GB691633A - Improvements in or relating to the measurement of resistance - Google Patents

Abstract

691,633. Resistance measurements. SHOTTER, G. F., and ELLIOTT BROS. (LONDON), Ltd. Feb. 20, 1952 [Feb. 20, 1951], No. 4124/51. Class 37. A resistance, such as that of a power transmission line, is measured by connecting it in series with a low-voltage D.C. source and a standard resistance adjusting the current in a separate measuring circuit comprising a second low-voltage D.C. source, another standard resistance, and a calibrated potentiometer slide wire until the voltage drops across the two standard resistances are equal, and then adjusting the slider on the slide wire until the voltage at the slider is equal to the voltage drop in the unknown resistance. The remote end 1a of the conductor 1 to be measured is connected to the remote ends of two other phase conductors 2, 3 by links 4, 5. The connection between the link 5 and the conductor 1 is made at a point PI near the end la. The near end 2b of the conductor 2 is earthed and connected, through a tuned parallel circuit 6 for rejecting induced A.C. voltages, and an ammeter 7, to one pole of a 4-volt battery 8, the other pole of which is connected to the commoned ends of a number of standard resistances 11. The free end 11b of a chosen one of these is connected to the near end 1b of the conductor 1. A separate measuring circuit comprises a 4-volt battery 14, a standard resistance 15 of the order of 2 ohms, a potentiometer 16, 16a, having a range-change portion 16 consisting of a tapped resistance and a calibrated slide-wire portion 16a, and a variable resistance 17. A galvanometer 18 in series with a tuned rejector circuit 21 for rejecting any remaining A.C. voltage, is connected by two two-position two-pole switches 19, 20 in alternative " set " and " test " positions. In the lower or " set " position of the switches 19, 20 the galvanometer circuit is connected between a point 11a on the resistance 11 and one end of the resistance 15, the other ends of these two resistances being connected together. The resistance 17 is then adjusted to give zero deflection on the galvanometer, indicating that the voltage drops across the standard resistances 11, 15 are equal. The switches 19, 20 are then thrown to the upper or " test " position in which the galvanometer circuit is connected between a potential point P2 on the conductor 1 near the end 1b and a point on the resistance 16, the potential point P1 on the conductor 1 being connected to the slider 16b, which is adjusted until balance is obtained. In a modification the far ends of the conductors 1, 2, 3 are connected together and the test connections are made to the near ends of two of them so that the resistance of the two conductors in series is measured. By measuring all the conductors in pairs, the resistance of each conductor may be obtained.