GB614628A - Improvements in or relating to resistance thermometers - Google Patents

Abstract

614,628. Electric thermometers. FOSTER INSTRUMENT CO., Ltd., and HACKETT, C. E. April 24, 1945, No. 10275. [Class 40 (i)] [Also in Group XXXVI] A resistance thermometer comprises a composite resistance made up of at least two component resistances of different materials such that the resistance-temperature curve is 'of predetermined form. For example, two wires such as platinum and nickel may be joined in series in the correct proportion on a common insulating former to produce a composite wire having a straight line characteristic. Two such thermometers can be used, e.g. in a Wheatstone bridge to give an accurate measure of the temperature difference regardless of the actual temperature. In the arrangement, Fig. 2, a Wheatstone bridge is balanced and a galvanometer 11 scaled 0‹ to 15‹ C. is at zero corresponding to thermometer 9 at 0‹ C. in series with external fixed resistance 13a which together form one arm of the bridge. Under these circuit conditions any increase in resistance of the thermometer 9 corresponding to its increase in temperature over the range 0‹ to 15‹ C. is directly measurable on the galvanometer 11. The measuring range may be increased to 25‹ C. by adding 10 to the scale reading and substituting a resistance 13b for 13a. Similarly, resistance 13c substituted for 13b adds 20 to the scale and so on to the lowest value resistance 13m, and finally with no external resistance at all in the circuit as at switch position 14n.