A high-accuracy calibration technique for thermochromic liquid crystal temperature measurements

There are a variety of phenomena which may impact the accuracy of wide-band thermochromic liquid crystal temperature measurements, including: irregula rities in liquid crystal and black paint layers, reflective components from light sources, and variations in the lighting/viewing angle across the sur face. A wide-band calibration technique has been developed which inherently accounts for these and other sources of uncertainty by employing a point-w ise calibration of the entire test surface. Both on and off-axis lighting a rrangements are assessed for ease of implementation and accuracy of color d isplayed under uniform temperature conditions. The technique employs a seri es of uniform-temperature images to construct calibration curves relating t he local hue component to temperature in a point-wise manner for the entire test surface. An off-axis lighting/viewing arrangement is found to be most practical for typical experimental setups. Hysteresis effects are quantifi ed for excursions beyond both the lower and upper clearing point of the liq uid crystals. Finally, the total uncertainty of the measured temperature is determined to vary from +/- 1.2% to +/- 7.2% across the bandwidth of the l iquid crystals.