Measurement of Window Glass Temperature With a Fluorescence Intensity Ratio Optical Fibre Sensor

A prototype optical fibre temperature sensor employing the fluorescence intensity ratio (FIR) technique has been utilised to measure the surface temperature of window glass during a fire. A comparison has been made between the intrinsic optical fibre sensor and thermocouples (the conventional temperature measuring device used in fire research). Neodymium doped fibre was used as the temperature sensing element. Due to the destructive nature of the fire tests on the neodymium doped fibre, a new section of bare doped fibre was spliced for each test. Before each fire test, the (non-glass) coating on the sensing fibre was removed. The detector was calibrated against K-type thermocouples in a stabilised temperature environment. This same bare optical fibre was attached to the window glass pane with an adhesive that was appropriate for the fire test conditions. A preliminary investigation was undertaken to compare the effect of a radiant heat environment on the sensing fibre and thermocouples. The bare fibre showed a significantly lower temperature (about 25C lower) than the average thermocouple temperature. This is consistent with the expectation that the fibre is less subject to the effects of radiation than the thermocouples. Thus it was demonstrated that the thermocouple did not accurately represent the time-dependent temperature behaviour of window glass, and specifically, the temperature within the core of the fibre. Fire tests were conducted in a chamber, which was designed and built to simulate a combustion fire starting in a small room with a window. Both sensor types were used to measure the temperature of the inside surface of the window glass during a fire. The observed temperature difference was smaller than that observed during the preliminary tests where the thermocouples were subject to a radiant heat environment. Reasons for this are discussed within the thesis. The measurement of window glass temperature during a fire has been demonstrated using an optical fibre sensor based on the fluorescence intensity ratio technique. This clearly establishes the existence of a discrepancy between window glass temperature and the temperature measured by thermocouples when they are subjected to a radiant heat environment