scope:

This guideline describes typical variables influenc-ing the results of dimensional measurements that are performed using industrial computed tomogra-phy (CT). To this end, the various dimensional measurement tasks which can be performed using industrial CT are classified. Due to the plurality of types of CT devices and their applications, the list of influencing variables dealt with cannot claim to be exhaustive.

The scope of this guideline therefore only extends to the CT devices described below. The Annex contains recommendations regarding quality assur-ance for computed-tomography dimensional meas-urements.

This guideline addresses axial CT systems. Such CT devices essentially rely on the rotation of the test object about a fixed axis. Rotation is orthogo-nal to the direction of the X-ray beam. The indus-trial CT devices considered in this guideline use X-ray tubes or linear particle accelerators (linacs) as X-ray sources.

The configuration of a typical industrial CT device for which the stated influencing variables are valid is described below. The influencing factors de-scribed hold for both fan-beam CT (2D-CT) and cone-beam CT (3D-CT). Differences are addressedin individual cases.

Further CT methods exist, which rely on measure-ment principles other than those considered here; they include, in particular, laminography, neutron CT and synchrotron-based CT. Certain influencing variables described in this guideline essentially apply to these CT methods as well.

Basic principles and definitions as well as the characteristics and functioning of the individual components of CT systems are described in VDI/VDE 2630 Part 1.1.

The CT devices considered in this guideline con-sist at least of the following components (see also VDI/VDE 2630 Part 1.1, Figure 1):

• X-ray source (here: X-ray tube or linear particle accelerator)

• shaft for rotation of the object to be radiogra-phed, fixture for clamping the object to the shaft, if required

• X-ray detector

• control unit (computer + control software) for recording the projections

• reconstruction unit (computer + reconstruction software) for generating the volume data

• X-ray shielding (as a rule, enclosures shielded as per German X-ray Ordinance - RöV)

• analyser unit (computer + analysis and visuali-sation software) - application examples: analy-sis, visualisation and measurement of volume data, generation of surface data from the vol-ume data, visualisation and dimensional meas-uremen