The purpose of this paper is to introduce the new ASME measurement uncertainty methodology which is the basis for two new ASME/ANSI standards and the ASME short course of the same name. Some background and history that led to the selection of this methodology are discussed as well as its application in current SAE, ISA, JANNAF, NRC, USAF, NATO, and ISO Standards documents and short courses. This ASME methodology is rapidly becoming the national and international standard.

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When data were being gathered in 1961 for National Bureau of Standards Monograph 40 [3] on Thermocouple Materials, a section was included to cover ceramic packed thermocouple stock “because of the wide use and increasing popularity.” New uses continue to be found for this unique heterogeneous materials combination. Compacted ceramic insulated thermocouple material consists of three parts as shown in Fig. 21.

Although there is some variation in the defined temperature range involved, cryogenics (kri-o-jen-iks) usually indicates concern with temperatures in the liquid oxygen range (about 90°K or -183°C) or lower. This temperature range will be discussed primarily in this chapter. Since a triple point (of water) or ice bath reference junction often is used, additional comments and values will be given for the entire subzero (0°C) range.

A complete thermocouple temperature sensing assembly, in accordance with the present state of the art, consists of the following: A. Sensing element assembly including, in its most basic form, two dissimilar wires, supported by an electrical insulator and joined at one end to form a measuring junction. Such assemblies usually fall into one of three categories; those formed from wires have nonceramic insulation, those with hard-fired ceramic insulators, and those made from sheathed, compacted ceramic-insulated wires.