A.C./D.C. voltage-ratio box and 9-decade a.c. ratio standard

The paper points out the limitations in trying to evaluate the d.c. performance of high-resistance d.c. voltage-ratio boxes directly from a series of a.c. measurements. It describes the design approach and gives design details of a guarded resistive a.c./d.c. voltage-ratio box (v.r.b.) the a.c. performance of which, in the band 20 Hz–80 Hz, is such as to produce an uncertainty of less than 1 part in 106 in extrapolating to 0 Hz (d.c.) This v.r.b. can then be used as a standard in direct d.c. calibration of other v.r.b.s. Design criteria and details are also given of the 9-decade low-frequency inductive voltage divider (i.v.d.) which serves as the standard in the a.c. measurements. Also described is a 1000 V 50 Hz single decade i.v.d. designed to precede the 9-decade i.v.d. in evaluating the self-heating effects when the v.r.b. is operated at rated voltage on its higher voltage ranges.