Aktywny transformator izolujący do zastosowań w pomiarach dokładnych w paśmie akustycznym

Scharakteryzowano dwurdzeniowy aktywny napięciowy transformator izolujący. Przedstawiono i porównano wyniki pomiarów impedancji wejściowej transformatorów o takiej samej konstrukcji z rdzeniami nanokrystalicznymi i permalojowymi. Przedstawiono charakterystyki częstotliwościowe błędów modułu fazy przekładni napięciowej transformatora.

In the paper the characteristic of an isolating instrument transformer is presented. The transformer is intended for use in a measurement system to calibrate low-value alternating-current standard resistors at audio frequencies. In the developed system a resistor RX is directly compared with a standard resistor RN (Fig. 1). The impedance ratio ZX/ZN of the resistors is determined from the measurement of the voltage ratio UX/UN. The measurement of floating voltages by a digitizer with grounded inputs requires isolating transformers (T1, T2). Due to the assumptions concerning the system being developed, transformers should be characterized by a relatively high input impedance and small errors of the transformer voltage ratio over a frequency bandwidth from 40 Hz to 10 kHz. The developed transformer has a two stage dual-core construction and an additional amplifier that increases the input impedance (Fig. 2). All the windings of the transformer have 100 turns each and are wound on a toroidal nanocrystalline core. The primary and secondary windings are placed in the electrostatic screens E1, E2. The frequency characteristics of the input impedance of two transformers of the same design made of nanocrystalline core and permalloy core operating without an amplifier W (Fig. 3) and with an amplifier (Fig. 4) are compared. In Figs. 5 and 6 the frequency characteristics of the module and phase error of the transformer voltage ratio are shown. They are determined by a digital system for measuring the complex voltage ratio, developed by the authors.