engleski

Thermal influences on X-ray source position in X-ray computed tomography

X-ray computed tomography (XCT) is becoming widely adopted for dimensional metrology tasks in various industrial sectors, primarily because it enables measurements of hidden / inaccessible geometry. Traceability of results obtained using XCT is difficult to establish, due to difficulties associated with numerous error sources which are not well-known. Standardization efforts, such as VDI/VDE 2630 rely primarily on substitution methods, circumventing a more detailed analysis of error sources. As previous research has shown, thermal influences are typically some of the largest sources of measurement errors in XCT. Thermal expansion of the X-ray source is especially significant, as it causes a displacement of the focal spot position and therefore directly influences the metrology loop of the system. In this paper, we present the methodology which applies to the X-ray source as a black-box in order to characterise the heat sources it contains. High-accuracy temperature sensors were used to determine the temperatures of various parts of the X-ray source, at different X-ray power levels, while simultaneously tracking the position of a precision sphere at high magnification. These results are used to determine the thermal constants of the system which can be used to establish the correct warm-up time and avoid significant displacements of the focal spot during the XCT measurement. In order to estimate the amount of focal spot displacement as a function of X-ray power, which can then be used to apply corrections to the measured data, a further analysis is also presented. Initial boundary conditions are calculated using 1D analytical methods, which then serve as an input in a CFD analysis of the entire XCT system.

X-ray computed tomography, thermal influences, accuracy

nije evidentirano