Infra-red temperature measurement of bright metal strip using multiple reflection in a roll-strip wedge to enhance emissivity

In a continuous annealing furnace, strip temperature was measured using radiation thermometers aimed, at a shallow angle to the strip, into the wedge-shaped cavity formed between the strip and a roll. The dependence of the observed temperature on thermometer operating wavelength, field-of-view, aiming and polarisation was investigated. Comparison was made against reference temperatures taken with a surface pyrometer and also derived from strip metallurgy. Control of the furnace, using a wedge thermometer, was demonstrated. The technique is potentially applicable in a wide variety of bright metal processing furnaces.