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Calibration Lab Achieves Measurement Uncertainties of Ten Nanometres

The DAkkS-accredited laboratory of eumetron GmbH in Aalen, Germany offers DAkkS calibrations traceable to national standards with an extremely high level of accuracy. The experts use special procedures to calibrate plug gauges, setting rings, calibration spheres and hemispheres as well as test specimens and other reference standards or reference workpieces. Standards are used to adjust, calibrate, check and set dimensional measuring systems and are therefore important tools in quality assurance. When it comes to roundness measurement, eumetron GmbH relies on two RONDCOM form measuring devices from ACCRETECH. In doing so, eumetron GmbH achieves measurement uncertainties of just ten nanometres.

Quality assurance is indispensable for practically all industries. And length measurement technology is at the centre of quality assurance in most manufacturing industries and their service providers. Exact dimensional accuracy in accordance with specified tolerance values must be guaranteed to ensure perfect usability, function, reliability and durability of the workpieces. Testing and compliance with tolerances, taking measurement uncertainty into account, is the task of quality assurance using a wide variety of length measuring devices, which must be subjected to a calibration process on a regular basis. Deviations due to geometric errors, thermal influences or deviations in shape and position cause measurement deviations that are different at every point in the measurement volume. By comparing current production with reference workpieces, changes in the production process can be recognised at an early stage.

Such dimensional measuring systems include, for example, coordinate, form, contour, height and surface roughness measuring devices, as well as profile and measuring projectors, but also measuring microscopes, computer tomographs, laser trackers, fringe light projection and photogrammetry systems.

Reference standards are used for setting, checking, adjusting and calibrating, which can be used to reliably and traceably assess the deviations and therefore the accuracy of the meas-uring systems. Measuring mandrels, setting rings, calibration spheres and calibration hemispheres or test specimens consisting of several reference standards must therefore be calibrated regularly. Calibrated reference workpieces are necessary in many cases to determine the measurement uncertainty of test characteristics occurring on site at the user’s premises.

Certified by the German Accreditation Body (DAkkS), eumetron GmbH in Aalen, Germany, is one of the world’s leading calibration laboratories for reference standards. The approximately 35 employees carry out traceable DAkkS calibrations with very low measurement uncertainties, which only a few accredited laboratories worldwide can offer. Its customers include extremely renowned manufacturers and users in the field of tactile and optical measuring systems as well as manufacturers of reference standards, calibration laboratories and measuring service providers. The company, run by the two managing directors Klaus Banzhaf and Theo Hageney, has several Class 1 precision measuring rooms, i.e. the highest category. This classification allows only minimal deviations from the reference temperature of 20 °C – essential for correct measurement results. Temperature and expansion are significant factors influencing the measurement uncertainty.

In their measuring rooms, the calibration experts use two form measuring devices from the RONDCOM product line of the Japanese measuring technology specialist ACCRETECH, which are popular with quality assurance experts all over the world for their stability and reproducibility as well as their powerful and user-friendly software. During one of the regular assessments, auditors from the Physikalisch Technische Bundesanstalt (PTB), the highest body in the national calibration hierarchy, paid great respect to the devices after a test measurement on a test specimen. Finally, the RONDCOM used was able to determine the exact value with a deviation of just a few nanometres.

Eumetron GmbH is able to offer the highest accuracy standards with its equipment and its enormous measurement technology expertise. This expertise includes stable and proven procedures with minimised measurement uncertainty for the DAkkS calibrations performed. For example, the multi-layer method for roundness measurements. The test standard is measured at different points and with different orientations. This sophisticated process allows systemic and random deviations to be almost completely eliminated. “This enabled us to reduce the measurement uncertainty from 100 nanometres to just ten nanometres,” explains eumetron GmbH technician Andreas Pierro. “Only a few laboratories in the world achieve this,” adds Klaus Banzhaf. For the measurement of roundness deviations in setting rings and mandrels, inner and outer cylinders as well as balls and hemispheres, eumetron GmbH has achieved a highly impressive expanded measurement uncertainty of U = 0.01 µm + 0.05 x10-6 x RONt (RONt: roundness deviation of the part to be calibrated). Around 180 test parts pass through the RONDCOM devices at the German company every month.

One nanometre corresponds to 10-9 metres, i.e. one millionth of a millimetre or one billionth of a metre – an order of magnitude that can only be grasped by comparison for hu-man understanding. For example, one nanometre is to one metre as the diameter of a one-cent coin is to the diameter of the globe.

With an accreditation, the DAkkS confirms that organisations such as calibration, testing, inspection or certification bodies perform their activities in accordance with internationally valid standards. Regular audits by the DAkkS ensure this in the long term. DAkkS calibrations are the highest calibration level below the national standards. Traceability to national standards is directly guaranteed with these calibrations. Only accredited laboratories carry them out in accordance with DIN EN ISO 17025. The laboratories calculate the exact measurement uncertainties and assign them to each measurement result. DAkkS laboratories must prove for all calibrations that the measurement uncertainties specified in the calibration certificate issued are adhered to or fallen below. This is ensured on an ongoing basis by a QM system in accordance with DIN EN ISO 17025 . Accredited DAkkS calibration laboratories such as eumetron GmbH thus guarantee the safety of products, processes and services.

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