A low-voltage and high-frequency ac-dc transfer system using inductive dividers

A setup for the calibration of high-input-resistance ac-measuring instruments for low voltages (mV) and high frequencies (1 MHz) is presented. The low voltages generated down to one hundredth of an ac standard voltage (0.5 V to 2 V) are traced by means of a one-decade inductive voltage divider (IVD) cascaded by a sub-IVD with a fixed ratio of 10-to-1. Construction details of the main IVD which are necessary to meet the requirements are given. The error characteristics are mainly determined by capacitive currents acting on stray and mutual inductances. The internally built-in resistive dc voltage divider and a special switch allow calibrations to be performed via effective ac-dc transfer at the standard voltage level. The first results for the calibration of a transfer standard, Fluke 792A, at 100 mV and 200 mV were in good agreement with results obtained with very sensitive multijunction thermal converters. Using such converters as standards in the new system will enable ac calibrations down to voltages below 1 mV