Several types of optical fibre temperature sensors have been developed during recent years, including point sensors based on fluorescence, distributed types that rely on backscatter and the latest developments which are quasi-distributed and utilise fibre Bragg grating (FBG) technology. FBGs are effectively narrow-band optical filters and are fabricated by exposing the core of a photosensitive optical fibre to intense UV light which causes a permanent, periodic modulation in the effective refractive index. The grating reflects a narrow spectrum - the Bragg wavelength - which is directiy proportional to the period of the modulation of the effective refractive index. In FBG sensors, external factors such as temperature or stain cause a shift in the reflected Bragg wavelength spectrum, which is quantified by the associated optics and electronics. A key advantage of FBG sensors is that they exhibit an intrinsic self-referencing capability, as the sensed information is encoded directiy into wavelength, which is an absolute parameter and independent of the light intensity and any loss in the transmission fibres. A recent and unique application of the latter is monitoring the temperature distribution of the helium in a prototype load-carrying airship. As the buoyancy of a balloon changes with temperature, a measure of the temperature distribution of the gas is required to achieve accurate height control. Whilst modern airships use inert helium rather than combustible hydrogen, as in the past, there are nevertheless very stringent EMI and lightning survival requirements which more or less dictate the use of an electrically inert sensor system. The present optical system was originally developed at the German Institute for Physical High Technology (IPHT) at Jena and was manufactured by Kayser-Threde of Munich. It was installed on a prototype CargoLifter 'CL 75 AirCrane', an unmanned craft. During a recent demonstration at CargoLifter's Brand site it successfully transported a 55 tonne army mine clearance tank.
Fibre bragg sensors used to measure gas temperature in an airship
Faseroptischer Sensor zur Messung der Gastemperatur in einem Luftschiff
Sensor Review ; 23 , 1 ; 30-32
2003
3 Seiten, 5 Bilder
Article (Journal)
English
Optical fibre grating gas temperature sensor network in airship
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