Mechanical Measurements

Force Measurements

Technical Contacts:
Rick L. Seifarth
Tel: 301/975-6652
E-mail: ricky.seifarth@nist.gov

Thomas W. Bartel
Tel: 301/975-6461
E-mail: thomas.bartel@nist.gov

Kevin L. Chesnutwood
Tel: 301/975-6653
E-mail: kevin.chesnutwood@nist.gov

Jeanne Bruins
Administrative and Logistics
Tel: 301/975-6624
Fax: 301/417-0514
E-mail: jeanne.bruins@nist.gov

Do not ship instruments or standards to the mailing address listed below. Contact the technical staff for the shipping address. 

Mailing Address:
National Institute of Standards and Technology
100 Bureau Drive, Stop 8222
Gaithersburg, MD 20899-8222

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Force Transducers (23010C-23250C)

NIST provides calibration services for force-measuring devices by applying known forces, either tension or compression, to the elastic device and recording the sensed deformation. Most calibrated devices are either proving rings or load cells. The deformation of proving rings is usually measured by means of a micrometer screw and vibrating reed, which are an integral part of the device. Load cells, which utilize strain gauge bridges, produce an electrical output that is related to the applied force.

The calibration report describes the relationship between the applied force and the measured deformation, either in electrical or mechanical units. A load cell can be calibrated using (1) a readout device furnished by the customer, in which case the load cell and the readout device are calibrated as a system, and the calibration is valid only when the load cell and the readout device are used together; or (2) instrumentation furnished by NIST, in which case data are reported in terms of the ratio of the output voltage to the DC excitation voltage (mV/V). In the latter case, the customer must possess the necessary electrical instrumentation and expertise to utilize the calibration results. The relative standard uncertainty of the calibration of the voltage-ratio measurement instrumentation used at NIST is 0.0005 %.

Tension or compression calibrations in the range of 0.445 kN to 4.448 222 MN (100 lbf to 1 000 000 lbf) are performed using deadweight machines. NIST has six deadweight machines with maximum capacities of 2 226 N (505 lbf), 27 134 N (6 100 lbf), 112 540 N (25 300 lbf), 498 201 N (112 000 lbf), 1 334 467 N (300 000 lbf), and 4 448 222 N (1 000 000 lbf). The standard uncertainty of the applied forces incorporates the uncertainties associated with the determination of the mass of the deadweight, the acceleration due to gravity and the air density. The relative standard uncertainty of applied force is 0.0005 %.

Comparison calibrations in the range of 4 448 226 N to 53 378 659 N (1 000 001 lbf to 12 000 000 lbf) in compression only are performed in a universal testing machine. In this case, the system to be calibrated is loaded in series with load cells that have been previously calibrated in a deadweight machine.

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Special Tests of Force Transducers (23260S)

Temperature sensitivity, pressure sensitivity, and creep tests of force transducers are measured. The ranges of test parameters and environmental conditions may be limited by the characteristics of the force transducer and the availability of special test fixtures. These special tests should be discussed with the designated NIST technical contact before the work is scheduled.

Figure 5.3 Relationship of Force to SI Units.

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References-Force Measurements

Force Measurement Services at NIST: Equipment, Procedures and Uncertainties , T. W. Bartel, S. L. Yaniv and R. L. Seifarth, Proc. Natl. Conf. Stand. Lab. and Symp. (1997).

Creep and Creep Recovery Response of Load Cells Tested According to U.S. and International Evaluation Procedures, T. W. Bartel and S. L. Yaniv J. Res. Natl. Inst. Stand. Technol. 102, 349-362 (May 1997).

ASTM E4-02, Standard Practices for Force Verification of Testing Machines, Annual Book of ASTM Standards 3.01 (2002).

Automation of Strain-Gauge Load-Cell Force Calibrations , K. W. Yee, Natl. Inst. Stand. Technol. NISTIR 4823 (Apr. 1992).

ASTM E74-02, Standard Practice of Calibration of Force-Measuring Instruments for Verifying the Force Indication of Testing Machines, Annual Book of ASTM Standards 3.01 (2002).

Summary of the Intercomparison of the Force Standard Machines of the National Institute of Standards and Technology, USA, and the Physikalisch-Technische Bundesanstalt, Germany, S. L. Yaniv, A. Sawla, and M. Peters, J. Res. Natl. Inst. Stand. Technol. 96, 529 (1991).

Metrological Regulations for Load Cells, OIML Recommendation No. 60, Intl. Org. for Legal Metrol., Paris 1991 (E).

A New Statistical Model for the Calibration of Force Sensors, C. P. Reeve, Natl. Bur. Stand. (U.S.) Tech. Note 1246 (June 1988).

Force Calibration at the National Bureau of Standards, R. A. Mitchell, Natl. Bur. Stand. (U.S.) Tech. Note 1227 (Aug. 1986).

Interlaboratory Comparison of Force Calibrations Using ASTM Method E74-74 , R. W. Peterson, L. Jenkins, and R. A. Mitchell, Natl. Bur. Stand. (U.S.), Tech. Note 1211 (Apr. 1985).

Progress in Force Measurement at NBS, R. A. Mitchell, Proc. 10th Conf. IMEKO TC-3 on Measurement of Force and Mass, Kobe, Japan (Sept. 1984).

Inherent Problems in Force Measurements, P. E. Pontius and R. A. Mitchell, Exper. Mech. 22 (3) (Mar. 1982).

Force Sensor-Machine Interaction , R. A. Mitchell and P. E. Pontius, Proc. 27^th Intl. Instrum. Symp. (ISA), Indianapolis, IN, Instrumentation in the Aerospace Industry 27, 225 (1981).

Characterizing the Creep Response of Load Cells , R. A. Mitchell and S. M. Baker, VDI-Berichte 312, 43 (1978).

Interlaboratory Comparison of Force Calibrations Using ASTM Method E74-74, Phase I , R. W. Peterson and R. L. Bloss, Natl. Bur. Stand. (U.S.), NBSIR 76-1145 (Aug. 1976).

A Study of the National Force Measurement System, D. E. Marlowe, Natl. Bur. Stand. (U.S.), NBSIR 75-929 (June 1975).

Universal Testing Machine of 12-Million-lbf Capacity at the National Bureau of Standards, A. F. Kirstein, Natl. Bur. Stand. (U.S.), Spec. Publ. 355 (Sept. 1971).

Studies of Calibration Procedures for Load Cells and Proving Rings as Weighing Devices , G. B. Anderson and R. C. Raybold, Natl. Bur. Stand. (U.S.), Tech. Note 436 (Jan. 1969).

Gravity Measurements and the Standards Laboratory, D. R. Tate, Natl. Bur. Stand. (U.S.), Tech. Note 491 (Aug. 1969).

Uncertainties Associated with Proving Ring Calibration , T. E. Hockersmith and H. H. Ku, Preprint No. 12.3-2-64 ISA Conference, Instr. Soc. of America, Res. Triangle Park, NC (Oct. 1964).

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