GB882071A - Improvements relating to the measurement of electrical resistance - Google Patents

Abstract

882,071. Resistance measurement. ASSOCI. ATED ELECTRICAL INDUSTRIES Ltd. Nov. 15, 1957 [Nov. 13, 1956], No. 34683/56. Class 37. In a circuit arrangement for measuring the electrical resistance of an electrical component R1 which is carrying a current, a light current is passed through a resistance box R2, the resistance of which is adjusted until the following relationship is achieved, this being indicated by detector means: where K is a predetermined constant. The detector means comprises a dynamometer having a rotatable shaft carrying a pair of deflectable elements; each element having both a high resistance voltage coil C or C1, and a low resistance current coil D1 or D, and each element being arranged to produce opposing torques on the shaft. The voltage and current coils C, D1 of the first element are connected respectively across the unknown resistor R1 1 and in series with the resistance box R2. The voltage and current coils Cl, D of the second element are connected respectively across R2 and in series with R1. When the torques in the two elements are equated by varying R2, it can be shown that R1=KR2 where K is the known predetermined constant, greater than unity, determined by a resistor R3 in shunt across coil D1 Alternatively, R3 may be in shunt across coil D, when K will be less than unity; or resistors may be placed across both D1 and D.