Patent
1987-01-29
1989-01-10
Miller, Stanley D.
328115, 328150, 328127, H03K 522, H03K 500
Patent
active
047976241
DESCRIPTION:
BRIEF SUMMARY
This invention concerns the editing, by excluding, of electrical pulses. More specifically, this invention concerns the excluding of certain electrical pulses from a large quantity thereof, which are generated as a result of particle analysis by a particle analyzing apparatus. One general form of such apparatus utilizes the Coulter sensing principle as disclosed in U.S. Pat. No. 2,656,508 and subsequently in numerous improvement patents worldwide. Products employing the Coulter sensing principle are manufactured and now sold by many companies, a primary one of which is Coulter Electronics, Inc. and these are identified by the trademarks Coulter Counter.RTM. and Coulter.RTM..
According to the Coulter sensing principle, when a microscopic particle in suspension in an electrolyte is passed through an electrical field of small dimensions approaching those of the particle, there will be a momentary change in the electric impedance of the electrolyte in the ambit of the field. This change of impedance diverts some of the excitation energy into the associated circuitry, giving rise to an electrical signal. Such signal has been accepted as a reasonably accurate indication of the particle volume for most biological and industrial purposes. Apparatus embodying the teachings of U.S. Pat. No. 2,656,508 has been used to count and size particles in biological fluids, industrial powders and slurries, etc.
In commercial versions of Coulter particle analyzing apparatuses, the electric field of small dimensions has been formed commonly by a microscopic right cylindrical passageway or aperture, as it is known, between two bodies of liquid in which the particles to be studied are suspended. The electrical excitation energy is coupled to these bodies by means of electrodes respectively located in the liquid bodies, the aperture being formed in an insulating wall between the bodies. The suspension is caused to flow through the aperture, carrying the particles with the flow, and gives rise to the electric signals produced by the momentary changes in impedance caused by the respective particles as they pass through the aperture. The electric field is concentrated in the aperture and normally comprises an electric current flowing through the aperture along with the physical flow of the suspension.
By counting the signals produced, one can count the particles passing through the aperture. By discriminating between different pulse amplitudes, one can make size studies.
The sensing aperture usually is short, that is, its length is the same as or less than its diameter. The optimal particle size-volume information is obtained from the pulse amplitude peak, if that amplitude peak is the result of the particle being in the electrical field approximately halfway through the aperture length and the path of the particle has been along the axis of the aperture. The reason that the pulse peak is optimal when the particle is in the electrical field halfway through the aperture is that such position is most remote from the entrance and exit of the aperture, is most uniform and has the most uniform current distribution for all paths through the aperture. At the entrance and exit of the aperture, the current density is greater at the edges of the aperture and correspondingly lesser on the axis of the aperture. This may be explained by pointing out that current paths other than the axial path are supplied from the sides of the aperture as well as straight ahead. The lower current density on the axis at the entrance and exit results in a lower instantaneous signal than is the case for particles entering the aperture and leaving it on other paths. In other words, the current density at the corners of the aperture is greater than at the axis.
Another reason that axially traversing particles provide optimal pulses is that the velocity of electrolyte flow, and hence the velocity of particles also, is somewhat greater on an axial path than on paths closer to the edges of the aperture or paths which are off-center, because the liquid does not have to ch
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Dunstan Harvey J.
Harfield John G.
Knight Paul
Podgorney Harvey J.
Callahan Timothy P.
Coulter Electronics, Ltd.
Hibnick Gerald R.
Miller Stanley D.
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