Calibrations and the measurement uncertainty of wide-band liquid crystal thermography

Abstract

Wide-band liquid crystal thermography is a high-resolution, non-intrusive optical technique for full-field temperature measurement. The paper presents comprehensive experimental results on the calibration and the measurement uncertainty for a thermochromic liquid crystal (TLC) with a bandwidth of 20 °C, examining the effects of the use of an image noise reduction technique, the lighting angle, the TLC coating thickness and the coating quality on the hue–temperature curve and the measurement uncertainty. It is found that combined with the image noise reduction technique of a 5 × 5 median filter, the measurement accuracy of the TLC can be significantly improved, and the high-accuracy usable bandwidth of the TLC can be considerably enlarged. The lighting angle has distinctive effects on the hue curve and the measurement uncertainty of the TLC, and a smaller lighting angle provides a smaller measurement uncertainty. The coating thickness has an appreciable effect on the TLC hue–temperature curve, but has a non-distinctive effect on the measurement uncertainty providing the coating thickness is over 20 µm. It is also found that the TLC coating quality has distinctive effects on the TLC hue curve and the measurement uncertainty. A finely prepared TLC coating produces a wider range of hue over the active temperature range, a considerably smaller measurement uncertainty and a larger high-accuracy usable bandwidth than the roughly prepared coating.