Patent ID: 8146407

Claim:
An apparatus for characterizing particles suspended in a liquid sample containing electrolyte, the apparatus comprising: (a) a sample chamber for holding the liquid sample and a collection chamber for holding an electrolyte solution, the sample and collection chambers separated by a wall; (b) an aperture in the wall for passage of particles between the sample chamber and collection chamber; (c) a pair of electrodes disposed on opposite sides of the aperture for inducing an electric current through the aperture; (d) a pressure source for drawing the liquid sample from the sample chamber into the collection chamber through the aperture; and (e) a processor for measuring a signal representative of electrical resistance variation between the electrodes to enable determination of the size of a particle within the liquid passing through the aperture, wherein the processor is adapted to detect a potential blockage of the aperture by detecting a predetermined change in one or more parameters characterizing a flow of particles through the aperture, wherein at least one of the one or more parameters is selected from the group consisting of flow rate, count rate, pulse concentration, and steady-state aperture resistance wherein the processor is further adapted to direct a preselected action when potential blockage of the aperture is detected, wherein the preselected action is preselected by a user of the apparatus from a choice of two or more actions.