Fast algorithm for spectral processing with application to on-line welding quality assurance

Abstract

A new technique is presented in this paper for the analysis of welding process emission spectra to accurately estimate in real-time the plasma electronic temperature. The estimation of the electronic temperature of the plasma, through the analysis of the emission lines from multiple atomic species, may be used to monitor possible perturbations during the welding process. Unlike traditional techniques, which usually involve peak fitting to Voigt functions using the Levenberg–Marquardt recursive method, sub-pixel algorithms are used to more accurately estimate the central wavelength of the peaks. Three different sub-pixel algorithms will be analysed and compared, and it will be shown that the LPO (linear phase operator) sub-pixel algorithm is a better solution within the proposed system. Experimental tests during TIG-welding using a fibre optic to capture the arc light, together with a low cost CCD-based spectrometer, show that some typical defects associated with perturbations in the electron temperature can be easily detected and identified with this technique. A typical processing time for multiple peak analysis is less than 20 ms running on a conventional PC.

Optical Methods for On-line Quality Assurance of Welding Processes in Nuclear Steam Generators

“…Two different alternatives have been explored in this regard. An initial approach has been carried out by means of a smoothing algorithm, which was already implemented in (Mirapeix et al, 2006) to perform the background subtraction stage. The only parameter to take into account is the size (in spectral bands) of the moving window.…”

“…For this task, the linear phase operator (LPO), a sub-pixel technique, has been proposed (Mirapeix et al, 2006). Figure 3 (left) shows a captured spectrum for a TIG (Tunsgten Inert Gas) welding in which several elements (Iron, Manganese…) have been identified in real time.…”

Brillouin frequency shift estimation in BOTDA via subpixel processing

“…In this paper we explore the employment of subpixel algorithms instead of the Lorentzian fitting. These algorithms have been extensively used for image processing [7], but they have been also applied in fiber Bragg grating (FBG) applications [8] or plasma optical spectroscopy for welding diagnostics [9]. Their computational performance as well as the resulting accuracy for different scanning granularities will be analyzed for distributed BOTDA measurements over 50km.…”

Welding diagnostics based on feature selection and optimization algorithms

“…The traditional approach when using plasma spectroscopy for welding diagnostics is based on the estimation of the plasma electronic temperature T e [1,3]. This is typically carried out using a simplified expression where only two emission lines of the plasma spectrum are involved.…”