Measurement of substances in liquids
In accordance with the present invention a measuring device compares the current generated by two working sensor parts and gives an error indication if they are too dissimilar, i.e., the current at one sensor part differs too greatly from what would be expected from considering the current at the other. Not only can this method detect when one of the sensor parts has not been properly covered with sample liquid, but it can also detect if there is a manufacturing defect in either sensor part or if either has been damaged after manufacture, since even with complete coverage of the working sensor parts, an anomalous current will be generated at the affected sensor part under such circumstances.
1. 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.
2. The method as claimed in claim 1 comprising measuring the current at each working sensor part after a predetermined time following application of the sample.
3. The method as claimed in claim 1 wherein the substance to be measured is glucose, and each of the working sensor parts generates charge carriers in proportion to the concentration of glucose in the sample liquid.