Traceable Technique to calibrate dc current shunts and resistors in the range from 10 µohm to 10 mohm

A traceable to dc Resistance and dc Voltage National Standards measurement technique to calibrate dc current shunts and resistors in the range from 10  to 10 m has been developed at National Institute of Metrological Research (INRIM) in addition to the primary reference system for low value resistors calibration. This technique is applicable in Secondary and Industrial metrological Laboratories It is based on a volt-amperometric method, to compare an unknown shunt with a standard one in 1:1 or 1:10 ratios. In the setup are involved: a dc current calibrator and a current generator to supply currents respectively up to 100 A and up to 1200 A, with a switch to reverse the current, two 7 1/2 digit nanovoltmeters (nVs) for the acquisition of the voltage on the standard and under calibration shunts and two Tinsley 100 µ and 1 m standard shunts kept in mineral oil and with a cooling system. An optional variation in the procedure that can reduce the measurement uncertainties is discussed. The 2 relative capabilities of the technique span from 6.010–6 to 4.610–4. Compatibility results with the INRIM reference measurement system for low value resistors calibration are also given.