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Metrological TraceabilityAccreditation Scheme

VIM (International Vocabulary of Basic and General Terms in Metrology) defines the term “traceability” as “the characteristics of reference values or measurement results that can be traced by means of a documented unbroken chain of calibrations linking them to an appropriate reference (national or international standards), each contributing to the measurement uncertainty”.

Furthermore, NIST Handbook 150 of the U.S. provides additional explanation: “A documented chain of comparison connecting the accuracy of a measuring instrument to other measuring instruments of higher accuracy and ultimately to a primary standard.”

Therefore, when intending to prove traceability to attain KOLAS accreditation, a calibration laboratory is required not only to demonstrate an unbroken chain of calibrations leading back to national standards, but also to indicate reliability of that chain by proving uncertainties, assuring the measurement process, continuously conforming to relevant standards, and practicing adequate calibration processes with the relevant criteria.

Why Metrological Traceability is required
Measurement is the foundation to produce goods and services, and national measurement standards are the ground to establish proper structures in our industries and societies. Measurement standards are the very foundation of manufacturing processes, product testing, health, safety and environmental monitoring, food processing, adoption of new technology, scientific advancement and fair trade in the national economy.

Although measurement is an essential part of our lives, we often underestimate its importance. In addition, since all testing is conducted based on measurement, mutual recognition of measurement and metrological traceability are the most imperative prerequisites for the mutual recognition of test results.

Nowadays the international market is well aware of the importance of quality, and ISO 9000 and other quality systems are being adopted widely. However, it is certain that quality systems themselves do not guarantee the quality outcomes. They are just mechanisms to oversee processes and assure consistency. In fact, the quality system can be a source of problem which continuously produces defective goods, if measuring or measuring processes associated with testing is not accurate.

Whether it is for raw material inspection, process management or testing on finished goods, factors to guarantee high quality measuring or measuring results can boil down to the following two: “competence” and “metrological traceability”. The term “competence” is related to that of operators who practice measuring as well as metrological methods and quality systems and third-party accreditation in accordance with ISO/IEC 17025 is the best way to prove the competence.

“Metrological traceability” is also related to the accuracy of measuring equipment. The indication values of measuring equipment or the results gained from measuring instruments must be accurate within the physical unit in which measurement is taking place, and ultimately, they must acquire traceability with measurement standards through calibration for the fundamental realization of the units. This is because there are increasing demands for international recognition on product testing and conformity, and traceability with international measurement standards is required to this end.

International Attention to Metrological Traceability
International measurement standards for SI units consist of the basic standards based on consensus and maintained by the International Bureau of Weights and Measures (BIPM) and the standards maintained by Korea Research Institute of Standards and Science (KRISS) that are proven to be equivalent to other international standards through international comparison programs, especially the BIPM Key Comparisons. Key tasks of KRISS researchers are establishing basic standards and proving their accuracy through international comparisons.

Internationally there are increasing understanding that basic standards to realize SI units often can be the standards with very specific single values and that proven traceability to such basic standards alone cannot be sufficient to handle cases with considerably wide range of amounts or values. Therefore, KRISS is under growing pressure to participate in wider range of international comparisons to wholly prove its metrological traceability and competence.

For instance, proving traceability of the 1-ohm in the electrical resistance field through international comparisons does not lead to the proof of the measuring competence for very large resistance values that require slightly different measurement techniques. This issue has been raised continuously by the BIPM and its advisory committees. Currently, the BIPM is developing comparison programs for each metrological field to improve the credibility on traceability and the competence of KRISS researchers. The new programs will form the foundation of international mutual recognition arrangements.

In conclusion, measurement is an essential element in building the foundations of testing, conformity assessment and international trade, all of which are vital ingredients for national economic development. Also, mutual recognition of national metrological standards and the competence of KRISS researchers are indispensable to maintain traceability with international measurement standards.