Development of a fast fiber-optic two-color pyrometer for the temperature measurement of surfaces with varying emissivities

A two-color pyrometer has been developed to measure the temperature of surfaces with unknown emissivities during high speed turning processes. Quartz fibers enable measurements at locations with limited optical access. The sensitivity of the pyrometer has to be high enough to measure temperatures down to 300 °C of an aluminum alloy with an emissivity as low as 0.2. The accuracy of the two-color pyrometer has been compared with the accuracy of monochromatic pyrometers for different metallic surfaces. The different arguments for the choice of the two pyrometer wavelengths 1.7 and 2.0 μm are explained. The influences of the surface emissivities, the digitization, and the noise on the absolute and relative measurement error have been determined. Fast amplifiers and data acquisition allow a maximum time resolution of a few microseconds and a local resolution of ∼0.5 mm2. Some test measurements of an aluminum alloy surface are presented.