Measurement of Inductance by the Shielded Owen Bridge

The study described in this paper shows that the Owen bridge is well adapted to the accurate measurement of inductance and effective resistance to above 3,000 cycles. The construction of a shielded bridge for audio frequencies is described and a theoretical discussion is also given. It was found possible to measure inductances ranging from 0.1 to 3 henrys with an error of measurement less than 0.1 per cent, and for 10 henrys the accuracy is better than 0.25 per cent. As a means of measuring effective resistance the bridge shows an accuracy of about 2 per cent. The sources of error and method of eliminating or correcting them are discussed. INTRODUCTION T HE accurate measurement of inductance and capacitance is essential to the correct design of practically all precision electrical apparatus. Particularly is this so in the field of electrical communication where the successful introduction of new circuits and equipment, such as the carrier telephone and the telephone repeater, depends largely on the accuracy with which the elements can be adjusted to the nominal values, this accuracy in turn depending on the accuracy with which the electrical measurements can be made. Owing principally to the ease with which a telephone receiver m a y be used to indicate a balance at audio frequencies, bridge measurements are very generally used for the measurement of capacitance and inductance in telephone work. The simplest type of bridge and the one used most for the comparison of like impedances is the equal ratio arm bridge described by Shackelton.