New radiation thermometry systems have been developed and applied to continuous annealing and continuous galvanizing lines. The new method, which is referred to as the TRACE method, uses a prior knowledge about the functional relationship between two spectral emissivities of target materials. Temperature and emissivities of galvannealed steel, whose emissivity variation is mainly caused by the change in surface roughness due to the growth of ironzinc alloy crystals, are measured by dual-spectral type TRACE systems. Polarized type TRACE systems are useful in measuring those of oxidizing cold-rolled steel, whose emissivity variation is mostly attributed to the oxidation.
Principle of measurement of the TRACE method, and the recent development of PbS-polarized TRACE system and scanning type of Ge-PbS dual spectral TRACE system are discussed.