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    Thermocouple Hardware and Fabrication

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    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. B. Protection tube—ceramic and metal protection tubes, sometimes referred to as thermowells, serve the purpose of protecting the sensing element assembly from the deleterious effects of corrosive or oxidizing or reducing atmospheres. In some cases, two concentrically arranged protection tubes may be used. The one closest to the sensing element assembly is designated the primary protection tube, while the outer tube is termed the secondary protection tube. Combinations such as an aluminum oxide primary tube and silicon carbide secondary tube often are used to obtain the beneficial characteristics of the combination, such as resistance to cutting flame action, and ability to resist thermal shock. C. Connector—sensing element assembly wire terminations are made to either (a) Terminals (b) Connection head 1. General purpose type 2. Screw cover type 3. Open type (c) Plug and jack quick-disconnect (d) Military standard (MS) type of connector D. Miscellaneous hardware such as (a) Pipe nipple or adapter to join the protection tube to the head (b) Thermocouple gland—used primarily with sheathed, compacted ceramic-insulated thermocouple assemblies to serve the dual function of mounting and sealing-off pressure in the mounting hole (see Section 5).

    Committee/Subcommittee: E20.04

    DOI: 10.1520/STP46140S