- CCST
Summary
CCST question
Primary standard reference units and physical constants are maintained by ________.
A. NIST
B. testing labs
C. instrument techs
D. the plant instrument shop
CCST Answer
The correct answer is A, “NIST (National Institute of Standards and Technology).”All measurement units in the U.S. are based on the NIST standard measurements.
All other calibration measurements, such as those performed by testing labs and plant instrument shops, are considered to be done against secondary standards. By definition, these are “standards of unit measurement that are derived from a primary standard.”
NIST-certified instruments are calibrated at NIST, whereas NIST-traceable instruments are factory calibrated against NIST-certified standards. NIST-certified and NIST-traceable instruments are considered to be secondary standards.
Reference: Goettsche, L.D. (Editor), Maintenance of Instruments and Systems, Second Edition, ISA, 2005.
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