Electromagnet motor control for constant volume pumping

摘要

A constant-volume increment pipetting arrangement for use particularly in connection with analysis of minute specimen volumes of biological fluids. The arrangement, which is designed to have a very low inertia factor, comprises a pumping unit having a pair of two-port valves with a duct running between a port from each valve, wherein at least a portion of the duct wall is movable to provide a variable volume pipetting chamber. The second port of one valve serves as the intake port for the fluid to be pipetted and the remaining port of the other valve serves as the delivery port. Three reciprocating drive elements are provided, connected one each to the valves and to the movable portion of the duct wall. Associated with the drive elements is a sequential control means, wherein the control means portion for the drive element connected to the moving portion of the duct wall constitutes an electromagnet arrangement energizable by a periodic supply. Means are associated with the duct wall drive element for controlling the travel amplitude of the electromagnet's armature and thus the travel amplitude of this drive element. The volume of liquid displaced by the movement of the movable portion of the duct wall which arises from the controlled movement of the drive element associated therewith corresponds to the volume required for the pipetted increment, whatever variations in resistance may be encountered by the duct-related drive element.