A Precise Low Temperature dc Ratio Transformer

A prototype low temperature dc ratio transformer is described. This transformer, which uses a new technique for the precise equalization of current ratios, provides dc ratios which have accuracies of the order of 0.01 ppm and may be calibrated to 0.002 ppm. The ratio transformer may be applied in low temperature current and resistance ratio measurements of high accuracy and may, without modification, be used as a sensitive current detector.