NAFL INST OF STANDARDS & TECH R.I.C. AIllQE MASEtM A11 102485264 , QC100 .US56 N0.174 1986 C.I NBS-PUB-C 19 NBS UBLICATIONS THERMOMETER CALIBRATION NBS MONOGRAPH 174 Jacquelyn A. Wise Robert J. Soulen, Jr. U.S. DEPARTMENT OF COMMERCE NATIONAL BUREAU OF STANDARDS "QC 100 .U556 No. 174 1985 C 2 . Tm he National Bureau of Standards' was established by an act of Congress on March 3, 1901. The f 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 measurement 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's technical work is performed by the National Measurement Laboratory, the National Engineering Laboratory, the Institute for Computer Sciences and Technology, and the Institute for Materials Science and Engineering The National Measurement Laboratory Provides the national system of physical and chemical measurement; • Basic Standards^ coordinates the system with measurement systems of other nations and • Radiation Research furnishes essentiaJ services leading to accurate and uniform physical and • Chemical Physics chemical measurement throughout the Nation's scientific community, in- • Analytical Chemistry dustry, and commerce; provides advisory and research services to other Government agencies; conducts physical and chemical research; develops, produces, and distributes Standard Reference Materials; and provides calibration services. The Laboratory consists of the following centers: The National Engineering Laboratory Provides technology and technical services to the public and private sectors to Applied Mathematics address national needs and to solve national problems; conducts research in Electronics and Electrical engineering and applied science in support of these efforts; builds and main- Engineering^ tains competence in the necessary disciplines required to carry out this Manufacturing Engineering research and technical service; develops engineering data and measurement Building Technology capabilities; provides engineering measurement traceability services; develops Fire Research test methods and proposes engineering standards and code changes; develops Chemical Engineering^ and proposes new engineering practices; and develops and improves mechanisms to transfer results of its research to the ultimate user. The Laboratory consists of the following centers: The Institute for Computer Sciences and Technology Conducts research and provides scientific and technical services to aid • Programming Science and Federal agencies in the selection, acquisition, application, and use of com- Technology puter technology to improve effectiveness and economy in Government • Computer Systems operations in accordance with Public Law 89-306 (40 U.S.C. 759), relevant Engineering Executive Orders, and other directives; carries out this mission by managing the Federal Information Processing Standards Program, developing Federal ADP standards guidelines, and managing Federal participation in ADP voluntary standardization activities; provides scientific and technological ad- visory services and assistance to Federal agencies; and provides the technical foundation for computer-related policies of the Federal Government. The In- stitute consists of the following centers: The Institute for Materials Science and Engineering Conducts research and provides measurements, data, standards, reference Ceramics materials, quantitative understanding and other technical information funda- Fracture and Deformation ^ mental to the processing, structure, properties and performance of materials; Polymers addresses the scientific basis for new advanced materials technologies; plans Metallurgy research around cross-country scientific themes such as nondestructive Reactor Radiation evaluation and phase diagram development; oversees Bureau-wide technical programs in nuclear reactor radiation research and nondestructive evalua- tion; and broadly disseminates generic technical information resulting from its programs. The Institute consists of the following Divisions: 'Headquarters and Laboratories at Gaithersburg, MD, unless otherwise noted; mailing address Gaithersburg, MD 20899. ^Some divisions within the center are located at Boulder, CO 80303. 'Located at Boulder, CO, with some elements at Gaithersburg, MD. RESEAECH nTFOEJflATION CEIITER Hierniometer Calibration: A IVIodel for State Calibration Laboratories /Oo no. Jacquelyn A. Wise Robert J. Soulen, Jr. Temperature and Pressure Division National Measurement Laboratory National Bureau of Standards Gaithersburg, MD 20899 o o 4r U.S. DEPARTMENT OF COMMERCE, Malcolm Baldrige, Secretary NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Director Issued January 1986 Library of Congress Catalog Card Number: 85-600636 National Bureau of Standards Monograph 174 Natl. Bur. Stand. (U.S.), Monogr. 174, 88 pages (Jan. 1986) CODEN: NBSMA6 US. Government Printing Offi<ce Washington: 1986 For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, DC 20402 TABLE OF CONTENTS Page 1. INTRODUCTION 1 2. LABORATORY AND EQUIPMENT 1 2.1 Laboratory Space and Environment 1 2.2 Temperature Baths 6 2.2.1 Ice bath 6 2.2.2 Variable, constant-temperature baths ... 8 2.3 Laboratory Standards 11 2.3.1 Primary standards 11 2.3.2 Check standards 13 2.4 Personnel 13 3. PERFORMING CUSTOMER'S CALIBRATIONS 14 3.1 Examination and Preparation of Thermometers for Calibration 14 3.2 Proper Method for Calibrating Specific Thermometers 15 3.2.1 Total-immersion thermometers 15 3.2.2 Partial-immersion thermometers 15 3.2.3 ASTM thermometers 16 3.2.4 Calorimetric thermometers 16 3.2.5 Beckmann thermometers 17 3.2.6 Clinical standard thermometers 17 3.2.7 Kinematic viscosity thermometers 17 3.2.8 Electronic temperature measuring systems 18 iii Page 3.3 Calibration Procedure 18 3.3.1 Number and choice of calibration points 18 3.3.2 Use of the ice-point bath 18 3.3.3 Steam point (100 °C) as reference point 19 3.3.4 Role of primary liquid-in-glass thermometers 20 3.3.5 Routine adjustment to primary standard thermometer calibration data 20 3.3.6 Placement of thermometers in calibration bath 24 3.3.7 Reading sequence and recording data ... 25 3.3.8 Computation of bath temperature from readings of primary standard thermometers 27 3.3.9 Determining corrections for thermometers being calibrated 30 3.3.10 Stem-temperature corrections 31 4. DOCUMENTATION 36 4.1 Report of Calibration 36 4.2 Report of Test 39 5. MAINTAINING LABORATORY STANDARDS AND ESTIMATION OF LABORATORY UNCERTAINTY 46 5.1 Estimates of Inaccuracy of Calibration of Liqu id- in-G lass Thermometers 46 5.2 Maintaining the Accuracy of Primary Laboratory Standards 46 5.3 Using Check Standards for Quality Assurance ... 47 iv Page 6. CONCLUSION . .' 51 7. ACKNOWLEDGMENTS 54 8. REFERENCES 54 9. COMMERCIAL SOURCES 55 9.1 Suppliers of Calibration Baths 55 9.2 Suppliers of Oils for Calibration Baths 55 9.3 Suppliers of Thermometers 56 9.4 Suppliers of Faden Thermometers 56 10. APPENDIX 57 Liquid-In-Glass Thermometry, NBS Monograph 150 57 V 1. INTRODUCTION This publication is written primarily to assist State calibration laboratories to establish temperature calibration capabilities. It can also be used by any industrial organization or independent testing laboratory that wishes to establish a similar facility. The range of the calibrations to be conducted extends roughly from 0 to 200 ^C, while the target accuracy is ±0.1 ^C. Several types of thermometers could be used to maintain this stated range and accuracy, but liquid- in-glass thermometers have been chosen because they are dependable, easy to use and maintain, and economical. Presented in this publication are detailed descriptions of the laboratory environment, equipment, type of training and personnel, calibration procedure, calculations, data analysis, and documentation needed for the calibration of thermometers. These descriptions and procedures are based on experience acquired at the National Bureau of Standards (NBS) for over 50 years. If a laboratory is established and maintained as described in this publication, liquid-in-glass thermometers and electronic temperature measuring systems can be calibrated to an accuracy somewhat better than 0.1 over a range of 0 to 200 ^C, and they will be traceable to NBS. A deviation from the procedures or specifications given may be acceptable, but any consequent errors should be determined and evaluated for acceptability by the manager of the laboratory. If laboratories follow these proce- dures, there will be more uniformity among these laboratories and this will result in better service to industry and to the public. A checklist for establishing a calibration laboratory to the specifications described in this publication is provided in Section 6 (see Table 10). 2. LABORATORY AND EQUIPMENT 2.1 Laboratory Space and Environment Liquid-in-glass thermometers submitted for calibration may be as long as 615 mm. They may be accidentally broken if an adequate distance is not kept between laboratory furnishings. Futhermore, any electronic temperature measuring systems submitted for calibration will require additional room around the calibration bath to place the digital readout device or other electronic components. The room chosen for the calibration lab- oratory should