CCDM comparison of gauge block measurements

Abstract

A world-wide comparison of gauge block measurement by interferometry, decided on by the Comité Consultatif pour la Définition du Mètre (CCDM), has been carried out. Four national metrology institutes, each representing one of the regional metrology organizations EUROMET, NORAMET, COOMET and APMP, measured a set of seven rectangular gauge blocks of steel with nominal lengths between 1 mm and 100 mm. This paper reports on the results of the comparison and draws conclusions with respect to the execution of future CCDM (now CCL) key comparisons.

Principal length specifying parameters of material artifacts, their physical meaning, methods for their measurements, and typical uncertainties

“…It characterizes the optical properties of the material artifact, and it is obtained through a double-sided method [8] as a result of four interferometric measurements [7], performed on non-absorbing transparent reference plate (Fig.2). The corresponding measurements are shown as experiments (1)(2)(3)(4). In case ofthe Lop measurement, the perpendicular distance is being measured between the two surfaces of light reflection.…”

“…The EFT varies from one wring to the other, so that the length of a block does not keep a constant value for consecutive wrings even to the same reference plate. The corresponding uncertainty component is usually evaluated as -12-15 urn at 95% confidence level [2,3]. To resolve this limitation of the standard method of optical interferometry [3][4] and to improve the accuracy of the realization of the SI length unit, we use the system of dfferential optical length measurements and new length specfyingparameters for the material standard [5][6][7].…”

Testing phase-shifting algorithms for uncertainty evaluation in interferometric gauge block calibration

“…Instrumentation used for dimensional quality control includes typically callipers, micrometers or coordinate measurement machines, which are calibrated by means of gauge blocks as transfer standards from the metre definition [3,4]. Gauge block calibration is usually done by means of interferometry techniques to achieve the required accuracy [5][6][7][8]. This technique is regularly based on Kösters, Twymann-Green or Fizeau [9] configurations and has been greatly improved over recent decades by replacing spectral lamps by highly stabilized laser sources, using CCD or CMOS sensors as image acquisition systems and employing modern phase evaluation methods [10][11][12].…”

Gauge block measurements with nanometre uncertainty

“…In this way, the practical realization of the metre, the SI unit of length, is carried out under laboratory conditions in the range from a fraction of a millimetre up to 1 metre. The typical combined standard uncertainties [2], reported in a Comité Consultatif pour la Définition du Mètre (CCDM) comparison of gauge blocks [3], are in the range 5 nm to 8 nm for 1 mm blocks, and about 11 nm to 16 nm for 100 mm blocks. It is generally considered that a 10 nm limit in accuracy cannot be bettered, and that the total uncertainty level of a few nanometres is not realistic at the present time.…”

“…The current definition of the length of a gauge block (International Standard ISO-3650 (1998) [4a]), which includes the thickness of the wringing layer between the gauge block and the reference plate, does not support a level of accuracy of 1 nm. The length of the block, in accordance with the standard practice of international comparisons, incorporates the mean value of the wringing film thickness obtained for wrings to different faces of the block [3]. As a result of the wringing film variability (which is usually reported in the range 10 nm to 30 nm at the 95 % confidence level), the length of the block is not an invariant in the wringing procedure.…”