Metrological traceability3 requires the establishment of an unbroken chain of calibrations to specified reference measurement standards: typically national or international standards, in particular realizations of the measurement units of the International System of Units (SI). NIST assures the traceability to the SI, or to other specified standards, of measurement results that NIST itself provides, either directly or through an official NIST program or collaboration. Other organizations are responsible for establishing the traceability of their own results to national reference standards maintained by NIST or to other specified reference standards. NIST has adopted this policy statement to document the NIST role with respect to traceability.
Merely using an instrument or artifact calibrated at NIST is not enough to make the measurement result traceable to reference standards developed and maintained by NIST. As detailed in 5.1.7, to establish traceability, the provider of a measurement result must document the measurement process or system used to establish the claim and provide a description of the chain of calibrations that were used to establish a connection to a specified reference: the instrument or artifact calibrated at NIST then being one of the links in this chain.
Chain Chronicle Artbook Pdf 15
To support a claim of traceability, the provider of a measurement result must document the measurement process or system used to establish the claim and provide a description of the chain of calibrations that were used to establish a connection to a specified reference. There are several common elements to all valid statements or claims of traceability:
Yes, traceability does need to be reexamined periodically, and the criteria for assessing the integrity of the traceability chain involve consideration of: the measurement requirements; the needs of the client; the dependability of the equipment and standards; the environmental effects; etc. For more details, refer to [34].
To achieve traceability of measurement results to standards maintained by NIST, you need to reference your measurement results through an unbroken chain of calibrations, including determining the uncertainties at each step, to NIST standards as the specified references. These references may be, for example, standards developed and maintained by NIST: broadcast signals controlled or monitored by NIST (such as standard time and frequency signals), NIST Standard Reference Materials (SRMs), NIST-Traceable Reference Materials (NTRMs), or those NIST Standard Reference Instruments (SRIs) whose certificates include a statement of metrological traceability. The chain of calibrations may be short if the user has instruments or artifacts calibrated by NIST or acquires standards from NIST and references measurement results to those. Or it may be long if the user references other calibrations in a chain of calibrations back to stated references developed and maintained by NIST. Also see Question 5.1.7 above and Checklist for Traceability through Calibration for additional guidance.
In general, NIST establishes the traceability of its own measurement results via an unbroken chain of calibrations, including evaluating measurement uncertainty at each step, to specified references. In the case of the SI base units, the ultimate stated reference is the definition of the units, including associated procedures to realize them, as established by the General Conference on Weights and Measures (CGPM) and specified in the SI Brochure [26]. The same process also applies in the case of derived units, which are formed as products of powers of the base units according to the algebraic relations linking the quantities concerned. For other measurement quantities, the reference may be a national standard defined de facto by a conventionally stated method.
NIST may use several internal standards to calibrate or validate its own measurement process or system. The measurement results with associated uncertainties are links in the traceability chain. The customer should claim traceability to the NIST system comprising the individual standards and should indicate who combined the data using what algorithm. Uncertainties should be documented, calculated, and reported accordingly.
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