Investigation of Temperature-Induced Errors in XCT Metrology

Abstract

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.

Traceable determination of non-static XCT machine geometry: New developments and case studies

“…Numerical simulations enable indirect determination of XCT geometry deviations caused by secondary signals such as temperatures changes [19] or heat dissipation. They can be used for estimation of local effects, e.g.…”

Photothermal effect in X-ray images for computed tomography of metallic parts: Stainless steel spheres

“…To improve the resolution with CT scans, it is important to position the workpiece close to the X-ray source and increase the number of projections. Under these conditions, the source induces temperature variations that may influence the precision of the dimensional measurement [9]; the X-ray beam scattering correlates with heat conduction according to the ballistic-diffusive heat-conduction equation in [10]. Moreover, high-resolution CT demands correction due to time-dependent electron beam drift and focal spot movement due to thermal deformation of the X-ray tube [8,11,12].…”