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RESEARCH PAPERS: Experimental Techniques

Liquid-Crystal Thermography: Illumination Spectral Effects. Part 1—Experiments

[+] Author and Article Information
M. R. Anderson

Senior Performance Engineer Calpine Corporation, 104 Woodmere Road, Folsom, CA 95630michael.anderson@calpine.com

J. W. Baughn

Department of Mechanical and Aeronautical Engineering,  University of California, Davis, One Shields Avenue, Davis, CA 95616jwbaughn@ucdavis.edu

J. Heat Transfer 127(6), 581-587 (Jan 08, 2005) (7 pages) doi:10.1115/1.1909207 History: Received June 27, 2004; Revised January 08, 2005

Experiments have been performed to examine the spectral effects of the illumination source on the hue-temperature characteristics of thermochromic liquid crystals (TLCs) used in a liquid-crystal thermography system. Five illumination sources were compared in this study. It was found that “full spectrum” sources, which have a relatively uniform radiant intensity across the visible spectrum, tend to have the lowest temperature uncertainties and the broadest useful ranges, which are desirable calibration attributes. Radiation in the infrared, which leads to (usually undesirable) heating of a test surface, and in the ultraviolet, which can damage TLCs, are discussed for the various light sources. Experimental observations of the effect that UV damage has on liquid crystal calibrations are also provided. The use of a new method called background subtraction and the use of white balancing are investigated as methods of improving the calibration characteristics of TLCs. The uncertainty in temperature associated with different illumination sources and both background subtraction and white balancing is determined and discussed. It is shown that these methods can reduce the uncertainty in some cases.

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Copyright © 2005 by American Society of Mechanical Engineers
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Figures

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Figure 1

Diagram of liquid-crystal thermography system

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Figure 2

Experimental RGB output versus temperature

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Figure 3

Experimental HSV output versus temperature

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Figure 4

Experimental hue-temperature sensitivity and uncertainty for various illumination sources

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Figure 5

Experimental hue and saturation data after background subtraction

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Figure 6

Experimental hue-temperature sensitivity and uncertainty for various illumination sources after background subtraction

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Figure 7

Experimental HSV output versus temperature after white balancing

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