extremeIy critical ¦ 30 that the in~ormation be'accurate~' The devices are typica,lly ut~lized ,~n l~e co~plç~ ap~r~us whose operators do not have the tlme and~or may not have the expertise constantl~ to monitor and correct every phase of operation o~ the apparatus, Various types of ~pparatus have been developed to overcome such problems as an aperture ~eing blocked ~y particles or other problems which cause erroneous in$ormation to be developed~ One deyice developed to overcome the pxoblems presented in employtng a single aperture devlce is shown in U.S~ Patent No. 3,444,463.
In this system the sample fluid is passed throu~h three apertures s~multaneously and separate respectiVe detectxng si~nals are de~eloped in response to the part~cles passing through each of the three apertures. The sxgnals de~eloped by each aperture are compared and then by -a p~ocess commonly known as "voting", should one of the s~gn~ls developed ~e ~eyond a predeterm~ned limit from the average of the other two signals, that aperture is considered to be ~alfunctioning and the signal ~rom that aperture i9 ignored in the processing of in~ormation using such si~nals.
The probab~lity of more than one aperture becoming blocked or otherwlse signi~lcantly malfunctioning at the same time is remote. The reliability of the ~5 information received from the particle study is thus enhanced as a blocked or other~ise ~ulty aperture is ignored in the study, A system utillzing the multiple apertures and votin~ as descri~ed above is dtsclosed ln the U.S.
Patent No. 3,549,994~ This system wa$ developed espec1ally ~ 163294 for use in the f~eld Qf ~edicinè and bi~lo~y for studying body fluids. ~s is well known~ bod~ fluids such as blood are studied to obtain information to be used in the diagnosis and treatment of patients. The need for accuracy of this information is thus ~ery critical~
Blood is composed of microscoplc cells or particles suspended ~n a serum and ~arious of these cells are important in the study of the blood. Three types of blood cells ~ay be o~ ~art~cular interest including red and white blood cells which are on the order o~ seven or more microns in size and plateIets which may range from one to four microns in s~ze~
~ n the systems ut~lizlng ~ult~ple apertures and voting, the need for accuracy o~ the detecting slgnals developed by the passage of the particles through each aperture is extremely important~ ~ the signals ~hich are "voted" on the voting apparatus are not equal for the same sized part~cles for any reàson, then the circuitry may vote out an aperture whicn is funct~oning normally.
Even if the s~nal d~erences are not sufficient ~or one aperture to be voted out, the resultant data and information developed in the particular study ~ill not be accurate~
The apertures in these and other particle study devices including those for industrial use, may range from 30 microns to 500 microns in dlameter with a typical range of 5Q to 100 microns for studying body ~luids. The apertu~es generall~ are formed ln wafers of sapphire or ruby and hare typical manufacturin~
tolerances wh~ch may cause the residue buildup to be 1 1~3294 greater in one ~pertu~e than another of the same or dlfferent size.,' Systems are available for detecting and clearing the complete or substant~all.y complete blockage of an aperture in particle study devices~ One such cirCuit i5 shown and descrlbed in U~S~ Patent No~ 3,259',891. This patent sho~s se~eral debris clearing devices which require either complex mech~n~cal linkages in orde~ to mechanically remove the ~perture debris or the'actual removal of the 10 ~perture and~or apeXture tube to manually remove the debris. The mechanical linkages are somewhat difficult to u~ilize and are cu~bersome in operation~ ~n the case of actually rem~vln~, cleanin~ and replacing an aperture tube, time is consu~ed wh~c~'~s to ~e avoidea in o~erating the '` 15 study devices, especially in a structure with more than one apexture and ~uxthermoxe'this seve~elyl'1~tts the through-put of the devices~ ~nother debris cleax~ng device shown in the patent emplo~ a capacitor charged to a hi~h potential Which is d~scharged via the electrodes cxeating a ~ery high ~,nitial current flow through the aperture~ thereby literally heat~ng the contents of the'apextuxe to explode and driviny the obstruction out of the aperture~ The rate of application of energy from the capac~tor is not optimum o~ uniform and when sufficient energy is utilized to clear a blocka~e lt creates a serious threat of damage to the aperture material or aperture holding structure, ~ second type of aperture clearing circuitry is shown in U~S~ P~tent No. 3,963,984 which includes a pulse generator coupled to the eIectrode inside the aperture tube and, to the electrode outside the particle 1 16329~

tube in the ~luid suspenS~on~ ~ pulse generator is coupled to the ~irst and second eIectrodes and develops a combinatt.on of pulses ha~ing predeterm~ned characteristics which'are coupled to the eIectrodes and hence are coupled through the ltqu~d contents o~ the apertuxe wh.ere t~e~ cause'the 11quid to vaporize and cause a microscopic explos~on', A~ain, the force of the exploslo~ ~s intended to be controlled to dislod~e the debris without causiny , da~age to the aperture or aperture structure~ however, even at the optimum Such an RF burst ~s hi~hly energy wasteful. Further~ore, RF ~re~uency appl~ed to the aperture ~a,~ cause a noise problem ~n the part~cle device itsel~, Furthexr it ha's been ~ound that such a high ~requency combin~t~on of pulses does n~t clean the intern~l surf~c 'o~ the'~perture as' completely as des~red~
The'pa,xt~le signals- may be' significantly e~ected even thou~h the apertureS are not blocked~ ~t the~e~ore would ~e'use~ul ~o m~,n~ain each aperture as clean as possible without wasting energy, deteriorating the aperture structure and so that the aperture does not become increasingly smaller as a number of particle fluid samples is passed therethrough.

~ 163?,94 Accoxdingly~ the invention provides a method of aperture clean.lng for a particle study devIce having at least one aperture throuyh which particles in fluid suspension a~e passed for study, character~zed by the step of applying energy continuously at a substantially constant level for a predetermined period of time to the fluid in the aperture sufficient to boil the fluid th.erein~
Further, apparatus also ls prov~ded for the practice of the aboYe mekhod includin a p~rticle stu~y device having at least one aperture for passage of fluid therethrough and through'which particles in suspension are passed for stud~ character~zed by a power supply connected to apply energy continuously at a substantially constant level for ~ predetermined duratic~n to the flutd in the aperture su~icient to boil the'fluid therein~
The p~eferrecl embodiments of thi,sinvention now will be described, by w~y of example, ~ith reference to the drawings accompanying thls speclfication in which:
Figure 1 is a partial block and schematic diayram of a particle study device embodying the aperture cleaning system of the invention, and Figuxe 2 is a schematic diagram of a cleaning energy gener~tion circuit~

~ ~8329~

Referxing now to Figure :l, the paxticle study device is indicated generally at 10, The type of particle study device ls not cri-tical; however, each device of interest generally will include a particle analyzer 12 which is coupled to at least one aperture 14 through which the part~cles in suspension are passed~
The structure containing the apertures also is not critical and may be a yl~ss vessel or ~ath 16 into which a suspension of part~cles to be stud~ed is moved.
For the proper operation o~ the device 10 and to enable accur~te data or information to be obtained therefrom, it is essent,al that the ampl~tude of a signal produced for a g~ven size particle be proportional to the size of th~t pa~ticl.e and, in addltion, that the actual amplitude o~ that same signal be identical for all apertures in a device havinc3 a plural,~ty of apertures if an identical pa.rt~cle had passed through each of the apertures, Three aperture tubes 18, 20 and 22 are immersed in a main body 24 of the:vessel 16~ The aperture tubes may be mounted on a plate 26 which en~ages an upper entrance of the ve~ssel 16 as a t~pe of closure. E'ach of the aperture tubes 18, 20 and 22 has the microscopic aperture - 14 in the bottom end thereof and individual electrodes 28, 30 and 32 internally of the respective aperture tubes.
The individual electrodes enable individual detecting circuits each to be coupled to the body of the suspension contained in the respective aperture tubes. The vessel 10 includes an electrode 34 common to all of the electrodes in the respective aperture tubes which is coupled by a 1 16329~

lead 36 t~ ~round. E.ach of the tubes is coupled to individual leads 38, 40 and 42 extending frorn respective electrodes 28, 30 and 32 to lndividual electronic detecting circults in the p~rticle analyzer 12 through a switch 44.
Each suspension of particles to be studied may be admitted into the vessel 16 by means of a sample conduit 46. Each of the aperture tubes 18, 20 and 22 is coupled to a suit~ble pressure differentlal (not sho~n) so that the suspension is sucked into or pushed through all the aperture tubes simultaneously, through the respective apertures 14, w~en the particle studying device 10 ~s in o~e~ation~
~ po~er supply 48 is counled to e'ach o~ the leads 38, 40 and 42 through'the switch 44 and hence to the respect~ve electrodes 28, 30 and 32~ In operation, electric cuxrent from the power supply passes through the respective apertures to the co~mon electrode 34 and then to ground. The current p~s~ng through'the suspension in each aperture will produce a volume of relatlvely high current density compared to the current density else~here in the suspension~ thereby establishing the above-mentioned sensln3zones in the respective apertures 14 and their immediate vicinities.
2S Since the suspension is chosen to be of a substantially dif'ferent impedance than the particles suspended therein, as the particles pass through each of the apertures they displace a f'lnite amount of khe suspension and hence change the impedance by a finite amount in each sensing zone. As previously ment~oned, the signals thus produced ~re dependent not only upon the size of the particles pa siny through the apertures but upon the intern~l dimensions of the apertures 14 themselves.
The change in impedance by the particles passing therethrough may be detected ln individual circuits in the particle analyzer 12 which is coupled to the respective apextuxes over respectt~e leads 38, 40 and 42 through the switch 44~ The particle analyzer 12 ~ay be Of the type described in U.S. Patent No~ 3,549,994.
The variations in impe~ance ln each senstny z~ne will cause an independent detecting slgnal to be developed indicative o~ the particle p~ssing through the respective aperture or sensing zone. The si~nals from the three sensing zones then-~ay be compared by the voting circuitry as previously described 1~ each is the same size. The resulting data or ln~ormat~on dertved from the signals from properly ope~at~n~ ape~tures may be displayed on a readout device (not shown) or otherwlse processed and used.
In operation o~ the part~cle study device 10, a suspension or sample ~lu~d containing particles is introduced into the bod~ o~ the vessel 16 through the sample conduit 46c The suspension is then sucked or pushed through the apertures 14 of all three aperture tubes while simultaneously electric current is pasSing through the apertures ~rom the power supply 48~ As each particle from the main body of suspension passes throuyh one of the apertures, the impedance in the respecting sensiny zone will ~a~y, This is detected by its individual 1 1632~4 detecting circuit i~n the partic].e ~n~lyze~ 12 by me~ns of the respective leads 38, 40 and 42~ The amplitudes of tl-e individual detecting sIgrla1.s caused ~y the pax~cles passin~ through'each o~'the sensiny zr~nes are then compared. The sens~ng si~nal amplitude gener~ted should be substantially equal. ~riations in the 1n~tial physical constructions o~ the apert~lres 14 may be balanced out in the particle analyzer 12 as described in U.S. Patent No. 4,078,211~
Once ~ sufficient ~mount of'suspension has been passed through each o~ the apertures, the solution may be drained through a drain con~u~t 5a and may be fr~llo~ed by a rinse'solut:lon introduced through a rinse conduit 52 Once the ~essel has been thorou~hly rinsed, tho xinse solution m~y be drained through the conduit 50 and the next sample ~ay be'~ntroduced through the conduit 46.
~s prev~ously ~ent~oned, the particular type of stxucture ~n wh~ch'the apertures 1~ are ~ounted and the particle analyzer 12 ~s not critical; however; each of the devices will include at least one apexture and will pass the particles in suspension therethrough for measurin~ as described above. In examining white cells, the red cells 'are lysed and in doing so their structure is destroyed releasing their internal chem~cals and protein into the suspension which then is passed through each of the apertures. The ~l~id of the suspenslon or electrolyte itself also contains chemicals and the protein and chemicals ~ay build up on the internal surfaces o~ the apertures 14~ Further, ~s previously mentioned, the ~ 1632~

buildu~ ~y not be uni~o~m in each of the apertures 14 whlch becomes a proble~ when thexe is more thar. a single aperture. As the buildup increases, the size of the aperture decreases ~nd hence the signal will vary S although the same size particle has been passed there-through each time~ The rinse solution does not eliminate this problem, As mentioned above the apertures may be cleaned physically or may be cleared by high bursts of energy applied to the aperture, but these are not wlthout xesultIng or potential problems including loss of time and~o~ energy~
The ape~tures 14 generally ~eing ~or~ed in members of sapphi~e or xub ~hich are then cemented or otherwise aff~xed to the ~pe~-ture tubes or other aperture mounting struct-~re are somewh~t ~r~gile~ ~pplying too high ~ buxSt of eneX~y such ~s a hicJh frequency burst or a capacitor discharge may rupture the aperture itself or the bond between the ape~ture and the mounting structure ~hich will result in erroneous readin~s until xeplacement of the ~erture and~or aperture structure. ~t has been found that a constant energy level applied to the fluid contents in the aperture for a predetermined time wi.ll boil the fluid therein and clean the aperture without affecting the apertu~e material or structure. The constant energy will be a D~C, current applled throu~h each aperture 14.
The switch 44 may be coupled to a control 54 which m~y switch an addit~onal power supply in the supply 48 across each of the leads 38, 40 and 42 to pass the required D.C. current through the apertures to cause the 1 1632~4 apertuXe contents to bo~l ~etween each of the c~cles of passing the sa~ple sUspensxon throuyh the apertures 14~ The switch 44 also may swi~tch the particle analyzer 12 off so that the higher ener~ supplied for the cleaning function S will not damage the an~lyzex or as is generally the case, the analyzer 12 may contain circuitry to protect against transients in the system~ ~n that case the an~lyzer may just remain coupled to the leads 38, ~0 and 42 without regard to the cleaning po~ex supplied~ The cleaning power may be supplied each cycle dur~ny the rlnse portion of the cycle between pasing the sample suspens~ons throu~h the apertures. The cle~n~ng energy also can ~e supplied from a separate power supply~
The invention employs a combined control and power supply cixcuit 156 ~nd is ~ll.ustrated in Figure 2.
The clrcuit 156 ~ould not be separately switched fro~ the from the part~cle analyzer 12 and the increased voltage level cle~ner pulse supplied to the lines 38, A0 and 42 and the apertures 14 would be blocked by the tnternal protection circu.it in the particle analyzer 12~ This protection circuit can include ~arious f~lters and neon protection circuits which wi11 prevent the power cleaniny pulse from damaging the circuitry in the part~cle analyzer 12.

The circuit 156 ~ncludes an input line 158 wh~ch receives a negative trigger pulse 160 whenever the cleaning cycle is initiated. The pulse 160 can be generated automatically following the end of each sample suspension passed through the apertures 14, during the rinse cycle of the particle study device 10, while the ~low is stopped ~ 12 -1 1632~4 in th.e ~pertures 14 to conserye energy, The pulse 160 also can be m~nually gene~ated, The rinse cycle then is continued to flush any bubbles remaining from the boiling of the apertures as well as any debrls boiled a~ay from the suxfaces thereof prior to running the next sample through the apertures 14~ The cleaning pulse 160 can be applled each time the r~nse cycle occurs or once every predetermined number of sample cycles,, Therefore, ln order to maintain the cleanliness and most accurate apert~re surfaces in the ~pe~tures 14 and appllcation of the pulse 160 for each rinse cycle is preferable~ , The trlgger pulse 160 is coupled through a current and power limiting resIstor 162 to the base of an in~erting transisto~ 164~ ne 166 couples the operating power for the control 156,,such'as a D.C~ voltage, through a lo~d resistor 168 to thb collector of the transistor 164.
Th,e negatiVe ~oing tr~g~er pulse 60 produces a posltive pulse 170 at the collector of the tr~nsistor 164. The pulse 170 is coupled on a line 172 over an isolation capacitor 17~ to a t~,mer 176~ The isolation capacitor 174, a diode 178 whlch cl~ps the positiYe portion of the pulse and a load resistor 180 generate a negative trigger'pul~e 182 from the tr~iling edge of the pulse 170. The pulse 182 is coupled to the tlmer 176 to trigger the operation o~ the timer 176.
The timer 176 generates a specific duration pulse 184 which operates both as a control and a switching pulse.
The timing of the timer 176 ~s controlled by a ~i~ed resistor 186, a capacitor 188 and a trimmer resistor or a potentiometer 190. The timer also includes a bypass ~ 163~94 capaci~or 1~2t The duxat~on pulse 184 2s co~pled on a line 194 through a current l.~m~ting resistor 196 to the base of a transistor 1~8 wh~ch i.nverts the duration pulse 184 to switch. or toggle a palr of transistors 200 and 202~ The collector of the transistor 198 also is coupled to the power line 66 through a load resistor 204, The negative pulse fro~ th.e transistor 198 is coupled on a line 206 to the b:~se cf the tran~,istor 200~ The collector of the transistor 200 2s coupled to a ixed D.C. supply yoltage o~, ~or example 300 volts, supplled on a line 208 through a lo~d res;stor 210~ The collector also is coupled by a line 212 to the base o~ the tr~nsisto~ 202. The ~ollector o~ the tr~nsistor 202 is coupled to the llne 208 through a load res~stor 214, lS The leading edge o~ the pulse from the tr~ns~stor 1~8 turns on the transistor 200, which then turns on the t~ans~stox 202 to couple the ~oltage on line 2Q8 to ~ voltage di~idxn~ c~rcu~t on a ltne 216~ The ~oltage d~yidxng cirCu~t inc~udes a pair o~ res~sto~s 218 and 220 connected to an output line 222~ The collector of the txansistor 200 is protected by a ~loc~ing d~ode 224~.
The transisto~ 200 re~a2ns an fax the duration of the pulse from the transistor 198~hich ~intains the transistor 2Q2 conducting which produces the cleaning pulse on the output line 222 for the dur~tion set b~ the timer 176, In this case, utilizing a 300 volt source on the line 208, a 40 millisecond pulse 187 is utilized~ This generates a.
cleaningpulse o~ 300 ~olts h~vin~ a duration of 40 milliseconds on the output line 222 which is coupled to the leads 38, 40 and 42 and hence the apertures 14 ~ 163~94, The determination of the voltage on the line 208 and the duration of the pulse 180 are determined by the watt seconds necessary to boil the fluid in the apertures 14. This is in the main part determined by the size of the aperture in the range from 30 to 500 microns since the major determining factor is the volume and resistance of fluid in the aperture. A minor factor ~o be taken into consideration is the temperature of the ~luid in the aperture which also will affect the amount of energy necessary to boil the fluid. Generating 300 volts for 40 milliseconds results in a power or energy applied to the apertures of approximately .27 watt seconds, since some oE the power is dissipated in the protection circuits in the particle analyzer 12. This figure is chosen ~or the particular device 10 involved and could be any other combination to provide the necessary watt seconds to boil the ~luid in the apertures 14. For instance, instead of 300 volts for 40 milliseconds, a 400 volt pulse could be applied for 30 milliseconds to apply essentially the same power to the aperture 14.
The basic requirement is to provide enough continuous energy to bring the liquid within the aperture to a boil, that is not instantaneously with vaporization but with the production of bubbles.
Other modifications and variations of the present invention are possible in light of the above teachings.
For example, one can provide a resistor in parallel with the normal excitation load current resistance which may be switched into the load circuit to increase the voltage for the cleaning cycle.

Claims (14)

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

1. A method of removing accumulated deposit from the inner wall of the scanning aperture of a particle study device of the type wherein particles of microscopic size are suspended in a liquid having an electrical characteristic substantially different from that of the particles, the liquid being passed through a microscopic aperture of predetermined diameter, volume and configuration formed in an electrically insulating wall, a sensing zone being provided within the aperture by establishing an electrical current therein, the electrical characteristic being changed upon passage of each particle through the sensing zone and the change being detected and monitored, said method comprising the steps of passing the liquid suspension through said aperture, applying sufficient low level energy noncyclically in the form of a constant magnitude level d.c. current continuously for a single predetermined finite length of time to the liquid within the aperture, the level of energy being only sufficient to bring the liquid therein rapidly to a boil generating a plurality of scrubbing bubbles for release in a stream within the liquid at a rate and number sufficient to impinge upon the inner wall removing any accumulated deposits therefrom.

2. A method as defined in claim 1 in which the energy is applied is greater than two tenths watt seconds.

3. A method as defined in claim 1 wherein different samples of particles in suspension cyclically are passed for study through the aperture, and the energy is applied to boil the liquid therein between cycles of passing said particle suspensions through said aperture.

4. A method as defined in any one of claims 1, 2 or 3 wherein movement of the liquid through the aperture is materially reduced while applying said energy to the liquid to conserve cleaning energy applied to the aperture.

5. A method as claimed in claim 1 wherein:
different samples of particles of suspension are passed in cycles through the aperture for study and the energy is applied as a d.c. current at greater than 300 volts for a duration less than one second for each application to the liquid within the aperture but only between the aforementioned cycles, the level of each application of energy being constant over the duration of each application.

6. A method as defined in any one of claims 1, 2 or 3 wherein the energy is applied in the form of a D.C.
current at greater than 300V for less than one second.

7 . A method as defined in claim 3 wherein the energy is applied to boil the liquid therein between cycles of passing said particle suspensions through said aperture.

8. A wall cleaning system for a particle study device of the type wherein particles of microscopic size are suspended in a liquid having an electrical characteristic substantially different from that of the particles, the liquid being passed through a microscopic aperture formed in an electrically insulating wall, a sensing zone being provided within the aperture by establishing an electrical current in the aperture, the electrical characteristic therewithin being changed upon passage of each particle through the sensing zone, the change in said electrical characteristic being detected and monitored, microscopic aperture being of predetermined diameter, volume and configuration, means for passing the liquid through said aperture along with the particles in suspension, liquid always remaining within the aperture, the improvement comprising: power supply means for supplying low level energy in the form of a constant level d.c.
current, means for applying said energy to the liquid within the aperture continuously for a finite duration, said energy being sufficient rapidly to generate a plurality of gaseous scrubbing bubbles against the inner wall which defines the interior of said aperture, said bubbles effecting scrubbing of the inner wall to remove therefrom any deposit which may have accumulated on the surface thereof and control means for applying said energy in a continuous substantially constant level for the predetermined duration, said scrubbing bubbles being generated by effecting rapidly gentle boiling of the liquid within the aperture at a rate sufficient to generate distinct bubbles and insufficient to effect conversion of all said liquid substantially instantaneously into a gaseous state by vaporization.

9. An apparatus as defined in claim 8 in that said power supply energy is greater than two tenths watt seconds.

10. An apparatus as defined in any one of claims 8 or 9 further including means for materially reducing the movement of said liquid through said aperture during application of said energy to said liquid.

11. An apparatus as defined in any one of claims 8 or 9 wherein said energy is applied in the form of a substantially constant magnitude D.C. current.

12. An apparatus as defined in claim 8 or 9 in which said power supply supplies substantially constant D.C. current applied at least at three hundred volts for less than one second.

13. An apparatus as defined in claims 8 or 9 including means for cyclically passing different samples of particles in suspension for study through the aperture, and means for applying the energy to boil the liquid therein between cycles of passing said particle suspensions through said aperture.

14. An apparatus as defined in claims 8 or 9 including means for cyclically passing different samples of particles in suspension for study through the aperture, and means for applying the energy to boil the liquid therein between cycles of passing said particle suspensions through said aperture.