Recent Development on the Joule Balance at NIM

The precise measurement of Planck constant h to establish a kind of quantum mass standard is an important but very difficult work. The Joule Balance method, for the same purpose but different from Watt Balance method, has been going on at the National Institute of Metrology for three years. All the measurements were carried out in the atmosphere of an air-conditioned room. The uncertainty is several parts in 10⁴ (k=1) and expected to be improved when superconducting coils and other approaches are used further. The principle and progress are described here.