Electronic Pipettor With Improved Accuracy

In a hand-held electronic pipettor having an aspiration cylinder and piston, a stepper motor that drives the piston in the aspiration cylinder, a microprocessor, and a user interface display, a method of aspirating and dispensing liquid volumes comprising the steps of:

• selecting an aspiration volume;
• using an aspiration lookup table to determine a number of motor steps necessary to aspirate the selected aspiration volume, wherein values in the aspiration lookup table representing the number of motor steps necessary to aspirate respective volumes are determined empirically to account for aspiration inaccuracies in the pipettor;
• instructing the motor to move the piston to a home position and then instructing the motor to retract the piston the determine number of motor steps in order to aspirate the selected aspiration volume into a disposable pipettor tip mounted to the pipettor;
• selecting a dispensing volume;
• using a dispensing lookup table to determine a number of motor steps necessary to dispense the selected volume, wherein the values of motor steps necessary to dispense respective volumes in the dispensing lookup table are determined empirically to account for dispensing inaccuracies;
• instructing the motor to extend the piston the determined number of motor steps in order to dispense the selected dispense volume from the disposable pipettor tip mounted to the pipettor.