1725. Principles and Practices for Accurate Load Cell Measurements

Paper

Abstract

Strain gage load cell systems can under ideal conditions produce weighings with accuracy as good as +/-.05% of the full scale indication. Less than ideal conditions can easily degrade that performance. This paper will describe those factors which tend to degrade load cell performance and the common practices which have been developed to enhance load cell accuracy. Specifically, the following points will be discussed. 1. Physical Arrangement – Side loading can seriously alter loadcell performance. The merit of tension loading and the use of good flextures will be discussed. For the benefit of those applications in which compression loading is inescapable, the preferred arrangements for compression loading will also be presented. 2. Internal Workings – There is a wide range of quality in loadcells. This quality is usually described in terms like linearity, hysteresis, temperature compensation, repeatability etc. The specific meaning and relevance of these qualities will be discussed and related to the physical characteristics which cause them. 3. Electronic System – Strain gage load cells all require a voltage ratio indicating system. The measurement of the voltage ratio is subject to several subtle effects which can seriously alter the indicated output. Some of these effects will be discussed and related to loadcell accuracy. The qualities of various types of indication systems will also be discussed. The paper will be arranged in an instructive format and will make liberal use of charts, diagrams and sketches. The intention will be to show how loadcell weighing systems, if properly used, can produce convenient and dependable force and mass measurement, when accuracy on the order of +/-.05% is required.