Patent ID: 6914677

Claim:
A device for optically measuring the concentrations of a substance in a fluid medium or the pH-value of the fluid medium, the device comprising: a layer containing a fluorescent substance to be detected, the layer comprising first and second separated areas; an exciting light source for directing an exciting light upon the first and second separated areas resulting in fluorescent light, a first excitation energy of the exciting light directed onto the first area differing with respect to a second excitation energy of the exciting light directed onto the second area over a determined time period, wherein differing excitation energies do not include differing wavelengths corresponding to the exciting light; at least one optical detector measuring the intensity, decay time or phase shift of the fluorescent light, the intensity, decay time or phase shift being locally and/or time separate for each area; and an electronic comparative and correction value determination unit, in which the measured values of intensity, decay time or phase shift are fed.