NBS PUBLICATIONS /(in A111QO ^Ol^D A UNITED STATES DEPARTMENT OF COMMERCE PUBLICATION NAT'L INST OF STANDARDS & TECH R.I.C. NBS MONOGRAPH 124 A1 11 009901 90 /NBS monograph QC100 .U556 V124;1972 C.1 NBS-PUB-C 1959 Reference Tables for Low-Temperature Thermocouples U.S. PARTMENT OF COMMERCE National Bureau of Standards I oo *US3h no. \9Ji ft. A NATIONAL BUREAU OF STANDARDS 1 The National Bureau of Standards was established by an act of Congress March 3, 1901. The Bureau's overall goal is to strengthen and advance the Nation's science and technology and facilitate their effective application for public benefit. To this end, the Bureau conducts research and provides: (1) a basis for the Nation's physical measure- ment system, (2) scientific and technological services for industry and government, (3) a technical basis for equity in trade, and (4) technical services to promote public safety. The Bureau consists of the Institute for Basic Standards, the Institute for Materials Research, the Institute for Applied Technology, the Center for Computer Sciences and Technology, and the Office for Information Programs. THE INSTITUTE FOR BASIC STANDARDS provides the central basis within the United States of a complete and consistent system of physical measurement; coordinates that system with measurement systems of other nations; and furnishes essential services leading to accurate and uniform physical measurements throughout the Nation's scien- tific community, industry, and commerce. The Institute consists of a Center for Radia- tion Research, an Office of Measurement Services and the following divisions: Applied Mathematics—Electricity—Heat—Mechanics—Optical Physics—Linac Radiation 2—Nuclear Radiation 2—Applied Radiation 2—Quantum Electronics 3— Electromagnetics 3—Time and Frequency 3—Laboratory Astrophysics 3—Cryo- 3 genics . 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THE INSTITUTE FOR APPLIED TECHNOLOGY provides technical services to pro- mote the use of available technology and to facilitate technological innovation in indus- try and Government; cooperates with public and private organizations leading to the development of technological standards (including mandatory safety standards), codes and methods of test; and provides technical advice and services to Government agencies upon request. The Institute also monitors NBS engineering standards activities and provides liaison between NBS and national and international engineering standards bodies. The Institute consists of the following divisions and offices: Engineering Standards Services—Weights and Measures—Invention and Innovation—Product Evaluation Technology—Building Research—Electronic Technology—Technical Analysis—Measurement Engineering—Office of Fire Programs. THE CENTER FOR COMPUTER SCIENCES AND TECHNOLOGY conducts re- search and provides technical services designed to aid Government agencies in improv- ing cost effectiveness in the conduct of their programs through the selection, acquisition, and effective utilization of automatic data processing equipment; and serves as the prin- cipal focus within the executive branch for the development of Federal standards for automatic data processing equipment, techniques, and computer languages. The Center consists of the following offices and divisions: Information Processing Standards—Computer Information—Computer Services —Systems Development—Information Processing Technology. THE OFFICE FOR INFORMATION PROGRAMS promotes optimum dissemination and accessibility of scientific information generated within NBS and other agencies of the Federal Government; promotes the development of the National Standard Reference Data System and a system of information analysis centers dealing with the broader aspects of the National Measurement System; provides appropriate services to ensure that the NBS staff has optimum accessibility to the scientific information of the world, and directs the public information activities of the Bureau. The Office consists of the following organizational units: Office of Standard Reference Data—Office of Technical Information and Publications—Library—Office of International Relations. 1 Headquarters and Laboratories at Gaithersburg, Maryland, unless otherwise noted; mailing address Washing- ton, D.C. 20234. 2 Part of the Center for Radiation Research. 3 Located at Boulder, Colorado 80302. OCT 4 1972 c Reference Tables ' for Low-Temperature Thermocouples Larry L. Sparks, Robert L. Powell, and William J. Hall Institute for Basic Standards (j . National Bureau of Standards Boulder, Colorado 80302 U.S. DEPARTMENT OF COMMERCE, Peter G. Peterson, Secretory NATIONAL BUREAU OF STANDARDS, Lawrence M. Kushner, Acting Director I ssued June 1972 Library of Congress Catalog Number: 74-186212 National Bureau of Standards Monograph 124 Nat. Bur. Stand. (U.S.), Monogr. 124, 61 pages, (June 1972) CODEN: NBSMA6 For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402 (Order by SD Catalog No. C 13.44:124). Price 60 cents. Stock Number 0303-0952 Table of Contents 1. Introduction j 2. Material Specifications 2 3. Preliminary Selection and Inhomogeneity Tests 3 4. Apparatus 4 5. Experimental Design and Technique 9 6. Data Analysis ] ] 7. Error Analysis 13 8. Standard Tables and Functions 15 9. References 55 Appendix A. Standard Designations for Thermocouples 55 List of Figures Figure Page 1. (a) Short-range inhomogeneity probe, (b) Medium-range, long-range, and inter-lot homogeneity probe, (c) Dif- ferential thermocouple probe 4 2. Schematic of thermocouple calibration cryostat 6 3. Flange and trough arrangement for using low melting point solder to make cryogenic vacuum seals 7 4. Schematic of thermal and electrical placement of thermometers in the calibration system 8 5. Block diagram of thermocouple calibration instrumentation 8 6. Four object measurement graph 9 7. Measurement graph used for calibration of thermocouple materials TP, KP (or EP), KN, TN (or EN), Pt, Ag-0.37 at% Au, and Ag-28 at% Au 11 8. Graph of A„ versus number of coefficients for thermocouple Type | T 12 | 9. Least squares approximations to typical data before the range shift constants are applied 13 10. Characteristic propagated standard deviation (ag) in voltage for the thermocouple calibrations 13 11. Illustration of the nonzero thermoelectric voltage at 1=0 K which results when experimental data are ex- trapolated from 5 K to OK 16 12. Thermoelectric voltage for primary thermocouple types E, K, and T 26 13. Seebeck coefficient for primary thermocouple types E, K, and T 26 14. Derivative of the Seebeck coefficient for primary thermocouple types E, K, and T 26 15. Thermoelectric voltage for thermocouple materials versus Pt 39 16. Seebeck coefficient for thermocouple materials versus Pt 39 17. Thermoelectric voltage for thermocouple materials versus Ag-28 at% Au 50 18. Seebeck coefficient for thermocouple materials versus Ag-28 at% Au 50 List of Tables Table Page 1. Total inventory of tested materials for thermocouple types E, K, and T and the reference materials Ag-28 at% Au and Pt 2 2. Range of chemical compositions for the tested thermocouple wires 2 3. Physical characteristics of some typical thermocouple test wires 3 4. Thermocouple wire inhomogeneity data 4 5. Comparison of differential thermocouple dip test data with previously published data and with data from NBS internal reports 5 6. Kink and strain effects on thermocouple wires 6 7. Average values of the standard deviations for the main thermocouple combinations 14 8. Average values of the standard deviation of the secondary thermocouple combinations, average values for the standard deviation of the adjustment constant, and the overall standard deviation resulting from the combined effect of these uncertainties 14 9. Estimates of systematic errors in temperature measurements 14 10. Estimated systematic errors in thermocouple voltage readings 15 11. Total uncertainties in thermocouple calibrations 15 12. Type E—thermoelectric voltage, E(T), Seebeck coefficient, S(T), and derivative of the Seebeck coefficient, dS{T) . 18 iii List of Tables—Continued Table Page 13. Type K—thermoelectric voltage, E(T), Seebeck coefficient, S(T), and derivative of the Seebeck coefficient, dS(T) 20 14. Type T—thermoelectric voltage, E(T), Seebeck coefficient, S(T), and derivative of the Seebeck coefficient, dS(T) 22 15. Type E—reduced precision tables, E(T) 24 16. Type K—reduced precision tables, E(T) 24 17. Type T—reduced precision tables, E(T) 25 18. Type E—reduced precision tables, T(E) 27 19. Type K—reduced precision tables, T(E) 29 20. Type T—reduced precision tables, T(E) 30 21. Type KP (or EP) versus Pt—thermoelectric voltage, E(T), Seebeck coefficient, S(T), and derivative of the Seebeck coefficient, dS(T) 31 22. Type Pt versus TN (or EN) —thermoelectric voltage, E{T), Seebeck coefficient, S(T), and derivative of the Seebeck coefficient, dS(T) 33 23. Type Pt versus KN—thermoelectric voltage, E(T), Seebeck coefficient, S(T), and