GB1023041A - Improvements in or relating to apparatus for measuring electrical impedances - Google Patents

Abstract

1,023,041. Measuring bridges. WAYNE KERR LABORATORIES Ltd. Feb. 19, 1963 [Feb. 19, 1962], No. 6329/62. Heading G1U. An unknown impedance 10 is connected between two cores 11, 12 of a threecore cable with a standard impedance 13 connected between other two cores 11, 14, with another unknown impedance 35 connected between the remaining two cores 12, 14. The cable extends from. the location of the impedances to that of the three terminal-impedance measuring apparatus 15, comprising a transformer ratio arm bridge wherein an input transformer 20, A.C. energized over primary 21, has two series close-coupled secondaries 23, 24 whose neutral position is connected to a tap of the primary fan output transformer 27 whose secondary energizes detector 29 and null indicator 30. Taps on the secondary of transformer 20 and the primary of transformer 26 are interconnected by resistive and capacitative standards 31,32 while the free ends of the windings are connected to cores 11, 12 and the neutral to core 14. The taps are adjusted for zero unbalance output, and the impedance value of 10 plus the impedances of cores 11, 12 can be obtained from knowledge of standard resistance 31 and capacitance 32 and the corresponding tap ratios on secondary 24 and primary 26, irrespective of shunt impedances between cores 11, 14 and 12, 14. Interchange of cores 12,14 enables the total impedance of standard 13 and the cores to be measured, so that the core impedance may be subtracted from that of 10, 11, 12 thus giving the value of the unknown impedance. A further unknown impedance may be similarly measured by connection of cores 12, 14 to windings 23, 26 and of core 11 to the neutral 25. A self-balancing bridge such as that described in Specification 1,023,043 may be used, and switching means 36 effect core interchange. It is stated that n(n-1/2) impedances may be measured in succession using n cores of a multiple cable; one such impedance being a standard impedance and the remainder being unknown; the unused cable cores being connected to the neutral line. Other direct reading selfbalancing impedance measurement apparatus as described in Specification 852,011 may be used.