Evaluation of Two Alternative Methods to Calibrate Ultrahigh Value Resistors at INRIM

In the framework of the preparation of the National Institute of Metrological Research (INRIM) to its participation at the “Supplementary Comparison EURAMET.EM-S32 Comparison of Resistance Standards at 1 TΩ and 100 TΩ,” an evaluation of two measurement techniques for high resistance measurements at INRIM has been made. The first method, working between 10 MΩ and 1 TΩ, is based on a digital multimeter and on a dc voltage (dcv) calibrator, the second, working up to 100 TΩ, is based on a modified Wheatstone bridge with two programmable dcv calibrators in two arms of the bridge and a programmable electrometer as null detector. A description of both methods, a detailed uncertainties budget at 1 TΩ at 1000 V level according to the ISO Guide to the Expression of Uncertainty in Measurements, and the comparison of the results at 100 GΩ and at 1 TΩ are reported.