Low-Temperature Thermocouple Thermometry
Precision temperature measurements are becoming increasingly Important in industrial and military cryogenic engineering. Of the many ways of measuring cryogenic temperatures, thermocouples are among the simplest and most useful. Four general considerations are of importance in designing and determining the feasibility of thermocouple systems. First, the selection of the best thermocouple pair depends on the temperature range since both the sensitivity and reliability of a junction change markedly with temperature and are quite different for different systems. Second, a calibration curve must be obtained for each junction pair since the thermoelectric potential differences are not primary temperature scales, Third, estimates must be made of the effects of inhomogeneities and other sources of error that will affect the reliability of the temperature readings. And fourth, for high accuracy at the lowest temperatures the electrical circuitry and measuring apparatus must be carefully designed. The last item is one of instrumentation and will not be discussed here. The other three considerations are discussed for gold-cobalt and constantan versus copper or “normal” silver, chromel versus aiumel, and iron versus constantan.
KeywordsThermoelectric Power Lead Wire Thermocouple Wire Alumel Thermocouple Thermo Electric
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