GB684547A - Improvements in electric resistances - Google Patents

Abstract

684,547. Metal oxide resistors; temperaturevariable resistors. STEATIT - MAGNESIA. AKT.-GES. June 21, 1951, No. 14725/51. Drawings to Specification. Class 37. A resistor variable with temperature and voltage magnitude has a resistance element composed of a mixed ferrite which essentially comprises 50 to 85 per cent ferric oxide with zinc oxide and nickel oxide and may comprise minor proportions of manganese dioxide and magnesium oxide. One example utilizes 0.5 to 10 per cent magnesium oxide, 3 to 5 per cent manganese dioxide, 5 to 10 per cent zinc oxide, 5 to 10 per cent nickel oxide and 70 to 85 per cent ferric oxide. Another example utilizes 10 to 20 per cent zinc oxide, 10 to 30 per cent Manufacture consists in heat treatment according to known technique and forming into required shapes, e.g. cylindrical shapes. The resistance element may be surrounded by a heat conductive, e.g. cement, covering or heat insulating, e.g. ceramic covering, or both forms of covering may be used. Applications to radio circuits are described, Figs, 2, 3 and 4 (not shown), with resistors according to the invention serving as current and voltage delay devices, current peak suppressors and scale lamp resistors ensuring cathode heater circuit continuity. In such applications the speed of response may be controlled according to the thickness of the ceramic or cement covering.