Intercomparison for coefficient of thermal expansion of gauge blocks

Project Description

The exact knowledge of the coefficient of thermal expansion is crucial for highly accurate dimensional measurements. Is has got additional actuality by the discussions concerning an eventual change of the reference temperature for length measurements. Within the EUROMET intercomparison #229 for short gauge blocks, only two laboratories contributed results for the coefficient of thermal expansion. Several NMI's (NPL, PTB, OFM) are actually developping dedicated instrumentation for the measurement of the expansion coefficient. An intercomparison in this field is therefore very helpful to ascertain the measurement capabilities of the new instruments.

Three 100 mm gauge blocks of different material (steel, tungsten carbide, ceramic) are circulated. The expansion coefficient has to be measured around 20 °C. Otherwise, no detailed instructions should limit the variety of measurement methods.

Final Report 1995-09-15

Four gauge blocks of 100 mm length of different material (steel, tungsten carbide, ceramic, zerodur) werecirculated during 1993 / 1994. The quantity to be measured was the coefficient of thermal expansion of the four materials at 20 °C. Not only the linear coefficient, but also the higher terms were reported. Seven entirely different measurement setups were involved in this intercomparison. The last measurements were reported in June 94. A first compilation of the results was sent to all participants in September 94. The final report has been completed in September 1995.
The agreement of the measured expansion coefficients is generally better than 0.1 ppm/K. It depends on the material of the gauge block. All participating laboratories reported detailed uncertainty estimations. A comparison of the measurement results with the stated combined uncertainties shows, that the uncertainties were probably estimated too conservatively.

The results are published in the September 1995 issue of the EUROMET Length Bulletin.