An optical sensor based on surface plasmon resonance (SPR) for water measurement in process has been developed. The optical setup of this sensor is made in a simple and compact way, by the use of a laser diode as a point light source, providing an angularly spread (convergent) beam incident to the sensing part with imaging optics. Multichannel detection by a photodiode array and the Fourier transform optical setup eliminates the need for a mechanical angle scanner or a rotary stage in the system, resulting in a reduction in the size, the weight, and the cost of the sensor. Water concentrations in ethanol were measured by this sensor. Water concentrations of from 0.3% to 10% were obtained. Temperature dependence of the sensor and the method for compensation are discussed.

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