Investigation of Temperature-Induced Errors in XCT Metrology

The presented research shows the time dependent temperature distribution and thermal time constant within a typical industrial X-ray computed tomography (XCT) system used for dimensional metrology. Temperature effects can significantly affect measurement results of XCT scans either by directly changing the dimensions of the measurement object, or by indirectly changing the geometry of XCT scanner. In either case, the effect is not known well enough to be used for correction of measurement results or estimation of measurement uncertainty. In order to determine these effects, traceable temperature measurements were performed with a custom measurement system designed for this application. The influence of temperature fluctuations on length errors was determined by correlation of the measured temperature fluctuations with measurement deviations of a reference standard in repeated CT scans at different X-ray power levels. After experimental determination of X-ray focal spot displacement due to thermal expansion, a simple mathematical model of X-ray source displacement as a function of its temperature was developed and validated for a selected X-ray power level.