NIST’s New Watt Balance Brings World Closer to Redefining the Kilogram
The National Institute of Standards and Technology (NIST) has made a significant advancement in its quest to redefine the kilogram using a high-tech balance scale called the NIST-4 watt balance. This measurement of Planck’s constant, a fundamental physical quantity, demonstrates the scale’s accuracy and brings the international community closer to redefining the kilogram by 2018.
The redefinition will not change the kilogram’s mass value, but will define it in terms of unchanging fundamental constants of nature. This will remove uncertainty in the kilogram’s mass, which can change slightly when touched. The NIST-4 watt balance measurement of Planck’s constant (6.62606983×10^-34 kg·m²/s) with an uncertainty of plus or minus 22 in the last two digits is a key step towards this goal.
Multiple countries are building watt balances to make independent measurements of Planck’s constant, which must agree within a statistical confidence level of 95%. The results must also be reconciled with the Avogadro method, which involves counting atoms in a silicon sphere. Fixing Planck’s constant’s value will benefit electrical metrology by connecting quantum-based standards for the ohm and volt to the international system of units for the first time.
Keywords: h, Planck’s constant, kilogram, watt balance
