ASME B89.4.23 pdf download

ASME B89.4.23 pdf download.X-Ray Computed Tomography (CT) Performance Evaluation.
ASME B89.4.23 specilies the dimensional measurement accuracy of industrial X•ray computed tomography (CT) systems for length, size, and form measurands of sphere-based test objects made of homogeneous materials. Medical CT systems are outside the scope ol this Standard. The material properties of the measured test objects are restricted to three classes olmaterial selected to be representative of industrial materials: plastic polymers, aluminum alloys, and steel alloys; other materials are outside the scope of this Standard. However, this Standard may be used as a guide for testing the performance ola CF system for other materials. The evaluation of workpieces composed of multiple materials or of materials with density gradients. le.. gradual density variations within the material, Is outside the scope of this Standard
This Standard Is applicable to dimensional measurements made at the surface of the workpiece, l,e., at the workplece material-air interface, including those of internal cavities, The elect of complex workpiece.material influence is simubted by test objects composed olspheres (servtng as the metrological geometric elements) and an obstructing body; the obstructing body’s dimensions are uncalibrated and its shape may be arbitrary. The spheres and obstructing body shall be of the same class of material and their combined length shall not exceed the maximum penetration length for this class of material, as stated by the CT system manufacturer.
This Standard applies to a variety oICT systems that may vary by scanning mode and system components involved in the acquisition of Images. In cases where a system provides multiple configurations of X-ray sources, detectors, and scanning modes, the dimensional measurement accuracy may he specified for each scanning mode.
This Standard does not mandate testing (by either the CT manufacturer or the user) to verify CT performance. The amount of testing, and which party will bear the cost of testing. is a business decision and must be negotiated between the two parties. Calibrated test objects can be expensive; hence, the parties should recognize the costs Involved and plan the testing accordingly.
Due to contrast sensitivity Issues that can arise when X-rays must penetrate through large amounts of material, this Standard does not provide maximum permissible error specifIcations that apply to detecting high spatial-frequency lorm errors.
2 INTRODUCTION
ASNE 1389 performance evaluation standards for dimensional coordinate measuring systems specify the dimensional measuring accuracy for common measurements of industrial workpieces. Ideally the uncertainty associated with each point coordinate within the system’s measurement work zone would be reported, but because the arniracy of an individual point coordinate in space is impossible to experimentally verify. ASME 1389 standards typically use a point-to- point length measurand that is both realizable and practical for system testing. The advantage of evaluating test objects with point-to-point length measuz-ands is twofold: first, test objects are simple to manufacture and calibrate, and second, different point-to•point length measurands can be used to evaluate different effects, Long-range effects are evaluated by the point-to-point length error between the center of two spheres on a test object, which can span the entire work zone. Short-range effects areevaluated by the errors in the point-to-point distance from the centerof the test spheres to various points on their surface, i.e.. sphere form measurands. Image thresholding issues that are associated with the detenninalion of a surface are evaluated by the error of the size of the test spheres.
A primary goal of ASME 1389.4 standards is to define maximum permissible error (MPE) specifications and their associated rated operating conditions, which are useful when the user is measuring similar measurands on a typical workpiece. For example, although a CT system might be tested with a calibrated steel test object, the user should be confident that the combined MPE specifications for center-to-center length, form, and size error would limit the error if a point-to-point length measurement were composed of a point on the exterior ol a steel workpiece and a point on an interior surface of a fully enclosed cavity of the workpiece.