Topography fidelity determination of optical surface texture measuring instruments - an inter-laboratory comparison

The topography fidelity is one of the fundamental metrological characteristics defined by the new ISO calibration framework. It must be considered and analyzed within the scope of a comprehensive calibration. However, there is still a lack of practical experience in the evaluation and comparison of topography fidelity. To generate a broad database and identify relevant factors that influence the topography fidelity of a surface topography measuring instrument, three additively manufactured chirp material measures were circulated in an interlaboratory comparison as part of the EMPIR project TracOptic. 15 participants in nine European countries performed 658 areal surface topography measurements with 120 different optical measurement configurations. Various optical instruments were employed, including confocal microscopes, coherence scanning interferometers, focus variation instruments, phase-shifting interferometers, and optical profilers. We describe the results of the inter-laboratory experimental comparison and identify influence parameters on the topography fidelity. The results emphasize that topography fidelity is a metrological characteristic with a high information content that allows a comparison of the transfer characteristics of various types of surface topography measuring instruments. Although many optical surface topography measuring instruments produce comparable results, their ability to measure large slopes can be identified as a key variable.