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This study is proposed for obtaining simultaneous measurements of the level and specific gravity of a liquid using a dual-optical-fiber-sensor system comprising a fiber Bragg grating (FBG) level sensor and a Fabry-Pérot (FP) pressure sensor. In the FBG level sensor, the liquid level is derived from the FBG wavelength shift induced when the buoyancy is applied on a cantilever beam. Meanwhile, in the FP sensor, the pressure is calculated from the change in cavity length which takes place when the sensor is immersed. The experimental results show that the FBG level and FP pressure sensors have sensitivities of 0.01491 nm/cm and 0.1569 μm/kPa, respectively. Analytical formulae are derived for the level and specific gravity of the liquid in terms of the Bragg wavelength shift, the change in cavity length, and the vertical separation distance between the two sensors. The average measurement errors of the liquid level and specific gravity are found to be 0.0323 and 0.0528 m, respectively.
Date of Publication: April 2012