Francisco Javier Madruga Saavedra

Optical fiber and integrated optics accelerometers for real-time vibration monitoring in harsh environments: in-lab and in-field characterization

The reliability of rotating machines such as electrical generator is critical to the overall reliability and operation of electrical power plants. The very high cost of these machines, makes it necessary to improve the lifetime of a wide set of currently installed hydrogenerators around the world and avoid costly maintenance. Vibration monitoring is essential in maintenance and protection programs. However, due to the harsh environment and the very low frequency spectrum of the vibrations, the above mentioned machines cannot be appropriately monitored by piezoelectric sensors. Several combination of optical fiber with silicon microstructures or in integrated optics, but because of technical or economic reasons, up to now, these sensors are not fully suited for the above-mentioned applications. In this paper both optical fiber and integrated optics accelerometers developed in order to satisfy specifications required for these applications are presented. Their developments were a part of a European project dedicated to real time defect detection and predict forthcoming failures of a generator group in an electric power plant in Spain. In-laboratory and in-field test are reported.

Temperature, displacement, and acceleration fiber optic sensor for large machinery monitoring

In this paper, a multi-parameter optical sensor system for vibration, temperature and strain monitoring is presented. It is based on a hybrid singlemode-multimode fiber optic transducer, where the vibration is detected by means of a fiber cantilever beam and extrinsic coupling of light, while two fiber Bragg gratings measure the temperature and strain. Experimental results show good performance for the monitoring of large electric machines.

New optical cell design for pollutant detection

A new and simple optical gas cell, developed to perform as the transducer for a methane fiber optic sensor, is presented. Its main advantage lies in the fact that, employing low-cost components and an easy alignment process, the path where the light beam is in contact with the pollutant becomes maximized to as much as four times the physical length of the optical cell. This increment in optical length is directly related to the optimization of the fiber optic sensor since low levels of methane concentration can be measured as stated by Beer-Lamberts law. One of the main advantages of this design lies in the simplicity of the optic cell, which makes it very interesting when one has to deal with the manufacturing process. The cell is mounted on a reflective configuration which improves the connection as only one optical fiber is employed. The main elements of the cell are an optical fiber, a mirror of high reflectivity and a converging lens arranged in an appropriate fashion to obtain the desired result. With this relatively reduced and low cost set of devices the insertion losses achieved are in the range of the 4-5 dBs.

High-temperature optical fiber transducer for a smart structure on iron-steel production industry

The quality of the steel, among others, depends on the temperature profile during the last cooling process. Because of that, the capability of real-time temperature measurements at several points of the steel bars during the aforementioned production process is highly desirable in order to build a smart structure. To measure temperatures in the range of 800 - 1300 degrees centigrade, the sensor system proposed, is doted of new fiber optic transducers. They are based on the measurement of the optical radiation generated by the hot steel bars through a geometric cavity which is properly designed and fabricated to maximize its accuracy.

Phenomenological approach to the analysis of the polarization effects in fiber optic interferometers

Using the scattering matrices and the graph theory, three basic structures of all-fiber interferometers, Mach-Zehnder, Michelson, and Sagnac have been analyzed. The influences that, the couplers with losses and constant coupling polarization dependent, and the birefringent of the optical fibers, both used for making these optical systems, introduce in the performances of the three interferometers, are studied and compared.

Analog optical U-shaped fibre transducer based on index modulation for quasi-distributed sensing

Optical time domain reflectometry (OTDR) is a very useful tool used in optical fibre communications and in sensor networks. The cost of an OTDR instrument prohibits sometimes its use in fibre optic sensor networks. Desforges et al presented a scheme that allows the monitoring of 10 to 50 on/off microswitches along a fibre in industrial environments using retroreflected light.