Calibration of thermal expansion coefficient of length bars and long gauge blocks.

NPL services for thermal expansion measurement of length bars & long gauge blocks

One of the biggest sources of uncertainty for users of long gauge blocks and length bars is the lack of knowledge of the coefficient of thermal expansion (CTE). This can lead to measurement errors up to 1 µm for a 1 m standard used in a laboratory with 1 °C control. This uncertainty can limit the effectiveness of using these standards on large equipment such as high accuracy CMMs.

To reduce this uncertainty in the calibration and use of end standards, NPL offers a UKAS accredited measurement service for the coefficient of thermal expansion of long series gauge blocks and length bars. This service is available by prior booking.

Calibration service details

Measurement of the thermal expansion coefficient of length bars and gauge blocks over 100 mm in length is performed by interferometry.

The CTE at 20 °C is calculated from length measurements made over the temperature range 15 °C to
25 °C.

The overall uncertainty of measurement of the coefficient of thermal expansion depends on the length of the bar, the value of the expansion coefficient and the spread in the measurement results. It is normally less than 0.5 x 10^-6 / °C.

Further information

• Contact us for more details, to request a quotation or to schedule a calibration
• Notes on the care and use of gauge blocks ( PDF 18 KB)

Publications

• Lewis, A J, Long-term study of gauge block interferometer performance and gauge block stability, Metrologia,  2010, 47, 473-486
• Lewis, A J, Measurement of length, surface form and thermal expansion coefficient of length bars up to 1.5 m using multiple-wavelength phase-stepping interferometry, Meas. Sci. Technol., 1994, 5, 694 – 703
• Lewis A J, Pugh D J, Interferometer light source and alignment aid using single-mode optical fibres, Meas. Sci. Technol., 1992, 3, 929-930
• Lewis A J, Absolute length measurement using multiple-wavelength phase-stepping interferometry, PhD Thesis, 1993, Imperial College, University of London
• Lewis A J, Key Comparison CCL-K2 – Measurement of long gauge blocks – Final Report, Metrologia, 2003, 40 Tech. Suppl. 04004
• Lewis A J, Final Report on EUROMET Key Comparison EUROMET.L-K2: Calibration of long gauge blocks, Metrologia, 2006, 43 Tech. Suppl. 04003

Contact

Customer Service tel: +44 20 8943 8631
E-mail: dimensional_enquiries@npl.co.uk