Patent ID: 7361509
Filing Date: 2008-04-22
Classification: G01N,Y10T

Abstract:
1. A method for dynamically determining the volume of a liquid dispensed by a metering system, said metering system including a metering pump, a metering probe, a conduit between said metering probe and said metering pump, a pump motor and at least one sensor disposed in relation to said conduit for measuring a parameter of said metering system, said pump motor having a positive displacement element, said method including the steps of: aspirating a quantity of liquid into said metering probe using said metering pump; moving said metering probe relative to a reaction vessel; and dispensing the quantity of liquid onto said reaction vessel, said dispensing step including the steps of: monitoring said parameter continuously using said at least one sensor, each said at least one sensor producing a parameter profile; identifying an onset point associated with said parameter which can be measured by said at least one sensor, said onset point being determined by a first detectable change of said parameter in said parameter profile; identifying an end point associated with said parameter, said end point being determined by a second detectable change in said parameter profile, thereby defining a specific time period; and measuring the displacement of said positive displacement element of said metering pump during the time period between said identified onset point and said identified end point, wherein said measurement provides a determination of dispensed liquid volume, wherein said at least one sensor includes at least one pressure transducer for measuring pressure changes in said metering probe and producing a pressure profile, said onset point relating to a change in said pressure profile indicative of a reduction in pressure in said metering probe that is further indicative of a meniscus of dispensed liquid first contacting said reaction vessel and the end point relating to an abrupt reduction in pressure according to said pressure profile occurring after the entire quantity of liquid has been dispensed from the metering probe.