Comparison of national standards of Russia and Finland for the unit of length

Abstract

We present the results of comparison of line gage and end gage standards of length of Russia and Finland with nominal lengths 1 m. We have obtained good agreement between the length measurement results. The mean discrepancy between results of measurement of the length intervals was O. 046 #m for the line gage and 0.01 izm for the end gage.According to a previously approved program, during the period from October 1993 through January 1994 standard interference apparatus of Russia (VNIIM, All-Russian Scientific-Research Institute of Metrology) and Finland (CMA) for certification of line and end length gages were compared. Intercomparisons of standards are the most effective method for determining the accuracy level for measurement devices included in standard systems and the sources of errors in reproduction of the unit of length and dissemination of the length scale.The comparison was done with two standard reference gages (line and end) of length 1000 mm provided by the D. I. Mendeleev All-Russian Scientific-Institute of Metrology (VNIIM). Line gage No. 0127-78 was made from Invar-Stabil alloy (SSNi) of "H" cross-section, lines of width 4 tzm were engraved on the neutral plane of the gage, axial lines were located at a distance of 200 /zm, the thermal coefficient of linear expansion is equal to 11.46.10 -6 K -1. Gage No. 0127-78 was investigated at VNIIM in 1984. The instability of the length gage, connected with the material, was no greater than 0.1/~m/y. This gage was used in the period from 1989 through 1992 in round-robin comparisons of national standards of Bulgaria, Hungary, Czechoslovakia, and Russia [1]. The end gage was made of steel at the Kalibr plant in 1978, its thermal coefficient of linear expansion is equal to (11.5 _+ 0.05).10 -6 K -~. The end gage was assembled with an auxiliary steel plate by VNIIM (Ref 1), 40 x 40 • 10 mm. In measurements at CMA, a glass auxiliary plate made from material K8, 35 x 24 • 11 m, was also used.At VNIIM, measurements of the length of both gages were made on the primary state standard of the length unit [2, 3]. During measurement of the length, the temperature of the gages varied within the range 19.86-20.05~ the temperature gradient along the gage was 5 mK. The length of the line gage was measured with a start--stop procedure. The gages were mounted on supports at the Bessel points so that the zero lines and the 1000 lines were at the focus of the microscope. A photoelectric microscope with a scanning slit was focused on the lines of the gage. The length was measured at two positions of the gage: "+" and "-". The refractive index correction was determined by a laser interference refractometer with a vacuum chamber of length 1000 mm and an electronic circuit with counting step k/200. In measuring the length of the end gage, we used the auxiliary plate Ref 1. In order to compensate for its mass, the gage was mounted on supports at points located respectively at distances of 222 mm and 172 mm from the free surface and the surface fitted into the plate. The overall sta...