This work presents high-resolution sensors based on Phase-Shifted Bragg Gratings (PSBG) for low-frequency vibrations monitoring and mass deposition sensing. We analyzed the reflected spectrum using a commercial interrogator for six values of deposited mass: 0, 0.22, 0.27, 0.32, 0.40, and 0.47 g. For the experimental data, a linear regression was calculated for PSBG 1 (R ² = 0.9379 with a sensitivity of 0.0491 nm/g) and for uniform FBG (R ² = 0.909 with a sensitivity of 0.05182 nm/g). Machinery Fault Simulator was used for the vibration monitoring setup for engine rotation frequency of 4 to 14 Hz in steps of 2 Hz. We used an alternative non-commercial interrogation system that consisted of a tunable laser, an optical circulator, an optical power acquisition board, and a prefixed Phase-Shifted Bragg. The proposed alternative interrogation system has the ability to center the tunable laser in the narrow valley region of the PSBG reflected spectrum, increasing the resolution for monitoring vibration at low frequencies. As a reference, the PSBG measurement results were compared with those of a piezoelectric accelerometer fixed at the same bearing. For 4, 6, 8, 10, and 14 Hz, the relative error was 15, 10, 0, 0, and 1.43%, respectively. According to these results, PSBGs are a suitable option for monitoring low-frequency vibrations and for mass deposition sensing.

This paper presents the development of a thermal measurement system for density, specific heat capacity and thermal conductivity in fluids. Due to toxic and flammable environment often found in oil industry, Fiber Bragg Gratings (FBGs) were used in the sensor development, which consists in a diaphragm-embedded FBG, to estimate density, and a FBG temperature sensor, to estimate specific heat and thermal conductivity. The diaphragm system, with sensitivity of 0.025 nm/kPa, was employed for density measurements in water, diesel and crude oil, becoming a feasible option for density estimation in fluids. The temperature sensor, with sensitivity of 11.5 pm/°C, was used to propose a method to estimate specific heat and thermal conductivity. The method uses the quantity of heat equation to estimate specific heat, then, density and specific heat to estimate thermal conductivity. To validate the method, it was presented three setups based in an acrylic tank, a Becker and a test tube. The tests were performed with water, mineral oil and kryo 51 oil. In addition the proposed system can be integrated in order to realize simultaneous measurements of density, specific heat and thermal conductivity with the same structure.

The assessment of heat transfer is a complex task, especially for operations in the oil and gas industry, due to the harsh and flammable workspace. In light of the limitations of conventional sensors in harsh environments, this paper presents a fiber Bragg grating (FBG)-based sensor for the assessment of the heat transfer rate (HTR) in different liquids. To better understand the phenomenon of heat distribution, a preliminary analysis is performed by constructing two similar scenarios: those with and without the thermal insulation of a styrofoam box. The results indicate the need for a minimum of thermal power to balance the generated heat with the thermal losses of the setup. In this minimum heat, the behavior of the thermal distribution changes from quadratic to linear. To assess such features, the estimation of the specific heat capacity and the thermal conductivity of water are performed from 3 W to 12 W, in 3 W steps, resulting in a specific heat of 1.144 cal/g °C and thermal conductivity of 0.5682 W/m °C. The calibration and validation of the HTR sensor is performed in a thermostatic bath. The method, based on the temperature slope relative to the time curve, allowed for the measurement of HTR in water and Kryo 51 oil, for different heat insertion configurations. For water, the HTR estimation was 308.782 W, which means an uncertainty of 2.8% with the reference value of the cooling power (300 W). In Kryo 51 oil, the estimated heat absorbed by the oil was 4.38 kW in heating and 718.14 kW in cooling.