Patent GB-246963-A (GB)
Title: A method and means for measuring electrical quantities
IPC: G01R11/48
Filed: 1924-12-09
Abstract: 246,963. Siemens Bros. & Co., Ltd., and Grinsted, W. H. Dec. 9, 1924. Frequency, inductances, phase-differences, and power-factors, measuring.-The method of measurement employed is based on the fact that the vector difference of two alternating current of equal strength but differing in phase is in quadrature with the vector sum of the currents and consists in balancing an electromotive force induced by the vector difference, and therefore proportional to and in quadrature therewith against a potential difference in phase with the proportional to the vector sum of the currents. A transformer having a core of air or other non-magnetic material, is provided with two identical differentiallywound primary windings P1, P2, Fig. 1, and a secondary winding M. In series with the prim. ary winding P2 is the impedance Z to be measured, and in series with the winding PI is a variable non-inductive resistance R. The two circuits are arranged in parallel with one another and in series with a source G of alternating current and with a potentiometer wire resistance S. The secondary M is connected through a telephone receiver T to a slider on the resistance S. The resistance R and the slider on the resistance S are adjusted until no sound is heard in the receiver T, under which conditions the electromotive force in the secondary winding M, which is proportional to and in quadrature with the vector difference of the currents through the impedance Z and the resistance R is balanced against the potential drop in the tapped-off portion of the resistance S., which is proportional to the vector sum of the currents. The tapped-off portion of the resistance R is equal to the ohmic value of the impedance Z, and the slider on the resistance S indicates on a calibrated scale the phase angle of the current in the impedance branch, or the argument of the impedance. The two primary windings P1, P2 may be wound from two wires twisted together. Instead of the slide wire resistance S, a fixed resistance may be used and the transformer arranged with variable mutual coupling between the secondary and primary windings, in which case the transformer is calibrated to show tht phase angle. For measuring large impedances the mutual inductance between the windings M, P2 is made n times that between the windings M, PI, and a resistance S1, Fig. 3, is inserted in series with the impedance Z and has a value n-1 times the tapped-off portion of the resistance S. The resistance S1 may be a slide wire and the sliders of the resistances S, S1 may be mechanically connected so that the ratio S1 =S (n-1) always obtains. For testing apparatus at different frequencies, tappings from the secondary winding may be made in accordance with chosen frequencies, or tappings may be taken from the fixed resistance S in accordance with the frequencies and a variometer type transformer employed. The apparatus may be employed for measuring frequency when the capacity and inductance of the test apparatus Z are known. According to the Provisional Specification, the invention is also applicable to telephone transmission measurements and to measurements of repearter gains.