Hydrogen leak detection using an optical fibre sensor for aerospace applications

An optical fibre sensor has been developed for the detection of hydrogen le akages on the cryotechnic engine of the European rocket ARIANE V. The princ iple of this sensor is based on the variation of reflectivity of a palladiu m micromirror deposited at the output end face of a multimode optical fibre . An experimental set-up using a monitored high power laser diode provides an optical heating of the palladium layer, which allows to keep up the perf ormances in the wide range of temperatures between - 196 degrees C and + 23 degrees C. Depending on both the concentration and the temperature, detect ion responses between 1% and 17% with response times shorter than 5 s have been demonstrated. Fast and accurate detection of hydrogen concentrations i nferior to the explosive limit has been performed. (C) 2000 Elsevier Scienc e S.A. All rights reserved.