## 5 Conclusions  
Performing dynamic line scan thermography measurements is a difficult task without consulting an expert. The various parameters have an impact on each other, making it challenging to estimate the correlation between one and another. Using a response surface however, it is possible to find the best parameter set based on the defect parameters such as diameter and depth beneath the inspected surface. The algorithm to find the optimal parameter set focuses on maximising the temperature difference between the area above the defect and a sound area. In order to prevent the sample from overheating a maximum use temperature can be given as input parameter next to the defect parameters and the ambient temperature. The resulting parameter set consists of following parameters: Defect  
Figure 12: The influence of the intermediate distance between samples on the contrast is visualised in four situations. Image (**a**) represents a simulation of three defects with a diameter of 25 mm, a depth of 5 mm under the surface and an intermediate distance of 27 mm between the centres of the defects. The heat reflected by the defects influences each other resulting in a reduction of the contrast between the separate defects. The resulting hotspot is bigger than the area of the defects. Visualisation (**b**) represents a similar simulation performed on defects of 12 mm diameter, starting 5 mm underneath the top surface and at an intermediate distance of 15 mm of each other. The heat reflected by the separate defects influences the contrast making it impossible to distinguish the defects. Smaller defects, however, reflect less energy in comparison to bigger defects making it harder to detect them. Multiple small defects close to each other will show as a bigger defect, but with more contrast than the individual defects. Defects of different diameters are simulated in subfigure (**c**) where the intermediate distance is 25 mm between the defects. The defects have diameters of 25 mm, 20 mm and 12 mm. The two bigger defects can still be distinguished from each other. The smallest defect however shows as a part of the other defect. Subfigure (**d**) shows the influence of defects placed at different starting depths from the top surface. The defects all have a diameter of 25 mm and are placed at a depth of 5 mm, 10 mm and 15 mm underneath the surface. As the heat wave requires a specified amount to reach the top of the defect and reflect to the top surface, the different defects will not result in hotspots at the same moment in the inspection. Therefore, the influence of deeper defects will effect the top defect minimally. Deeper defects, however, will be less visible to detect because of the hotter regions caused by defects above. The defects closest to the surface will not have the biggest contrast since the parameters are not optimal, but they will still remain hot, disturbing the detection of defects at a greater distance from the top surface. This occurrence makes a flat bottom hole plate with defects at different depths not the most suitable test case. Diameter \(D_{defect}\), Defect Starting Depth \(d_{start}\), Ambient Temperature \(T_{ambient}\), Maximum Use Temperature, Heat Load \(P_{heat}\), Source Velocity \(v_{source}\), Distance Between Heat Source and Thermal Camera \(d_{heat-cam}\) and Height Thermal Camera \(d_{height}\). Measurements performed with an optimised parameter set result in good contrast rapidly. Differing from the optimised parameter set will result in contrast loss and even losing the possibility to detect the defects. This research paper only focused on the creation of a response surface for DLST measurements on PVC samples as this is the standard testing material for thermography. In order to increase the usability of the technique in the industry, the routine will be expanded towards a general optimisation. The material properties of PVC will be replaced by additional input parameters for the response surface.