1 Dual-Using an AC-DC Transfer Standard for Determining Current Difference of Precision Shunt Valentyn Isaiev Abstract—The commercial AC-DC transfer standards are widespread at leading calibration and measurement laboratories for DC and low-frequency me trolog y. Therefore, possibilities of various combinations of applying such instruments, particularly to verify the results of calibrating the precision current shunts or for optimizing the available facility, are of interest. The peculiarities of dual-using the AC-DC transfer standard are outlined, investigated, and discussed. The analytical and computer modeling, as well as the technical and theoretical analyses, are presented. Deriving the set of equations for the description of current distribution in the measurement techni que for determining the AC-DC current transfer difference of the tested shunt is one of the work achievements. The measurement results obtained following the presented approach were verified using two voltage converters (Fluke 792A and PMJTC). Some points of measurement uncertainty evaluation also are illuminated in the paper. Index Terms —AC-DC transfer standard; analytical models; calibration; current measurement; shunts; vectors. I. INT RODUCT ION owadays, a situation in measuring the alternating current allows accurately determining the magnitude fro m 10 μA to 100 A in the frequency range from 10 Hz to 100 kHz [1], [2]. The electric current is one of the seven base physical quantities, so the measurement uncertainty is the main characteristic, for instance, in electricity metering. Regarding calibration and measurement capabilities, the lowest level of measurement uncertainty reaches 7 μA/A in the range from 0.051 to 10 A for the frequency of power supply networks [1]. The thermal transfer standard and the precision shunt frequently are used to determine the magnitude of alternating current with high precision [3]. Several manufacturers have developed commercially available precision shunts to measure the current from 1 mA to 100 A [4], [5]. The internal batteries often should be used to deal with currents lower than 20 mA. The general nature of design features of both the precision shunts and the reference test systems causes the growth of measurement uncertainty both at the high rated currents and frequencies and at the low currents [6], [7]. There is a potential difference when the current flows through the shunt. As a result, the voltage is transmitted to the output terminals of the shunt. This signal enters the input of the thermal transfer standard combined with the shunt, which operates as a high-precision current sensor. In electrical measurements, the metrologists typically use a reference shunt combined with a reference thermal converter to determine the AC-DC transfer difference of the current thermal converter [8]. It is also possible to use both the reference shunt in combination with the reference thermal voltage converter and the second reference thermal voltage converter for measuring the output voltage of the tested shunt to determine a similar characteristic of the precision shunt [9]. In the case of applying one AC-DC transfer standard, it is possible to exclude its AC-DC transfer difference due to the presence of this quantity in both measuring channels compared. The primary purpose of the work is to verify the possibility of dual-using the AC-DC transfer standard during the metrological characterization of a precision shunt using a reference shunt. The author analyzes whether the switching of the AC-DC transfer standard in the procedure for determining the AC-DC transfer difference of the tested shunt distorts the measured voltage magnitude used in calculating the characteristic. The analytical models of electrical processes at different stages of determining the AC-DC transfer difference are used widely throughout the paper. Using a mathematical apparatus and computer modeling, in particular, the analysis of current redistribution in the measuring circuit is yielded. The contribution of this work to the body of instrumentation and measurement science is proposing the analytical description of the current distribution at the stages of determining the AC-DC transfer difference of the tested shunt. In particular, a vector diagram was composed for the case of applying the AC-DC transfer standard Fluke 792A used in national metrology institutes [10]-[13] and other leading calibration and measuring laboratories. II. TECHNICAL AND THEORETICAL ANALYSIS OF DUAL-USING THE AD-DC TRANSFER ST ANDARD A. Peculiarities of Current Branching in Applying the AC-DC Transfer Standard Since the impedances of the compared shunts are different (especially when shunts are from several manufacturers), there is a difference in the voltage signal at the output terminals of the shunts for a current flow of the same magnitude. Looking at Fig.1 with base elements of the calibration setup, one can see that the current will branch due to the input measuring circuit of the AC-DC transfer standard. Inversely proportional to the impedance of the shunt and the transfer standard, most of the current will flow through the shunt, and a small part of the current will flow through the Fluke 792A input circuit. At the stage of measuring the output N