Comparison of squareness measurements

Project Description

The comparison measurements of squareness standards are aimed to compare and verify the declared calibration measurement capabilities of participating laboratories and to investigate the effect of systematic influences in the measurement process and their elimination.

The standards are to be calibrated by the measurement process currently used in the participant’s lab (e.g. in the horizontal or vertical position of the square).

Two standards shall be calibrated:

• Granite square of the rectangular shape (500x300x70) mm with two marked functional surfaces
• Cylindrical squareness standard of steel with 100 mm diameter and 400 mm height with marked positions for the profile lines
   

The following parameters have to be calibrated:

• interior angle between the two functional surfaces of the granite square, defined by the angle between the LS regression-lines fitted through the measurement profiles
• interior angles between the LS-line fitted through the measurement profiles at 0°, 90°, 180°, 270° and the envelope plane of the basis (resting on a surface plate)
• local LS straightness deviation for all measured profiles of both standards (results to be reported in electronic format)
   

For all reported results, an uncertainty budget and the combined standard uncertainty uc, evaluated according to ISO-guide to the expression of uncertainty of measurement, has to be given.

Final report 2005-03-25

This regional supplementary comparison was the first comparison in this field. It has provided the independent information about metrological properties of measuring equipment and method comparing to participated NMIs.

Comparison results of squareness were in the good conformity with expected values of standards for most of participated laboratories. Some NMIs probably did not include all the possible error sources into the calculation, and therefore their uncertainties were too small in relation to the deviations from the reference.

Shape of profile lines provided by some NMIs was significantly different from the weighted mean. The reason could be in the insufficient compensation of the errors of guiding probing part in the measuring procedure.