GB694016A - Improvements in a device for measuring resistance changes - Google Patents

Abstract

694,016. Electrical tests and measurements. GUSTAFSSON, G. V. A. Nov. 16, 1951 [Nov. 24, 1950], No. 26874/51. Class 37. Apparatus for determining the value of a low resistance 1 (Fig. 1) at a distance from a measuring bridge without introducing inaccuracies due to contact resistance, lead resistance, &c. comprises duplicate connecting wires 5, 6 between the ends of the pairs of arms 1, 2 and 3, 3, one of which 5 contains an ammeter 7, and the other 6 a potentiometer 8 whose slider is joined to the power supply, the potentiometer 8 being adjusted until meters 7 read zero, after which the meters are short-circuited and a reading taken on the bridge balance meter 4. The bridge arms may include a number of seriesconnected resistors 10, 11 (Fig. 3), connected on either side of a slide-wire 12, the overall resistance of the two arms being maintained constant by mechanically connecting the switch arms 13 so that the resistance cut out in one arm is added in the other. The range may be increased by further joint-operated banks of resistances 15, 16. When the resistors 1, 2 are themselves some distance apart they may be interconnected by double wires 18, 19 (Fig. 5), the wires 18 being joined through two equal resistors 20 to the balance meter 4, and the wires 19 being joined together. The variable resistor 1 may be shunted by a resistor 23, and fixed resistor 2 by variable resistor 22 to allow the bridge to be used with different resistors 1<SP>1</SP>, chosen by switches O<SP>1</SP>, O<SP>2</SP>. The bridge arms 1, 2 and 3, 3 may be fed from separate D.C. or A.C. supplies, the voltages being adjusted to give zero readings on meters 7, thus obviating the need for potentiometers 8.