ASME B89.4.23:2020 pdf download.X-RAY COMPUTED TOMOGRAPHY (CT) PERFORMANCE EVALUATION.
2.1 Organization
ASME B89.4.23 is organized into the following sections:
(a) Sections 1 and 2 provide the scope and introduction, respectively.
(b) Section 3 provides the normative references.
(c) Section 4 defines terminology specific to this Standard.
(d) Section 5 describes some examples of the rated operating conditions specified by the CT system manufacturer.
(e) Section 6 describes the required measurands for length, size, and form.
(Q Section 7 describes the test protocol.
(g) Section 8 provides the decision rules for determining whether a set of test values yields a test outcome that verifies the conformance of the CT system to its MPE specifications.
(h) Mandatory Appendix I describes the material classes.
(i) Mandatory Appendix II describes the mathematical adjustment needed for test objects with low-density and lowCTE (coefficient of thermal expansion) base materials.
U) Mandatory Appendix Ill provides a statement of metrological traceability described further in ASME B89.7.5-2006.
(k) Mandatory Appendix IV describes test value uncertainty.
(1) Nonmandatory Appendix A provides examples of test objects.
(m) Nonmandatory Appendix B describes how to calculate a bidirectional length MPE.
(o) Nonmandatory Appendix C describes a supplementary test procedure when using test objects with low-density and low-CTE base materials.
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 B89.4.23 test protocol. A CT system that generates measurement errors greater than the MPE values is not in conformance with this Standard. These MPE5 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 for the M PE value (i.e., the urating) to be verified. The M PEcan be thought of as a type of mathematical function over the domain of rated operating conditions, and ityields an interval of permitted errors that is bounded by the MPE value or values. Often the MPE function is just a single value; i.e., the function is a 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 is 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 test 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.
(c) 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 test but also saves on the cost of testing because it provides a targeted and acceptable testing procedure.
(d) The ASME B89.4 standards typically define test protocols with some user-selectable test conditions.ASME B89.4.23 pdf download.