Isolated-Section Inductive Divider and Its Self-Calibration

A high-precision isolated-section inductive divider, designed for self-calibration, has been developed. In this new design principle, the two major sources of ratio error, excitation current and current through stray capacitance between sections of divider windings, have been greatly reduced by the use of a separate excitation winding and a guard for the divider winding. In a self-calibration divider ten divider winding sections are electrostatically isolated from each other by their guards. The divider can be calibrated by internal exchange of the winding sections and comparison with an auxiliary divider having a fixed nominal ratio of 0.1, similar to the calibration of a resistive divider. The design principle is also applied to another divider in which a second winding is added. This divider can be used for a high-precision multidecade divider and for the calibration of other ininductive dividers using a "boot-strapping" method. Construction details of the dividers, sources of errors, results of self-calibration, and evaluation of uncertainties are presented. The uncertainties of the self-calibration are estimated to be ±3 X 10-9 of the input at 100 Hz to 1 kHZ, and ±30 X 10-9 at 10 kHz.