Alternating-current magnetic measurements with a bridge network employing inductively coupled ratio arms

The paper describes the theory and use of a bridge network employing inductively coupled ratio arms for the measurements of core loss and permeability in magnetic materials subjected to alternating excitation. The bridge combines the inherent advantages of the parallel resonance bridge and the inductively coupled bridge, but it differs technically from the conventional forms of either of these bridges. In common with all bridge methods, the magnetic test coil (sample) forms one arm of this bridge, and its self inductance and effective resistance are found from the conditions at bridge balance. The core loss and the permeability are then easily calculated. A variable capacitor is used in this bridge as reactance standard. Selected experimental results are given to illustrate the use of the bridge for a.c. magnetic measurements over a frequency range of 50c/s¿20kc/s under various conditions of excitations in the core. It has been shown that the bridge offers definite advantages and flexibility of measurements, in spite of operating with a very small number of components. A variable standard capacitor and a variable resistor are the only components used for the bridge arms in addition to the test coil and a tapped coupling transformer. Error due to earth capacitances of the components is also negligibly small.