Investigating the Measurement Errors of the Components of the Complex Resistance of Mutual Induction by the Phase Method

Abstract

A microcontroller measurer of the complex resistance components of mutual induction (MI) of magnetically coupled coils is considered for the case when, due to the effects of “capacitance” and “eddy currents”, an active component arises in the EMF of the secondary coil, the 90° phase shift angle between this electromotive force and the current of the primary coil is violated (“phase defect”). At the same time, corrective terms ("admixture" and "frequency correction") appear in the resistance MI. These phenomena increase with an increase in the frequency and value of the supply current of the coils, when using ferromagnetic cores. Balanced AC bridges are used in well-known resistance component MI measurers; their disadvantages are listed. The developed measurer uses the phase method using a temporary separation of the measurement channel. The measuring circuit (MC) is powered by the current of a controlled generator of sinusoidal signals. In the MC, the measured parameters are converted into the phase shift angle between the two output voltages. These voltages are supplied to the analog inputs of a programmable microcontroller (MCC), in which angle is measured by the discrete counting method. During the measurement process, the MCC sets the frequency of the MC power generator, controls the position of the electronic switch of the measurement channel, measures angle and determines the values of the components of the MI complex resistance according to the specified algorithms. A method of theoretical investigation of measurement errors has been developed. The errors are caused by the inaccuracy and instability of the parameters of the MC and MCC elements appearing in the algorithms for determining the measured values. The method of error calculation is accompanied by a numerical example. The results of calculation of measurement errors are presented.