GB244657A - Electric shunts for instruments or other devices - Google Patents

Abstract

244,657. British Thomson-Houston Co., Ltd., (General Electric Co.). June 22, 1925. Resistances, self-supporting; contacting solid resistances; temperature errors, compensating for. -A shunt for an instrument &c. is provided with means for adjusting its temperature coefficient of resistance. A cast-iron member 10, ribbed as shown to dissipate heat, is provided with a central bore 13 threaded to receive adjustable nuts 15 and lock-nuts 16, between which is a stack of carbon discs 14. The temperature coefficient of the shunt is varied by adjusting the resistance of the carbon discs 14 by altering their number or dimensions or by screwing up or unscrewing the nuts 15, thereby varying the ratio of the resistances of the current paths through the cast iron and the carbon discs, which are of positive and negative coefficients of resistance respectively. Owing to the coefficient of expansion of carbon being somewhat higher than that of cast iron, the compression increases at increasing temperature. This has the same effect as the negative coefficient of the carbon. Bolt holes 17, 18, 19, 20, 21 are provided for the shunt lead terminals. Since the temperature coefficient of that portion of the shunt between the upper terminal 17 and the upper nut 15 is entirely positive, a further adjustment of the total temperature coefficient is obtainable by changing the position of the upper shunt lead from one to another of the terminal holes 17, 19, 20, 21. The upper and lower surfaces of the shunt are machined, the line terminals 12 being bolted thereto.