Some Aspects of Measurement Uncertainty Calculation in Gauges Block Calibration

Gauge block calibration is one of the oldest high precision calibrations made in dimensional metrology. Measurement Assurance Method determine calibration or measurement uncertainty based on systematic observations of achieved results. All length measurement processes are comparative operation, directly or indirectly. A comparator is device for measuring difference. The unknown length of a block is determined by measuring the difference between it and a reference block of the same nominal size and then calculating the unknown length. Measurement process is continually affected by perturbations from variety of sources. The uncertainty in the result of measurement generally consists of several components which may be grouped in two categories according to the way in which their numerical values are estimated: A-those which are evaluated by statistical methods and B-those which are evaluated by other means. 1. INTRODUCTION A gauge block is a length standard having flat and parallel opposing surfaces. The length of the gauge block is defined at standard reference conditions: temperature 0°C, barometric pressure 101,325 Pa and CO 2 content of air 0,003%. In length measuring by mechanical comparison the length of the test gauge is compared to that of standard gauge and the measured difference in their lengths determines the length of the test gauge. Factors influencing the measurement are: the length calibration of the standard, factors inherent in the comparator equipment used to measure the length difference such as scale linearity and reading capability, gauge geometry with respect to its effect on probing the length difference, the temperature of the environment as it influences the gauge temperatures and etc [1,2].