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In this paper, the deployment of a newly developed, multipoint, fiber-optic temperaturesensor system for temperature distribution measurements in a 6 MW gas turbine is demonstrated. The optical sensor fiber was integrated in a stainless steel protection cable with a 1.6 mm outside diameter. It included six measurement points, distributed over a length of 110 mm. The sensor cable was mounted in a temperature probe and was positioned radially in the exhaust-gas diffusor of the turbine. With this temperature probe, the radial temperature profiles in the exhaust-gas diffusor were measured with high spatial and temporal resolution. During a test run of the turbine, characteristic temperature gradients were observed when the machine operated at different loads. [ABSTRACT FROM AUTHOR]

In this paper, the deployment of a newly developed, multipoint, fiber-optic temperature-sensor system for temperature distribution measurements in a 6 MW gas turbine is demonstrated. The optical sensor fiber was integrated in a stainless steel protection cable with a 1.6 mm outside diameter. It included six measurement points, distributed over a length of 110 mm. The sensor cable was mounted in a temperature probe and was positioned radially in the exhaust-gas diffusor of the turbine. With this temperature probe, the radial temperature profiles in the exhaust-gas diffusor were measured with high spatial and temporal resolution. During a test run of the turbine, characteristic temperature gradients were observed when the machine operated at different loads.

In this letter, a pair of regenerated gratings with Bragg wavelengths of 1547 and 1304 nm in a single piece of singlemode fiber has been fabricated for simultaneous monitoring of temperature and strain in ultrahigh temperature environment. A 3 × 3 matrix is used to characterize the cross sensitivity of the proposed sensor in which the strain sensitivity varies with temperature change. The proposed structure exhibits the deviation of 28.3 με and 4.1 °C at the ranges of 0-1000 με and 25 °C- 900 °C, respectively. [ABSTRACT FROM PUBLISHER]

In a highly Ge-doped photosensitive fiber co-doped with phosphorus and fluorine and with a doped inner cladding, we observed, during annealing experiments, an anomalous variation of the FBG strength as a function of temperature and time. This characteristic only occurred when the fiber had been loaded with hydrogen. During a stepwise temperature increase from room temperature to 1200°C with 15min dwell times, the gratings showed, after an initial thermal decay, in two distinct temperature ranges a significant increase in reflectivity with time. One range with an increase in reflectivity was found between 850°C and 1000°C. The behavior of the FBGs in this range was very similar to that known from chemical composition or regenerated gratings. Another temperature range with increasing reflectivity was found between 500°C and 700°C, followed by a strong decrease in reflectivity at temperatures between 750°C and 800°C. Both regimes of regeneration might be associated with changes in the core and the doped inner cladding of this type of fiber. At different temperatures the drift behavior of and was investigated. In specific temperature regions a positive wavelength drift combined with a decrease in has been observed. This is in contradiction to the standard thermal decay model and seems to be a characteristic of regenerated gratings. [ABSTRACT FROM AUTHOR]

• Regenerated Fibre Bragg Gratings (RFBG) and Chemical Composition Gratings (CCG) • An up to date examination of the research status on RFBG and CCG. • Crystallization theory, chemical composition theory and negative index theory are discussed. • Key parameters for RFBG/CCG production are reviewed. • An overview of actual and future RFBG/CCG applications is given. Regenerated fibre Bragg gratings are formed when specially pre-treated seed gratings are heated up to several hundred degrees centigrade. During this process, the fibre Bragg grating (FBG) reflectivity vanishes and regrows, forming a regenerated grating, which can survive temperatures of more than 1000 °C. Right from the beginning, it was clear that the extraordinary temperature stability of regenerated FBGs will open new fields of applications for FBGs. Multiple investigations have been made to explore the mechanisms of the regeneration effect, often presenting contradictory explanations of the processes leading to their formation. To date, there is no comprehensive theory which can explain all the observed phenomena regarding the regeneration effect. However, a broad base of knowledge exists, which can be used for tailored manufacturing and application of regenerated FBG. In this article, we present a summary of the breadth of regenerated FBG research, including a critical overview and discussion of the various competing theories published to date. We conclude with an outlook on present and future applications of regenerated FBGs and identify further research necessary to unambiguously identify and explain the key processes occurring during regeneration. [ABSTRACT FROM AUTHOR]

A low-drift fiber-optic sensor system, consisting of 24 regenerated fiber Bragg gratings (RFBG), equally distributed over a length of 2.3 m, is presented here. The sensor system can monitor spatially extended temperature profiles with a time resolution of 1 Hz at temperatures of up to 500 °C. The system is intended to be used in chemical reactors for both the control of the production ramp-up, where a fast time response is needed, as well as for production surveillance, where low sensor drifts over several years are required. The fiber-optic sensor system was installed in a pilot test reactor and was exposed to a constant temperature profile, with temperatures in the range of 150–500 °C for more than two years. During this period, the temperature profile was measured every three to five months and the fiber-optic temperature data were compared with data from a three-point thermocouple array and a calibrated single-point thermocouple. A very good agreement between all temperature measurements was found. The drift rates of the 24 RFBG sensor elements were determined by comparing the Bragg wavelengths at a precisely defined reference temperature near room temperature before and after the two-year deployment. They were found to be in the range of 0.0 K/a to 2.3 K/a, with an average value of 1.0 K/a. These low drift rates were achieved by a dedicated temperature treatment of the RFBGs during fabrication. Here, the demonstrated robustness, accuracy, and low drift characteristics show the potential of fiber-optic sensors for future industrial applications. [ABSTRACT FROM AUTHOR]