NAT'L INST. OF STAND & TECH NIST PUBLICATIONS AlllOb 722D0A NBSIR 75-928 The National Measurement System for Mass, Volume and Density Paul E. Pontius, James R. Whetstone, and John A. Simpson National Engineering Laboratory National Bureau of Standards Washington, D.C. 20234 Final May 1978 DEPARTMENT OF COMMERCE )NAL BUREAU OF STANDARDS * 75-119 NBSIR 75-928 THE NATIONAL MEASUREMENT SYSTEM FOR MASS, VOLUME AND DENSITY Paul E. Pontius, James R. Whetstone, and John A. Simpson National Engineering Laboratory National Bureau of Standards Washington, D C. 20234 Final May 1978 U.S. DEPARTMENT OF COMMERCE, Juanita M. Kreps, Secretary Or. Sidney Harman, Under Secretary Jordan J. Baruch, Assistant Secretary for Science and Technology NATIONAL BUREAU OF STANDARDS, Ernest Ambler. Director CONTENTS Page TABLE OF CONTENTS i LIST OF FIGURES iii LIST OF TABLES iii 0.0 EXECUTIVE SUMMARY 1 1.0 INTRODUCTION 3 2.0 STRUCTURE OF THE MEASUREMENT SYSTEM 4-33 2.1 Conceptual System 6 2.1.1 Mass 6 2.1.2 Volume 8 2.1.3 Density 9 '. 2.2 Basic Technical Infrastructure . 9 2.2.1 Documentary Specification System 12 2.2.1.1 Standardization Institutions 12 2.2.1.2 Survey of Documentary Standards 14 2.2.2 Instrumentation System 16 2.2.2.1 Measurement Tools and Techniques 17 2.2.2.2 The Instrumentation Industry 19 2.2.3 Reference Data 20 2.2.4 Reference Material 23 2.2.5 Science and People 23 2.3 Realized Measurement Capabilities 25 2.3.1 Quality of Reference Standards 25 2.3.2 The Measurement Process 29 2.4 Dissemination and Enforcement Network 30 2.4.1 Central Standards Authorities 30 2.4.2 State and Local Offices of Weights and Measures. 30 2.4.3 Standards and Testing Laboratories and Services. 31 2.4.4 Regulatory Agencies 32 2.5 Organizational Input-Output Transactions Matrix 33 3.0 IMPACT, STATUS AND TRENDS OF MEASUREMENT SYSTEM 33-38 3.1 Impact of Measurements 33 3.1.1 Functional, Technological and Scientific Applications 33 3.1.2 Economic Impacts — Costs and Benefits 36 3.1.2.1 Processes Relating to Quality of Material 36 3.1.2.2 Processes Associated With Quality Control and Regulation 36 3.1.2.3 Processes Associated With Preparations of Objects or Materials 36 3.1.3 Social, Human, Man-on-the-Street Impacts 36 3.2 Status and Trends of the System 37 4.0 SURVEY OF NBS SERVICES 38-55 4.1 The Past 38 4.2 The Present—Scope of NBS Services 39 4.2.1 Description of NBS Services 39 4.2.1.1 Mass Measurement 39 4.2.1.2 Volumetric Measurements — Glassware 39 4.2.1.3 Metal Volumetric Standards 40 4.2.1.4 Density Measurements 40 4.2.1.5 Measurement Assurance Program 40 4.2.1.6 Office of Weights and Measures 40 4.2.2 Users of NBS Services 41 CONTENTS Page *. 4.2.3 Alternate Sources . 42 4.2.4 Funding Sources for NBS Services 45 4.2.5 Mechanism for Supplying Services 45 4.3 Impact of NBS Services 46 4.3.1 Economic Impact of Major User Classes 46 4.3.2 Technological Impact of Services 48 4.3.3 Pay-off from Changes in NBS Services 50 4.4 Evaluation of NBS Program 51 4.5 The Future 53 5.0 SUMMARY AND CONCLUSIONS 54 References 55-56 Appendix A. METHODOLOGY OF THE STUDY 57-59 Appendix B 60-65 References 66 i i LIST OF FIGURES Page Figure 1: Measurement Process Infrastructure 5 Figure 2: Infrastructure Associated with the Metric 5 Figure 3: Voluntary Standards Infrastructure 7 Figure 4: Practical Hydrometer Scales 13 Figure 5: Mass Customer Profile (Major SIC Groups) 43 Figure 6: Mass Customer Profile (Three Digit SIC Groups) 43 Figure 7: Volume Customer Profile (Two and Three Digit SIC Groups) ... 44 Figure 8: Density Customer Profile (Two and Three Digit SIC Groups) . 44 LIST OF TABLES Table 1: Voluntary Standards Organizations 8 Table 2: Industrial Effort Relating to Mass, Volume and Density .... 21 Table 3: Commercial Weighing Devices in Use 22 Table 4: Devices Used in States' Weights and Measures Activities. ... 22 Table 5: Tolerances for Commercial Test Weights 27 Table 6: Typical Commercial Scale Tolerances 28 Table 7: Typical Measurement Uncertainties 29 Table 8: Summary for Users of NBS Calibration Services 47 Table 9: Petroleum Measurement Commitment 49 i i i I I THE NATIONAL MEASUREMENT SYSTEM FOR MASS, VOLUME AND DENSITY Paul E. Pontius, James R. Whetstone, and John A. Simpson National Bureau of Standards Mass, a property of all matter, is to be a property of a material, however, unique in the sense that the concept is such extension requires an assumption on generally deduced from the motion of a the homogenity of the sample measured. body under the influence of an applied Considering that most of the measurement force. It is for this reason the mass processes within the mass, volume and unit for measurements over the range of density measurement systems are based on objects which can be physically handled economic compromise rather than technolog- is now, and for some time to come will ical capabilities, it is presumptuous to continue to be, embodied in an artifact assume that NBS has any substantial impact standard. The mass of one object with on the total system. On the other hand, respect to another is deduced from a NBS, by providing a means for access to comparison of the gravitational forces the unit, is generally considered to be acting on the two objects. The additive a partner in all measurement activity. nature of mass makes it possible to con- Consistency of results commensurate with struct appropriate subdivisions and requirements is a fundamental to all of multiples of a single defining artifact. the activities the system supports. Reso- The present mass unit, the International lution of inconsistencies, by referral mea- Prototype Kilogram, is one of the Base surements, by suggested process modifica- Units of the International System of tion, or by basic changes in measurement units. Access to the unit is provided by concept is the essential support to the Bureau International des Poids and Mesures system provided by NBS. (Sevres, France) through prototype kilogram In spite of the size of the system, it replicas of the unit. Prototype Kilograms appears to be in almost complete control No. 20 and No. 4 provide such access for and operating to the general satisfaction the United States, and are in turn the of all concerned. There are several rea- basis for the U.S. practical mass scale as sons for this: (1) mass standards are established by the ni chrome kilograms Nl intrinsically stable so that the unit once and N2. injected into a subsystem remains reason- Volume is a quantity derived from the ably consistent; (2) the instruments used length unit. It is inseparably coupled are reliable; and (3) the size of large with mass. The intent of the founders of subsystems concerned with voluntary stan- the Metric System was that one cubic deci- dards, weights and measures activities, meter of water at maximum density have a government requirements, etc., result in mass of one kilogram. The realization was inertia with respect to change. Through proven to be imperfect, thus introducing the mechanism of Measurement Assurance for a period of time the liter as a volume Programs, NBS or any other interested unit. (The current unit for volume is the party, can test the effectiveness of a cubic meter). Precise mass measurement given subsystem relative to the intended requires a knowledge of the displacement use of the measurement results. The volume of the objects being compared. same medium provides a means for a running Hydrostatic weighings are used to (a) audit of the subsystem to insure that determine the displacement volume ratio stability is not lost. relative to an object with displacement With the advent of the NBS-2 kilogram volume established by direct measurement comparator the precision of measurement and (b) displacement volume relative to has reached the point where factors a known density of the fluid. affecting the short term stability of the Density is defined as mass per unit defining artifact can be studied. These volume. Density is a property of factors include cleaning procedures, mois- interest for a variety of fluid mixtures. ture films and environmental contamination. The density of a fluid in conjunction Problems associated with the air density with mass measurement is a means to algorithm, e.g., oversimplification and determine the containment volume of a non-uniformity, introduce small offsets variety of volumetric standards. Mass and in the practical mass scales of the vari- volume are both used to determine quantity ous countries. These offsets, too small of material. Density is usually considered to be of concern in most weighing 1 operations, do not affect the consistency of relates to specific problems, the practical measurements in a given country. resolution of which has no visibility. Resolution of the problem, however, is Generally, most of these problems relate to important in support of work on fundamental specifying what the measurement is supposed physical constants. to accomplish and there are those who There are certain identifiable expect NBS to address his particular constituencies within the system which rely problem, however ill defined. exclusively on NBS services. Support to On the other hand, there are pressures the State Weights and Measures activities, to work through an interface (identifiable coordinated by the NBS Office of Weights constituency) both from within NBS and and Measures, extends to about 84,000,000 from other sources.