Biosensing meter with fail/safe procedures to prevent erroneous

Abstract

A biosensing meter receives a sample strip that includes electrically isolated sense and excitation electrodes bridged by a reaction zone. When a drop of biological sample fluid is placed in the reaction zone, a plurality of fail/safe tests are performed. A drop size test is performed by a circuit that detects the size of the drop placed in the reaction zone. The circuit both detects that a drop has been placed in the reaction zone and further measures a test current level, after a delay, to determine that the drop size is sufficient to enable hydration of reactants in the reaction zone. Subsequently, during the reaction, a 'delta' current change is measured at succeeding sample time. This test measures the difference between succeeding current samples during a measurement time. If each succeeding sample is not less than preceding sample by a delta value, a determination is made that the current is not monotonically decreasing and the test is aborted. At the termination of the measurement time, a current sum test is performed wherein a processor calculates a linear sum of all sample test currents and calculates a ratio between that sum and the last current sample. If that ratio matches a pre-calculated constant for the Cottrell relationship, then it is known that the measurement values exhibit the Cottrell relationship.