Two-spheres method for evaluating the metrological structural resolution in dimensional computed tomography

In recent years, x-ray computed tomography has been successfully applied as an innovative coordinate measurement technology for dimensional metrology. An important characteristic to be evaluated when testing the metrological performances of computed tomography systems is the metrological structural resolution for dimensional measurements, which describes the size of the smallest structure that can still be measured within error limits to be specified. The 'two-spheres' concept allows for the investigation of the metrological structural resolution by using a simple reference standard consisting of two touching spheres with the same nominal diameter. This work is aimed at defining and validating an enhanced method based on the 'two-spheres' concept and on a new measurement strategy. Advantages in using this method are discussed and a selection of the factors influencing the results are evaluated through experimental and simulation analyses.