Some aspects concerning the calibration procedure are shown for a fiber optic sensor to be used for on-line chromium (VI) concentration measurements. The sensor is based on the measurement of light absorption of a sampling volume between transmitting and receiving optics, made by means of GRIN lenses for sensor size miniaturizing purposes. In particular, the geometrical design of the probe has been discussed, together with the effects of optical and mechanical solutions. These have been set in the probe, referring to the measuring performances to be achieved and, in particular measuring range, sensitivity, accuracy and time stability. The results of preliminary experimental analysis are also described, which allowed validation of the design indication and getting information for probe development.
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