18 May 2012 Accurate thermal imaging of low-emissivity surfaces using approximate blackbody cavities
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Abstract
Remote temperature sensing and thermal imaging can be invaluable tools for process control and optimization. Their utilization is limited within the metal processing industries, however, as bright metal surfaces are highly reflective, with low emissivity that can vary critically with oxide thickness and alloy composition. Any infrared temperature measurement is vulnerable to background reflection and limited to the uncertainty in the emissivity. An enclosure or cavity made of any material offers an approximation to blackbody radiation, as both emitted and reflected radiation are collected within the cavity, and background radiation is excluded by the geometry. By exploiting natural cavities formed during processing, emissivity-independent measurements can be made. This paper presents thermal imaging data from an aluminum rolling application. Data was gathered using Land's FTI-E imaging system. Based on an uncooled amorphous silicon array, the system provides measurement in the range 200°C to 600°C to an accuracy of ±1°C. The 320 x 240 pixels each have field of view 570:1, providing a total viewing angle of 32° by 24°. Data was processed by Land's LIPS ASPS software, which features a patented algorithm for identifying the area of true temperature measurement within the cavity. The software automatically locates the wedge as the strip is coiled, and tracks its position as the coil increases in size. Successive profile graphs are collated to form a '2D map' of the whole strip. The results demonstrate that accurate, emissivity-independent temperature measurements can be obtained from the wedge-shaped cavity formed where the sheet aluminum joins the roll.
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S. Fiona Turner, S. Fiona Turner, Stuart F. Metcalfe, Stuart F. Metcalfe, Andrew Mellor, Andrew Mellor, Jon Willmott, Jon Willmott, Peter Drögmöller, Peter Drögmöller, } "Accurate thermal imaging of low-emissivity surfaces using approximate blackbody cavities", Proc. SPIE 8354, Thermosense: Thermal Infrared Applications XXXIV, 83540Z (18 May 2012); doi: 10.1117/12.918557; https://doi.org/10.1117/12.918557
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