Inventors:
Randolph E. Elmquist - Gaithersburg MD
Ronald F. Dziuba - Gaithersburg MD
Assignee:
The United States of America as represented by the Secretary of Commerce - Washington DC
International Classification:
G01R 33035
Abstract:
A cryogenic current comparator device is based on the magnetic shielding properties of superconducting tubes and maintains electrical currents being compared in a highly exact integer ratio. One pair of superconducting tubes are arranged adjacent to each other so that the longitudinal axis of each tube are parallel. A coil of current carrying wire is formed by winding the wire down through a longitudinal bore of the first tube and then back up the longitudinal bore of the second tube to form at least one turn or loop of the coil. A second, identical pair of superconducting tubes is placed adjacent and longitudinally parallel to the first pair of tubes so that a superconducting quantum interference device magnetometer is surrounded by the four tubes in order to measure a magnetic field induced by the current traveling through the coils. The device operates at a temperature of 77 degrees K. and is used to predict the relative uncertainty of a wide range of resistance and current ratio measurements to approximately one part in one hundred million.