Calibration of line scales EUROMET.L-K7

Project Description

Distances between the centers of lines will be calibrated on one 100 mm glass line scale. The measurements will be performed in a predefined section (along the line height).
The artifact will be provided by NPL (NPL product).
The comparison will be a key comparison in the framework of the Mutual Recognition Arrangement (MRA) of the Metre Convention and shall support confidence in calibration and measurement certificates issued by the participating national metrology institutes.

This project – comparison was agreed at the EUROMET TC-L meeting in 2005. Participants from all RMO’s will be invited.

Final Report 2012-08-31

The project has been completed and the the resultes are available in the KCDB.

The intention of this comparison was to determine and to document capabilities of the participating NMIs to carry out line scale calibrations on high quality line scales produced for industrial purposes. The line scales used for the comparison were designed and produced by NPL in UK. Two scales of same design and very similar quality were kindly donated by NPL.
The idea for the comparison arised at the Euramet TCL meeting in October 2005.

The comparison started in July 2006 and the last measurement was performed in December 2008.

Originally, 31 NMIs expressed interest for participating in the comparison. During the comparison, two laboratories decided not to perform measurements due to technical reasons and one new laboratory was approved to take part. At the end, 30 laboratories reported their results.
Participating laboratories were divided into 2 groups in accordance with their geographical position (in order to minimize travel times and expenses for the transportation of the standards). Linking laboratories between the groups were chosen among participants in Nano3 project (NPL and METAS).
Although the standards traveled through a large number of laboratories, no significant damages were noticed. Some laboratories reported some dirt and scratches, but no significant influence on the results were indicated. The comparison ran quite well within the schedule in spite of some customs problems.

Results were evaluated for each group separately and also after linking groups by using Bayesian statistics. The performance of the participants was evaluated by using En value as the acceptance criterion. The reference value was calculated as the weighted mean of reported results for each measuring point. The Birge criterion and Chi-test were used for approving calculated reference values.
In the conclusion it can be summarised that the comparison was successful and has shown realistic picture about calibration and measurement capabilities of participating laboratories.