A low-cost intensity-based polymer optical fiber (POF) sensor for liquid detection applied to volumetric flasks is presented. Experimental results demonstrate the viability of the POF-based sensor system in a high-accuracy liquid level measurement scenario. Moreover, a wireless mesh sensor network based on ZigBee specification protocol to address multiplexed POF-based sensor is also developed. Experimental results demonstrate the feasibility to address a high number of optical sensors in an industrial process framework by means of this low-cost wireless solution. 1. Introduction Fiber-optic sensors exhibit a set of very attractive characteristics, including immunity to electromagnetic interference, small-sized capability, resistance to hostile environments that may comprise hazardous chemicals or of any other kind, geometric versatility, ruggedness, sensor multiplexing, and distributed sensing over a single fiber. There are numerous realizations of fiber-optic sensors but one extensively investigated transducing mechanism in optical sensing applications is the intensity modulation of the propagating light. Approaching simple configurations, intensity sensors modulate the optical power loss as the physical magnitude changes, thus providing the measurement as an optical intensity modulation signal. Intensity-based fiber-optic sensors have been demonstrated in literature to be very reliable, simple in concept, easily made selective to specific measurand, easily integrated in optical networks by means of different multiplexing techniques, and cost-effective sensing approach for a wide range of applications. In particular, if a flammable environment is a critical concern for industrial sensor applications, an intensity-based fiber-optic sensor is one of the best candidates. Moreover, these fiber-optic sensors have attractive properties for liquid-level measurements in practice. By using reflective intensity modulation to represent a change in the surrounding material, submersion or flooding can be monitored. These applications can be carried out in oil tanks, flood areas, and underground [1, 2]. It should be outlined that in the optical sensing field, fiber-optic sensors can be constructed using polymer optical fibers (POFs) rather than silica-based versions, both singlemode (SMF) and multimode (MMF), because POFs have large numerical apertures, simple alignment to optical devices, high coupling efficiency, more flexibility, and lower cost. These are some reasons why new POF-based sensors have appeared and are still appearing, most of them based on optical
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