ASTM D4678-15a(2019)

3.2.1.1 Industry Reference Materials (IRM)—Materials that have been prepared according to a specified production process to generate a uniform lot; the parameters that define the quality of the lot are evaluated by a specified measurement program.

3.2.1.2 Common-Source Reference Materials (CRM)—Materials that have been prepared to be as uniform as possible but do not have established property (parameter) values; the knowledge of a common or single source is sufficient for certain less critical applications.

3.2.3.1 Accepted Reference Value (AR Value)—An average IRM property or parameter value established by way of a specified test program.

3.2.3.2 Test Lot Limits (TL Limits)—These are limits defined as ±3 times the standard deviation of individual IRM test results across the entire lot for the property or parameter(s) that defines lot quality; the measurements are conducted in the laboratory of the organization producing the IRM.

3.2.3.3 Although the limits as defined in 3.2.3.2 are given in terms of ±3 times the standard deviation, the rejection of individual portions of the lot as being outlier or non-typical portions in assessing the homogeneity of the lot is done on the basis of ±2 times the appropriate standard deviation, that is, on the basis of a 95 % confidence interval. See Annex A3 and Annex A4 for more information and the evaluation procedures.

3.2.4.1 Global AR Value—This AR value is obtained from an interlaboratory test program where the word “global” indicates an average value across many laboratories.

3.2.4.2 Local AR Value—This is an AR value obtained in one laboratory or at one location, usually the laboratory responsible for preparation of the homogeneous lot.

3.2.5.1 Between-Laboratory Limits (BL)—The group of laboratories that conduct interlaboratory testing to establish an AR-value are not equivalent to a system or population typical of industrial production operations that use the usual ±3 standard deviation limits. Such production operations are systems that have been purged of all assignable causes of variation and are in a state of ‘statistical control’ with only random variations that cannot be removed. Thus, the recommended limits on all IRMs are the ±2 standard deviation limits that pertain to a 95 % confidence level. If for serious reasons that can be totally justified, ±3 standard deviation limits are required, these may be used provided that full and complete documentation is supplied to justify the limits.

3.2.6.1 Uniformity Level 1 (UL-1)—This is the most uniform or highest level of homogeneity that can be attained by the use of 3.2.6.2 Uniformity Level 2 (UL-2)—This is the lesser degree of uniformity that is attained by the use of3.3 IRMs have a number of use applications in the technical areas, as cited in 3.1.

3.4 Average values play an important role in various operations and decisions in this practice. For this practice, “average” is defined as the arithmetic mean.

3.5 The various characteristics of IRMs and CRMs (categories, classes, types) are listed in summary form in Table 1.

3.6 This practice and the IRM program it describes was developed to replace a standardization program conducted by the National Institute of Standards and Technology (NIST) that began in 1948 and has been phased out.

3.7 It is not feasible to write into this practice all the necessary specifications, modes of preparation, sampling, and testing protocols, for the wide variety of materials that will eventually become IRM. Therefore this practice is published to give general guidelines for IRMs.

3.8 A permanent IRM Steering Committee within Subcommittee D11.20 shall be constituted by Subcommittee D11.90 to assist in the utilization of this practice and to make technical and, where required, policy decisions regarding the preparation and administration of IRM.