Patent ID: 7250105

Claim:
A method of measuring the concentration of a substance in a sample liquid comprising the steps of: providing a measuring device said device comprising: a first working sensor part for generating charge carriers in proportion to the concentration of said substance in the sample liquid; a second working sensor part downstream from said first working sensor part also for generating charge carriers in proportion to the concentration of said substance in the sample liquid wherein said first and second working sensor parts are arranged such that, in the absence of an error condition, the quantity of said charge carriers generated by said first working sensors part are substantially identical to the quantity of said charge carriers generated by said second working sensor part; and a reference sensor part upstream from said first and second working sensor parts which reference sensor part is a common reference for both the first and second working sensor parts, said reference sensor part and said first and second working sensor parts being arranged such that the sample liquid is constrained to flow substantially unidirectionally across said reference sensor part and said first and second working sensor parts; wherein said first and second working sensor parts and said reference sensor part are provided on a disposable test strip; applying the sample liquid to said measuring device; measuring an electric current at each working sensor part proportional to the concentration of said substance in the sample liquid; comparing the electric current from each of the working sensor parts to establish a difference parameter; and giving an indication of an error if said difference parameter is greater than a predetermined threshold.