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Mercury Barometers and Manometers

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Mercury Barometers and Manometers NBS MONOGRAPH 8 Mercuiy Barometers and Manometers U.S. DEPARTMENT OF COMMERCE NATIONAL BUREAU OF STANDARDS THE NATIONAL BUREAU OF STANDARDS Functions and Activities The functions of the National Bureau of Standards are set forth in the Act of Congress, March 3, 1901, as amended by Congress in Public Law 619, 1950. These include the development and maintenance of the national standards of measurement and the provision of means and methods for making measurements consistent with these standards; the determination of physical constants and properties of materials; the development of methods and instruments for testing materials, devices, and structures; advisory services to government agencies on scientific and technical problems; in- vention and development of devices to serve special needs of the Government; and the development of standard practices, codes, and specifications. The work includes basic and applied research, development, engineering, instrumentation, testing, evaluation, calibration services, and various consultation and information services. Research projects are also performed for other government agencies when the work relates to and supplements the basic program of the Bureau or when the Bureau's unique competence is required. The scope of activities is suggested by the listing of divisions and sections on the inside of the back cover. Publications The results of the Bureau's work take the form of either actual equipment and devices or pub- lished papers. These papers appear either in the Bureau's own series of publications or in the journals of professional and scientific societies. The Bureau itself publishes three periodicals available from the Government Printing Office: The Journal of Research, published in four separate sections, presents complete scientific and technical papers; the Technical News Bulletin presents summary and pre- liminary reports on work in progress; and Basic Radio Propagation Predictions provides data for determining the best frequencies to use for radio communications throughout the world. There are also five series of nonperiodical publications: Monographs, Applied Mathematics Series, Handbooks, Miscellaneous Publications, and Technical Notes. Information on the Bureau's publications can be found in NBS Circular 460, Publications of the National Bureau of Standards ($1.25) and its Supplement ($1.50), available from the Superin- tendent of Documents, Government Printing Office, Washington 25, D.C. UNITED STATES DEPARTAIEXT OF COMAIERCE • Frederick H. Mueller, Secret, NATIONAL BUREAU OF STANDARDS . A. V. Astin, Director Mercury Barometers and Manometers W. G. Brombacher, D. P. Johnson, and J. L. Cross National Bureau of Standards Monograph 8 Issued May 20, 1960 For sale by the Superintendent of Documents, U.S. Government Printing Office Washington 25, D.C. - Price 40 cents Foreword Preparation of this Monograph on mercury barometers and manometers was undertaken to fill the need of manufacturers and users for information which is now scattered thi-ough the literature and im some cases unpublished. This mformation is primarily on the sources of error and methods for their correction. Moderately extensive tables of corrections for temperatm-e, gravity, capillarity, and other errors are included, mainly for application to portable instruments. The various types of instruments are defined and design features affecting the accuracy discussed in some detail. The preparation of this monograph is part of the work on pressure stand- ards now in progress in the Mechanics Division, B. L. Wilson, Chief, imder the direct supervision of E. C. Lloyd, Chief of the Mechanical Instruments Section. A. V. AsTiN, Director. 11 Contents Page Page Foreword 8. Scale errors 22 8.1. Zero error 22 1. Introduction 1 8.2. Methods of test 23 2. Definitions 1 8.2.1. Fortin barometers 24 3. Principle of measurement and standards 2 8.2.2. Altitude barometers 24 3.1. Principle of measurement 2 8.2.3. Manometers 25 3.2. Standard conditions 3 8.3. Barostat 25 3.3. Pressure units 3 9. Temperature errors 26 4. Properties 4 9.1. Basic formula 27 4.1. Density of mercury 4 9.2. Fortin barometers, U-tube barometers and 4.2. Vapor pressure of mercury 4 manometers 28 4.3. Surface tension of mercury 4 9.2.1. Scale accurate at 0° C 28 4.4. Compressibility of mercury 5 9.2.2. Fortin barometers, scale accurate 4.5. Purity and composition 5 at 62° F 28 4.6. Electrical resistance of mercury 6 9.2.3. Scale accurate at unknown tem- and manometers 6 5. Types of barometers perature 29 5.1. Fortin barometers. 6 9.2.4. Scale indicates pressure, instru- and manometers 7 5.2. U-tube barometers ment temperature not 0° C 29 5.3. Fixed cistern barometers and manometers. 7 9.3. Fixed cistern barometers and manometers. 29 5.4. Standard barometers 8 9.3.1. Scale accurate at 0° C 30 5.5. Recording mercury barometers 8 9.3.2. Scale accurate at unknown tem- pressure manometers 9 5.6. High perature 5.6.1. Single U-tube high pressure ma- ^^ii 9.3.3. Scale indicates pressure, instru- nometers 9 ment temperature not 0° C 30 5.6.1. Multiple tube manometers .. 9 9.3.4. Fixed cistern barometers with an 5.6.3. Ring balance 10 altitude scale 31 Design elements of barometers 10 6. 9.4. Method of test 31 6.1. Methods of detecting the mercury surface. 10 9.5. Temperature correction tables 32 6.1.1. Sighting on the meniscus by eye.. 10 10. Gravity errors 33 6.1.2. Sighting on an index 10 10.1. Basic relations . 33 6.1.3. Mercury float 1 11 10.2. Value of gravity at the instrument loca- with telescope 11 6.1.4. Sighting a tion 33 6.1.5. Photocell detector 12 10.3. Variation of gravity error with latitude and detector 13 6.1.6. Capacitance elevation 34 6.1.7. Optical reflection detectors 13 10.4. Gravity correction tables 34 6.1.8. Interference fringes 14 11. Capillary errors 34 6.1.9. Resistance wire 14 11.1. Tube 35 6.1.10. Gamma-ray pickup 15 11.2. Cistern 35) Measurement of mercury column height.. 15 6.2. 11.3. Correction table 36) 6.2.1. Scale and vernier 15 12. Return head and elevation correction 36 6.2.2. Cathetometer and scale 15 12.1. Definition of symbols 37s 6.2.3. Precision screw 16 12.2. Change in gas pressure with elevation— 37 6.2.4. Gage blocks 16 12.3. Return head correction 38 Illumination of the mercury surface 16 6.3. 12.4. Elevation correction, gas head 39 above mercury column 17 6.4. Vacuum 12.4.1. U-tube manometers 40 6.4.1. Mercury sealed valve 17 12.4.2. Cistern manometers 40 6.4.2. Pump 18 12.4.3. Barometers 40 6.5. Tubing 18 12.5. Elevation correction, Uquid head 40 j 6.6. Alinement of scales and sighting devices.. 18 13. Vacuum error of barometers 41 6.7. Instrument temperature 19 14. Compression of mercury 41 6.7.1. Measurement of temperature 19 15. Computation of corrections 42 r 6.7.2. Control of the temperature 19 15.1. Fortin barometer 42 compensation for temperature 6.8. Automatic 15.2. Altitude barometer, fixed cistern 43 i and gravity error 20 15.3. Manometer, U-tube 43 6.9. Damping and lag 21 16. Testing at National Bureau of Standards 44 7. Sources of error 21 17. References 45 IV Mercury Barometers and Manometers W. G. Brombacher, D. P. Johnson, and J. L. Cross The various designs of mercury barometers and manometers are briefly described, with a more extended discussion of the various design elements which may affect the achievable accuracy. Sources of error in measuring pressures are described in considerable detail, par- ticularly for portable instruments, including scale, temperature, gravity, capillarity, vacuum errors and return gas column. Methods of minimizing those errors and of making the cor- rections, including extensive tables, are presented. Standard conditions are defined and the pertinent properties of mercury given. The paper contains 65 literature references. 1. Introduction . Mercury barometers and manometers are widely in obtaining precision and accuracy; and (c) in used in aeronautics, ;j meteorology, science, and some measure to contribute to national standardi- ' industry. In aeronautics they are used to cali- zation of practices and methods of measuring brate a multitude of pressure ; measuring instru- pressure with mercury columns. rnents, including altimeters, rate-of-climb meters, A great deal of the material in this report reflects airspeed indicators, manifold pressure gages and the experience of the National Bureau of Standards Mach meters, of these , many instruments demand- in this field of pressure measurement. However, ing continually increasing accuracy [581].^ In a number of manufacturers have made substantial meteorology, mercury barometers are used to contributions to the art. , measure the atmospheric pressure. In industry Present day needs are not only for increased and industrial research laboratories barometers accuracy in pressure measurements, but also for are used principally to ^ measure atmospheric pres- an extension of the range of mercury barometers sure, whereas the , mercury manometer has a and manometers. Mercury barometers and ma- ; multitude of applications. nometers up to 10 ft in height are now being The principal objectives in preparing this required but such instruments are relatively Monograph are : (a) To outline the inherent errors of mercury barometers and manometers and to awkward to transport and use. The reading diffi- provide information and tables for correcting these culty is in a fair way of being eluninated by the errors; (b) to briefly describe the variety of design use of the photocell detector coupled with auto- elements of these instruments which are critical matic setting of the photocell to the mercury level.
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