Development of the D-C instrument transformer for the precision measurement of highest direct currents

IN 1936, a simplification of the magnetization curve that was intended to facilitate the explanation of the pre-saturation phenomena led to the development of a d-c instrument transformer having genuine current-transformer characteristics. It was found that the assumption of a rectangular hysteresis loop for the combined effect of d-c and a-c magnetization would fulfill the condition of strict equality of the primary and secondary magnetomotive forces (mmf) of the transformer, at least periodically. This applied to all types of current transducer circuits.