The Theory, Design and Construction of Sensitive Vacuum Thermopiles

Citation

Cartwright, Charles Hawley (1930) The Theory, Design and Construction of Sensitive Vacuum Thermopiles. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/rvjf-jd23. https://resolver.caltech.edu/CaltechTHESIS:08122024-224929369

Abstract

Part I

A more complete theory of vacuum thermopile design for N junctions for four types of construction. 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 negligable for practical design. The design of a thermopile for sensitivity is made by considering the whole galvanometer circuit. If we assume the approximate correctness of the Wiedemann-Franz Law, simple optimum conditions are obtained. The theory of design is general; however, it is especially adapted to high thermoelectric power bismuth alloy wires at room temperature and for a critically damped galvanometer circuit. The design of a thermopile and choice of a galvanometer for maximum sensitivity depend on the sensitivities, resistances and characteristics 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. curves are plotted to facilitate the best choice of a galvanometer and design of a thermopile for use in many experiments. The formulae were verified experimentally at room temperature. Greater sensitivity was gained by having the thermopile at the temperature of liquid oxygen, as predicted by the theory.

Part II

The thermocouple herein described had a sensitivity of about 1µv for 10^-8cal, sec^-1 falling on the receiver, and reached practical thermal equilibrium in 0.1 sec. The sensitivity in vacuum was usually 20 to 40 times the sensitivity in air. Very short fine wires of high thermoelectric power, bismuth alloys, were soldered to a gold leaf receiver which was blackened on one side by electroplating it with platinum black. The lightness of the gold leaf receivers made the instrument extremely rugged.

Greater sensitivity was obtained for visible radiation by using a receiver of silver leaf tarnished on one side with H₂S; however, the sensitivity decreased for wave-lengths longer than 1µ.

Thesis Files