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Gauge Block Handbook

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Gauge block calibration is one of the oldest high precision calibrations made in dimensional metrology. Since their invention at the turn of the century gauge blocks have been the major source of length standardization for industry. In most measurements of such enduring importance it is to be expected that the measurement would become much more accurate and sophisticated over 80 years of development. Because of the extreme simplicity of gauge blocks this has only been partly true. The most accurate measurements of gauge blocks have not changed appreciably in accuracy in the last 70 years. What has changed is the much more widespread necessity of such accuracy. Measurements, which previously could only be made with the equipment and expertise of a national metrology laboratory, are routinely expected in private industrial laboratories.

1. Length
1.1 The meter
1.2 The inch

2. Gauge blocks
2.1 A short history of gauge blocks
2.2 Gauge block standards (U.S.)
2.2.1 Scope
2.2.2 Nomenclature and definitions
2.2.3 Tolerance grades
2.2.4 Recalibration requirements
2.3 International standards

3. Physical and thermal properties of gauge blocks
3.1 Materials
3.2 Flatness and parallelism
3.2.1 Flatness measurement
3.2.2 Parallelism measurement
3.3 Thermal expansion
3.3.1 Thermal expansion of gauge block materials
3.3.2 Thermal expansion uncertainty
3.3 Elastic properties
3.4.1 Contact deformation in mechanical comparisons
3.4.2 Measurement of probe force and tip radius
3.5 Stability

4. Measurement assurance programs
4.1 Introduction
4.2 A comparison: traditional metrology vs measurement assurance programs
4.2.1 Tradition
4.2.2 Process control: a paradigm shift
4.2.3 Measurement assurance: building a measurement process model
4.3 Determining Uncertainty
4.3.1 Stability
4.3.2 Uncertainty
4.3.3 Random error
4.3.4 Systematic error and type B uncertainty
4.3.5 Error budgets
4.3.6 Combining type A and type B uncertainties
4.3.7 Combining random and systematic errors
4.4 The NIST gauge block measurement assurance program
4.4.1 Establishing interferometric master values
4.4.2 The comparison process Measurement schemes - drift eliminating designs Control parameter for repeatability Control test for variance Control parameter (S-C) Control test for (S-C), the check standard Control test for drift
4.4.3 Calculating total uncertainty
4.5 Summary of the NIST measurement assurance program

5. The mechanical comparison procedure
5.1 Introduction
5.2 Preparation and inspection
5.2.1 Cleaning procedures
5.2.2 Cleaning interval
5.2.3 Storage
5.2.4 Deburring gauge blocks
5.3 The comparative principle
5.3.1 Examples
5.4 Gauge block comparators
5.4.1 Scale and contact force control
5.4.2 Stylus force and penetration corrections
5.4.3 Environmental factors Temperature effects Control of temperature effects
5.5 Intercomparison procedures
5.5.1 Handling techniques
5.6 Comparison designs
5.6.1 Drift eliminating designs The 12/4 design The 6/3 design The 8/4 design The ABBA design
5.6.2 Example of calibration output using the 12/4 design
5.7 Current NIST system performance
5.7.1 Summary

6. Gauge block interferometry
6.1 Introduction
6.2 Interferometers
6.2.1 The Kosters type interferometer
6.2.2 The NPL interferometer
6.2.3 Testing optical quality of interferometers
6.2.4 Interferometer corrections
6.2.5 Laser light sources
6.3 Environmental conditions and their measurement
6.3.1 Temperature
6.3.2 Atmospheric pressure
6.3.3 Water vapor
6.4 Gauge block measurement procedure
6.5 Computation of gauge block length
6.5.1 Calculation of the wavelength
6.5.2 Calculation of the whole number of fringes
6.5.3 Calculation of the block length from observed data
6.6 Type A and B errors
6.7 Process evaluation
6.8 Multiple wavelength interferometry
6.9 Use of the line scale interferometer for end standard calibration

7. References

Appendix A. Drift eliminating designs for non-simultaneous
comparison calibrations
Appendix B. Wringing films
Appendix C. Phase shifts in gauge block interferometry
Appendix D. Deformation corrections

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