Abstract: A process provides for measuring particles in suspension in a liquid in an particle response analyzing instrument comprising a cytometric flow cell head, wherein the suspension is injected into the head at an injection rate, the head comprises one or several sensors which deliver responses when measuring particles injected therein and which yield a significant response for a set measurement frequency range. The response is processed and used to generate results in the instrument. When a first response is significant, measurements continue at the same injection rate in order to obtain a result thats likely to continue being a significant response during subsequent measurements and, conversely, when the first response is not significant, the injection rate is modified in order to bring the response within a significant response range and to continue with measurements in order to obtain a result.

Abstract: Particulates are trapped by laser beam and brought into contact with electrodes to electrochemically and spectroscopically measure the reaction process thereof.Precise measurement of the process of chemical reactions such as electrochemical and photochemical ones of a single particulate is made possible.

Abstract: An electrode assembly (1) for resistive pulse spectroscopy comprises two flat electrodes (3) substantially equal in size and shape and supported in face-to-face, parallel relationship to one another, and a plate-like fluid-tight insulator (2) positioned between electrodes and extended beyond the periphery of the electrodes with the electrodes (3) being fixed to the insulator (2). Each electrode has a hole (4) extending through the electrode in a central region thereof (4), the holes (4) of the two electrodes (3) being aligned with one another. The insulator (2) having a preformed aperture (16) therein which is located substantially centrally with respect to the holes (4) in the electrodes (3) and has a smaller diameter than the holes, the aperture (16) being located such as to allow a flow of liquid to pass therethrough and through the holes in the electrode.

Abstract: A linear position sensor has first and second output signal generators each of which outputs an output signal in accordance with the position of a detection object. As the detection object moves from an initial position, the output signal of the first output signal generator linearly increases from an output value corresponding to the initial position of the detection object. The output signal of the second output signal generator linearly increases from an output value that is greater than the output value corresponding to the initial position of the detection object. After reaching a maximum value, the output signal of the second output signal generator remains at the maximum value when the detection object further moves to a maximum displacement position.

Abstract: Apparatus for quantitatively measuring groups of magnetic particle. The particles are complexed with substances to be determined and are excited in a magnetic field. The magnetic particles are thereby caused to oscillate at the excitation frequency in the manner of a dipole to create their own fields. These fields are inductively coupled to sensing coils fabricated in a gradiometer configuration. The output signals from the sensing coils are appropriately amplified and processed to provide useful output indications.

Abstract: There is provided a detector for detecting conductive contaminants entrained in an airflow. The detector comprises first and second electrically conductive meshes mounted in a spaced apart relationship to provide an operational gap. Each of the meshes is sized to provide a relatively large surface for substantially intersecting the airflow and is sufficiently porous so as not to substantially attenuate the airflow. The meshes form part of an energizable electric circuit wherein the operational gap constitutes a discontinuity of the circuit. The detector includes a capacitor connected in parallel to the portion of the circuit containing the operational gap for releasing a charge stored in the capacitor through the circuit discontinuity when one of the conductive contaminants simultaneously contacts the first and second meshes. The detector further provides for indication of a discharge of the capacitor and thereby the presence of one of the airborne conductive contaminants entrained in the airflow.

Abstract: In a process for determining the solids content of a gas flow, in particular for regulating the firing of a boiler with coal dust in a coal-fired power plant, electromagnetic waves are sent from a transmitter (20) to a receiver (21) through the solids-laden gas flow. The attenuation of these electromagnetic waves due to the absorption of part of them by the solids is then determined.

Abstract: An on-line somatic cell analyser and a method for measuring a somatic cell count (SCC) are provided. A flow cell is connected to a milking hose and admits a constant volume of sampled milk into the flow chamber. A probe with two electrodes is positioned in a zone of optimal sensing inside the flow chamber, and provides a modulated signal according to the number of sodium ions present in the sample. A control unit receives the modulated signal, generates an ion count, and compares same with a plurality of SCC thresholds for classifying the sample in a quality category. A set of parameters characterizing the respective quality category, as well as the presence of mastitis in the animal, are finally displayed.

Abstract: A disposable first tube (68) extends axially through, and is detachably connected to, an annular main body (10'). An input piezo electric element (38) is attached to a first end of the tubular main body (10'). A second, sensor piezo electric element (40) is attached to the opposite end of the main body (10'). A nozzle (20') having a nozzle passageway (110) and a discharge opening (112) is detachably secured to an outlet end of the first tube (68). A second tube (102) within the first tube (68) delivers a core liquid to the nozzle passageway (110). A sheath liquid is delivered through a space in the first tube (68) surrounding the second tube (102). The nozzle passageway (110) forms the core and sheath liquids into a small diameter jet stream. Electrical energy is delivered to the input piezo electric element (38), to vibrate the nozzle (20') and break the jet stream into droplets.

Abstract: Substrate beads for combinatorial synthesis are selected individually from a mixture by suspending the mixture in an electrically conductive liquid, in a bead selection vessel, causing the liquid to flow at a controlled rate through an aperture in the side wall of a pipette extending through the vessel, and detecting the passage of a bead through the aperture by monitoring an electrical resistance across the aperture. In an alternative embodiment, beads are passed through a tube into a collection passage in which a continuous laminar flow takes place. Detection takes place at the tip of the tube, and, in response to the detection of a bead, the flow through the collection passage is diverted to cause the bead to be deposited. In both cases, the selected bead is deposited into a well of a plate having rows and columns of wells in a rectangular array, while a vacuum is drawn through a filter in the bottom of the well.

Abstract: A method of measuring electrical characteristics of a molecule including providing a first metal contact having a major surface, an insulating layer overlying the major surface of the first metal contact and a second metal contact overlying the insulating layer so as to have an edge spaced a molecular distance from the major surface of the first metal contact. A conductive organic molecule including a metal binding group is coupled between the metal contacts.

Abstract: A method and apparatus are provided for differentiating cells in an automated particle analyzer, such as for use in hematological analysis, by measuring apparent cell size (or volume), membrane integrity and intracellular complexity ("voltaic fragility"). The cells are suspended in a selected reagent mixture including an electrolytic fluid, such as diluent, and if necessary, one or more membrane-modifying agents are selected and mixed in relative quantities in order to selectively alter the membrane structure (i.e., the membrane integrity) of certain cells and thereby enhance cell discrimination. A predetermined dc voltage is applied across a sensing orifice to thereby create a dc electric field within and around the orifice, and the reagent mixture is passed through the center of the orifice.

Abstract: A sensing device and a method for sensing the presence and absence of an object in a machine using the sensing device. The sensing device generally including a sensing mechanism, a resistive element, and a control mechanism communicatively coupled to the sensing mechanism and resistive element. The sensing mechanism being coupled to the resistive element. The method comprising actuating the sensing mechanism so that it senses the location of the object. Recording the voltage across the resistive element in the control mechanism when the sensing mechanism senses the location of the object. Reactuating the sensing mechanism at least one more time to sense the location of the object. Measuring a subsequent voltage across the resistive element when the sensing mechanism is reactuated and comparing the subsequent voltage with the recorded voltage across the resistive element when the resistive element sensed the location of the object.

Abstract: A method and apparatus for detecting and measuring suspended solid particles in a molten metal, even if the metal also contains liquid and/or gaseous inclusions. The method involves moving molten metal through an orifice of predetermined hydrodynamic diameter provided in an electrically non-conductive barrier. As the molten metal is moved through the orifice, a current path is established by passing a current through the orifice from electrodes positioned on opposite sides of the barrier. Changes in voltage of the current are measured as the metal is drawn through the orifice, and the number of particles suspended in said metal drawn through the orifice is detected from the voltage changes.

Abstract: A disposable first tube (68) extends axially through, and is detachably connected to, an annular main body (10'). An input piezo electric element (38) is attached to a first end of the tubular main body (10'). A second, sensor piezo electric element (40) is attached to the opposite end of the main body (10'). A nozzle (20') having a nozzle passageway (110) and a discharge opening (112) is detachably secured to an outlet end of the first tube (68). A second tube (102) within the first tube (68) delivers a core liquid to the nozzle passageway (110). A sheath liquid is delivered through a space in the first tube (68) surrounding the second tube (102). The nozzle passageway (110) forms the core and sheath liquids into a small diameter jet stream. Electrical energy is delivered to the input piezo electric element (38), to vibrate the nozzle (20') and break the jet stream into droplets.

Abstract: A system diagnoses the operability of a rotating electrical apparatus such as a reactor coolant pump (RCP) motor. The RCP motor includes a rotatable shaft, a stator, a bearing assembly and a bearing insulator. The bearing assembly electrically contacts the rotatable shaft and the bearing insulator at least partially electrically insulates the rotatable shaft and the bearing assembly from the stator. The system includes a shaft transformer and voltage source for inducing a voltage in the rotatable shaft; a variable resistor in parallel with the bearing insulator having first and second resistances; an analog-to-digital converter for sensing a first voltage associated with the first resistance and a second voltage associated with the second resistance; and means for determining the operability or the impedance of the bearing insulator from the first and second voltages and the second resistance.

Abstract: A system for the remote measurement of the protection ground associated with an electrical system, and which employs a telephone line for the transmission of the control signals and the results of the measurement. The system includes a centralized ground measuring device (1) having two reference grounds (11, 12) which are connected to the soil, a line selector (2) and remote actuators (3) which also include two ground terminals which are connected to the soil and which may be located near the region in which the measurement is required.

Abstract: A molten metal inclusion sensor probe which is immersed in the molten metal and detects inclusions therein by the electric sensing zone method comprises inner and outer steel tubes disposed one within the other to form an annular gas containing space, the tubes being spaced apart from one another by electrically insulating spacing rings between the two tubes at or adjacent to the opposite ends thereof. The space is vented to the exterior of the outer tube, or in the case of a one-shot probe to the interior of the inner tube. A sensing zone member, which may also act to space the tube lower ends, is mounted by the tubes at their lower ends and provides the sensing zone orifice. In some embodiments the seals between the sensing zone member and the tube lower ends are maintained despite differences in expansion coefficients of the materials.

Abstract: A system for monitoring debris in a fluid by detecting electrostatic charges associated with the fluid. Both the electrostatic characteristic of the fluid and of the debris are sensed and then separated by a processor that compares their mobility. The monitoring system may be used to detect debris in any fluid capable of being electrostatically charged, such as oil and superheated steam.

Abstract: An apparatus for position detection using signal patterns created by use of a fixed disk having three conductive patterns disposed thereon. The first and second patterns are annular conductive paths which are concentric with respect to one another and the third pattern consists of radially extending conductive portions which are electrically connected to the second pattern. A brush carried by a rotating member whose position is sought to be determined is maintained in contact with the first and third pattern. In this manner an electrical signal variation is encountered as the radially extending conductive portions are encountered by the brush upon rotation thereof. This variation is thus correlated to the pattern defined on the third pattern. A microprocessor is used to add and subtract signals as the brush is rotated from a reference position based upon an indicia of motor direction.

Abstract: A sensing device and a method for sensing the presence and absence of an object in a machine using the sensing device. The sensing device generally including a sensing mechanism, a resistive element, and a control mechanism communicatively coupled to the sensing mechanism and resistive element. The sensing mechanism being coupled to the resistive element. The method comprising actuating the sensing mechanism so that it senses the location of the object. Recording the voltage across the resistive element in the control mechanism when the sensing mechanism senses the location of the object. Reactuating the sensing mechanism at least one more time to sense the location of the object. Measuring a subsequent voltage across the resistive element when the sensing mechanism is reactuated and comparing the subsequent voltage with the recorded voltage across the resistive element when the resistive element sensed the location of the object.

Abstract: A voltage follower is incorporated within a molded electrical connector interface of a position sensor in a way that does not detract from the dimensions or the performance of the finished sensor. The incorporation of the voltage follower into the housing of the variable resistor provides several advantages over the prior art, including: an immunity to sag; substantially reduced sensitivity to noisy contactors; and short lead length and low output impedance, both of which result in reduced interference from external source.

Abstract: Particle measuring apparatus 1 comprising slide plate 3 set between tanks 2a and 2b and having through-holes 8 to 11 passing through slide plate 3 and a pair of electrodes 4a and 4b, wherein through-holes 8 to 11 on slide plate 3 are formed by a group of through-holes with different diameters. When one of the through-holes 8 to 11 is brought to a position corresponding to connective holes 2c and 2d by driving unit 7, particle distribution is measured and analyzed in accordance with the electrical impedance when a sample suspension passes through the through-hole.

Abstract: A method of determining cell membrane strength is disclosed, using focused light of selected frequency and energy density. The method is also useful in diagnosing the presence of certain diseases in cells, by comparing the membrane strength of cells exposed to cell-characteristic altering drugs to the membrane strength of a control group of cells.

Abstract: The Integrated Grid Particle Impact Detector (IGMID) uses an integrated semiconductor grid system to detect hypervelocity article impacts on space vehicles and to indirectly determine article diameter of impacting particles. The detector consists of multiple sets of parallel aluminum electrical paths. The first set of parallel aluminum electrical paths is located on the top surface of the detector. The second and subsequent sets are located some distance below the top surface of the detector with the paths being perpendicular and/or parallel to the first set of paths. When a particle traveling at hypervelocity impacts the detector one or more detector paths will be vaporized, resulting in an electrically open path. This in turn will result in the output of the n-type and p-type CMOS circuits to change state. Using standard CMOS VLSI design techniques, specific electrically open grid paths can be identified.

Abstract: A circuit is provided for generating a voltage signal corresponding to a wiper position in a linear or circular potentiometer having an open wiper position or an open wiper angle, respectively. The voltage signal circuit includes provisions for determining when a wiper is in an open wiper position or angle region. When the circuit is used with a freely rotating circular potentiometer, the voltage signal may be used to determine wind direction. The circuit includes a voltage source coupled to a conducting element and a wiper. A pulling resistor driven by an operational amplifier is coupled to the wiper and voltage source to provide an identifiable voltage signal corresponding to the open wiper state during rotation through the open wiper angle region.

Abstract: Method and apparatus for obtaining the average aspect ratio of non-spherical particles in suspension. The particles are caused to orient generally in one direction and the conductivity of the particles are measured in such direction while simultaneously measuring the conductivity of the particles in a traverse direction. The difference between the two conductivity measurements is indicative of the average aspect ratio of the particles in suspension.

Abstract: A calibration method for a potentiometer which provides indicia reflecting an accurate indication of actual electrical resistance throughout the resistive range of a particular potentiometer. The indicia includes a number of graduation marks or symbols having a range and spacing unique to the resistive characteristics of the particular potentiometer. The indicia is fixed with respect to a known location associated with the particular potentiometer. The range and spacing of the indicia graduations is derived from measured resistance values at predetermined locations along the resistive member of the particular potentiometer.

Abstract: A microphotolysis and microphotoanalysis process applying precise quantities of focused light energy to a precise microscopic area of a very small cell sample to activate a chemical agent which permits measurement of cell fragility.

Abstract: A method of making a count probe for counting particles comprises the following steps. A count wafer is formed along with a core member having an opening for accepting the count wafer. The count wafer is applied to the opening in the core member to form an interference fit between the count wafer and the core member. After application of the count wafer to the opening in the core member, the core member is annealed to relieve stress in the core member.

Abstract: A method and apparatus for continuously sorting living cells from a mixture of many unlike cells to obtain separate populations of like cells. The invention comprises cell and fluid intake ports, a cell deflection chamber, and a series of output vacuum pumps attached to a like number of collection reservoirs. The cell intake section is a two-stage system that first mixes the incoming cells with a deionized, buffered, processing medium then sheathes the output stream with a centering carrier fluid. An expansion chamber contains one or more electrodes connected to one or more RF generators that act upon the passing cells so that they are fanned out within the expansion chamber according to their size, physical construction, chemical composition and electronic properties. Vacuum pumps draw the fluids through the system and deposit the sorted cells in separate reservoirs.

Abstract: A system and method for digitally detecting the presence of analyte particles within a sample is disclosed herein. Each analyte particle is disposed to emit an optical response upon illumination in a known manner. The digital analyte detection system includes optical apparatus for illuminating a multiplicity of distinct pixel regions within the sample so as to induce each of the analyte particles included therein to emit at least one optical response. The pixel regions are dimensioned such that the number of analyte particles included within each region is less than a maximum detection threshold proportional to variability of the optical responses.The digital detection system further includes apparatus for measuring the emitted signal emitted from each pixel region. A data processing network receives the measurements of the emitted signals and, based on the measurements, counts the number of analyte particles within each pixel region so as to determine the number of analyte particles within the sample.

Abstract: A flow cytometer utilizes multiple lasers for excitation and respective fluorescence of identified dyes bonded to specific cells or events to identify and verify multiple events to be sorted from a sheath flow and droplet stream. Once identified, verified and timed in the sheath flow, each event is independently tagged upon separation from the flow by an electrical charge of +60, +120, or +180 volts and passed through oppositely charged deflection plates with ground planes to yield a focused six way deflection of at least six events in a narrow plane.

Abstract: A circuit for generating a linear current proportional to the displacement of the movable member of a transducer receives an undetermined supply voltage from a monitoring circuit which has a relatively high internal resistance. The circuit is provided with two parallel current paths with one path including a resistive potentiometer strip and other path including a transistor and resistor connected in series. The movable member of the transducer has an electrical contact member attached thereto with the contact member having one end making contact with the resistive potentiometer strip and with the other end thereof making contact with a conductive strip which is connected to the gate of the transistor so that the current drawn by the circuit will be linearly related to the movement of the movable member.

Abstract: A Faraday cage enclosing the flow chamber of a cytometer and ground planes associated with each field deflection plate in concert therewith inhibit electric fields from varying the charge on designated events/droplets and further concentrates and increases forces applied to a charged event passing therethrough for accurate focus thereof while concomitantly inhibiting a potential shock hazard.

Abstract: An electrode structure of a metallic particle detecting sensor capable of detecting with high efficiency metal powders floating in a wide range in an oil tank. The electrode structure is formed by opposing, on a substrate, a pair of electrodes (1, 2), formed of thin film metals of such as Ta, W, Pt, Cr, Au or the like, having combed (toothed) structures with their respective teeth being meshed or interdigitated with each other.

Abstract: A method of making a count probe comprises the following steps. A member is made having a conduit and an opening. A wafer is made including an aperture. The wafer is removably inserted into the opening such that the wafer is removably retained within the opening by an interference fit between the wafer and the member.

Abstract: Device for detecting a position of an actuator on a printing press includes two potentiometers having respective wipers connected to the actuator and driven with mutually different transmission ratios, the two potentiometers being serially connected in a measuring circuit, and an evaluation device connected to the measuring circuit for receiving signals therefrom corresponding to measuring-circuit voltages of the potentiometers and for determining therefrom the position of the actuator.

Abstract: A particle count probe comprises a wafer having an aperture. A first member is provided having a fluid passageway. A second member is removably mounted to the first member, and cooperates with the first member and the wafer to position the wafer so that the aperture of the wafer aligns with the fluid passageway.

Abstract: An angular position sensor having at least one resistive track which is circular, for example, and at least one cursor. The cursor is adapted to move while in electric contact with the track. The track is closed and continuous and has at least two electric access points. The sensor cooperates with an arrangement for applying separate predetermined electric potentials to the access points and with an arrangement for measuring the resulting electric potential at one of the access points. The cursor is therefore able to rotate through a complete turn without leaving the one resistive track. All angles can be measured and rotation through several turns is possible.

Abstract: An apparatus and method for counting and measuring the size of particles, particularly in the range 10 nanometers to 10 micrometers in diameter, and for measuring both the size and deformability of deformable particles, primarily red and white blood cells, in which are provided, in combination: --a membrane 10 containing multiple apertures 12 providing the only means of continuity between two fluid reservoirs 16 and 18; electrodes 20 and 22 mounted one in each reservoir; and another electrode 14 situated inside each aperture, forming part of the wall. The position of electrode 14 effectively divides the aperture into two aperture regions 28 and 30 having similar electrical resistance. In use, a conductive fluid containing the particles is placed into reservoir 16 and aspirated through the apertures into reservoir 18. A voltage V.sub.in applied between electrodes 20 and 22, causes a corresponding voltage V.sub.out at each electrode 14.

Abstract: A particle counting apparatus for counting a total particle counting value contained in a liquid sample comprising, a flow cell in which the liquid sample flows, a light source for irradiating a light beam to the sample liquid in the flow cell, a detector for detecting pulse-wise signal scattered from the particles by the irradiating of the light beam, and a computer for obtaining the total particle counting value contained in the liquid sample as a counting value measured when the top end of the liquid sample is irradiated with the light beam and the plural particles in the top end does not overlapped in the light beam, multiplied by a coefficient.

Abstract: In a method and apparatus for examining samples comprising individual objects (28) of macromolecular or similar size, or smaller, an instrument element (14) comprises a substrate (16) overlaid with a thin film layer (18) of a material that is electrically conductive and/or at last partly optically opaque. A discontinuity comprising an aperture (26) or an asperity is formed in or on the element (14) in a known location, and the sample (28) is brought to this discontinuity so that it is not necessary to search for the sample by scanning. Energy (e.g. electrical energy or light) is applied to the element (14) and, with the latter and the sample in intimate association, e.g. with the sample inside the aperture (26), changes in the radiation from the sample site resulting from the presence of the sample are detected.

Abstract: An apparatus for detecting corpuscles such as blood cells. The apparatus has an aperture and a constant-current source that supplies an electrical current to the aperture for detection of corpuscles. When corpuscles to be investigated pass through the aperture, the electrical impedance changes, producing a signal (herein referred to as the corpuscle signal). The apparatus further includes a pseudo signal-generating means for producing a pseudo signal in the form of pulses. The pseudo signal has a peak value proportional to the amplitude of the input current and is equivalent to the corpuscle signal detected when the corpuscles pass through the aperture. A signal selector means is disposed among the aperture, the constant-current source, and the pseudo signal-generating means. The signal selector means assumes either a first state or a second state.

Abstract: A sheet size detection device for detecting a size of sheets which are held in a cassette body comprises a first guide member for defining the position of the sheets which are held in the body of the cassette, in a first direction of the sheets, the first guide member being movable in accordance with the size of sheets, a second guide member for defining the position of the sheets, in a second direction of the sheets, the second direction being orthogonal to the first direction, the second guide member being movable in accordance with the size of sheets, a first arm having a first resistor and movable with the first guide member, a second arm having a second resistor and movable with the second guide member, the first and second resistors constituting a variable resistor, and a size detector for detecting the size of the sheets on the basis of the resistance value of the variable resistor.

Abstract: A system and method for digitally detecting the presence of analyte particles within a sample. Each analyte particle is disposed to emit an optical response upon illumination in a known manner. The digital analyte detection system includes optical apparatus for illuminating a multiplicity of distinct pixel regions within the sample so as to induce each of the analyte particles included therein to emit at least one optical response. The pixel regions are dimensioned such that the number of analyte particles included within each region is less than a maximum detection threshold proportional to variability of the optical responses. The digital detection system further includes apparatus for measuring the emitted signal emitted from each pixel region. A data processing network receives the measurements of the emitted signals and, based on the measurements, counts the number of analyte particles within each pixel region so as to determine the number of analyte particles within the sample.

Abstract: A circuit for monitoring contact between the resistance track and the wiper of a potentiometer provides for an adjustable DC voltage which can be tapped from the wiper. An alternating voltage is applied to the wiper via a series connection of a resistor and a capacitor. The resistance is greater than the impedance formed by the capacitance of the capacitor plus one-fourth of the track resistance. Circuitry for rectifying the voltage connects to a junction point between the resistor and the capacitor.

Abstract: The particle counting apparatus is intended to count the number of particles such as blood corpuscles, by passing through a minute aperture, and detecting the particles electrically. In this particle counting apparatus, the liquid specimen is passed into the minute aperture at a specific flow rate by means of a liquid specimen discharge device, and the particles are counted preliminarily, and the dilution proportion of the liquid specimen is determined when the value of this preceding counting is over a specific value. According to this dilution proportion, the liquid specimen discharge device and diluent discharge device discharge so that the flow rates may be as specified, and the mixture is passed through the minute aperture for main counting. In this way, if there are many particles, simultaneous passes do not occur in the detecting region.

Abstract: A method of correcting first approximation data obtained from a conventional electrozone particle sensing apparatus includes steps for calculating factors for correcting for binary and tertiary coincidences, from the raw data and from physical characteristics of the sensing equipment, to yield an accurate measure of particle distribution within the sample.

Abstract: A particle detector is designed to detect particles such as cells and blood corpuscles, and this particle detector includes means for passing and recovering a multilayer flow consisting of an inner layer A of conductive liquid specimen, a middle layer B of conductive first sheath liquid, and an outer layer C of nonconductive second sheath liquid surrounding them, in an orifice 12, and a pair of electrodes disposed on both sides of the orifice so as to contact the conductive liquid respectively. A detector circuit 44 is connected to the pair of electrodes so as to detect a particle signal on the basis of difference of electric impedance between the electrodes. The diameter of the orifice 12 is substantially the diameter of the middle layer. By varying the flow rate balance of the conductive liquids and nonconductive liquid, the diameter of the middle layer may be freely changed. Accordingly, the diameter of the orifice may be apparently changed as desired.