||NIST Standard Reference Materials®
NIST continually defines and refines physical and chemical measurements. It pushes back the limits of accuracy and precision developing innovative methods for measuring time, length, mass, energy, electrical current, resistance, chemical composition, and the other quantities on which science, technology and commerce depend. Just as important, the institute transfers the results of its research to those who rely most on metrology by providing reference data, calibration services, and reference materials. These services support disciplines as varied as industrial materials production, environmental analysis, radiation threat detection, and health measurements. They enable manufacturers, scientific and technical organizations, government agencies, academia, and commercial concerns to perform required measurements accurately and consistently.
NIST issued “standard samples” almost immediately after its creation in 1901. In 1910 it began using the name Standard Reference Material and its current numbering system. Since issuing its first, SRM 1, Argillaceous Limestone, the institute has developed more than 4,900 SRMs, many of which have been replaced, updated, or discontinued as the world’s measurement requirements have changed. Today, NIST’s active catalog offers over 1,300 SRMs, and 30 to 40 new or updated materials are added each year.
The need for ever more precise standards of measurement is insatiable, propelled by rapid advancements in technology and manufacturing processes, the expanding rules of international commerce, and pressing requirements in crucial areas such as homeland security. In response, NIST has devised a process that brings together its diverse resources to meet the challenge.
There are three phases to SRM development. The first is research the constant effort to discover ways to entice nature to give up its secrets and ongoing investment in advanced facilities, equipment and the best people. Without these, NIST would be unprepared when the need for an SRM or other measurement service arises. Research activities are funded primarily by the annual congressional appropriation process.
The development phase begins when customer needs and market assessments indicate that an SRM is required to address barriers to innovation or the competitiveness of U.S. industry. Development is triggered when the NIST technical labs are satisfied that a broad customer base will benefit from the SRM and that the benefit is really something that NIST should provide. NIST involvement is usually indicated when U.S. industry must be able to link measurements of quantities to the International System of Units, or SI, which NIST’s measurement services are specifically designed to do. This traceability leads to the worldwide acceptance of U.S. product measurements and specifications, and the technical design of an SRM certification effort is defined by the degree of accuracy required by the intended user community. Many commercial and manufacturing applications, for example, do not require state-of-the-art measurements at the ultimate limits of NIST capability. Accurately matching measurements to customer requirements saves unnecessary costs on all sides and results in SRMs that are practical and affordable.
Once NIST labs are satisfied that an SRM is warranted, the development of a prototype material is undertaken. The purpose of prototype development is to ensure that NIST’s measurement expertise can be transferred through a stable artifact. Suitable sources of the specific material are investigated, keeping in mind the required range for the intended measured quantities (the measurands) and the target levels of uncertainty in the resulting certified values. Measurement methods both for assessing material homogeneity and for assigning certified values and uncertainties to the measurands are tested.
Cost is an important consideration in any SRM program. Development efforts are funded in part by a service development surcharge that is collected through the sale of NIST’s current SRMs in stock. Partnerships with other federal agencies and standards organizations are also used to fine-tune the measurement design to meet customer needs while controlling costs. Special programs such as the NIST Traceable Reference Material program provide a mechanism for linking commercially produced reference materials to NIST primary standards.
When all research and development questions have been answered and NIST is confident that a candidate material can be obtained and characterized to meet the technical specifications of the SRM design, production begins. The production phase for most NIST SRMs takes an average of three years. SRMs are priced to recover the production costs within five years of sales. Using this process, NIST produces and sells over 30,000 SRM units per year with a value of over $8 million.
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