A non-inductive natural-air-cooled four-terminal resistance standard for alternating currents up to 2000 amperes

A four-terminal resistance standard designed to provide a voltage of 2 volts with a current of 2000 amperes has been constructed at the National Physical Laboratory. The time-Contant is 0.1 ×10×6, and the resistance departs by less than 1 part in 10 000 from its cold value for all currents up to 1900 amperes. The variation with frequency up to 100 cycles per sec. is less than 1 part in 100 000. The resistance is designed to be reasonably astatic to magnetic fields, and under ordinary conditions of use the value and time-constant are unaffected by the magnetic fields produced by other conductors in the circuit.