Analysis of thermal contribution to the measurement uncertainty in step gauge calibration

Thermal expansion errors represent an important source of measurement uncertainty in precision length measurements. The authors present research performed on thermal error minimisation in calibration of step gauges, with the goal to develop a new high precision procedure for step gauge calibration in the Slovenian National Dimensional Metrology Laboratory. Thermal conditions during step gauge calibration were analyzed by using a combination of experimental measurements and Finite Element Method (FEM) simulations. Good final agreement between the experimental measurements and the simulation proves that the FEM simulation is a useful tool for studying and compensating thermal errors. The final outcome of the research is a non-linear model for compensating thermal expansion of a step gauge during calibration in a microclimatic chamber, where the temperature is controlled within the limits of (20 +/- 0.1) degrees C. Different types of step gauges were examined and modelled which are used commonly for testing the performance of Coordinate Measuring Machines (CMMs). The results show that the developed error compensation method is effective enough for our metrology purposes as regards measurement uncertainty.