Uncertainty in NIST force measurements

Abstract

This paper focuses upon the uncertainty of force calibration measurements at the National Institute of Standards and Technology (NIST). The uncertainty of the realization of force for the national deadweight force standards at NIST is discussed, as well as the uncertainties associated with NIST’s voltage-ratio measuring instruments and with the characteristics of transducers being calibrated. The combined uncertainty is related to the uncertainty of dissemination for force transfer standards sent to NIST for calibration.

Automation and upgrade of the 27.1 kN dead weight machine at the National Institute of Standards and Technology

“…After the force is applied to the force measuring device, a timed delay is executed and the computer takes the readings (ratios in V/V) from the DVM. Detailed information on this system and the uncertainty involved can be found in the paper "Uncertainty in NIST Force Measurements" by Thomas W. Bartel [3].…”

Stress Analysis of Conical Contact Joints in the NIST 4.45 MN Deadweight Machine

“…In this study we model the behavior of the 4.45 MN DWM using each of the two material constitutive relations. The constitutive relations are described in terms of three parameters, 2 Certain commercial equipment, instruments, or materials are identified in this article in order to describe the experimental procedure adequately. Such identification is not intended to imply recommendation or endorsement by the National Institute of Standards and Technology, nor is it intended to imply that the materials or equipment identified are necessarily the best available for the purpose.…”

“…We now describe structural finite element modelling of the components of the 4.45 MN DWM, which was performed using the software package COMSOL Multiphysics 4.4 2 . In considering the potential sources of uncertainty in modelling the components of the 4.45 MN DWM (e.g., friction, boundary conditions, material constitutive relations), we perform parameter sweeps for a given unknown or model two opposing extrema between which the true solution lies.…”

“…In these machines, the force applied to a transducer is generated by Earth's gravity acting on a calibrated mass, which may be written F = mg where m is mass and g is Earth's gravitational acceleration, wherein the mass has been corrected for buoyancy effects of the local atmosphere. In general, the calibration uncertainty achieved using these machines is transducer-dependent, but expanded uncertainties (k = 2) can be as small as 0.0012 % [2].…”

Invited Article: Concepts and tools for the evaluation of measurement uncertainty

“…For example, when calibrating a force transducer, the orientation of the transducer relative to the loading platens of the deadweight machine is a persistent effect because a change in such orientation may shift the transducer's response up or down at all set-points of the applied force, by unknown and possibly variable amounts, but all in the same direction, as illustrated in Figure 5 of Bartel. 126 An alternative classification of uncertainty evaluation modalities recognizes and distinguishes bottom-up and topdown evaluations.…”