816. Considerations in the Calibration on Electronic Load Cells

Paper

Abstract

The results of repetitive calibrations of a number of precision four arm bridge load cells over several years at the McDonnell Douglas Astronautics Corporation, Western Division are presented. Two interesting and significant observations are made: (1) the cell outputs under tension loading are generally very repeatable and show no tendency to change with time; (2) the cell outputs in compressive loading are several times less repeatable than for the tension application. An explanation of the non-repeatability phenomenon in compression loading is offered. Methods and equipment for improving the repeatability of compressive calibrations are presented. A definite correlation is shown to exist between the non-repeatability of the cells and their individual sensitivities to bending moments. The concept of a coefficient of sensitivity to bending is proposed. Methods of determining this coefficient are shown. Economic and reliability aspects of the weighing function are discussed. Recommendations are presented for achieving more reliable weighing systems with appreciably lower operating costs.