Understanding the Importance of Traceability to the SI

Understanding the Importance of Traceability to the SI


 

I have seen some interesting discussions in cyberspace about the recent shutdown of the U.S. Government. The measurement services of the National Institutes of Standards and Technologies (NIST) are on the “not critical” list of services, as is most of NIST itself. Many of these dedicated public servants are personal friends of mine, and I am saddened that they are prevented from doing what they enjoy the most, providing some of the world’s best calibrations. I personally hope that they will be back on the job soon. 

However, this also brings to light recent developments regarding concepts about traceability and the need to think beyond the borders of the United States. In the past, most calibration quality documents specified traceability to their local National Metrology Institute (NMI); for example, NIST in the United States, PTB in Germany, or NIM in China. When ISO 17025 was first introduced in 1999, the requirements for metrological traceability were not directed towards an NMI, but instead required traceability to the International System of Units (SI) through natural physical constants, ratiometric techniques, or through appropriately recognized NMIs. Even though ISO 17025 has been largely accepted in the last fourteen years, many companies – even those accredited to ISO 17025 -- still specify traceability to NIST for their calibrations.

Fluke is an international corporation, and we obtain our measurement traceability from many different NMI’s, depending on their locations and capabilities. In many cases, because of our products’ precise accuracies, we are required to use the NMI that can provide the world’s best uncertainty for a particular parameter. Therefore, Fluke does not claim to be traceable to NIST for all measurement parameters. Each Fluke calibration certificate now contains a statement of traceability to the International System of Units (SI) and identifies the quality systems with which Fluke Calibration presently complies.

I encourage each of you to consider if your company would be best served by specifying traceability to the SI instead of to your local NMI. You may even want to consider reviewing your quality manual, purchasing documentation and updating the language to require traceability to the SI.

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