ABSTRACT
Thermographic testing is an inspection method that primarily indicates the presence of discontinuities in a tested sample. Its application to coatings can indicate a presence of local thickness variations; however, it mostly does not bring any quantitative information about the thickness of the coatings. This contribution is focused on a quantification of the thermographic inspection, which would make possible an evaluation of coating thickness differences. Flash-pulse thermographic testing was applied to thermally sprayed coatings. The importance of a precise synchronization of flash source and thermographic recording was determined. Different evaluation methods were analyzed, and their comparison showed that a time-power transformation method is the most suitable for quantification of the inspection results.
ABSTRACT
The paper deals with flash-pulse thermography, which is one of the most used thermographic inspection methods. The method is based on flash excitation of an inspected object and an analysis of its thermal response recorded by an infrared camera. This paper deals with a time-power transformation method (P-function) for an evaluation of the flash-pulse thermography measurement. The method is based on a transformation of the measured thermal response using a power function of time. An adaptation of the method is introduced, and an experimental investigation of the method is presented. The method and the evaluation procedure are described. A flash-pulse inspection of an experimental sample is performed, and the results of the inspection obtained by the P-function method and by a fast Fourier transform evaluation are compared using a contrast-to-noise ratio ranking. Advantages of the P-function method resulting from its numerical outputs for an estimation of the depth of defects are described. An influence of noise reduction and data preprocessing is discussed.
ABSTRACT
Active thermography is an infrared-based technique for nondestructive testing of materials. It often uses advanced evaluation techniques based on temperature spatial and temporal changes. Results of active thermography are contrast differences, which indicate possible defects in an inspected material. These differences cannot be quantified by temperature. This contribution is focused on the active thermography results' evaluation parameters and the contrast-to-noise ratio method, which can be used for quantitative evaluation of the results. Different result interpretation procedures are introduced. The influence of a selection method for indication and reference regions and the effect of image scaling on inspection results are discussed.
ABSTRACT
Inspection of solar cells is an important part of their production process because even small defects can cause a significant drop of a whole photovoltaic module performance. LED illuminated lock-in (LEDILIT) and flash-pulse thermographic techniques (FPT) were compared in this study. Lock-in methods are more commonly used for solar cell inspection. The aim of the study was to discover if the FPT is the appropriate method for inspection of defects of multicrystalline solar cells. Experimental setup, inspection results, and advantages/disadvantages of both methods are presented. It is demonstrated that the LEDILIT is the suitable technique for inspection of defects connected with a photovoltaic effect. Local shunts, cracks, and artificial laser-made defects were detected. Only some of the most significant shunts and laser-made defects were identified by the FPT. However, the FPT inspection is much faster than the LEDILIT. The FPT was also able to indicate an inhomogeneity at a bottom layer of a cell, which was not connected with a photovoltaic effect and not revealed by the LEDILIT.
