The preparation and performance of thin film thermocouples

Abstract

The preparation of simple thin film thermocouples by vacuum deposition is described. Thermocouple combinations were constructed from nickel, iron, copper, constantan, Chromel and Alumel, the metal elements being evaporated by using conventional resistance heating methods and the alloys by flash evaporation. Measurements of temperature against e.m.f. for metal element combinations gave almost bulk metal characteristics; for example, a thermal e.m.f. value of 0.027 mv degC-1 is obtained for a Ni-Fe combination. However, for alloy-metal element film combinations, while bulk material thermal e.m.f. values were not obtained, a high order of sensitivity was measured; for example a copper-constantan combination gave 0.035 mv degC-1. Results indicate that the maximum thermal e.m.f. of a thin film thermocouple is obtained when the film thickness of each element is greater than 2500 Å. Ni-Fe pairs prepared under given conditions gave stable thermocouples reproducible to ±2 degC at 250°C.