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

摘要

This paper describes the development, experimental investigation and laboratory testing of a non-contact temperature measuring technique utilizing the method of phosphor thermography using a blue light emitting diode (LED) optical excitation source. This work aims at measuring the phase shift between the excitation wave and the returning fluorescent signal and keeping the shift constant at 35.3° for accurate temperature measurements and an improved signal to noise ratio. In harsh environments and in places where temperature measurements are to be made on remote areas, like inside boiler tubes, turbines etc., phosphor thermometry is a well-developed non-contact temperature measurement technique. In this paper, all the work has been done using magnesium fluorogerminate (Mg_(4)FGeO_(6):Mn), a thermographic phosphor, for measuring surface temperatures. The 650nm-emission line of the phosphor was used for all measurements and calibration purposes. A 470nm blue LED provided means of phosphor excitation. The fluorescent return signal was measured with a miniature photomultiplier tube, which had a 650±10nm band pass filter attached to it. A digital oscilloscope provided the analog to digital conversion and also the averaging of the fluorescent signal. The oscilloscope was in turn connected to a computer via a GPIB and by means of a suitable LabVIEW program which calculated the phase shift occurring between the two waves for a given pulsing frequency. The phase shift of the two waves could be maintained constant at 35.3° by varying the frequency at which the LED was being pulsed for a given temperature. Phase shift measurements were made at temperatures ranging between room temperature 25°C (77°F) and 600°C (1112°F) with an accuracy of ±2°C (3.5°F).