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Werth Messtechnik and international standardisation

Werth Messtechnik and international standardisation

For a global exchange of goods, manufacturers and buyers must come to an agreement on the conditions. This is made much easier if the same specifications apply across countries or even worldwide. It is the task of the standardisation bodies to define these.

Transnational standardisation is primarily carried out by the International Organisation for Standardisation (ISO). At the national level in Germany, the tasks are performed by the German Institute for Standardisation (DIN) and the Association of German Engineers (VDI). The VDI issues guidelines on technical problems. DIN and ISO, as well as the corresponding bodies in other countries (e.g. ASME and ASTM), publish standards, for example geared to the acceptance and reverification test of coordinate measuring systems.
The characteristics defined in standards (also called specifications) characterise the basic machine performance and thus enable potential customers to make an initial comparison of different coordinate measuring machines and, together with other criteria (costs, availability, etc.), to decide in favour of a machine or a machine type. The most important specifications in coordinate metrology are the permissible length measurement error (MPE E: Maximum Permissible Error of length measurement) and the permissible probing error (MPE P: Maximum Permissible Probing Error). The length measurement error describes the behaviour of the machine in the entire measuring volume, the probing error is essentially determined by the behaviour of the sensor used. Based on these characteristics, the ISO 10360 series of standards provides clear rules for the acceptance and reverification test. If the corresponding standard is part of the contract conditions, the customer can be sure that the measuring machine actually works within the given specifications. The certificate of the German national accreditation body (DAkkS) serves as proof of the correct application of the standards, for example in the Werth calibration laboratory. The use of the calibrated test specimens (standards) described in the standards ensures the traceability of the measuring machines to national and international standards. Furthermore, procedures for determining the measurement uncertainty are described and supplemented by general information on the different technologies of coordinate metrology.

The people behind the standards

VDI and ISO guidelines initially existed only for tactile sensors, although the first coordinate measuring machines contained optical sensors. Since the early 1990s, the guidelines for acceptance and reverification tests of coordinate measuring machines with image processing (VDI 2617-6.1), optical distance sensors (VDI 2617-6.2) and multi-sensor systems (VDI 2617-6.3) have been developed with the significant involvement of Dr. Ralf Christoph, the owner and president of Werth Messtechnik GmbH.

The international standards are jointly developed by representatives from different countries. With Werth's active participation, it was possible to incorporate a large part of the contents from the VDI guidelines into the corresponding ISO standards 10360-7 for image processing, 10360-8 for optical distance sensors and 10360-9 for multi-sensor systems. According to the Vienna Agreement, the member countries of the European Community are obliged to adopt the ISO standards at national level, in the case of Germany as DIN standards. The original VDI guidelines are then withdrawn (VDI 2617-6.3) or redesigned as so-called application guidelines for the application of ISO or DIN standards with further instructions (VDI 2617-6.1 and VDI 2617-6.2).
Dr. Ingomar Schmidt, Head of Standardisation and Industrial Property Rights at Werth, leads the national work in the field of dimensional computed tomography as chairman of the corresponding VDI Expert Committee 3.33 and, together with other German experts, represents the position of the German industry in the responsible ISO committee ISO TC213 WG 10.
The guideline VDI 2617-13 on the acceptance and reverification test of coordinate measuring machines with computed tomography (CT) sensors was developed in the VDI technical committee 3.33 and published in 2011. The transfer to an ISO standard began as early as 2012. This has not been completed to date, as there are differing opinions on the question of whether the specifications should describe the "best" performance of the machines for selected measuring tasks or the worst imaginable performance (so-called worst case). If the specifications are tested on relatively "simple" workpieces such as multi-sphere standards, the performance of the machines can be demonstrated under good conditions and comparability with coordinate measuring systems with other sensors can be created. From the point of view of the VDI committee, this is the most important basic specification. However, for coordinate measuring systems with CT, workpiece material and geometry can also have a great influence on the measurement uncertainty, especially for metal or multi-material workpieces. In such cases, it is possible that the measurement uncertainties for measurements on real workpieces differ significantly from the specifications of the basic machine. This measurement task-specific measurement uncertainty is part of the measurement process capability and is dealt with in separate guidelines and standards.
Werth is particularly involved in the standardisation of coordinate metrology with optics, computed tomography and multi-sensor systems. This includes participation in meetings and working sessions at national (VDI, DIN) and international (ISO) level as well as bilateral discussions with international stakeholders.

By participating in standardisation committees, Werth actively shapes the future of coordinate metrology.

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