The SI, the Kilogram, and Kibble: Past, Present, and Future*

The 2019 redefinition of the International System of Units has defined the kilogram with respect to the set value of Planck’s constant, replacing the historical physical artifact, the International Prototype Kilogram. From this invariant value, metrologists can now realize mass from quantum electrical measurements instrumentation like the National Institute of Standards and Technology’s (NIST) NIST-4 Kibble balance. Though the definition of mass has shifted from an artifact to the Planck constant, mass is still disseminated via a lengthy chain of primary, secondary, and sometimes even tertiary calibrations labs before being used to calibrate industrial force sensors. This dissemination chain is convoluted, costly, and inefficient.

The Fundamental Electrical Measurements group at NIST has developed several prototypes to bring the Kibble principle closer to the “end-user” through in-air, table-top Kibble principle devices which can realize mass and torque from calibrated electrical standards of resistance and voltage. KIBB-g2 is a small, flexure-based balance which can realize gram-level masses to uncertainties on the order of parts in 10⁵ while the Electronic NIST Torque Realizer (ENTR) is a rotary Kibble device which can realize <1 N·m torques with uncertainties on the order of parts in 10³. This talk will discuss the theory behind the Kibble principle as well as highlight progress in development of both table-top Kibble projects.