Importance

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Abstract

A method and an apparatus for measuring concentration of a dissolved substance are disclosed. In accordance with the method, measurements are made with two instruments having different permeability characteristics to obtain two readings, and these readings are corrected in accordance with a pre-determined relationship. The apparatus provides an electrochemical cell wherein a common anode is surrounded by closely-spaced cathodes. The cathodes are in at least two groups, wherein the first group has a first response characteristic to the dissolved substance and the second group has a second response characteristic. In the preferred embodiment, the two characterisitcs are produced by providing different distances between a substance-selective membrane and respective cathodes. In one embodiment, the cathodes are annular and surround the anode at different radii, while in another embodiment the cathodes are discrete and are spaced from the anode by equal distances.

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First Claim