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Some quantities can each be simply traceable to one single quantity with the same unit but lower uncertainty. For instance, a weight of 50 g ± 1 g might be calibrated with another weight of 50 g ± 0.1 g. Meanwhile, some quantities each can be derived from multiple quantities. A simple example would be measuring DC current with a volt meter and a standard resistor. In this case the DC current is derived from DC voltage and resistance. A more complicated example of a derived quantity is phase noise. The question is: how do we establish traceability for such derived quantities?
Starting with introducing the concepts of SI, base and derived quantities, and traceability, this paper presents the general approach of establishing traceability for a quantity which is derived from multiple traceable quantities. A measurement procedure will be required, including measurement method, measurement setup and connections, measurement equation, uncertainty analysis, etc. The traceability of phase noise is then considered as an example based upon two common measurement techniques—with a spectrum analyzer and with a phase detector.
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