EXPERIMENTAL INVESTIGATION OF PHOSPHOR THERMOGRAPHY USING A BLUE LED OPTICAL EXCITATION SOURCE

摘要

This paper describes the development, experimentalinvestigation and laboratory testing of a non-contacttemperature measuring technique utilizing the method ofphosphor thermography using a blue light emitting diode(LED) optical excitation source. This work aims at measuringthe phase shift between the excitation wave and the returningfluorescent signal and keeping the shift constant at 35.3° foraccurate temperature measurements and an improved signal tonoise ratio. In harsh environments and in places wheretemperature measurements are to be made on remote areas, likeinside boiler tubes, turbines etc., phosphor thermometry is awell-developed non-contact temperature measurementtechnique. In this paper, all the work has been done usingmagnesium fluorogerminate (Mg4FGeO6:Mn), a thermographicphosphor, for measuring surface temperatures. The 650nmemissionline of the phosphor was used for all measurementsand calibration purposes. A 470nm blue LED provided meansof phosphor excitation. The fluorescent return signal wasmeasured with a miniature photomultiplier tube, which had a650 ±10nm band pass filter attached to it. A digital oscilloscopeprovided the analog to digital conversion and also the averagingof the fluorescent signal. The oscilloscope was in turnconnected to a computer via a GPIB and by means of a suitableLabVIEW program which calculated the phase shift occurringbetween the two waves for a given pulsing frequency. Thephase shift of the two waves could be maintained constant at35.3° by varying the frequency at which the LED was beingpulsed for a given temperature. Phase shift measurements weremade at temperatures ranging between room temperature 25°C(77℉) and 600°C (1112℉) with an accuracy of ± 2°C (3.5℉).