Abstract: In a so-called Coulter-device with a first and a second chamber, a separag wall between them and a measuring aperture in the separating wall, through which particle-free electrolyte flows from the first chamber into the second chamber, and with first and second electrodes in the first and second chamber resp., at which a measuring impulse indicating a certain property (e.g. volume) is derived upon the passage of a particle, which is supplied to it through a supply capillary ending in front of the measuring aperture, the improvement consisting in means to supply additional particle-free electrolyte to the particle stream at and/or in the neighborhood of the downstream end of the measuring aperture to deflect those particles, which, after passage through the measuring aperture, travel backward to the same and cause error impulses.

Abstract: An apparatus for performing at least two measurements of characteristics in suspension of particles, including two chambers separated by a measuring orifice through which the suspension of particles flows in response to a pressure difference between the two chambers. A glass plate is disposed a short distance beyond the measuring orifice in the direction of flow and at right angles to the direction of flow, and diverts the flow at substantially right angles to its flow direction through the measuring orifice. An optical measuring device is provided and situated coaxially with the flow through the measuring orifice and downstream of the glass plate. The optical measuring device produces an irradiation of the particles in suspension and the fluorescence thereby induced is measured. Another measurement is achieved by measuring a voltage pulse utilizing a pair of electrodes, one in each of the two chambers. The voltage pulse is varied as a function of the particle size passing the measuring orifice.

Abstract: An apparatus for investigating the properties of particles held in liquid spension using the Coulter process, U.S. Pat. No. 2,656,508, wherein the flowrate of the particle suspension into the particle-free electrolyte carrier depends on the pressure difference between these two liquids. This pressure difference is made readily adjustable by setting the height of the level of the electrolyte by means of a separate, vertically movable chamber attached with a flexible lead to the main measuring chamber. The main measuring chamber is closed to the atmosphere, permitting maintenance of a pressure differential with respect to the atmosphere and with respect to the particle suspension.

Abstract: Calibration apparatus for use with particle volume measuring equipment us the Coulter process, which detects and analyzes the voltage pulses produced by particles passing a narrow aperture in which an electric field is maintained.The calibration apparatus includes a calibration pulse generator with pulse-shaping circuitry which produces a sequence of calibration pulses, approximately trapezoidal in shape, which are introduced into the particle measurement path, in series with the measurement aperture traversed by the particles. The generator includes precision attenuation resistors for varying the amplitude of the calibration pulses.The apparatus also provides for adjusting and maintaining a constant current through the measurement aperture and for amplifying the pulses produced by particles passing through the aperture whose amplitude is compared with the amplitude of the calibration pulses.