Mahr offers DAkkS-accredited calibration according to new roughness standard

The new surface standard ISO 21920 has been in force worldwide since the end of 2021. It has brought important changes – for example, new terms and symbols, a new evaluation length_le or the so-called nesting indexes_Nic, _Nis. It also eliminates the distinction between periodic and aperiodic profiles for selecting the correct nesting index. With the introduction of ISO 21920, the previous profile standards ISO 4287, ISO 4288, ISO 13565(-2/-3) and ISO 1302 were withdrawn: they no longer covered all the possibilities of modern measuring devices, in some cases no longer corresponded to current industry practice and showed imprecision in the definition of some characteristic value algorithms.

Supporting the changeover process
Mahr played a key role in driving forward the new international standard – even at project manager level. The DAkkS laboratory has also been accredited for the new roughness standard since January 2024. It can calibrate surface metrology standards – based on the new DIN EN ISO 21920 series of profile standards – and report the corresponding parameters on the calibration certificate. "However, the transition process from the previous profile standards to ISO 21920 will still take some time," says Arne Deppe, Manager Calibration Center Systems Göttingen. "When long-standing parameters or designations disappear and are replaced by new terms, this first has to become firmly established in the minds of those responsible and practitioners." To support this changeover process, the DAkkS laboratory in Göttingen issues calibration certificates for surface standards in accordance with the previous standards and the new DIN EN ISO 21920 series of standards. This allows a direct comparison and makes the innovations visible.

The following changes have been made to the calibration certificates:

1. Specification of the measuring conditions including the setting class Scn in accordance with DIN EN ISO 21920-3

2. Specification of the measurement results in accordance with
a. DIN EN ISO 21920 (2022) → new series of profile standards
b. DIN EN ISO 4287 (1998) → previous standard for specifying the characteristic values

3. Replacement of the characteristic value Rmax/Rz1max by the characteristic value Rzx(l) according to DIN EN ISO 21920-2. The length l is equal to the section length lsc (former length of the single measuring section) according to the default values according to DIN EN ISO 21920-3, Tab. 7.

4. Selection of the standard filter for core roughness parameters
a. DIN EN ISO 21920 → Robust Gaussian filter according to DIN EN ISO 16610-31 (2017)
b. Previous profile standards → Filter method according to DIN EN ISO 13565-1 (1998)

Smallest possible measurement uncertainties reduced
In addition, some designations of the parameters have been adapted, such as the parameters Mr1 (now Rmrk1) and Mr2 (now Rmrk2). Regardless of the standard used for evaluation, the measurement uncertainty of the core roughness parameters is now given as a percentage of the characteristic value itself and no longer in relation to the Rz value of the calibration certificate. "The percentage figures therefore appear higher than before, but when converted into the corresponding value, there is a significant reduction in uncertainty compared to previous figures," says the calibration expert. As part of the accreditation for the new series of standards, the smallest measurement uncertainties that can be specified for all surface parameters have been reduced.
Since mid-2024, surface measuring devices can also be calibrated on site in accordance with DIN EN ISO 21920 at DAkkS level. The prerequisites for this include a roughness measuring device with reference surface and a new MarWin version from v14.30. To find out about the possibilities for on-site calibration of your roughness measuring station, please get in touch with your contact person from the service planning department at Mahr or send your inquiry to dispo-service@mahr.com.

Are you interested in the services of Mahr's DAkkS laboratory? Then please contact our experts directly at dkd@mahr.com.