A thermoelectric standard cell

This paper considers a means of obtaining a secondary standard of e. m. f. by utilizing the e. m. f. of a thermocouple. The standard thermo cell is fundamentally a standard of current, in that it requires a definite value of current to function properly. The operation of the cell consists in balancing the potential across a resistance against the thermoelectric e. m. f. of the thermocouple. This requires a definite value of current through a filament which is a source of heat for the thermocouple. The temperature coefficient has different values, depending upon the temperature of the heating filament. Means are provided for compensating for the temperature coefficient of the cell. The construction of the cell is discussed in detail, particularly the use of gas in the bulb. A review of the characteristics brings out several advantages of the thermoelectric standard cell. The results of permanency tests on a number of cells are shown. The standard cell has been successfully applied to potentiometers designed for thermocouple work. Further experimental work on this cell is now under way.