Werth Messtechnik and international standardisation

International standardisation is primarily carried out by the International Organisation for Standardisation (ISO). At national level in Germany, the tasks are performed by the German Institute for Standardisation (DIN) and the Association of German Engineers (VDI). The VDI draws up guidelines on technical problems. DIN and ISO, as well as the corresponding committees in other countries (e.g. ASME and ASTM), publish standards, for example focussing on the acceptance and reverification test of coordinate measuring systems.
The characteristics defined in standards (also known as 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 (cost, availability, etc.), to decide on a machine or 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, while the probing error is largely determined by the behaviour of the sensors used. The ISO 10360 series of standards provides clear rules for the acceptance and reverification test based on these characteristics. If the corresponding standard is part of the terms of the contract, the customer can be sure that the measuring machine actually works within the specifications. The certificate issued by the German national accreditation body (DAkkS) serves as proof of the correct application of the standards, for example in the Werth calibration laboratory. By using the calibrated test specimens (calibration standards) described in the standards, the traceability of the measuring machines to national and international standards is ensured. Procedures for determining measurement uncertainty are also described and supplemented by general information on the various coordinate metrology technologies.

The people behind the standards

VDI and ISO guidelines initially only existed for tactile sensors, although the first coordinate measuring machines contained optical sensors. Since the early 1990s, the guidelines for the acceptance and reverification test 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 being jointly developed by representatives from various countries. With the active participation of Werth, a large part of the content from the VDI guidelines was incorporated 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 states 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 the 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 Technical Committee 3.33 and, together with other German experts, represents the position of German industry in the relevant 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 VDI Technical Committee 3.33 and published in 2011. The transition to an ISO standard began in 2012. This has not yet been finalised, as there are different opinions on the question of whether the specifications should describe the "best" performance of the machines for selected measurement tasks or the worst conceivable 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 established. From the point of view of the VDI committee, this is the most important basic specification. In the case of coordinate measuring systems with CT, however, the workpiece material and geometry can also have a major influence on the measurement uncertainty, particularly in the case of 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 device. 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 level (ISO) as well as bilateral discussions with international stakeholders.

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