Analysis of a three-voltmeter measurement method designed for low-frequency impedance comparisons

The principle of the three voltmeter method designed for precise impedance comparison is presented. Generalization of the classical approach is proposed and analysed. Formulas for impedance parameters determination are derived and measurement uncertainty analysed for various kinds of comparisons, and next optimal measurement conditions specified. Important voltmeter parameters, such as random error and non-linearity error, are experimentally investigated. The presented results show that by using the method and commercially available apparatus it is possible to compare two impedances with a relative uncertainty of (1-5)×10 in the low frequency range.