Handbook of MASS MEASUREMENT

Handbook of MASS MEASUREMENT FRANK E. JONES RANDALL M. SCHOONOVER CRC PRESS Boca Raton London New York Washington, D.C. © 2002 by CRC Press LLC Front cover drawing is used with the consent of the Egyptian National Institute for Standards, Gina, Egypt. Back cover art from II Codice Atlantico di Leonardo da Vinci nella Biblioteca Ambrosiana di Milano, Editore Milano Hoepli 1894–1904. With permission from the Museo Nazionale della Scienza e della Tecnologia Leonardo da Vinci Milano. Library of Congress Cataloging-in-Publication Data Jones, Frank E. Handbook of mass measurement / Frank E. Jones, Randall M. Schoonover p. cm. Includes bibliographical references and index. ISBN 0-8493-2531-5 (alk. paper) 1. Mass (Physics)—Measurement. 2. Mensuration. I. Schoonover, Randall M. II. Title. QC106 .J66 2002 531’.14’0287—dc21 2002017486 CIP This book contains information obtained from authentic and highly regarded sources. Reprinted material is quoted with permission, and sources are indicated. A wide variety of references are listed. Reasonable efforts have been made to publish reliable data and information, but the author and the publisher cannot assume responsibility for the validity of all materials or for the consequences of their use. Neither this book nor any part may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, microfilming, and recording, or by any information storage or retrieval system, without prior permission in writing from the publisher. The consent of CRC Press LLC does not extend to copying for general distribution, for promotion, for creating new works, or for resale. Specific permission must be obtained in writing from CRC Press LLC for such copying. Direct all inquiries to CRC Press LLC, 2000 N.W. Corporate Blvd., Boca Raton, Florida 33431. Trademark Notice: Product or corporate names may be trademarks or registered trademarks, and are used only for identification and explanation, without intent to infringe. Visit the CRC Press Web site at www.crcpress.com © 2002 by CRC Press LLC No claim to original U.S. Government works International Standard Book Number 0-8493-2531-5 Library of Congress Card Number 2002017486 Printed in the United States of America 1 2 3 4 5 6 7 8 9 0 Printed on acid-free paper © 2002 by CRC Press LLC Preface “A false balance is abomination to the Lord: but a just weight is his delight.” — Proverbs 11.1 The purpose of this handbook is to provide in one location detailed, up-to-date information on various facets of mass measurement that will be useful to those involved in mass metrology at the highest level (at national standards laboratories, for example), in science and engineering, in industry and commerce, in legal metrology, and in more routine mass measurements or weighings. We have pursued clarity and hope that we have in some measure succeeded. Literature related to mass measurement, historical and current, has been cited and summarized in specific areas. Much of the material in this handbook is our own work, in many cases previously unpublished. We take this opportunity to recognize the considerable contributions to mass measurement of the late Horace A. Bowman, including the development of the National Bureau of Standards (NBS) 2 balance with an estimate of standard deviation of 1 part per billion (ppb) and the development of the silicon density standard with estimate of standard deviation of 2 parts per million (ppm), adopted worldwide. In addition, he was mentor to each of us and positively affected our careers. Chapter 1 introduces mass and mass standards. Historical background material in Section 1.2 is an excerpt from NBS monograph, “Mass and Mass Values,” by Paul E. Pontius, then chief of the U.S. NBS section responsible for mass measurements. Chapter 2 presents recalibration of the U.S. National Prototype Kilogram and the Third Periodic Verification of National Prototypes of the Kilogram. Chapter 3 discusses contamination of platinum-iridium mass standards and stainless steel mass standards. The literature is reviewed and summarized. Carbonaceous contamination, mercury contamination, water adsorption, and changes in ambient environmental conditions are studied, as are various methods of analysis. Cleaning of platinum-iridium mass standards and stainless steel mass standards are discussed in Chapter 4, including the BIPM (Bureau International des Poids et Mesures) Solvent Cleaning and Steam Washing procedure. Results of various cleaning methods are presented. In Chapter 5, the determination of mass differences from balance observations is treated in detail. In Chapter 6, a glossary of statistical terms that appear throughout the book is provided. The U.S. National Institute of Standards and Technology (NIST) guidelines for evaluating and express- ing the uncertainty of measurement results are presented in Chapter 7. The Type A and Type B evaluations of standard uncertainty are illustrated. In Chapter 8, weighing designs are discussed in detail. Actual data are used for making calculations. © 2002 by CRC Press LLC Calibration of the screen and the built-in weights of direct-reading analytical balances is described in Chapter 9. Chapter 10 takes a detailed look at the electronic balance. The two dominant types of electronic balance in use are the hybrid balance and the electromagnetic force balance. Features and idiosyncrasies of the balance are discussed. In Chapter 11, buoyancy corrections and the application of buoyancy corrections to mass determination are discussed in detail. For illustration, the application of buoyancy corrections to weighings of titanium dioxide powder in a weighing bottle on a balance is demonstrated. The development of the air density equation for use in calculation of values of air density to be used in making buoyancy corrections is presented in detail in Chapter 12. The development of the air density equation by Jones is used as background material. Then, the BIPM 1981 and the BIPM 1981/1991 equations are presented and discussed. Direct determination of air density, experimental determination of air density in weighing on a 1-kg balance in air and in vacuum, a practical approach to air density determination, and a test of the air density equation at differing altitude are summarized from original papers and discussed. Chapter 13 discusses the continuation of programs undertaken by NIST to improve hydrostatic weighing and to develop a density scale based on the density of a solid object. Central to this development is the classic paper, “Procedure for High Precision Density Determinations by Hydrostatic Weighing,” by Bowman and Schoonover. Among the subjects discussed in Chapter 13 are the principles of use of the submersible balance, determination of the density of mass standards, an efficient method for measuring the density or volume of similar objects, and the measurement of liquid density. The calculation of the density of water is the subject of Chapter 14. Redeterminations of the density of water and corresponding equations developed by three groups of researchers were corrected for changes in density of water with air saturation, compressibility, and isotopic concentration. In Chapter 15, the conventional value of weighing in air, its concept, intent, benefits, and limitations are discussed. Examples of computation are included. Comparison of error propagations for mass and the conventional mass is presented in detail in Chapter 16. OIML Recommendation R111 is used for the comparison. Parameters that can cause error in mass determinations are examined in detail in Chapter 17. Subjects covered are mass artifacts, mass standards, mass comparison, the fundamental mass relationship, weighing designs, uncertainties in the determination of the mass of an object, buoyancy, thermal equilibrium, atmospheric effects, cleaning of mass standards, magnetic effects, and the instability of the International Prototype Kilogram. In Chapter 18, the problem of assigning mass values to piston weights of about 590 g nominal mass with the goal of accomplishing an uncertainty in mass corresponding to an error in the maximum pressure generated by the piston-gauge rotating assembly of 1 ppm is discussed. The mass was determined with a total uncertainty of 0.1 ppm. The response of apparent mass to thermal gradients and free convective currents is studied in Chapter 19, based on the known experimental fact that if an artifact is not at thermal equilibrium with the balance chamber the apparent mass of the artifact deviates from the value at thermal equilibrium. In Chapter 20, magnetic errors in mass metrology, that is, unsuspected vertical forces that are magnetic in origin, are discussed. © 2002 by CRC Press LLC The “gravitational configuration effect,” which arises because for weights of nominally equal mass the distance of the center of gravity above the base of each weight depends on the size and shape of the weight, is examined in Chapter 21. In Chapter 22, the “between-time” component of error in mass measurements is examined. The between-time component manifests itself between groups of measurements made at different times, on different days, for example. Chapter 23 illustrates the key elements for the most rigorous mass measurements. In Chapter 24, control charts are developed and used to demonstrate attainment of statistical control of a mass calibration process. Tolerance testing of mass standards is discussed in Chapter 25. Procedures to be followed for deter- mining whether or not mass standards are within the tolerances specified for a particular class of weights are reviewed. Surveillance testing of weights is discussed in Chapter 26. Surveillance looks for signs that one or more members of a weight set may have changed since the latest calibration. Chapter 27 describes a project to disseminate the mass unit to surrogate laboratories using the NIST portable mass calibration package. A surrogate laboratories project began with the premise that a NIST- certified calibration could be performed by the user in the user’s laboratory. The very informal, low- budget project was undertaken to expose the technical difficulties that lay in the way.

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