Quality control of radiant heaters

Abstract

Based on infrared thermography, a non-destructive testing and evaluation (NDT&E) procedure is proposed for defects assessment on radiant heaters. Under a short electrical excitation, an infrared camera captures the cooling process of the heaters. Breaking the thermographic images down not only makes easiest the location of defects but it also allows their classification. Several kinds of defects have been taken into account: lack of supporting brackets; defects originated by a deficiency in the heating material; those from an excess of heating material; and those parts of the heating elements which are in wrong contact (non-contact or semi-buried) with the substrate. Each kind of analyzed defect has a different thermal history after the electrical excitation because of its nature. By means of computer vision techniques, the defects can be spatially located. The "chain code" was employed to follow the pattern of the heating element and so concentrate the analysis in points belonging to the pattern. A good agreement with analysis made under human's criteria is achieved. However, using infrared cameras and processing the data with computer vision algorithms allows controlling in-site the quality of the product without any subjectivity. So, the heaters manufacturing industry could come along with the implementation of this automatic detection procedure. Experimental results that validate the proposed method will be presented and discussed in this paper.