ASME B89.4.23-2020 pdf download

ASME B89.4.23-2020 pdf download.X-Ray Computed Tomography (CT) Performance Evaluation.
penetration length, Lp: for any radiograph in a scan, the longest material path length through which the X-ray must penetrate; this length always includes the spheres used as metrological geometric elements and the obstructing body. It will also include the fixturing material if the fixturing material is of the same class of material as the test object and is in the X-ray material path.
NOTES:
(1) lIthe base material, fixturing material, or both are less dense than the test object, the less dense material(s) shall be excluded from the penetration length even though the less dense material(s) may influence the surface determination.
(2) Fixturing material denser than the test object material class shall not be used in the X-ray material path.
pixel size: the horizontal or vertical center-to-center distance between adjacent pixels in an X-ray detector.
NOTE: If the detector pixels are nonsquare, the pixel size is the smaller of horizontal or vertical center-to-center distance between adjacent pixels.
preknowledge: the nominal geometry, surface normal vectors, dimensions, chemical composition, or reference dimensional measurements of a workpiece or test object acquired by means other than the sensors of the CT system under verification.
NOTE: The use ofpreknowledge is denoted in the symbol for an M PE specification by the subscript UCAD) (computer-aided design), e.g., Psize.sphII:CA[),Ci,MPE.
rated operating condition: operating condition that must be fulfilled during measurement in order that a measuring instrument or measuring system perform [sic] as designed.
NOTES:
(1) Rated operating conditions generally specify intervals of values for a quantity being measured and for any influence quantity.
(2) In this Standard, “as designed” means “to meet the specified MPE values.”
(3) Conditions that are not explicitly constrained by the CT system manufacturer are acceptable conditions under which the system can be tested.
(4) In this Standard, “rated operating condition” is also referred to as “rated condition.”
[This definition, including Note (1), is identical to JCGM 200:2012, definition 4.9. Notes (2) through (4) are specific to this Standard.]
sphericity: spherical form.
NOTE: The sphericity of a test object may pertain to a portion of a sphere, e.g., a hemisphere.
voxel: a unit in a three-dimensional (3D) array that discretizes a reconstructed work zone using the principle of computed tomography.
voxel size: the size of a magnified pixel for a CT scan, which is calculated as pixel size divided by magnification.
NOTES:
(1) Magnification is the X-ray source-to-detector distance divided by the X-ray source-to-object distance.
(2) Other definitions ofvoxel size are possible. This definition is common and chosen for convenience. It is expressed as a unit of length rather than volume, e.g., in millimeters rather than in cubic millimeters.
work zone: a rated operating condition that is the boundary of the physical region within which measurements can be performed.
NOTE: In this Standard, the work zone may depend on the magnification used for the test.
5 EXAMPLES OF RATED OPERATING CONDITIONS
The rated operating conditions are stated by the CT system manufacturer and represent the conditions for which the CT system has MPE values. Although a CT system may be capable of obtaining measurements outside its rated operating conditions, the user cannot be sure of the accuracy of such measurements. The rated conditions make up the applicable domain where measurements can be accurately obtained. Consequently, when selecting a CT system, users should review all the rated operating conditions and especially the rated material classes and their maximum penetration lengths. If the largest penetration length of a workpiece, in any radiograph, exceeds the maximum penetration length (stated by the CT system manufacturer) for that material class, then that measurement is outside the rated operating conditions of the CT system. Since material effects are a major source of error in CT measurements, the user should ensure that the accuracy of the CT system is sufficient at the largest penetration length of any workpiece measurement anticipated and should also test the system at this condition. Any condition that is specified by the CT system manufacturer for the proper operation of the system is a rated condition — this includes requirements described in the operating manual. Paragraphs 5.1 through 5.7 list examples of rated operating conditions.