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.