Mass (22010C-22110C)
NIST maintains the national standard for mass in the form of the prototype kilogram (K20) and provides services to support the parts of the national measurement system that rely directly or indirectly on mass measurements.
These services include the calibration of suitable weight sets. A calibration consists of establishing a mass value and the appropriate uncertainty for that value for each weight that has been designated to be a reference standard. It is desirable, but not necessary, that a weight meet the adjustment tolerances established for NBS Classes A, B, M, S, S-1, or equivalent prior to submission. Weights are available from manufacturers, many of whom can directly furnish documentation suitable for meeting quality assurance contracts and requirements.
NIST calibrates individual weights or sets in the range of 1 mg to 30 kg or 0.45 kg to 22.7 kg (1 lb to 50 lb) in decimal subdivisions. If the weights are designated as reference standards, they must be of design, material, and surface finish comparable to NBS Classes A, B, M, S, or S-1. These include ASTM Type I and II, classes 1, 2, 3, 4, and OIML E1, E2, F1 and F2. NIST also calibrates large mass standards 27.3 kg to 27 300 kg (60 lb to 60 000 lb) if the design, material, and surface finish are compatible with the intended usage. For these large mass standards, an adjustment with reference to a nominal or desired value can be included as a part of the calibration procedure.
In the absence of instructions from the customer, weights will be cleaned prior to calibration. If weights are to be calibrated "as found" (without cleaning), and returned without cleaning, customers should note this in their instructions to NIST. If weights are to calibrated "as found" and calibrated again after cleaning, double the fee will apply. The values of true mass (and an apparent mass correction) included in the report will be determined by using computed volumes based on the manufacturer's statement of density of the material, or on the density computed from measured volumes, or, in the absence of this information, on estimated density values.
However, 1 kg mass standards fabricated from stainless steel and of one-piece construction will have their density determined as part of a "first-time" calibration at NIST. The apparent mass corrections are computed for 20 °C with reference to Normal Brass (density 8400kg/m3 at 0 °C and volume coefficient of expansion 0.000054/°C) and to stainless steel (density 8000 kg/m3 at 20 °C) in a conventional air density of 1.2 kg/m3. Apparent mass corrections to any other basis can be furnished if requested. Typical relative standard uncertainties range from 50 x 10-9 at 1 kg, up to 330 x 10-6 at 1 mg, and 0.2 x 10-6 at 10 kg.
Figure 5.2 NIST's Relative Expanded Uncertainties for Normal Calibrations of Mass Standards.
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Single Weights for Deadweight Pressure Testers (22130C-22150C)
Weights are compared to discrete standards by the method of double substitution weighing.
Special Mass Measurement Services (22170S)
For tests not covered by the previous descriptions, the NIST technical contact cited at the beginning of this section should be consulted to determine whether a test can be performed and to obtain an estimate of the price of the test.
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References-Mass Standards
Equation for the Determination of the Density of Moist Air (1981/91), R. S. Davis, Metrologia 1992, vol. 29, pp. 67-70.
New Assignment of Mass Values and Uncertainties to NIST Working Standards , R. S. Davis, J. Res. Natl. Inst. Stand. Technol. 95 (1), 79-92 (1990).
NIST Measurement Services: Mass Calibrations , R. S. Davis, Natl. Inst. Stand. Technol. Spec. Publ. 250-31 (Jan. 1989).
A Primer for Mass Metrology, K. B. Jaeger and R. S. Davis, Natl. Bur. Stand. (U.S.), Spec. Publ. 700-1 (Nov. 1984).
Air Buoyancy Correction in High-Accuracy Weighing on Analytical Balances , R. M. Schoonover and F. E. Jones, Anal. Chem. 53 (6), 900 (May 1981).
National Bureau of Standards Mass Calibration Computer Software , R. N. Varner and R. C. Raybold, Natl. Bur. Stand. (U.S.), Tech. Note 1127 (July 1980).
Quick and Accurate Density Determination of Laboratory Weights , R. M. Schoonover and R. S. Davis, Proc. 8th Conf. IMEKO, Krakow, Poland (1980).
Precision Laboratory Standards of Mass and Laboratory Weights . A reprint of NBS Circular 547, Section 1, T. W. Lashof and L. B. Macurdy, August 1954, Natl. Bur. Stand. (U.S.), NBSIR 78-1476 (Oct. 1978).
The National Measurement System for Mass, Volume, and Density , P. E. Pontius, J. R. Whetstone, and J. A. Simpson, Natl. Bur. Stand. (U.S.), NBSIR 75-928 (May 1978).
Direct Determination of Air Density in a Balance through Artifacts Characterized in an Evacuated Weighing Chamber, W. F. Koch, R. S. Davis, and V. E. Bower, J. Res. Natl. Bur. Stand. (U.S.), 83 (5), 407 (Sept.-Oct. 1978).
Designs for the Calibration of Standards of Mass , J. M. Cameron, M. C. Croarkin, and R. C. Raybold, Natl. Bur. Stand. (U.S.), Tech. Note 952 (June 1977).
Measurement Assurance , J. M. Cameron, Natl. Bur. Stand. (U.S.), NBSIR 77-1240 (1977).
Mass and Mass Values, P. E. Pontius, Natl. Bur. Stand. (U.S.), Monogr. 133 (Jan. 1974).
Weight Cleaning Procedures , H. E. Almer, Natl. Bur. Stand. (U.S.), NBSIR 74-443 (Nov. 1973).
On Uncertainty in Mass Measurement , J. R. Donaldson, Natl. Bur. Stand. (U.S.), NBSIR 73-151 (Mar. 1973).
Method of Calibrating Weights for Piston Gages , H. E. Almer, Natl. Bur. Stand. (U.S.), Tech. Note 577 (May 1971).
Realistic Uncertainties and the Mass Measurement Process, P. E. Pontius and J. M. Cameron, Natl. Bur. Stand. (U.S.), Monogr. 103 (Aug. 1967).
Introduction to Intercomparison Methods in Mass Measurement, H. E. Almer, Natl. Bur. Stand. (U.S.), Report 9487 (Feb. 1967).
Measurement Philosophy of the Pilot Program for Mass Calibration , P. E. Pontius, Natl. Bur. Stand. (U.S.), Tech. Note 288 (May 1966).
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