FRONT END APPARATUS AND METHOD

摘要

Air is supplied from an air supply through a disposable pipette tip (11). With no obstructions in the path from the supply through the tip, air will flow freely and little back pressure will be measured by a pressure transducer (12) located upstream from the tip in an air supply circuit. The tip is lowered toward the surface (16) of the liquid by a robotic arm (20). As the lip contacts the surface, the liquid blocks airflow and the pressure sensed by the transducer increases. This increase signals that the pipette tip has located the liquid level. The tip is lowered beneath the liquid level and a vacuum source is then coupled to the air supply circuit The liquid is drawn onto the tip. The transducer measures a negative pressure. The measured pressure depends on air flow rate, liquid viscosity and a number of other secondary factors. If flow rate and these other factors are known, viscosity and change in viscosity can be measured. A clot or gel in the liquid u the tip produces a larger increase in the partial vacuum and hence the clot or gel is detected.