Development of a CCD-based pyrometer for surface temperature measurement of casting billets

In order to achieve high accuracy and good stability of temperature measurement results, an online vision-based temperature field measurement system for continuous casting billets is developed instead of the conventional single-point radiation pyrometer in this paper. This system is a hybrid temperature measurement system which consists of a monochrome array CCD camera with high resolution and a single spot colorimetric thermometer simultaneously. In this system, a narrow-band spectrum radiation temperature measurement model is established for the optical CCD-based pyrometer system, and the non-uniformity of the temperature field measurement due to the inter-element sensitivity deviations of the CCD-array detector and photometric distortion caused by the vignetting in the optical system is analyzed in detail and compensated. Furthermore, in order to eliminate the temperature fluctuation caused by the stripped iron oxide scale on billets, a temperature field reconstruction approach, which took full advantage of the high resolution characteristic of CCD and the distribution character of the surface temperature field of billets, is introduced in this system. Meanwhile, based on the narrow band spectral thermometry theory, the spot temperature measured by the colorimetric thermometer is used to correct the temperature field measured by the CCD camera on-line so as to reduce the temperature measurement error caused by the inconclusive absolute emissivity of different grades of steel and the interference of industrial dust. Currently, the system has been successfully applied and verified in some continuous casting production lines. Industrial trials indicate that the system could effectively eliminate false temperature variation caused by striped iron oxide scale and provide information about changes of processing parameters in the continuous casting production line in real time. (paper)