Volume 89, Issue 10 - Tagung Messunsicherheit Erfurt 2021 / Gastherausgeber: Klaus-Dieter Sommer, Thomas Fröhlich, Olaf Schnelle-Werner

Zusammenfassung In diesem Beitrag wird das Konzept der Redundanz aus metrologischer Sicht betrachtet. Anstatt die Anzahl der Messungen und der Freiheitsgrade des Systems zu zählen oder informationstheoretische Betrachtungen der Entropie zu machen, wird ein relativ praktischer und anschaulicher Ansatz gewählt, in dem der Redundanzbegriff eng mit der Messunsicherheit verknüpft wird. Metrologische Redundanz wird definiert über eine Änderung in der Messunsicherheit der Messgröße, wenn Sensoren aus dem Netzwerk herausgenommen werden. Eine alternative Angabe ist die Höchstanzahl der Sensoren, die aus dem Netzwerk herausgenommen werden können, ohne dass die Unsicherheit der Zielgröße über einen vorher gewählten Wert steigt. Verschiedene Metriken werden definiert, um die Redundanz zu quantifizieren. Die Begriffe und Metriken werden anhand verschiedener Beispiele erläutert. Diese beinhalten sowohl simulierte als auch reale Netzwerke und die Sensoren messen entweder dieselbe Größe (homogenes Netzwerk) oder unterschiedliche Größen (heterogenes Netzwerk).

Currently, aeroplane assembly is carried out in rigid, aeroplane-specific assembly lines which causes high costs for reconfiguration. One approach to reduce the costs is to use automated lineless assembly systems. To enable automated reconfiguration of assembly processes, continuous availability of factory-wide position data is required. When providing these data, a challenge is the combination of large-volume, “global” measurement sensors and high-precision, “local” measurement sensors to a single easily interpretable indication. The aim of this research work is the fusion of local and global measurement data within a so-called Global Reference System (GRS). For data fusion, sensors are linked to a reference measurement system covering the entire assembly area. The relationships between the coordinate systems of the individual measurement systems are described using homogeneous transformations. Using Kalman filters, the transformed measurement data are fused into a vector containing information about the pose of aeroplane components. Furthermore, a GUM-compliant statement about the measurement uncertainty of the fused sensor data is made by specifying the covariance matrix. The method is validated using a demonstrator covering the essential aspects of the assembly process. The result is a validated procedure for data fusion and for the determination of the combined measurement uncertainty in a GRS.

The ability of industrial X-ray computed tomography (CT) to scan an object with several internal and external features at once causes increasing adoption in dimensional metrology. In order to evaluate the quality of a measurement value, the task-specific measurement uncertainty has to be determined. Currently, VDI/VDE 2630 part 2.1 gives a guideline to determine the uncertainty of CT measurements experimentally by conducting repeated measurements. This is costly and time-consuming. Thus, the aim is to determine the task-specific measurement uncertainty numerically by simulations (e. g. according to the guide to expression of uncertainty in measurement (GUM) Supplement 1). To achieve that, a digital twin is necessary. This contribution presents a simple first approach how a digital twin can be built. In order to evaluate this approach, a study comparing measurements and simulations of different real CT systems was carried out by determining the differences between the measurement results of the digital twin and of the measurement results of the real-world CT systems. The results have shown a moderate agreement between real and simulated data. To improve on this aspect, a standardized method to characterize CT systems and methods to implement CT parameters into the simulation with sufficient accuracy will be developed.

In this article a new approach for the direct traceability of interferometric length measurements in nanopositioning- and measuring machines is presented. The concept is based on an optical frequency comb tied to a GPS disciplined oscillator. The frequency comb serves as a highly stable reference laser with traceable optical frequencies. By directly stabilizing the metrology lasers of a nanopositioning and -measuring machine to a single comb line a permanent link of the laser frequency to an atomic clock is created allowing direct traceability to the SI meter definition. The experimental conditions to provide traceability will be discussed. Furthermore, it is demonstrated how the long-term frequency stability of an individual comb line can be transferred onto the metrology lasers enhancing their stability by three orders of magnitude.

Micro and nano coordinate measuring machines (CMMs) require small and well characterized micro spheres as probing elements. However, established strategies and instruments have mostly been designed for and applied to the characterization of larger spheres in the range of millimetres or above. That is why we have recently focused our attention towards a novel strategy which is based on a set of atomic force microscope (AFM) surface scans in conjunction with a stitching algorithm. Initial experimental results are promising, but point to several influences which require further attention. We have, therefore, begun to model the measurement strategy and applied it on simulated spheres, in order to investigate and reduce some of these influences. The model is currently limited to effects which are related to the radius and form of the sphere. Other influences, like the AFM tip, are being ignored. In this paper, we introduce the essential parts of this model and apply it on spheres of different mean radii (60 µm, 100 µm and 150 µm) and of different qualities (Grade 3 and Grade 5). The investigations illustrate that the measurement object can have a significant influence on the measurement result and needs to be considered.

Zusammenfassung Eine der neuesten Entwicklungen im Bereich der mobilen Kommunikation heißt 5G, für Mobilfunksystem der fünften Generation. In Europa hat die Einführung der 5G-Technologie viele Ängste in der Bevölkerung hervorgerufen. Die Technologie ist komplex und erfordert Spezialwissen. Der Nachweis, dass eine Basisstation die Anforderungen an die Strahlenbegrenzung erfüllt, erfordert zuverlässige Messmethoden. Die Messunsicherheit, die jedoch schwer abzuschätzen ist, spielt dabei eine wichtige Rolle. Dieser Artikel behandelt die Problematik der Konformitätsbewertung komplexer Systeme am Beispiel einer 5G-Basisstation.

Recent research activities in dynamic pressure metrology have been mainly focusing on the development of primary standards like the shock tube or drop-weight apparatus to establish traceability to SI. However, these calibration facilities require a high level of expertise leading to elaborate and time-consuming calibrations. The development of secondary calibrators, based on the reference sensor principle, offering efficient and cost-effective calibrations is essential to meet the needs for industry and to disseminate the dynamic pressure quantity to a wide end-user community. This paper reports a novel secondary calibrator for dynamic pressure measurements up to 300 bar with an expanded uncertainty of about 3.0 %. A heating option enable calibrations at elevated temperatures up to 200 °C making it an ideal solution for convenient calibrations of dynamic pressure transducers used for measurement in internal combustion engine applications.