A measurement standard that realizes a unit from its definition using a primary method, so no higher standard of the same quantity sits above it in the chain. Josephson voltage arrays, quantum Hall resistance systems and Kibble balances are examples, realizing the volt, ohm and kilogram from fixed physical constants. Most sit at national metrology institutes, though Josephson systems also appear in a few high-end commercial labs.
The Josephson array is our primary standard for DC volts, the Zeners only get compared against it.
Also heard as
- primary measurement standard
Related terms
Reference standard
A lab's highest-level standard for a quantity, used only to calibrate other standards and never for routine work.
Calibration hierarchy
The ranked levels of standards, from primary realizations down to working instruments, through which values flow.
NMI
National metrology institute, the body that realizes a country's measurement units at the top of its traceability chain.
SI
International System of Units, the coherent set of seven base units on which all traceable measurement rests.
Transfer standard
A stable, portable standard used to carry a value from one lab or standard to another for comparison.