ASME B89.4.23-2020 pdf free
ASME B89.4.23-2020 pdf free.X-Ray Computed Tomography (CT) Performance Evaluation.
ASME B89.4.23 applies to a variety of CT 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 be 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 form errors.
2 INTRODUCTION
ASME B89 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 accuracy of an individual point coordinate in space is impossible to experimentally verify, ASME B89 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 measurands 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 are evaluated by the errors in the point-to-point distance from the center of the test spheres to various points on their surface, i.e., sphere form measurands. Image thresholding issues that are associated with the determination of a surface are evaluated by the error of the size of the test spheres.
A primary goal of ASME B89.4 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 of a steel workpiece and a point on an interior surface of a fully enclosed cavity of the workpiece.
2.2 SpecificatIons
The accuracy specifications are the MPEs associated with the measurement of the specific dimensional and geometric characteristics of the test objects. These values are specified by the CT system manufacturer, and they represent the largest CT measurement errors permitted when a CT system is tested per the ASME B894.23 test protocol. A CT system that generates measurement errors greater than the MPE values is not in conformance with this Standard. These MPEs may be of significant value when actual workpieces are measured. The rated operating conditions are specified by the CT system manufacturer and shall be satisfied forthe MPE value (i.e., the “rating9 to be verified. The M PEcan be thought ofas a type of mathematical function over the domain of rated operating conditions, and it yields an interval of permitted errors that is bounded by theM PE value or values. Often the MPE function Is just a single value; i.e., the function isa constant over all rated operating conditions. Typical rated operating conditions include such quantities as the size of the system work zone under specification, data collection speeds, ambient temperature conditions, the number of radiographs in a scan, Xray source voltages and currents, operator training and skill requirements, and other metrological factors that are required to be satisfied for the system to function properly: these are described in section 5.
2.3 Objectives of the Test ProtocoL
Testing s designed to verify the metrological specifications of the CT system. The test protocol described In this Standard has several objectives: to provide a thorough yet efficient test, to limit time and money spent on testing, and to assure users of the capabilities of their CT system. This Standard meets these objectives in several ways.
(a) To facilitate commerce, both the CT system manufacturer and the user need an agreed-upon amount of testing to consider the system acceptable. A large amount of testing requested by a user can drive up the manufacturer’s costs, but insufficient testing might miss errors that could demonstrate nonconformance with MPE specifications. This Standard establishes the recommended amount of testing required to be reasonably thorough without being overly burdensome.
(b) By recommending test-object designs that can realize the measurands specified in this Standard, the CT system manufacturer need only maintain this limited set of Lest objects, thus avoiding the expense of multiple different test objects that might be otherwise requested by the user. Similarly, the user is protected because the manufacturer has used carefully designed test objects that reveal CT errors in an effective manner.
fr) The test protocol may require specific testing conditions (e.g.. locations and orientations) for the test object that are sensitive to known error sources in the CT system and hence will reveal them with a minimum number of measurements. This well-crafted protocol protects the inexperienced user from performing a weak Lest but also saves on the cost of testing because it provides a targeted and acceptable testing procedure.ASME B89.4.23 pdf download.
