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Session Topic: 3E, Temperature Session

   

Paper Title: The Practical Significance of Seebeck Inhomogeneity in Measurement Interoperability of Thermocouple Calibration

   

Date & Time: TUESDAY, August 6, 2002

 

8:30 - 10:00am - PARALLEL SESSIONS - SESSION 3

   

Speaker: Ray P. Reed Proteun Services

Email: rpreed@asme.org

   

Measurement interoperability, assurance that measurements and calibrations are repeatable, comparable between laboratories, and traceable is subverted by unrecognized Seebeck inhomogeneity of thermocouples. Definite Self-Validation (SEVA) of thermocouples is defeated as well. Well-developed and reported, but rarely applied, Seebeck Inhomogeneity Methods of Test (SIMOT) have provided data, understanding, and concrete answers to practical questions concerning the actual prevalence and severity of Seebeck inhomogeneity in present day thermometry. SIMOT measurements have demonstrated conclusively that traceability of thermocouple calibration unaccompanied by authentic test of Seebeck inhomogeneity can not assure measurement quality as is imagined. An economic analysis was performed for NIST by personal interview of specialists broadly representative of producers, suppliers, and users of thermocouple products and calibration services. Incidental to the directed economic objective, many comments and assertions of respondents implicitly confirmed the widespread misunderstanding of insidious Seebeck inhomogeneity and its practical impact in calibration and applied thermometry. A working familiarity with the simple principles of authentic inhomogeneity testing and its quantitative results clearly explains the reason for such frustrated user’s comments reported in that study, as: “ internal calibration testing is ... necessary ... because of the inconsistent nature of thermocouple calibrations ...”, “ ... due to the random nature of thermocouple calibration ...”, and “ ... users can not rely on suppliers to provide correct calibrations for thermocouple products.” Both simplified and advanced SIMOT methods and common pitfalls of illusory simplistic inhomogeneity test methods are described. An appended bibliography lists many papers by several investigators on the well-established principles of thermoelectric inhomogeneity testing and its practice.

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