GENERAL THEORY, DESIGN, AND CONSTRUCTION OF SENSITIVE VACUUM THERMOPILES (PART I)A More Complete Theory of Vacuum Thermopile Design for N Junctions for Four Types of Construction

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Abstract
Attention is paid to the practical construction and application of the thermopiles. The sensitivity and quickness of reaching thermal equilibrium are both calculated by considering radiation from the receivers and conduction through the wires; the other factors are proved theoretically and experimentally to be negligible for designs found practical. In designing a thermopile for sensitivity, the whole galvanometer circuit has been considered. If we assume the approximate correctness of the Wiedemann‐Franz Law, simple optimum conditions are obtained. Maximum sensitivity is found to depend on the sensitivities, resistances and characteristic of the galvanometers available and the size of the area into which the radiation to be measured can be concentrated. If it is impossible to concentrate the light into as small a receiver as can be made, the number of junctions to be used in series can be calculated. While the theory given is general, it is especially adapted to high thermoelectric power bismuth alloy wires at room temperature and for a critically damped galvanometer circuit. Curves are plotted to facilitate the best choice of a galvanometer and best design of a thermopile for use in many experiments. The formulas were verified experimentally at room temperature. Greater sensitivity was gained by having thermopile at the temperature of liquid oxygen, as predicted by the theory.

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