US3546583A - Electrode assembly for detecting particles in fluid suspension - Google Patents

Electrode assembly for detecting particles in fluid suspension Download PDF

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US3546583A
US3546583A US758561A US3546583DA US3546583A US 3546583 A US3546583 A US 3546583A US 758561 A US758561 A US 758561A US 3546583D A US3546583D A US 3546583DA US 3546583 A US3546583 A US 3546583A
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particles
nozzle
electrode assembly
fluid
droplet
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US758561A
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James D Perrings
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US Atomic Energy Commission (AEC)
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N15/00—Investigating characteristics of particles; Investigating permeability, pore-volume, or surface-area of porous materials
    • G01N15/10—Investigating individual particles
    • G01N2015/1028—

Definitions

  • Such an electrode assembly is used in a particle counter or a particle separator for sorting minute particles present in a suspension fluid in accordance with a selected characteristic such as size, conductivity or any other characteristic that can be translated into an analogous electrical quantity.
  • An improved form of the electrodes in the sensor prevents spurious modulations of the current due to gas bubble accumulation at the electrodes from interferring with the sensor signal.
  • each droplet will be deflected an amount dependent upon its particular charge and because the charge depends upon the information obtained at the sensing nozzle, the deflection is in accordance with the desired characteristic.
  • the present invention also relates to a device for counting particles suspended in a fluid as shown by Coulter Pat. 2,656,508 wherein the sensing nozzle is a short dielectric duct or aperture of appropriate cross section through which the suspension fluid is forced to flow and a pair of electrodes are disposed on opposite ends of the aperture in contact with the fluid.
  • the electrical resistance between the electrodes is affected by the presence and size of a particle in the fluid within the duct.
  • Detectors, counters, and sorters of this type are useful in medical research. Particles in body fluids such as blood cells may be counted or actually sorted in accordance with size or other characteristics. The particles to be counted or sorted are usually suspended in a liquid such as a saline solution.
  • a primary objective of the present invention is to provide an electrode assembly which is not susceptible to the generation and release of gas bubbles in a manner which gives rise to electrical signals confusingly similar to the signals generated by particles of interest.
  • FIG. 1 is a schematic diagram of a particle separator incorporating the electrode assembly of this invention.
  • FIG. 2 is an exploded cross-sectional view of the electrode assembly used in the prior art.
  • FIG. 3 is an exploded cross-sectional view of an improved electrode assembly.
  • FIG. 1 A particle separator that includes the sensing element of the present invention is shown in FIG. 1.
  • Liquid containing particles in suspension is stored in any suitable container 5.
  • Means for pressurizing the fluid may be any suitable means such as a pump in the outlet of the container 5 or gas pressure means 3 and controllable pressure reducing means 4.
  • the fluid container 5 is connected by a strainer 6 and pipe 7 to nozzle 10.
  • Strainer 6 is provided to pass particles within the range of interest and to stop particles of gross size from clogging the system.
  • the fluid in passing through the nozzle may be jetted and separated into droplets by suitably vibrating the nozzle, it is preferred to apply pulsations directly to the fluid and avoid vibration of the nozzle.
  • This method of drop formation is accomplished by resilient acoustic insulation 9 between nozzle 10 and acoustic coupler 8.
  • the acoustic coupler 8 is directly driven by an electrically driven vibrator 9 such as a piezoelectric driver 2 which in turn is energized by adjustable frequency generator 1.
  • the frequency and amplitude of the output of generator 1 is correlated with the viscosity and velocity of fluid passing through the nozzle in order to produce equal size discreet droplets from the resulting jet.
  • the sensor element 14 is shown associated with the fluid containing system at the outlet of the nozzle. At the outlet of the nozzle the fluid has obtained its jet cross section and velocity so that the transport time between the passage of the fluid through the sensor and the point along the path of breakup of the jet into droplets is a fixed and calculable quality.
  • the sensor 14 is selected to be responsive to the particular characteristic of the particles of interest, i.e., it Will be responsive to particle size, electrical conductivity, and any other characteristic which is capable of transformation into an electrical quantity.
  • the electric pulse generated in the sensor by the passage of a particle is amplified and shaped by proportional pulse generator 13.
  • the utilization of the pulse to detect the associated droplet is delayed an amount of time equal to the time consumed by the fluid containing the particle in traversing the distance from the sensor to the point where the liquid is detaching from the jet as a droplet.
  • the pulse after appropriate delay in delay element 12, controls the amplitude and time of generation of droplet charging potentials. More specifically, each droplet or group of droplets is charged by collar pulse generator 11 in response to the delayed pulse from delay element 12.
  • the collar pulse generator 11 produces the proper potential which is inductively impressed along the jet stream between charging collar 15 and sensor 14.
  • the charging collar surrounds the jet stream at a location which includes the droplet separation zone.
  • the potential which exists between the collar and the sensor at the time of Separa tion of the droplet determines the bound charge on the droplet.
  • the droplet or train of droplets continues in the direction of the jet stream until it passes between defleeting plates 16 and 17.
  • Deflecting plates 16 and 17 are energized with a steady-state potential of suitable magnitude. Each droplet in passing between the deflection plates is deflected by an amount determined by the charge on the droplet.
  • the droplets are thus segregated in accordance with the amount of a selected characteristic and can be collected in any desirable manner.
  • FIG. 2 A sensing nozzle of the prior art is shown in FIG. 2.
  • the nozzle element 10 constitutes one electrode of a suitable noncorrosive metal such as stainless steel, platinum or gold.
  • a dielectric disc 19 having an aperture 20 is affixed in any convenient manner in liquid leak-proof fashion to the end of the nozzle element 10.
  • a second electrode 21 having an aperture 22, the walls of which contact the liquid, is afiixed to the downstream face of the dielectric disc 19 also in liquid leak-proof fashion. Liquid is forced into the nozzle by inlet tube 7 and is vibrated in the manner described above.
  • the nozzle element 10 and the end electrode 21 are impressed with a difference in potential to detect changes in electrical conductivity as particles pass through the dielectric disc 19. As explained above, the electric charge across the solution causes bubbles to be formed and accumulated at the elec trodes 19 and 21. Periodically the bubble accumulation is washed through the apertures and a false signal generated that masks the true signal of particles passing through the apertures.
  • the nozzle element constitutes one electrode of a suitable noncorrosive metal such as stainless steel, platinum or gold.
  • a dielectric disc 19 having an aperture and recessed cavities 23 and 24 is affixed in any convenient manner in liquid leak-proof fashion to the end of the nozzle element 10.
  • a second electrode 21 having an aperture 22 and recessed cavity 25 is affixed to the downstream face of the dielectric disc 19 also in liquid leak-proof fashion.
  • liquid is forced into the nozzle by inlet tube 7 and is vibrated.
  • the nozzle element 10 and the end electrode 21 are impressed with a difference in potential to detect changes in electrical conductivity as particles pass through the dielectric disc 19.
  • the gas bubble accumulation caused by the charge across the solution fills the recessed cavities before being periodically washed through the apertures.
  • the bubble accumulation is of a greater magnitude than prior art devices because a greater portion of the electrodes 10 and 21 are exposed to the liquid and the recessed cavities 22, 24 and 25 allow more room for accumulation. Consequently, when the bubble accumulation is periodically washed through the device the pulse generated will be large and outside the range of the particles being investigated. In addition, the periodic washing through of bubbles is less frequent. This allows an easy separation of the false signals from those generated by true particles.
  • Various forms and shapes of the recessed cavities are contemplated dependent upon the size of the particles being investigated, the accuracy desired and the instrumentation to be used.
  • an electrode assembly sensor which eliminates spurious signals caused by gas bubbles formed on the electrodes, said assembly having first and second aligned electrodes each having a central aligned aperture separated by a dielectric spacer element also having a central aperture, the dielectric element having a countersunk seat on each end portion of larger diameter than the aperture to accommodate the accumulation of gas bubbles which are periodically washed through the device, the bubbles so accumulated being distinctly larger than the small particles in suspension so that the sensor generated signal triggered by the passage of the bubbles is identifiably different from that generated by the passage of a particle.

Description

Dec. 8,1970.
ELECTRODE ASSEMBLY FOR DETECTING PARTICLES IN FLUID SUSPENSION Filed Sept. 9, 1968 J. D. PERRINGS /Z ACOUSTIC AcousIrIc DRIvER DRIvER GENERATDR Va 3 4 9 GAs PRESSURE /0 PRESSURE REDUCING MEANS MEANS [/2 COLLAR PROPORTIONAL PULSE DELAY PULSE GENERAFR GENERATOR SENSOR 4 4?- r0 PULSE r0 PULSE GENERATOR v GENERATOR Fig. 2
7470, PRIOR ART T0 PULSE 2 GENE/M701? j INvINToR.
James 0. Parr/figs BY United States Patent 3,546,583 ELECTRODE ASSEMBLY FOR DETECTING PARTICLES IN FLUID SUSPENSION James D. Perrings, Los Alamos, N. Mex., assignor to the United States of America as represented by the United States Atomic Energy Commission Filed Sept. 9, 1968, Ser. No. 758,561 Int. Cl. G01n 27/00 US. Cl. 324--71 4 Claims ABSTRACT OF THE DISCLOSURE An improvement in an electrode assembly for detecting particles. Such an electrode assembly is used in a particle counter or a particle separator for sorting minute particles present in a suspension fluid in accordance with a selected characteristic such as size, conductivity or any other characteristic that can be translated into an analogous electrical quantity. An improved form of the electrodes in the sensor prevents spurious modulations of the current due to gas bubble accumulation at the electrodes from interferring with the sensor signal.
The invention described herein was made in the course of, or under, a contract with the US. Atomic Energy Commission.
Apparatus for sorting particles suspended in a liquid in accord with size or other desired characteristic is shown and described in US. Pat. No. 3,380,584, issued Apr. 30, 1968, to Mack I. Fulwyler. The sensing and sorting of particles suspended in a liquid is accomplished by passing the liquid at high speed through a sensing nozzle, followed by the fluid passing through a charging collar, then between two deflecting plates and finally into receptacles in accordance with the deflection imposed at the deflection plates. The fluid is formed into droplets at the sensing nOZZle and the sensor detects the information concerning the characteristics of each droplet that will later be used for sorting. As the droplet passes the charging collar an electric charge is imposed on each droplet in accordance with the information detected at the sensing nozzle. Then as the droplets pass the deflection plates each droplet will be deflected an amount dependent upon its particular charge and because the charge depends upon the information obtained at the sensing nozzle, the deflection is in accordance with the desired characteristic.
The present invention also relates to a device for counting particles suspended in a fluid as shown by Coulter Pat. 2,656,508 wherein the sensing nozzle is a short dielectric duct or aperture of appropriate cross section through which the suspension fluid is forced to flow and a pair of electrodes are disposed on opposite ends of the aperture in contact with the fluid. The electrical resistance between the electrodes is affected by the presence and size of a particle in the fluid within the duct.
Detectors, counters, and sorters of this type are useful in medical research. Particles in body fluids such as blood cells may be counted or actually sorted in accordance with size or other characteristics. The particles to be counted or sorted are usually suspended in a liquid such as a saline solution.
Early use of this type of device indicated that noise or static was masking the true signal. Investigation of the source of static led to the discovery that the liquid was being dissociated into atomic gas particles by the potential across the dielectric disc from the outer electrode to the nozzle element. The impression of an electric charge across an aqueous solution results in the decomposition of water into hydrogen and oxygen gases which migrate to and are collected on the electrodes. Hydrogen is a cation being ice positively charged and migrates along electropotential lines to deposit on the cathode. The oxygen, conversely, is an anion and collects as atoms of oxygen forming minute bubbles at the anode. The atomic gas rapidly accumulates on the exposed surface of the electrode as a growing bubble causing a corresponding increased resistance, and upon sufficient accumulation is washed through the aperture, thus generating a current pulse similar to that caused by a real particle.
Accordingly, a primary objective of the present invention is to provide an electrode assembly which is not susceptible to the generation and release of gas bubbles in a manner which gives rise to electrical signals confusingly similar to the signals generated by particles of interest.
Other objectives and advantages of the present invention will become apparent as the following description is read with reference to the drawings.
Referring to the drawings,
FIG. 1 is a schematic diagram of a particle separator incorporating the electrode assembly of this invention.
FIG. 2 is an exploded cross-sectional view of the electrode assembly used in the prior art.
FIG. 3 is an exploded cross-sectional view of an improved electrode assembly.
A particle separator that includes the sensing element of the present invention is shown in FIG. 1. Liquid containing particles in suspension is stored in any suitable container 5. Means for pressurizing the fluid may be any suitable means such as a pump in the outlet of the container 5 or gas pressure means 3 and controllable pressure reducing means 4.
The fluid container 5 is connected by a strainer 6 and pipe 7 to nozzle 10. Strainer 6 is provided to pass particles within the range of interest and to stop particles of gross size from clogging the system. Although the fluid in passing through the nozzle may be jetted and separated into droplets by suitably vibrating the nozzle, it is preferred to apply pulsations directly to the fluid and avoid vibration of the nozzle. This method of drop formation is accomplished by resilient acoustic insulation 9 between nozzle 10 and acoustic coupler 8. The acoustic coupler 8 is directly driven by an electrically driven vibrator 9 such as a piezoelectric driver 2 which in turn is energized by adjustable frequency generator 1.
The frequency and amplitude of the output of generator 1 is correlated with the viscosity and velocity of fluid passing through the nozzle in order to produce equal size discreet droplets from the resulting jet.
The sensor element 14 is shown associated with the fluid containing system at the outlet of the nozzle. At the outlet of the nozzle the fluid has obtained its jet cross section and velocity so that the transport time between the passage of the fluid through the sensor and the point along the path of breakup of the jet into droplets is a fixed and calculable quality.
The sensor 14 is selected to be responsive to the particular characteristic of the particles of interest, i.e., it Will be responsive to particle size, electrical conductivity, and any other characteristic which is capable of transformation into an electrical quantity. The electric pulse generated in the sensor by the passage of a particle is amplified and shaped by proportional pulse generator 13. The utilization of the pulse to detect the associated droplet is delayed an amount of time equal to the time consumed by the fluid containing the particle in traversing the distance from the sensor to the point where the liquid is detaching from the jet as a droplet. The pulse, after appropriate delay in delay element 12, controls the amplitude and time of generation of droplet charging potentials. More specifically, each droplet or group of droplets is charged by collar pulse generator 11 in response to the delayed pulse from delay element 12. The collar pulse generator 11 produces the proper potential which is inductively impressed along the jet stream between charging collar 15 and sensor 14. The charging collar surrounds the jet stream at a location which includes the droplet separation zone. Thus, the potential which exists between the collar and the sensor at the time of Separa tion of the droplet determines the bound charge on the droplet. The droplet or train of droplets continues in the direction of the jet stream until it passes between defleeting plates 16 and 17. Deflecting plates 16 and 17 are energized with a steady-state potential of suitable magnitude. Each droplet in passing between the deflection plates is deflected by an amount determined by the charge on the droplet. The droplets are thus segregated in accordance with the amount of a selected characteristic and can be collected in any desirable manner.
A sensing nozzle of the prior art is shown in FIG. 2. The nozzle element 10 constitutes one electrode of a suitable noncorrosive metal such as stainless steel, platinum or gold. A dielectric disc 19 having an aperture 20 is affixed in any convenient manner in liquid leak-proof fashion to the end of the nozzle element 10. A second electrode 21 having an aperture 22, the walls of which contact the liquid, is afiixed to the downstream face of the dielectric disc 19 also in liquid leak-proof fashion. Liquid is forced into the nozzle by inlet tube 7 and is vibrated in the manner described above. The nozzle element 10 and the end electrode 21 are impressed with a difference in potential to detect changes in electrical conductivity as particles pass through the dielectric disc 19. As explained above, the electric charge across the solution causes bubbles to be formed and accumulated at the elec trodes 19 and 21. Periodically the bubble accumulation is washed through the apertures and a false signal generated that masks the true signal of particles passing through the apertures.
It is not considered possible to prevent the formation of gas bubbles, but by causing the gas bubbles to be formed so that the electrical pulse they generate is of a range outside the range of the particles of interest it is possible to eliminate the masking effect. Hence, the signal-to-noise ratio is greatly improved and not only is the accuracy of the device improved but the range of particle size to be investigated is increased.
One embodiment of the improved nozzle assembly 14 incorporating applicants invention is shown in FIG. 3. The nozzle element constitutes one electrode of a suitable noncorrosive metal such as stainless steel, platinum or gold. A dielectric disc 19 having an aperture and recessed cavities 23 and 24 is affixed in any convenient manner in liquid leak-proof fashion to the end of the nozzle element 10. A second electrode 21 having an aperture 22 and recessed cavity 25 is affixed to the downstream face of the dielectric disc 19 also in liquid leak-proof fashion. As in the prior art, liquid is forced into the nozzle by inlet tube 7 and is vibrated. The nozzle element 10 and the end electrode 21 are impressed with a difference in potential to detect changes in electrical conductivity as particles pass through the dielectric disc 19. The gas bubble accumulation caused by the charge across the solution fills the recessed cavities before being periodically washed through the apertures. The bubble accumulation is of a greater magnitude than prior art devices because a greater portion of the electrodes 10 and 21 are exposed to the liquid and the recessed cavities 22, 24 and 25 allow more room for accumulation. Consequently, when the bubble accumulation is periodically washed through the device the pulse generated will be large and outside the range of the particles being investigated. In addition, the periodic washing through of bubbles is less frequent. This allows an easy separation of the false signals from those generated by true particles. Various forms and shapes of the recessed cavities are contemplated dependent upon the size of the particles being investigated, the accuracy desired and the instrumentation to be used.
What I claim is:
1. In an apparatus for sensing small particles suspended in a fiuid medium having sensor means for generating an analog electrical signal in response to the passage of a particle, the improvement comprising an electrode assembly sensor which eliminates spurious signals caused by gas bubbles formed on the electrodes, said assembly having first and second aligned electrodes each having a central aligned aperture separated by a dielectric spacer element also having a central aperture, the dielectric element having a countersunk seat on each end portion of larger diameter than the aperture to accommodate the accumulation of gas bubbles which are periodically washed through the device, the bubbles so accumulated being distinctly larger than the small particles in suspension so that the sensor generated signal triggered by the passage of the bubbles is identifiably different from that generated by the passage of a particle.
2. The improved electrode assembly of claim 1 wherein the second electrode has a centrally disposed countersunk seat located on an end portion of said electrode surrounding the aperture and facing the spacer element.
3. The improved electrode assembly of claim 2 where the countersunk seats are disc shaped.
4. The improved electrode assembly of claim 2 wherein the countersunk seats are hemispherical in shape.
References Cited UNITED STATES PATENTS EDWARD E. KUBASIEWICZ, Primary Examiner
US758561A 1968-09-09 1968-09-09 Electrode assembly for detecting particles in fluid suspension Expired - Lifetime US3546583A (en)

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Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2258045A (en) * 1938-03-02 1941-10-07 Soren L Christie Electrode structure for conductivity testing
US3380584A (en) * 1965-06-04 1968-04-30 Atomic Energy Commission Usa Particle separator

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2258045A (en) * 1938-03-02 1941-10-07 Soren L Christie Electrode structure for conductivity testing
US3380584A (en) * 1965-06-04 1968-04-30 Atomic Energy Commission Usa Particle separator

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FR2017665A1 (en) 1970-05-22
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DE1944667C3 (en) 1975-01-23
GB1213958A (en) 1970-11-25

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