Abstract
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.
Highlights
By leaving the laboratory-scale, multipoint fiber-optic temperature sensing based on fiber Bragg gratings has gained significance for industrial applications
We demonstrate the suitability of multipoint regenerated fiber Bragg gratings (RFBG) sensing for applications in catalytic fixed-bed tubular reactors by measuring high-temperature profiles over a length of 2.3 m in a representative industrial environment for more than two years
A fiber-optic multipoint sensor system based on 24 RFBG sensor elements that were procedure.over sensor system of four arrays with six sensor elements each, andtest the distributed a length of 2.3 m hasconsisted been presented and characterized during a long-term arrays were packaged in three-meter-long stainless-steel capillaries of a
Summary
By leaving the laboratory-scale, multipoint fiber-optic temperature sensing based on fiber Bragg gratings has gained significance for industrial applications. The main advantages arise from their immunity to electromagnetic interference, small size, and wavelength multiplexing capability. The latter is of special interest, because it enables a large number of measuring points in a single sensor cable, due to the wavelength-encoded sensor signal. When compared to conventional electrical sensors, such as thermocouples, the technology of multipoint FBG temperature sensing dramatically reduces the cabling efforts. In many fields of industrial applications, such as chemical reactors or gas turbines, the maximum temperatures exceed 400 ◦ C. This is out of the durability range of standard type I FBGs, because those
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