Novel two-dimensional phosphor thermography by decay-time method using a low frame-rate CMOS camera

Abstract

In this research, a novel, precise and cost-effective method of 2-dimensional (2D) temperature measurement based on lifetime technique is introduced without using a high-speed camera. The setup is simple and includes only a blue excitation light-emitting-diode (LED) and a low frame-rate CMOS camera. Instead of multiple frame capturing techniques in a single decay curve, the proposed technique takes a single image per excitation pulse in a stroboscopic mode. Two-dimensional thermographic imaging of a printed circuit board as a test sample was done based on the transient luminescence characteristics of magnesium fluoro-germanate (MFG) thermographic phosphor (TP). A cost effective, blue LED (425 nm) excitation source was used to illuminate the circuit board at a repetition rate of 33.33 Hz. The integration time of the camera was 10 ms and the detection window was applied after turning off the LEDs with an increasing delay during the successive periods. 100 pictures covering 4 milliseconds of the decay curve were then used to calculate the lifetime and temperature of each pixel of the image of the circuit board. Combined pixel-to-pixel and shot-to-shot uncertainty was only ±2.5 °C with a high spatial resolution of 50 µm.