Creep and creep recovery response of load cells tested according to US and international evaluation procedures

Abstract

The 60 min creep data from National Type Evaluation Procedure (NTEP) tests performed at the National Institute of Standards and Technology (NIST) on 65 load cells have been analyzed in order to compare their creep and creep recovery responses, and to compare the 60 min creep with creep over shorter time periods. To facilitate this comparison the data were fitted to a multiple-term exponential equation, which adequately describes the creep and creep recovery responses of load cells. The use of such a curve fit reduces the effect of the random error in the indicator readings on the calculated values of the load cell creep. Examination of the fitted curves show that the creep recovery responses, after inversion by a change in sign, are generally similar in shape to the creep response, but smaller in magnitude. The average ratio of the absolute value of the maximum creep recovery to the maximum creep is 0.86; however, no reliable correlation between creep and creep recovery can be drawn from the data. The fitted curves were also used to compare the 60 min creep of the NTEP analysis with the 30 min creep and other parameters calculated according to the Organization Internationale de Métrologie Légale (OIML) R 60 analysis. The average ratio of the 30 min creep value to the 60 min value is 0.84. The OIML class C creep tolerance is less than 0.5 of the NTEP tolerance for classes III and III L.

Instabilities and oscillations in isotropic active gels

“…In particular we are interested in characterizing the load and recovery creep of the material following the sudden application and removal, respectively, of a constant stress. Both responses are measured experimentally in cells [40][41][42].…”

“…Both responses are measured experimentally in cells. [40][41][42] Consider a muscle fiber of length L with free boundary conditions at the ends z ¼ 0 and z ¼ L, i.e. v z u(z ¼ 0,L) ¼ 0, and no fluctuation in motor densities being imposed at the ends.…”

Impacts of matric suction equalization on small strain shear modulus of soils during air drying

“…1. Bartel and Yaniv (1997) and Mohamed et al (2009), since the weight on the scale would be sustained for very long time for the continuous measurement of soil water content, the digital scale was calibrated to capture the deformation of the scale cantilever load cell subjected to long-term loads. The calibration factors, capturing the relationship between scale reading and time, were then established for the precise determination of the changes of the water content during the experiments.…”

Uncertainty in NIST force measurements

“…For the past eleven years NIST has been performing legal metrology load cell evaluations in accordance to specifications given by the Organization Internationale de Métrologie Légale (OIML) [ 13 ] and by the National Type Evaluation Program (NTEP) [ 14 ]. Discussions of NIST’s conduct of these procedures have been given previously [ 15 ]. During these measurements, the barometric pressure is recorded continuously, typically at 5 min intervals, for a period of two or more days for each load cell evaluation.…”