Metrological management of the high dc resistance scale at INRIM

In the framework of the revision of the high dc resistance scale from 10 kΩ to 1 TΩ at National Institute of Metrological Research (INRIM) a measurement method for calibration of high value resistors based on the use of a digital multimeter (DMM) and of a dc voltage calibrator (DCVC) was projected, developed and characterized. A method based on the Hamon scaling technique was revised and extended to 1 GΩ. Two other methods, based respectively on a modified Wheatstone bridge and on a current comparator bridge, were implemented. A new 100 MΩ step Hamon standard, a humidity generator to characterize high value resistors vs. relative humidity and a scanner for high resistances were developed and characterized. The relative 2σ best measurement capabilities, obtained in the range 10 kΩ ÷ 1 TΩ at INRIM with all these methods, span from 2.0 × 10−7 of the 10 kΩ standard resistor at the measurement voltage of 10 V to 1.0 × 10−3 of the 1 TΩ standard resistor at a voltage of 100 V. The relative standard uncertainties of the utilized methods at INRIM are summarized.