DC 10:1 Hamon divider with cryogenic contacts

A study on a DC Hamon divider with superconducting contacts (cryo-contacts Hamon divider) is described. The contact resistance error of the switch had been one of the most significant error sources in the conventional Hamon divider. A specially designed cryogenic switch made of Pb was used at liquid helium temperature for a series-parallel connection of the Hamon resistors which form the upper arm of a Wheatstone bridge for a self calibration. The 10:1 ratio uncertainty of the preliminary measurement is expected to easily reach a 0.1 ppm level.