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Abstract

A volume sensing device for determining the volume of liquid present in a standard plastic disposable pipette during a pipetting operation, which operation can be an aspiration or dispensing of liquid. The device comprises a cylinder made of hard synthetic material into which a disposable pipette is lowered at a predetermined velocity. The pipette which is being lowered into the cylinder holds an amount of liquid the volume of which the volume sensing device approximately determines. A pair of metal rings are coaxially mounted near the top end of the plastic cylinder. The pair of metal rings are preferably mounted in mating machined recesses of the plastic cylinder. This pair of metal rings is separated from each other by a small gap which forms the dielectric material of a capacitative circuit when the upper ring is connected to one portion of this circuit and the lower ring is connected to an other portion of the capacitative circuit. Below the pair of rings the plastic cylinder forms a blind bore of substantially larger axial length than the axial length of the pair of rings. The pair of rings and the blind bore of the cylinder have equal internal diameters. The upper ring of the pair of rings is connected to a pulse generator and the lower ring is connected to a circuit including an amplifier and a comparator, which circuit is connected to a computer data storage device.

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First Claim