Precise Calibration of Ratio Transformers

The output voltages of a ratio transformer are defined at open-circuit coaxial connectors. A special socket and a difference transformer, wound with coaxial cable, are used to construct a voltage comparator accurate to 1 in 1010. Subdivided transformers are calibrated by comparing the voltage difference between taps with that of an isolated winding on the same transformer. Two similar transformers are compared directly using two voltage comparators.