A current comparator for the precision measurement of D-C ratios

A magnetic d-c ratio device is described which is capable of attaining accuracies approaching one part in a million. The operating characteristics and some of the problems connected with its design are discussed and construction details of an experimental model, rated at 4,000 ampere-turns and capable of handling ratios up to 400/1, are given. The use of this device for the scaling of fundamental electrical resistance standards is proposed.