Automatic wavelength spectrometer calibration during arc-welding process

Abstract

Spectroscopic analysis techniques are widely used in a variety of scientific areas. The availability of low-cost CCD spectrometers has also allowed their development in several industrial applications, like on-line analysis of arc and laser welding processes. A correct spectrometer wavelength calibration is always required, specially when changes in ambient temperature are to be found, or when the optical fiber attached to the spectrometer is replaced. This calibration procedure commonly involves the recalculation of a pixelwavelength polynomial by means of regression techniques after having defined a new experimental setup. Besides, specific calibration lamps are needed to use some known emission lines in the regression stage. In this paper, a technique which allows a real-time, in-process automatic wavelength calibration of CCD spectrometers in arc-welding processes is presented. The key point in the automatic calibration process is the real-time identification of some particular emission lines emitted from the plasma generated during the welding process. TIG welding tests performed on stainless steel plates will show the feasibility of the proposed technique. As well as for laser welding, the automatic wavelength calibration procedure could be easily extended to some other spectroscopic techniques.