Measurements of long gauge blocks using a fringe-counting interferometer and subgauge blocks with lines

A new method for measuring long gauge blocks using a fringe-counting interferometer with a 633 nm wavelength-stabilized He-Ne laser is described. Two subgauge blocks, which have V-type graduation lines covered with glass plates, are optically contacted with both sides of a long gauge block. They are handled with bare hands and the surfaces of the glass plates are wiped with a paper towel after the optical wringing procedure. Using the National Research Laboratory of Metrology 2 m line standard automatic measuring machine, several gauge blocks up to 1 m long are measured with a repeatability less than 0,1 μm in standard deviation. A comparison between the lengths of gauge blocks measured by the new method and by the conventional excess fractions method is made. The results show that the length of gauge blocks up to 1 m can be determined with an expanded uncertainty U = 0,3 μm, corresponding to a level of confidence of about 95%.