Gage Block CTE

The diagram shows a typical coefficient of thermal expansion. While it does not change tremendously as the temperature changes, it does change enough that the details would need to be known for very accurate measurement.

The ASME B89.1.9 Gage Block Standard says that steel gage blocks should have a CTE between 10.5 - 12.5 ppm/°C at 20 °C. This block satisfies this criteria, but over a few degrees the CTE will change by a few per cent.

Calibration laboratories address the problem by keeping the lab temperature very near 20 °C, the lab at NIST stays within 0.1 °C of 20 °C at all times, making corrections for thermal expansion so small as to be negligible. This strategy is not possible in most factories, where temperature variations of 5-10 °C may occur.

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Date Created: Monday, October 15, 2001
Last Updated: Tuesday, November 09, 2004