Measurement of inductive components impedance at low frequencies

Abstract

The method of three voltmeters allows you to determine the components of the in-ductive impedance by measuring the voltages on the tested impedance, on the reference active resistance and at the output of the harmonic voltage source that feeds the meas-uring circuit. The analysis of the measuring circuit using the method of three voltmeters was carried out, mathematical expressions were found for calculating the active resistance and inductance as components of the investigated impedance based on the results of the measurement of three voltages. Regarding the values of the voltages on the investigated impedance, on the reference active resistance and on the output of the harmonic voltage source, there is a well-founded condition under which the obtained results will be valid. Using the method of three voltmeters, the frequency characteristics of the active resistance, inductance and Q-factor of the reference coil were experimentally determined in the range up to 100 kHz from a set of exemplary inductance measurements with previously known parameters. Experimental frequency dependences indicate the presence of a region of constant value of the impedance components at low frequencies. At frequencies higher than 30 kHz, there is a region of growth of the active component due to the influence of the proximity effect and skin effect and a region of apparent increase in inductance due to the influence of the distributed capacitance of the coil. The obtained characteristics make it possible to choose a frequency range in which the interfering influence of the distributed capacitance is minimal, as well as to determine the optimal frequency at which the Q-factor of the inductance is maximal. The relative error of inductance determination was no more than 0.3%, active resistance – 8.7%, Q factor – 5%.